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Journal articles

S Comeau, R C Carpenter, P J Edmunds (2013)  Coral reef calcifiers buffer their response to ocean acidification using both bicarbonate and carbonate.   Proc Biol Sci 280: 1753. 12  
Abstract: Central to evaluating the effects of ocean acidification (OA) on coral reefs is understanding how calcification is affected by the dissolution of CO(2) in sea water, which causes declines in carbonate ion concentration [CO(3)(2-)] and increases in bicarbonate ion concentration [HCO(3)(-)]. To address this topic, we manipulated [CO(3)(2-)] and [HCO(3)(-)] to test the effects on calcification of the coral Porites rus and the alga Hydrolithon onkodes, measured from the start to the end of a 15-day incubation, as well as in the day and night. [CO(3)(2-)] played a significant role in light and dark calcification of P. rus, whereas [HCO(3)(-)] mainly affected calcification in the light. Both [CO(3)(2-)] and [HCO(3)(-)] had a significant effect on the calcification of H. onkodes, but the strongest relationship was found with [CO(3)(2-)]. Our results show that the negative effect of declining [CO(3)(2-)] on the calcification of corals and algae can be partly mitigated by the use of HCO(3)(-) for calcification and perhaps photosynthesis. These results add empirical support to two conceptual models that can form a template for further research to account for the calcification response of corals and crustose coralline algae to OA.
Aaron M Dufault, Aaron Ninokawa, Lorenzo Bramanti, Vivian R Cumbo, Tung-Yung Fan, Peter J Edmunds (2013)  The role of light in mediating the effects of ocean acidification on coral calcification.   J Exp Biol Feb  
Abstract: We tested the effect of light and pCO(2) on the calcification and survival of Pocillopora damicornis recruits settled from larvae released in southern Taiwan. In March 2011, recruits were incubated at 31, 41, 70, 122, and 226 μmol photons m-2s-1 under ambient (493 μatm) and high pCO(2) (878 μatm). After 5 days calcification was measured gravimetrically and survivorship estimated as the number of living recruits. Calcification was affected by the interaction of pCO(2) with light, and at 493 μatm pCO(2) the response to light intensity resembled a positive parabola. At 878 μatm pCO(2), the effect of light on calcification differed from that observed at 493 μatm pCO(2), with the result that there were large differences in calcification between 493 μatm and 878 μatm pCO(2) at intermediate light intensities (ca. 70 μmol photons m-2s-1), but similar rates of calcification at the highest and lowest light intensities. Survivorship was affected by light and pCO(2), and was highest at 122 μmol photons m-2s-1 in both pCO(2) treatments, but was unrelated to calcification. In June 2012 the experiment was repeated, and again the results suggested that exposure to high pCO(2) decreased calcification of P. damicornis recruits at intermediate light intensities, but not at lower or higher intensities. Together, our findings demonstrate that the effect of pCO(2) on coral recruits can be light-dependent, with inhibitory effects of high pCO(2) on calcification at intermediate light intensities that disappear at both higher and lower light intensities.
Peter J Edmunds, Hollie M Putnam, Ruth D Gates (2012)  Photophysiological consequences of vertical stratification of Symbiodinium in tissue of the coral Porites lutea.   Biol Bull 223: 2. 226-235 Oct  
Abstract: In comparison to some corals, massive Porites spp. is physiologically resilient to environmental assaults and is becoming more abundant on coral reefs. To evaluate the extent to which thick tissues contribute to this physiological resilience, we tested the hypothesis that the Symbiodinium in Porites lutea are phenotypically and genetically homogeneous with regard to their distribution vertically within the tissue, and in their response to temperature. Symbiodinium density, genetic identity, and photophysiology were compared between outer and inner tissues defined as adjacent layers ~2 mm thick and beneath the skeleton surface. Symbiodinium densities were 5-fold greater and their cells contained less chlorophyll a in outer versus inner tissue, but ITS2 sequence identities were genetically uniform between layers. Maximum photochemical efficiency (F(v)/F(m)) in inner and outer tissue from the top and sides of the corals differed 6%-7%, with F(v)/F(m) greater in inner versus outer tissue on the top of colonies. On the tops of colonies, the initial slopes of the rETR versus irradiance relationship were not different between tissue layers, although they tended to be less steep for inner tissue. When exposed for 12 h to 28 °C, 30 °C, or 32 °C at ~700 μmol quanta m(-2) s(-1), there was a trend for F(v)/F(m) of the Symbiodinium in both tissue layers to be reduced at 32 °C. Our results do not conform well to shade acclimatization in inner versus outer tissue of P. lutea, and they imply within-tissue heterogeneity that may be an important determinant of physiological performance in perforate corals.
Aaron M Dufault, Vivian R Cumbo, Tung-Yung Fan, Peter J Edmunds (2012)  Effects of diurnally oscillating pCO2 on the calcification and survival of coral recruits.   Proc Biol Sci 279: 1740. 2951-2958 Aug  
Abstract: Manipulative studies have demonstrated that ocean acidification (OA) is a threat to coral reefs, yet no experiments have employed diurnal variations in pCO(2) that are ecologically relevant to many shallow reefs. Two experiments were conducted to test the response of coral recruits (less than 6 days old) to diurnally oscillating pCO(2); one exposing recruits for 3 days to ambient (440 µatm), high (663 µatm) and diurnally oscillating pCO(2) on a natural phase (420-596 µatm), and another exposing recruits for 6 days to ambient (456 µatm), high (837 µatm) and diurnally oscillating pCO(2) on either a natural or a reverse phase (448-845 µatm). In experiment I, recruits exposed to natural-phased diurnally oscillating pCO(2) grew 6-19% larger than those in ambient or high pCO(2). In experiment II, recruits in both high and natural-phased diurnally oscillating pCO(2) grew 16 per cent larger than those at ambient pCO(2), and this was accompanied by 13-18% higher survivorship; the stimulatory effect on growth of oscillatory pCO(2) was diminished by administering high pCO(2) during the day (i.e. reverse-phased). These results demonstrate that coral recruits can benefit from ecologically relevant fluctuations in pCO(2) and we hypothesize that the mechanism underlying this response is highly pCO(2)-mediated, night-time storage of dissolved inorganic carbon that fuels daytime calcification.
S R Dudgeon, J E Kübler (2011)  Hydrozoans and the shape of things to come.   Adv Mar Biol 59: 107-144  
Abstract: The physiological mechanisms that regulate adaptive plasticity of clonal organisms are key to their success in changing environments. Here, we review the mechanisms that regulate morphological plasticity of colonial hydrozoans. There is a heritable, genetic basis to colony form, but environmentally-induced plasticity and self-reinforcing developmental physiology explain much of total phenotypic variance. Morphological development of colonial hydrozoans emerges from interactions among (1) behaviors which drive gastrovascular transport, (2) architecture of the gastrovascular system that determines hydrodynamic characteristics of vascular flow, and, (3) gene products that vary in response to physiological signals provided by gastrovascular transport. Several morphogenetic signaling mechanisms have been identified, including, reactive oxygen species and nutrient concentrations in the hydroplasm, and hydromechanical forces associated with gastrovascular transport. We present a conceptual model of the interacting forces that drive hydrozoan morphological development. Several avenues for future research are suggested by the synthesis of information from prior studies of hydrozoans. Elucidating the morphogenetic signaling pathways responsive to metabolites or hydromechanical forces and the epigenetic effect of vascular architecture on colony form may give new insight into the self-maintenance of indeterminately growing and continuously developing vascular systems.
William M Goldenheim, Peter J Edmunds (2011)  Effects of flow and temperature on growth and photophysiology of scleractinian corals in Moorea, French Polynesia.   Biol Bull 221: 3. 270-279 Dec  
Abstract: To test for threshold effects in the response of coral physiology to increasing seawater flow, field and laboratory experiments were conducted in Moorea. First, the growth of juvenile massive Porites spp. and branching P. irregularis was compared among habitats differing in water motion. Growth of massive Porites spp. responded to flow in a pattern consistent with a threshold effect, whereas growth of P. irregularis increased linearly with flow. Second, a recirculating flume was used to test the effect of flow on photophysiology (ÎF/F(m)', effective photochemical efficiency) for massive Porites spp.; ÎF/F(m)' displayed a threshold response at 23 cm s(-1) and 28 °C, but not at 31 °C. Finally, intra-colony variation in the response of ÎF/F(m)' to flow and temperature was explored to evaluate the functional significance of colony shape in small corals. ÎF/F(m)' on the top and upstream surfaces of massive Porites spp. responded with a threshold effect of flow at 28 °C (but not 31 °C), but ÎF/F(m)' on downstream surfaces was unresponsive to flow. ÎF/F(m)' for P. irregularis was less responsive to flow than for massive Porites spp., suggesting that the photophysiological response of corals to varying flow speeds may differ between species and morphologies. Together, these results emphasize that flow can have diverse effects on the physiology of corals, with the outcome depending on flow speed, temperature, location on the colony, and perhaps morphology.
Rebecca L Kordas, Steve Dudgeon (2011)  Dynamics of species interaction strength in space, time and with developmental stage.   Proc Biol Sci 278: 1713. 1804-1813 Jun  
Abstract: Quantifying species interaction strengths enhances prediction of community dynamics, but variability in the strength of species interactions in space and time complicates accurate prediction. Interaction strengths can vary in response to density, indirect effects, priority effects or a changing environment, but the mechanism(s) causing direction and magnitudes of change are often unclear. We designed an experiment to characterize how environmental factors influence the direction and the strength of priority effects between sessile species. We estimated per capita non-trophic effects of barnacles (Semibalanus balanoides) on newly settled germlings of the fucoid, Ascophyllum nodosum, in the presence and absence of consumers in experiments on rocky shores throughout the Gulf of Maine, USA. Per capita effects on germlings varied among environments and barnacle life stages, and these interaction strengths were largely unaltered by changing consumer abundance. Whereas previous evidence shows adult barnacles facilitate fucoids, here, we show that recent settlers and established juveniles initially compete with germlings. As barnacles mature, they switch to become facilitators of fucoids. Consumers caused variable mortality of germlings through time comparable to that from competition. Temporally variable effects of interactors (e.g. S. balanoides), or spatial variation in their population structure, in different regions differentially affect target populations (e.g. A. nodosum). This may affect abundance of critical stages and the resilience of target species to environmental change in different geographical regions.
Steeve Comeau, Jean-Pierre Gattuso, Anne-Marin Nisumaa, James Orr (2011)  Impact of aragonite saturation state changes on migratory pteropods.   Proc Biol Sci Aug  
Abstract: Thecosome pteropods play a key role in the food web of various marine ecosystems and they calcify, secreting the unstable CaCO(3) mineral aragonite to form their shell material. Here, we have estimated the effect of ocean acidification on pteropod calcification by exploiting empirical relationships between their gross calcification rates (CaCO(3) precipitation) and aragonite saturation state Ω(a), combined with model projections of future Ω(a). These were corrected for modern model-data bias and taken over the depth range where pteropods are observed to migrate vertically. Results indicate large reductions in gross calcification at temperate and high latitudes. Over much of the Arctic, the pteropod Limacina helicina will become unable to precipitate CaCO(3) by the end of the century under the IPCC SRES A2 scenario. These results emphasize concerns over the future of shelled pteropods, particularly L. helicina in high latitudes. Shell-less L. helicina are not known to have ever existed nor would we expect them to survive. Declines of pteropod populations could drive dramatic ecological changes in the various pelagic ecosystems in which they play a critical role.
Thomas C Adam, Russell J Schmitt, Sally J Holbrook, Andrew J Brooks, Peter J Edmunds, Robert C Carpenter, Giacomo Bernardi (2011)  Herbivory, connectivity, and ecosystem resilience: response of a coral reef to a large-scale perturbation.   PLoS One 6: 8. 08  
Abstract: Coral reefs world-wide are threatened by escalating local and global impacts, and some impacted reefs have shifted from coral dominance to a state dominated by macroalgae. Therefore, there is a growing need to understand the processes that affect the capacity of these ecosystems to return to coral dominance following disturbances, including those that prevent the establishment of persistent stands of macroalgae. Unlike many reefs in the Caribbean, over the last several decades, reefs around the Indo-Pacific island of Moorea, French Polynesia have consistently returned to coral dominance following major perturbations without shifting to a macroalgae-dominated state. Here, we present evidence of a rapid increase in populations of herbivorous fishes following the most recent perturbation, and show that grazing by these herbivores has prevented the establishment of macroalgae following near complete loss of coral on offshore reefs. Importantly, we found the positive response of herbivorous fishes to increased benthic primary productivity associated with coral loss was driven largely by parrotfishes that initially recruit to stable nursery habitat within the lagoons before moving to offshore reefs later in life. These results underscore the importance of connectivity between the lagoon and offshore reefs for preventing the establishment of macroalgae following disturbances, and indicate that protecting nearshore nursery habitat of herbivorous fishes is critical for maintaining reef resilience.
Peter J Edmunds, Vivian Cumbo, Tung-Yung Fan (2011)  Effects of temperature on the respiration of brooded larvae from tropical reef corals.   J Exp Biol 214: Pt 16. 2783-2790 Aug  
Abstract: This study describes the effects of temperature on the respiration of brooded larvae of scleractinian corals, and evaluates the implications of these effects relative to seawater temperature when peak larval release occurs. Respiration rates of larvae from Pocillopora damicornis, Seriatopora hystrix and Stylophora pistillata were quantified in darkness as oxygen uptake during 1-3 h exposures to five temperatures between 26.4 and 29.6°C. To assess the biological significance of these experiments, the temperature of the seawater into which larvae of P. damicornis and S. hystrix were released was measured for 32-34 months over 5 years between 2003 and 2008. Mean respiration varied from 0.029 to 0.116 nmol O(2) larva(-1) min(-1), and was related parabolically to temperature with a positive threshold at 28.0°C. The temperature coefficients (Q(10)) for the ascending portion of these relationships (Q(10)=15-76) indicate that the temperature dependency is stronger than can be explained by kinetics alone, and probably reflects behavioral and developmental effects. Larval release occurred year-round in synchrony with the lunar periodicity when seawater temperature ranged from 21.8 to 30.7°C, and more than half of the sampled larvae were released at 27.5-28.9°C. The coincidence on the temperature scale of peak larval release with the thermal threshold for respiration suggests that high metabolic rates have selective value for pelagic coral larvae. The large and rapid effects of temperature on larval respiration have implications for studies of the effects of climate change on coral reproduction, particularly when seawater temperature exceeds â¼28°C, when our results predict that larval respiration will be greatly reduced.
Peter J Edmunds, Hollie M Putnam, Roger M Nisbet, Erik B Muller (2011)  Benchmarks in organism performance and their use in comparative analyses.   Oecologia 167: 2. 379-390 Oct  
Abstract: Evaluating the response of organisms to stress assumes that functional benchmarks are available against which the response can be gauged, but this expectation remains unfulfilled for many taxa. As a result, attempts to describe the organismic effects of environmental degradation and physiological stress can prove misleading. Functional benchmarks and the effects of stress are particularly germane to coral reefs that globally are exposed to significant environmental challenges, and in this study, we compiled data on scleractinian corals to describe a reference against which stress responses can be gauged. Based on this construct, we tested the veracity of well-established contrasts--involving differences in physiological function among depths and families--to evaluate the capacity of available data to support synthetic analyses. Our analysis used 126 papers describing 37 genera, and at least 73 species, and described 13 traits, first independent of depth, and second, by depth. Data appropriate for these analyses were so sparse that depth- and family-level effects were inconspicuous, although the depth contrast revealed a decline in dark respiration and an increase in calcification (both normalized to area) in deeper water. Our analyses of scleractinian literature revealed limitations of the data available for synthetic analyses, as well for describing functional benchmarks within this taxon. We attribute some of these effects to differences in the physical environment under which measurements were made, and suspect that such problems are commonplace for other taxa. Dynamic Energy Budget (DEB) models provide one means to overcome some of these problems, and they can be used for any taxon to quantitatively summarize data for comparative analyses of stressor responses. The suitability of these models is illustrated for scleractinian corals by predicting from first principles the ratio of Symbiodinium to holobiont carbon and the respiration.
Janna L Fierst, Janet E Kübler, Steven R Dudgeon (2010)  Spatial distribution and reproductive phenology of sexual and asexual Mastocarpus papillatus (Rhodophyta).   Phycologia 49: 3. 274-282 May  
Abstract: Species of the genus Mastocarpus exhibit two distinct life cycles, a sexual alternation of generations and an obligate, asexual direct life cycle that produces only female upright fronds. In the intertidal red alga, M. papillatus (Kützing) sexual fronds dominate southern populations and asexual fronds dominate northern populations along the northeast Pacific coast, a pattern of spatial separation called geographic parthenogenesis. Along the central coast of California, sexual and asexual variants occur in mixed populations, but it is not known whether they are spatially separated within the intertidal zone at a given site. We investigated reproductive phenologies and analyzed patterns of spatial distributions of sexual and asexual M. papillatus at three sites in this region. Sexual M. papillatus were aggregated lower on the shore at two sites and only reproduced during part of a year, while asexual M. papillatus occurred throughout the intertidal range at all sites and reproduced throughout the year. The distribution patterns of sexual and asexual M. papillatus are consistent with a hypothesis of shoreline topography influencing their dynamics of dispersal and colonization. Spatial and temporal partitioning may contribute to the long-term coexistence of sexual and asexual life histories in this, and other, species of Mastocarpus. The occurrence of geographic parthenogenesis at multiple spatial scales in M. papillatus provides an opportunity to gain insight into the phenomenon.
J Wilson White, Jameal F Samhouri, Adrian C Stier, Clare L Wormald, Scott L Hamilton, Stuart A Sandin (2010)  Synthesizing mechanisms of density dependence in reef fishes: behavior, habitat configuration, and observational scale.   Ecology 91: 7. 1949-1961 Jul  
Abstract: Coral and rocky reef fish populations are widely used as model systems for the experimental exploration of density-dependent vital rates, but patterns of density-dependent mortality in these systems are not yet fully understood. In particular, the paradigm for strong, directly density-dependent (DDD) postsettlement mortality stands in contrast to recent evidence for inversely density-dependent (IDD) mortality. We review the processes responsible for DDD and IDD per capita mortality in reef fishes, noting that the pattern observed depends on predator and prey behavior, the spatial configuration of the reef habitat, and the spatial and temporal scales of observation. Specifically, predators tend to produce DDD prey mortality at their characteristic spatial scale of foraging, but prey mortality is IDD at smaller spatial scales due to attack-abatement effects (e.g., risk dilution). As a result, DDD mortality may be more common than IDD mortality on patch reefs, which tend to constrain predator foraging to the same scale as prey aggregation, eliminating attack-abatement effects. Additionally, adjacent groups of prey on continuous reefs may share a subset of refuges, increasing per capita refuge availability and relaxing DDD mortality relative to prey on patch reefs, where the patch edge could prevent such refuge sharing. These hypotheses lead to a synthetic framework to predict expected mortality patterns for a variety of scenarios. For nonsocial, nonaggregating species and species that aggregate in order to take advantage of spatially clumped refuges, IDD mortality is possible but likely superseded by DDD refuge competition, especially on patch reefs. By contrast, for species that aggregate socially, mortality should be IDD at the scale of individual aggregations but DDD at larger scales. The results of nearly all prior reef fish studies fit within this framework, although additional work is needed to test many of the predicted outcomes. This synthesis reconciles some apparent contradictions in the recent reef fish literature and suggests the importance of accounting for the scale-sensitive details of predator and prey behavior in any study system.
Casey P Terhorst, Steve R Dudgeon (2009)  Beyond the Patch: Disturbance Affects Species Abundances in the surrounding Community.   J Exp Mar Bio Ecol 370: 1-2. 120-126 Mar  
Abstract: The role of disturbance in community ecology has been studied extensively and is thought to free resources and reset successional sequences at the local scale and create heterogeneity at the regional scale. Most studies have investigated effects on either the disturbed patch or on the entire community, but have generally ignored any effect of or on the community surrounding disturbed patches. We used marine fouling communities to examine the effect of a surrounding community on species abundance within a disturbed patch and the effect of a disturbance on species abudance in the surrounding community. We varied both the magnitude and pattern of disturbance on experimental settlement plates. Settlement plates were dominated by a non-native bryozoan, which may have established because of the large amount of initial space available on plates. Percent cover of each species within the patch were affected by the surrounding community, confirming previous studies' predictions about edge effects from the surrounding community on dynamics within a patch. Disturbance resulted in lower percent cover in the surrounding community, but there were no differences between magnitudes or spatial patterns of disturbance. Disturbance lowered population growth rates in the surrounding community, potentially by altering the abiotic environment or species interactions. Following disturbance, the recovery of species within a patch may be affected by species in the surrounding community, but the effects of a disturbance can extend beyond the patch and alter abundances in the surrounding community. The dependence of patch dynamics on the surrounding community and the extended effects of disturbance on the surrounding community, suggest an important feedback of disturbance on patch dynamics indirectly via the surrounding community.
Rebecca L Kordas, Steve Dudgeon (2009)  Modeling variation in interaction strength between barnacles and fucoids.   Oecologia 158: 4. 717-731 Jan  
Abstract: The strength by which species interact can vary throughout their ontogeny, as environments vary in space and time, and with the density of their populations. Characterizing strengths of interaction in situ for even a small number of species is logistically difficult and may apply only to those conditions under which the estimates were derived. We sought to combine data from field experiments estimating interaction strength of life stages of the barnacle, Semibalanus balanoides, on germlings of Ascophyllum nodosum, with a model that explored the consequences of variability at per capita and per population levels to the abundance of year-old algal recruits. We further simulated how this interaction affected fucoid germling abundance as the timing of their respective settlements varied relative to one another, as occurs regionally across the Gulf of Maine, USA. Juvenile S. balanoides have a weak estimated per capita effect on germlings. Germling populations are sensitive to variation in per capita effects of juvenile barnacles because of the typically large population sizes of the latter. However, high mortality of juvenile barnacles weakens the population interaction strength over time. Adult barnacles probably weakly facilitate fucoid germlings, but greater survival of adults sustains the strength of that interaction at the population level. Germling abundance is positively associated with densities of adult barnacles and negatively associated with that of juvenile barnacles. Metamorphosing cyprid larvae have the strongest per capita effect on germling abundance, but the interaction between the two stages is so short-lived that germling abundance is altered little. Variation in the timing of barnacle and A. nodosum settlement relative to one another had very little influence on the abundance of yearling germlings. Interactions between barnacles and germlings may influence the demographic structure of A. nodosum populations and the persistence of fucoid-dominated communities on sheltered rocky shores in New England.
Peter S Petraitis, Elizabeth T Methratta, Erika C Rhile, Nicholas A Vidargas, Steve R Dudgeon (2009)  Experimental confirmation of multiple community states in a marine ecosystem.   Oecologia 161: 1. 139-148 Aug  
Abstract: Small changes in environmental conditions can unexpectedly tip an ecosystem from one community type to another, and these often irreversible shifts have been observed in semi-arid grasslands, freshwater lakes and ponds, coral reefs, and kelp forests. A commonly accepted explanation is that these ecosystems contain multiple stable points, but experimental tests confirming multiple stable states have proven elusive. Here we present a novel approach and show that mussel beds and rockweed stands are multiple stable states on intertidal shores in the Gulf of Maine, USA. Using broad-scale observational data and long-term data from experimental clearings, we show that the removal of rockweed by winter ice scour can tip persistent rockweed stands to mussel beds. The observational data were analyzed with Anderson's discriminant analysis of principal coordinates, which provided an objective function to separate mussel beds from rockweed stands. The function was then applied to 55 experimental plots, which had been established in rockweed stands in 1996. Based on 2005 data, all uncleared controls and all but one of the small clearings were classified as rockweed stands; 37% of the large clearings were classified as mussel beds. Our results address the establishment of mussels versus rockweeds and complement rather than refute the current paradigm that mussel beds and rockweed stands, once established, are maintained by site-specific differences in strong consumer control.
Steve Dudgeon, Kylla M Benes, Stacy A Krueger, Janet Kübler, Paul Mroz, Christin T Slaughter (2009)  On the use of experimental diets for physiological studies of hydrozoans.   J Mar Biol Assoc U.K. 89: 1. 83-88 Feb  
Abstract: Recent studies of hydrozoans suggest that metabolic factors associated with the physiology of gastrovascular fluid transport play a role in regulating morphogenetic development of colonies. In that context, the objective of this study was to develop a system to experimentally control diets of hydrozoans in culture that could be used to test effects of specific compounds. This diet delivery system consisted of a known concentration of homogenate of brine shrimp nauplii that was solidified in a 1% agar block cut to the size of, and containing the equivalent of, a single, 2-day old brine shrimp nauplius larva. We tested the utility of this system by comparing the frequencies of ingestion, and rates of gastrovascular transport and growth following feeding, between polyps of Podocoryna carnea fed either a single brine shrimp nauplius (controls) or an agar cube including brine shrimp homogenate. Polyps fed experimental diets showed similar rates of gastrovascular transport (6 and 12 h after feeding) and growth (24 h after feeding) to those of polyps fed a brine shrimp nauplius suggesting that no significant artefacts existed associated with these response variables. However, the frequency of ingestion of experimental foods by polyps was much less than that by control polyps. These results imply that this system of delivery of experimental diets has potential as a means to manipulate physiological state and assay the effects on morphogenesis of hydrozoan colonies, but must first overcome limitations of low ingestion frequency.
Jameal F Samhouri, Mark A Steele, Graham E Forrester (2009)  Inter-cohort competition drives density dependence and selective mortality in a marine fish.   Ecology 90: 4. 1009-1020 Apr  
Abstract: For organisms with complex life cycles, the transition between life stages and between habitats can act as a significant demographic and selective bottleneck. In particular, competition with older and larger conspecifics and heterospecifics may influence the number and characteristics of individuals successfully making the transition. We investigated whether the availability of enemy-free space mediated the interaction between adult goldspot gobies (Gnatholepis thompsoni), a common tropical reef fish, and juvenile conspecifics that had recently settled from the plankton. We added rocks, which provide refuge from predators, to one-half of each of five entire coral reefs in the Bahamas and measured the survival and growth of recent settlers in relation to adult goby densities. We also evaluated whether mortality was selective with respect to three larval traits (age at settlement, size at settlement, and presettlement growth rate) and measured the influence of refuge availability and adult goby density on selection intensity. Selective mortality was measured by comparing larval traits of newly settled gobies (< or = 5 d postsettlement) with those of survivors (2-3 week postsettlement juveniles). We detected a negative relationship between juvenile survival and adult goby density in both low- and high-refuge habitats, though experimental refuge addition reduced the intensity of this density dependence. Juvenile growth also declined with increasing adult goby density, but this effect was similar in both low- and high-refuge habitats. Refuge availability had no consistent effect on selective mortality, but adult goby density was significantly related to the intensity of size-selective mortality: bigger juveniles were favored where adults were abundant, and smaller juveniles were favored where adults were rare. Given the typically large difference in sizes of juveniles and adults, similar stage-structured interactions may be common but underappreciated in many marine species.
Erik B Muller, Sebastiaan A L M Kooijman, Peter J Edmunds, Francis J Doyle, Roger M Nisbet (2009)  Dynamic energy budgets in syntrophic symbiotic relationships between heterotrophic hosts and photoautotrophic symbionts.   J Theor Biol 259: 1. 44-57 Jul  
Abstract: In this paper we develop and investigate a dynamic energy budget (DEB) model describing the syntrophic symbiotic relationship between a heterotrophic host and an internal photoautotrophic symbiont. The model specifies the flows of matter and energy among host, symbiont and environment with minimal complexity and uses the concept of synthesizing units to describe smoothly the assimilation of multiple limiting factors, in particular inorganic carbon and nitrogen, and irradiance. The model has two passive regulation mechanisms: the symbiont shares only photosynthate that it cannot use itself, and the host delivers only excess nutrients to the symbiont. With parameter values plausible for scleractinian corals, we show that these two regulation mechanisms suffice to obtain a stable symbiotic relationship under constant ambient conditions, provided those conditions support sustenance of host and symbiont. Furthermore, the symbiont density in the host varies relatively little as a function of ambient food density, inorganic nitrogen and irradiance. This symbiont density tends to increase with light deprivation or nitrogen enrichment, either directly or via food. We also investigate the relative benefit each partner derives from the relationship and conclude that this relationship may shift from mutualism to parasitism as environmental conditions change.
Michelle J Paddack, John D Reynolds, Consuelo Aguilar, Richard S Appeldoorn, Jim Beets, Edward W Burkett, Paul M Chittaro, Kristen Clarke, Rene Esteves, Ana C Fonseca, Graham E Forrester, Alan M Friedlander, Jorge García-Sais, Gaspar González-Sansón, Lance K B Jordan, David B McClellan, Margaret W Miller, Philip P Molloy, Peter J Mumby, Ivan Nagelkerken, Michael Nemeth, Raúl Navas-Camacho, Joanna Pitt, Nicholas V C Polunin, Maria Catalina Reyes-Nivia, D Ross Robertson, Alberto Rodríguez-Ramírez, Eva Salas, Struan R Smith, Richard E Spieler, Mark A Steele, Ivor D Williams, Clare L Wormald, Andrew R Watkinson, Isabelle M Côté (2009)  Recent region-wide declines in Caribbean reef fish abundance.   Curr Biol 19: 7. 590-595 Apr  
Abstract: Profound ecological changes are occurring on coral reefs throughout the tropics, with marked coral cover losses and concomitant algal increases, particularly in the Caribbean region. Historical declines in the abundance of large Caribbean reef fishes likely reflect centuries of overexploitation. However, effects of drastic recent degradation of reef habitats on reef fish assemblages have yet to be established. By using meta-analysis, we analyzed time series of reef fish density obtained from 48 studies that include 318 reefs across the Caribbean and span the time period 1955-2007. Our analyses show that overall reef fish density has been declining significantly for more than a decade, at rates that are consistent across all subregions of the Caribbean basin (2.7% to 6.0% loss per year) and in three of six trophic groups. Changes in fish density over the past half-century are modest relative to concurrent changes in benthic cover on Caribbean reefs. However, the recent significant decline in overall fish abundance and its consistency across several trophic groups and among both fished and nonfished species indicate that Caribbean fishes have begun to respond negatively to habitat degradation.
Jameal F Samhouri, Richard R Vance, Graham E Forrester, Mark A Steele (2009)  Musical chairs mortality functions: density-dependent deaths caused by competition for unguarded refuges.   Oecologia 160: 2. 257-265 May  
Abstract: Structural refuges within which prey can escape from predators can be an important limiting resource for the prey. In a manner that resembles the childhood game of musical chairs, many prey species rapidly retreat to shared, unguarded refuges whenever a predator threatens, and only when refuges are relatively abundant do all prey individuals actually escape. The key feature of this process is that the per capita prey mortality rate depends on the ratio of prey individuals to refuges. We introduce a new class of mortality functions with this feature and then demonstrate statistically that they describe field mortality data from a well-studied coral reef fish species, the Caribbean bridled goby Coryphopterus glaucofraenum, substantially better than do several mortality functions of more conventional form.
Graham A Ferrier, Robert C Carpenter (2009)  Subtidal benthic heterogeneity: flow environment modification and impacts on marine algal community structure and morphology.   Biol Bull 217: 2. 115-129 Oct  
Abstract: The shallow subtidal zone of rocky coastlines is a highly dynamic environment characterized by micro- and macroscopic benthic structures that alter the ambient flow environment, creating "flow microhabitats." We examined the impact of macroscopic benthic structure on the maximum flow speeds and the corresponding macroalgal community cover and morphological diversity observed in response to microhabitats in both exposed and sheltered near-shore sites. Flow speeds were reduced by a factor of 2 within crevices and also in the flow-shadow of protruding rock substrate when compared to neighboring unobstructed planar microhabitats. Algal communities within crevices and in the wake of protrusions were found to have greater cover of foliose red algal species compared to horizontal microhabitats in exposed sites, but reduced cover of these species in sheltered sites. The morphologies of two rhodophytes common to all microhabitats, Chondracanthus spinosus and Pterocladiella capillacea, were examined at both exposed and sheltered sites. Exposed horizontal morphotypes of both species were generally smaller and streamlined, whereas thalli from within crevices and in the wake of protrusions were larger and bushier. We conclude that algal cover and morphology is affected by the alteration in flow around both protruding bodies and crevices when compared to unobstructed sites.
Hollie M Putnam, Peter J Edmunds, Tung-Yung Fan (2008)  Effect of temperature on the settlement choice and photophysiology of larvae from the reef coral Stylophora pistillata.   Biol Bull 215: 2. 135-142 Oct  
Abstract: To better understand the consequences of climate change for scleractinian corals, Stylophora pistillata was used to test the effects of temperature on the settlement and physiology of coral larvae. Freshly released larvae were exposed to temperatures of 23 degrees C, 25 degrees C (ambient), and 29 degrees C at light intensities of approximately 150 micromol photons m(-2) s(-1). The effects were assessed after 12 h as settlement to various substrata (including a choice between crustose coralline algae [CCA] and limestone) and as maximum quantum yield of PSII (F(v)/F(m)) in the larvae versus in their parents. Regardless of temperature, 50%-73% of the larvae metamorphosed onto the plastic of the incubation trays or in a few cases were drifting in the water, and 14% settled on limestone. However, elevated temperature (29 degrees C) reduced the percentage of larvae swimming by 81%, and increased the percentage choosing CCA nearly 7-fold, both relative to the outcomes at 23 degrees C. Because temperature did not affect settlement on limestone or plastic, increased settlement on CCA reflected temperature-mediated choices by larvae that otherwise would have remained swimming. Interestingly, F(v)/F(m) was unaffected by temperature, but it was 4% lower in the larvae than in the parents. These results are important because they show that temperature can affect the settlement of coral larvae and because they reveal photophysiological differences between life stages that might provide insights into the events associated with larval development.
Robin Elahi, Peter J Edmunds (2007)  Tissue age affects calcification in the scleractinian coral Madracis mirabilis.   Biol Bull 212: 1. 20-28 Feb  
Abstract: In this study, two factorial experiments were used to investigate the role of tissue age in affecting the phenotypic expression of calcification in scleractinian corals. Both experiments tested whether calcification was altered by tissue age and whether corals of different ages exploit plasticity to differing degrees by altering calcification rates under new environmental conditions. To isolate age and size effects, branches of the Caribbean coral Madracis mirabilis were broken into a distal portion that was functionally young and a proximal portion that was functionally old. Fragments were transplanted from a deep (17 m) to a shallow (9 m) site in a Jamaican lagoon to test whether age affected the plasticity of calcification. Both experiments demonstrated that calcification scaled isometrically in the two age groups, and although scaling exponents were indistinguishable statistically among ages, young fragments calcified faster than old fragments. Thus, the effect of age on calcification rate was absolute and independent of size. However, the interactive effect of age and depth was not significant, demonstrating that ability to alter calcification rate (i.e., the extent of phenotypic plasticity for this trait) was unaffected by age. Together, these patterns are consistent with the hypothesis that the proximal modules (i.e., polyps) of M. mirabilis are subject to physiological senescence, as has been reported for other clonal organisms, including algae, fungi, plants, bryozoans, ascidians, and other cnidarians.
Robert C Carpenter, Peter J Edmunds (2006)  Local and regional scale recovery of Diadema promotes recruitment of scleractinian corals.   Ecol Lett 9: 3. 271-280 Mar  
Abstract: The phase change from coral to macroalgal dominance on many Caribbean reefs was exacerbated by the mortality of the echinoid Diadema antillarum in 1983-1984, and until recently, this sea urchin has remained rare on reefs throughout the western Atlantic. By the late 1990s, Diadema started to reappear in large numbers on some Jamaican reefs, and by 2000, the high densities were correlated with significantly greater abundances of juvenile corals. Here, we show that dense populations of Diadema now occur over a multi-kilometre-wide scale at six locations scattered along a 4100 km arc across the entire Caribbean. In all cases, these dense populations are found in shallow water (< 6 m depth) on outer reef communities and are associated with reduced macroalgal cover and enhanced coral recruitment. We conclude that population recovery of Diadema is occurring at both local and regional scales, and that grazing by this echinoid is creating conditions favouring the recruitment of corals.
Graham E Forrester, Bryn Evans, Mark A Steele, Richard R Vance (2006)  Assessing the magnitude of intra- and interspecific competition in two coral reef fishes.   Oecologia 148: 4. 632-640 Jul  
Abstract: Many field experiments have tested for effects of competition in nature, but relatively few have used designs allowing simultaneous assessment of the influence of intra- and interspecific competition. Using a response surface design and a press manipulation of densities, we tested effects of competition within and between two species of coral reef fishes (Coryphopterus glaucofraneum and Gnatholepis thompsoni). By tracking individually tagged fishes, we showed that the per-capita effect of intraspecific competitors on individual growth was at least twice as great as the effect of interspecific competitors. Growth rate was better predicted by measures of density that incorporated body size, rather than numerical density, suggesting interference competition. Individuals of both species interacted aggressively with conspecifics at least twice as often as with heterospecifics. Individuals of both species also covered more area while foraging and spent less time in shelter when crowded than when at lower densities. In combination, these behaviours suggest that increased metabolic costs at high density contribute to competitive effects on growth. These competitive interactions occurred among adult fishes, so reduced growth may translate to reduced fecundity as well as reduced survival, and so contribute to population regulation.
Peter J Edmunds (2006)  Temperature-mediated transitions between isometry and allometry in a colonial, modular invertebrate.   Proc Biol Sci 273: 1599. 2275-2281 Sep  
Abstract: The evolutionary success of animal design is strongly affected by scaling and virtually all metazoans are constrained by allometry. One body plan that appears to relax these constraints is a colonial modular (CM) design, in which modular iteration is hypothesized to support isometry and indeterminate colony size. In this study, growth rates of juvenile scleractinians (less than 40mm diameter) with a CM design were used to test this assertion using colony diameters recorded annually for a decade and scaling exponents (b) for growth calculated from double logarithmic plots of final versus initial diameters. For all juvenile corals, b differed significantly among years, with isometry (b=1) in 4 years, but positive allometry (b>1) in 5 years. The study years were characterized by differences in seawater temperature that were associated significantly with b for growth, with isometry in warm years but positive allometry in cool years. These results illustrate variable growth scaling in a CM taxon and suggest that the switch between scaling modes is mediated by temperature. For the corals studied, growth was not constrained by size, but this outcome was achieved through both isometry and positive allometry. Under cooler conditions, positive allometry may be beneficial as it represents a growth advantage that increases with size.
Mark A Steele, Graham E Forrester (2005)  Small-scale field experiments accurately scale up to predict density dependence in reef fish populations at large scales.   Proc Natl Acad Sci U S A 102: 38. 13513-13516 Sep  
Abstract: Field experiments provide rigorous tests of ecological hypotheses but are usually limited to small spatial scales. It is thus unclear whether these findings extrapolate to larger scales relevant to conservation and management. We show that the results of experiments detecting density-dependent mortality of reef fish on small habitat patches scale up to have similar effects on much larger entire reefs that are the size of small marine reserves and approach the scale at which some reef fisheries operate. We suggest that accurate scaling is due to the type of species interaction causing local density dependence and the fact that localized events can be aggregated to describe larger-scale interactions with minimal distortion. Careful extrapolation from small-scale experiments identifying species interactions and their effects should improve our ability to predict the outcomes of alternative management strategies for coral reef fishes and their habitats.
Peter J Edmunds (2005)  The effect of sub-lethal increases in temperature on the growth and population trajectories of three scleractinian corals on the southern Great Barrier Reef.   Oecologia 146: 3. 350-364 Dec  
Abstract: To date, coral death has been the most conspicuous outcome of warming tropical seas, but as temperatures stabilize at higher values, the consequences for the corals remaining will be mediated by their demographic responses to the sub-lethal effects of temperature. To gain insight into the nature of these responses, here I develop a model to test the effect of increased temperature on populations of three pocilloporid corals at One Tree Island, near the southern extreme of the Great Barrier Reef (GBR). Using Seriatopora hystrix, S. caliendrum and Pocillopora damicornis as study species, the effects of temperature on growth were determined empirically, and the dynamics of their populations determined under natural temperatures over a 6-month period between 1999 and 2000 [defined as the study year (SY)]. The two data sets were combined in a demographic test of the possibility that the thermal regime projected for the southern GBR in the next 55-83 years--warmer by 3 degrees C than the study year (the SY+3 regime), which is equivalent to 1.4 degrees C warmer than the recent warm year of 1998--would alter coral population trajectories through the effects on coral growth alone; the analyses first were completed by species, then by family after pooling among species. Laboratory experiments showed that growth rates (i.e., calcification) varied significantly among species and temperatures, and displayed curvilinear thermal responses with growth maxima at approximately 27.1 degrees C. Based on these temperature-growth responses, the SY+3 regime is projected to: (1) increase annualized growth rates of all taxa by 24-39%, and defer the timing of peak growth from the summer to the autumn and spring, (2) alter the intrinsic rate of population growth (lambda) for S. hystrix (lambda decreases 26%) and S. caliendrum (lambda increases 5%), but not for P. damicornis, and (3) have a minor effect on lambda (a 0.3% increase) for the Pocilloporidae, largely because lambda varies more among species than it does between temperatures. Ten-year population projections suggest that the effects of a sub-lethal increase in temperature (i.e., the SY+3 regime) are relatively small compared to the interspecific differences in population dynamics, but nevertheless will alter the population size and increase the relative abundance of large colonies at the expense of smaller colonies for all three species, as well as the Pocilloporidae. These effects may play an important role in determining the nuances of coral population structure as seawater warms, and their significance may intensity if the coral species pool is depleted of thermally sensitive species by bleaching.
D J Gardella, P J Edmunds (2001)  The effect of flow and morphology on boundary layers in the scleractinians Dichocoenia stokesii (Milne-Edwards and Haime) and Stephanocoenia michilini (Milne-Edwards and Haime).   J Exp Mar Bio Ecol 256: 2. 279-289 Jan  
Abstract: Mass transfer characteristics of scleractinian corals are affected by their skeletal morphology and the concentration gradients that develop as a consequence of the interactions of their morphology and biomass with the overlying seawater. These interactions can have a profound effect on coral metabolism. In this study, boundary layer characteristics were compared between different size colonies of the corals Dichocoenia stokesii and Stephanocoenia michilini to determine the relative roles of colony size and corallite structures (i.e. surface roughness) in mass transfer. Colonies of both species were rounded in shape, but differed in small-scale roughness as measured by the elevation of corallites. Additionally, D. stokesii had a greater aspect ratio than S. michilini, and their colonies were slightly taller for a given diameter. Boundary layers were characterized by placing dead coral skeletons in a flow tank and estimating shear velocities (u(*)) at different flow speeds. The effects of flow speed, size, and roughness on shear velocities were estimated for two juvenile size classes (10-20 and 30-40 mm diameter) of each species that were exposed to unidirectional flow regimes (4 and 17 cm s(-1)). Shear velocities were significantly greater in high, compared to low flow, and there was a significant interaction between colony size and surface roughness; the interaction was caused by a difference in magnitude, rather than direction, of the effect of roughness and size on u(*). Thus, there was a greater degree of turbulence at high flow compared to low flow, regardless of roughness or size, and the greatest turbulence occurred over large colonies of D. stokesii at high flow. Together, these results suggest that boundary layers around small corals are heavily influenced by upstream roughness elements, and more strongly affected by flow regimes than skeletal features. The relationship between colony morphology (i.e. aspect ratio and, possibly, surface roughness) and boundary layer characteristics may be non-linear in small corals.
G F River, P J Edmunds (2001)  Mechanisms of interaction between macroalgae and scleractinians on a coral reef in Jamaica.   J Exp Mar Bio Ecol 261: 2. 159-172 Jul  
Abstract: After several decades of disturbance, many coral reefs in the Caribbean are dominated by macroalgae. One process affecting this transition is coral-macroalgal competition, yet few studies have addressed the mechanisms involved. In this study, we investigated competition between the tall and bushy macroalga Sargassum hystrix (J. Agardh) and the branching coral Porites porites (Pallas) on a shallow reef in Jamaica. Experiments were designed to expose coral branches to different treatments to test the role of shading and abrasion by Sargassum on coral growth and polyp expansion. Corals exposed to Sargassum grew significantly more slowly (80% reduction) than controls, but this effect was absent when corals were caged to prevent physical contact with macroalgae. Light levels were reduced in both the algal and cage treatments, but shading apparently had little effect on the growth of corals in cages. Short-term measurements of integrated net water flow did not detect variation among treatments. In algal-mimic treatments, where clear plastic strips could touch but not shade the corals, growth rates were 25% lower than controls, but this effect was not statistically significant. Thus, the growth of corals in contact with Sargassum was reduced by abrasion and, to a lesser extent, by factors unique to living macroalgae. Analysis of polyp expansion showed that polyps were more frequently retracted when corals were in contact with macroalgae or algal-mimics compared to controls or cage treatment; the frequency of polyp contraction was correlated positively with growth. Together, these results suggest that abrasion-mediated polyp retraction is one of the primary mechanisms of competition utilized by tall (ca. 17 cm) macroalgae against scleractinian corals.
P J Edmunds, R C Carpenter (2001)  Recovery of Diadema antillarum reduces macroalgal cover and increases abundance of juvenile corals on a Caribbean reef.   Proc Natl Acad Sci U S A 98: 9. 5067-5071 Apr  
Abstract: The transition of many Caribbean reefs from coral to macroalgal dominance has been a prominent issue in coral reef ecology for more than 20 years. Alternative stable state theory predicts that these changes are reversible but, to date, there is little indication of this having occurred. Here we present evidence of the initiation of such a reversal in Jamaica, where shallow reefs at five sites along 8 km of coastline now are characterized by a sea urchin-grazed zone with a mean width of 60 m. In comparison to the seaward algal zone, macroalgae are rare in the urchin zone, where the density of Diadema antillarum is 10 times higher and the density of juvenile corals is up to 11 times higher. These densities are close to those recorded in the late 1970s and early 1980s and are in striking contrast to the decade-long recruitment failure for both Diadema and scleractinians. If these trends continue and expand spatially, reefs throughout the Caribbean may again become dominated by corals and algal turf.
S V Vollmer, P J Edmunds (2000)  Allometric scaling in small colonies of the scleractinian coral Siderastrea siderea (Ellis and Solander).   Biol Bull 199: 1. 21-28 Aug  
Abstract: Although most physiological traits scale allometrically in unitary organisms, it has been hypothesized that modularity allows for isometric scaling in colonial modular taxa. Isometry would allow increases in size without functional constraints, and is thought to be of central importance to the success of a modular design. Yet, despite its potential importance, scaling in these organisms has received little attention. To determine whether scleractinian corals are free of allometric constraints, we quantified metabolic scaling, measured as aerobic respiration, in small colonies (< or =40 mm in diam.) of the scleractinian Siderastrea siderea. We also quantified the scaling of colony surface area with biomass, since the proposed isometry is contingent upon maintaining a constant ratio of surface area to biomass (or volume) with size. Contrary to the predicted isometry, aerobic respiration scaled allometrically on biomass with a slope (b) of 0.176, and colony surface area scaled allometrically on biomass with a slope of 0.730. These findings indicate that small colonies of S. siderea have disproportionately high metabolic rates and SA:B ratios compared to their larger counterparts. The most probable explanations for the allometric scaling of aerobic respiration are (1) a decline in the SA:B ratio with size such that more surface area is available per unit of biomass for mass transfer in the smallest colonies, and (2) the small size, young age, and disproportionately high growth rates of the corals examined. This allometric scaling also demonstrates that modularity, alone, does not allow small colonies of S. siderea to overcome allometric constraints. Further studies are required to determine whether allometric scaling is characteristic of the full size range of colonies of S. siderea.
Cheroske, Williams, Carpenter (2000)  Effects of physical and biological disturbances on algal turfs in Kaneohe Bay, Hawaii.   J Exp Mar Bio Ecol 248: 1. 1-34 May  
Abstract: Disturbance in coral reef environments commonly results in an algal community dominated by highly productive, small filamentous forms and cyanobacteria, collectively known as algal turf. Research on the types of disturbance responsible for this community structure has concentrated mainly on biological disturbance in the form of grazing, although physical and other forms of biological disturbances may be important in many coral reef areas. On the reef flat in Kaneohe Bay, Oahu, Hawaii, algal turfs grow primarily upon coral rubble that tumbles with passing swells. We manipulated the frequency of rubble tumbling in field experiments to mimic the effects of physical disturbance by abrasion and light reduction on algal biomass, canopy height, and community structure. Treatments approximated a gradient of disturbance intensities and durations that occur on the reef flat. Although sea urchins and herbivorous fishes are not widespread and abundant on the reef flat, biological disturbances to algal turf communities in the form of herbivory by small crabs and abrasion by tough macroalgae contributed significantly to the variation in algal turf biomass. Within all experiments increasing disturbance significantly reduced algal biomass and canopy heights and the community structure shifted to more disturbance-tolerant algal forms. This study shows that the chronic physical disturbances from water motion and biological disturbances other than grazing from large herbivores can control algal communities in coral reef environments.
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