Abstract: Phenotypic plasticity enables multicellular organisms to adjust morphologies and various life history traits to variable environmental challenges. Here, we elucidate fixed and plastic architectural rules for colony astogeny in multiple types of colonial ramets, propagated by cutting from genets of the branching coral Stylophora pistillata from Eilat, the Red Sea. We examined 16 morphometric parameters on 136 one-year old S. pistillata colonies (of seven genotypes), originating from small fragments belonging, each, to one of three single-branch types (single tips, start-up, and advanced bifurcating tips) or to structural preparative manipulations (representing a single or two growth axes). Experiments were guided by the rationale that in colonial forms, complexity of evolving phenotypic plasticity can be associated with a degree of structural modularity, where shapes are approached by erecting iterative growth patterns at different levels of coral-colony organization. Analyses revealed plastic morphometric characters at branch level, and predetermined morphometric traits at colony level (only single trait exhibited plasticity under extreme manipulation state). Therefore, under the experimental manipulations of this study, phenotypic plasticity in S. pistillata appears to be related to branch level of organization, whereas colony traits are controlled by predetermined genetic architectural rules. Each level of organization undergoes its own mode of astogeny. However, depending on the original ramet structure, the spherical 3-D colonial architecture in this species is orchestrated and assembled by both developmental trajectories at the branch level, and traits at the colony level of organization. In nature, branching colonial forms are often subjected to harsh environmental conditions that cause fragmentation of colony into ramets of different sizes and structures. Developmental traits that are plastic, responding to fragment structure and are not predetermine in controlling astogeny, allow formation of species-specific architecture product through integrated but variable developmental routes. This adaptive plasticity or regeneration is an efficient mechanism by which isolated fragments of branching coral species cope with external environmental forces.
Abstract: This study investigated aspects of the biology of the monogenean gill ectoparasite Polylabris cf. mamaevi (Polyopisthocotylea: Microcotyleae) infecting rabbitfish, Siganus rivulatus (Forskal) (Teleostei: Siganidae). Both host and parasite are Lessepsian immigrants that have co-invaded the Mediterranean Sea via the Suez Canal. The infection prevalence and mean intensity of the polyopisthocotylean was examined in both native and immigrant host populations and found to be three times greater in the new biogeographical region. In vitro observations on parasite eggs from both areas indicated that hatching occurred almost exclusively in the dark. The reaction of the larval oncomiracidia to water flow and secreted host chemicals indicated that neither Red Sea nor Mediterranean oncomiracidia exposed to waterborne host metabolites displayed any significant response or change in behavior; however, upon encountering flow, they ceased to swim and drifted passively downstream. Host specificity of P. cf. mamaevi may have co-evolved with temporal synchronization of the parasite with the host's diurnal activity. Hatching of P. cf. mamaevi eggs was rhythmical and the timing coincided with the known nocturnal resting behavior of the hosts, when their schools lie immobile on the sea bottom. After hatching, abrupt cessation of active swimming by the oncomiracidia upon sensing host inhalant gill-ventilating currents is likely to facilitate rapid, passive entry into the gill chamber of a suitable host. The greater abundance of P. cf. mamaevi in the invading (Mediterranean) populations is probably due to the changed, new environment, possibly impacting host resistance to the parasite and encouraging heavier infections.
Abstract: The architecture of the colony in a branching coral is an iterative process in which new layers of calcium carbonate compile atop existing structures that remain unchanged. Colony growth and development, known as astogeny, is believed to be a continuous process, characterized by replication of lower rank unites, polyps, and branches. This study seeks to explore the genetic blueprint of branch-to-colony developmental trajectory in the branching coral Stylophora pistillata, within an astogeny period of 1 year. One hundred small branches (initially 2-4 cm long) were sampled from 10 colonies. A year later, 63 remaining colonies were analyzed for their architectural rules by using 15 morphometric parameters. Multivariate statistical tests were preformed. Cluster and two-dimensional nonmetric Multi-Dimensional Scaling analyses revealed that the 10 genotypes could be divided into two major morphometric groups and two intermediate groups, whereas SIMPER analyses (a similarity percentage test) on within-genet similarities showed high similarity between the ramets developed from each of the 10 genotypes. Although, at first, it seemed that different colonies exhibited variable and different architectural designs (each characterized by specific morphometric parameters), a comprehensive analysis revealed that all 10 coral genotypes exhibited a single common developmental plan that was characterized by a continuum of architectural design with several distinct stages. Each stage is marked by its own characteristic morphometric parameters. Changing of developmental rules during the trajectory from branch to coral colony may help the colony to cope better with environmental constraints.
Abstract: The accelerating deterioration of the coral reefs of Eilat has raised debate over the exact causes and how they affect the reefs. The hypothesis of the present study was that a low recruitment rate of reef-building coral species may play an important role in the decline of the Eilat reefs. Our goal was to assess spatial and temporal recruitment patterns in Eilat, focusing on examining the possible impact of human activities. The results of coral recruitment to 10 series of ceramic tiles on metal racks, revealed very low overall recruitment relative to other geographical regions. In addition, we found that recruitment rates and recruit survival were lowest at sites closest to the major eutrophication sources in Eilat. The low recruitment rates may be chronically too low to compensate for the elevated coral mortality rates of recent years. The significant differences between the present study and a similar study carried out during the same period using a different method, emphasize the crucial need for a standardized method for recruitment assessment in coral reefs worldwide.
Abstract: The extensive deterioration of coral reefs worldwide highlights the importance of creating efficient monitoring methods to best assess their state of health. At present, several suggested parameters serve such indicators. None of these, however, is well accepted as reliably representing reef community health. In the present study we examine a new approach based on the ratio between mortality and recruitment rates of branching corals, which we term 'Deterioration Index' (DI). It aims at providing a quantitative indication of the state of health of reef-building coral communities. The method was developed and tested on 16 coral communities on artificially laid rocks along the coast of Eilat, Red Sea (Gulf of Aqaba). In contrast to frequently used indices (i.e. mortality rate, abundance and species richness), which did not demonstrate a consistent result in comparing disturbed vs. undisturbed coral communities, the DI revealed significant differences between these communities. Our results suggest that the use of the DI may enable the detection of disturbed coral communities in one instance monitoring, where the other parameters had failed. The DI, therefore, may provide a comparable quantitative assessment of the deterioration process and its intensity in a coral community. We propose the DI approach as an efficient and applicable tool for coral reef monitoring.
Abstract: The biota of the eastern basin of the Mediterranean Sea has experienced dramatic changes in the last decades, in part as a result of the massive invasion of Red Sea species. The mechanism generally hypothesized for the 'Red-to-Med' invasion is that of natural dispersal through the Suez Canal. To date, however, this hypothesis has not been tested. This study examines the mode of invasion, using as a model the mussel Brachidontes pharaonis, an acclaimed 'Lessepsian migrant' that thrives along the eastern Mediterranean coast. Our findings reveal two distinct lineages of haplotypes, and five possible explanations are discussed for this observation. We show that the genetic exchange among the Mediterranean, Gulf of Suez and the northern Red Sea is sufficiently large to counteract the build up of sequential genetic structure. Nevertheless, these basins are rich in unique haplotypes of unknown origin. We propose that it is historic secondary contact, an ongoing anthropogenic transport or both processes, that participate in driving the population dynamics of B. pharaonis in the Mediterranean and northern Red Sea.
Abstract: The detection and location of specific organisms in the aquatic environment, whether they are mates, prey or settlement sites, are two of the most important challenges facing aquatic animals. Large marine invertebrates such as lobsters have been found to locate specific organisms by navigating in the plume of chemicals emitted by the target. However, active plume tracking in flow by small organisms such as marine larvae has received little scientific attention. Here, we present results from a study examining host location in flow by nauplius larvae of the barnacle Trevathana dentata, which inhabits the stony reef coral Cyphastrea chalcidicum. The experiments included analysis of larval motion in an annular flume under four conditions: (i) still water, (ii) in flow, (iii) in still water with waterborne host metabolites and (iv) in flow with host metabolites. Our results show that T. dentata nauplii are unable to locate their target organism in still water using chemotaxis, but are capable of efficient host location in flow using odour-gated rheotaxis. This technique may enable host location by earlier, less-developed larval stages.
Abstract: Over the last two centuries, the marine life of the Eastern Mediterranean has been influenced by two major factors: one is beneficial, and concerns species migration, such as the opening of the Suez Canal, which enriched the impoverished eastern Mediterranean Sea with over 300 species of fish and invertebrates of Red Sea origin; while the other, a negative and possibly wider-reaching factor, is that of man-made pollution, which has induced unpredictable changes, destabilizing the biological world in both magnitude and duration. Initially cryptic, the effects caused by pollutants first occur at the biochemical and cellular levels of an organism, causing alterations and deviations from the normal, strongly mobilizing its defense systems. Conventional methodologies of ecological analyses, based on species and specimen numbers, cannot detect such alterations. Studying several mollusk populations from polluted and reference sites of the Red Sea and Mediterranean littoral of Israel, we used specific markers for in vivo and in vitro studies to expose the state of micronucleation; levels of defense transport systems such as membrane transport system of organic anions (SATOA) and organic cations (OCT); the state of the multi-xenobiotic resistance-mediating transporter (MXRtr). Based on fluorescent microscopy and microfluorometry, these markers offer powerful tools to expose cryptic changes in the affected populations and provide data necessary for planning and management to protect animal communities and preserve their biological diversity. Comparative analysis of general gene-expression in polluted and reference sites indicates that stress factors have differentially affected the various biological taxa and separated phenotypic sub-populations, producing a novel type of punctuated selection. Such factors, although negative in their influences, in some instances altering the qualities of organisms, and establishing alterations in their hereditary information, pre-adapt them to survive and succeed in new situations.
