Seriatopora

Abstract: Reef-building corals are fundamental to the most diverse marine ecosystems, yet a detailed understanding of the processes involved in the establishment, persistence and ecology of the coral-dinoflagellate association remains largely unknown. This study explores symbiont diversity in relation to habitat by employing a broad-scale sampling regime using ITS2 and denaturing gradient gel electrophoresis. Samples from Pocillopora damicomis, Stylophora pistillata and Seriatopora hystrix all harboured host-specific clade C symbiont types at Heron Island (Great Barrier Reef, Australia). While Ser. hystrix associated with a single symbiont profile along its entire depth distribution, both P. damicomis and Sty. pistillata associated with multiple symbiont profiles that showed a strong zonation with depth. It is shown that, with an increased sampling effort, previously identified 'rare' symbiont types within this group of host species are in fact environmental specialists. A multivariate approach was used to expand on the common distinction of symbionts by a single genetic identity. It shows merit in its capacity not only to include all the variability present within the marker region but also to reliably represent ecological diversification of symbionts. Furthermore, the cohesive species concept is explored to explain how niche partitioning may drive diversification of closely related symbiont lineages. This study provides thus evidence that closely related symbionts are ecologically distinct and fulfil their own niche within the ecosystem provided by the host and external environment.

Abstract: 1. This paper summarizes observations performed during 1966, 1968, and 1972, on coral reef flats 7 km south of Eliat (Gulf of Aqaba, Red Sea). The aim of this research was to describe the change in numbers of living coral colonies found on the coral tables in connection with pollution occuring in this habitat. A transect technique, developed by Loya and Slobodkin (1971) was used in this research. 2. In each of the three years, 19 ten metre transects were performed in various directions, on the same coral tables. 3. In 1966, 541 living coral colonies were counted in a total of 190 m of transects. At the identical place, this number had decreased to only 195, in 1972. The decrease in corals was found to be accompanied by a prominant increase in algae growth, that expend and develop, thus covering the coral specimens. 4. Especially sensitive to algal development are the branching micropolypal, coral species, that are the representatives of the genera Acropora, Seriatopora, and Stylophora. Of the above three genera counted in 1966, only 10 out of 192 colonies were found intact, in 1972. 5. The high mortality of corals in this locality occured during the years in which an oil terminal plus a mineral and phosphate loading harbour were developed at Eilat. 6. The frequent oil spills, together with the phosphate dust that reaches the sea, seem to be the factors that cause eutrophication in the shallow lagoon waters of the coral region, and thus the development of algae on the coast of corals is stimulated.

Abstract: The morphology of branching corals effectively blocks impinging currents. Weak flows in the colony’s inner sections can hinder some of the corals’ basic physiological functions. At night, high respiration by the coral and the absence of photosynthesis by the symbiotic algae sometimes generate severe hypoxia near coral branches. Nevertheless, branching corals thrive in flow-protected areas. Many of them host resident fish that seek shelter between their branches during the night. In situ observations using an infrared-sensitive video camera revealed that, unlike crevice-dwelling fishes, which sleep motionless, fish ( Dascyllus marginatus, D. aruanus,and Chromis viridis) that spend the night in living hard corals (Stylophora pistillata, Acropora spp., Pocillopora spp., and Seriatopora spp.) exhibit a unique sleep-swimming mode that is characterized by energetic, high-frequency fin motions. In the reef, the presence of fish in the coral S. pistillata increased gypsum dissolution and, hence, mass transfer, by ;17% compared with colonies without fish. The extent to which the fish enhanced water replenishment in the inner zone of the coral was assessed in the laboratory using oxygen measurements. In the absence of fish, oxygen levels near the coral tissues (;1 mm) rapidly declined, reaching 10‐30% of ambient levels, which was much lower than the nearly steady levels of 60‐80% when sleep-swimming fish were present. Individual sleep-swimming fish were spatially separated across the coral, so that most of the coral’s inner zone was frequently ventilated. This common, yet so-far overlooked mutualistic relationship is unique by the virtue of its effect, the active modulation of hydrodynamic conditions, and its operation during the sleep of the active animal. The modulation of hydrodynamic conditions by the fish can mitigate flow limitation on the growth and survival of branching corals.