Trophic status and population density of zooxanthellae in hermatypic corals

This paper discusses experimental data and theoretical concepts characterizing the trophic status of symbiotic zooxanthellae and the mechanisms regulating their density in hermatypic corals. Under natural conditions, the growth of zooxanthellae is not limited by the deficiency of nitrogen. The main factor regulating the density of zooxanthellae is their ingestion by the animal host.     

Individual and population growth in the asexually reproducing anemone Aiptasia pallida Verrill

The effects of feeding regime and zooxanthellae on individual and population growth of Aiptasia pallida (Verrill) were studied in a series of laboratory experiments. Individual and population growth were measured as biomass increase. Both individual and population growth were significantly affected by feeding regime while zooxanthellae enhanced growth only at the most infrequent feeding regime. Feeding regime had no significant effect on the number of individual anemones in the population produced asexually by pedal laceration after 8 wk, although there were temporal differences in pedal laceration between feeding regimes during this 8-wk period. Anemones fed three times per wk underwent little pedal laceration prior to week 4 with most individuals produced after week 4. In contrast, anemones fed once per 4 wk produced almost all anemones prior to week 4 with little subsequent pedal laceration. Zooxanthellae significantly increased the number of anemones produced by pedal laceration only among individuals fed at 4-wk intervals. Zooxanthellae had no effect on pedal laceration among individuals fed three times per week.

Population growth, measured as weight change, after 4 wk was greater than individual growth for all treatments except aposymbiotic anemones fed at 4-wk intervals for which there was no significant difference between individual and population percent weight change. These results suggest that zooxanthellae enhance growth only during periods of prey scarcity and that asexual reproduction by symbiotic individuals increases biomass at a greater rate than does individual anemone growth.     

Is the coral‐algae symbiosis really ‘mutually beneficial’ for the partners?

The consideration of ‘mutual benefits’ and partner cooperation have long been the accepted standpoint from which to draw inference about the onset, maintenance and breakdown of the coral‐algae endosymbiosis. In this paper, I review recent research into the climate‐induced breakdown of this important symbiosis (namely ‘coral bleaching’) that challenges the validity of this long‐standing belief. Indeed, I introduce a more parsimonious explanation, in which the coral host exerts a ‘controlled parasitism’ over its algal symbionts that is akin to an enforced domestication arrangement. Far from being pathogenic, a range of well‐established cellular processes are reviewed that support the role of the coral host as an active ‘farmer’ of the energy‐rich photoassimilates from its captive symbionts. Importantly, this new paradigm reposes the deleterious bleaching response in terms of an envelope of environmental conditions in which the exploitative and captive measures of the coral host are severely restricted. The ramification of this new paradigm for developing management strategies that may assist the evolution of bleaching resistance in corals is discussed.     

Comparative Proteomics of Symbiotic and Aposymbiotic Juvenile Soft Corals

The symbiotic association between corals and photosynthetic unicellular algae is of great importance in coral reef ecosystems. The study of symbiotic relationships is multidisciplinary and involves research in phylogeny, physiology, biochemistry, and ecology. An intriguing phase in each symbiotic relationship is its initiation, in which the partners interact for the first time. The examination of this phase in coral–algae symbiosis from a molecular point of view is still at an early stage. In the present study we used 2-dimensional polyacrylamide gel electrophoresis to compare patterns of proteins synthesized in symbiotic and aposymbiotic primary polyps of the Red Sea soft coral Heteroxenia fuscescens. This is the first work to search for symbiosis-specific proteins during the natural onset of symbiosis in early host ontogeny. The protein profiles reveal changes in the host soft coral proteome through development, but surprisingly virtually no changes in the host proteome as a function of symbiotic state.     

The energetics of asexual reproduction: Pedal laceration in the symbiotic sea anemone Aiptasia pulchella (Carlgren, 1943)

Asexual reproduction of the symbiotic sea anemone Aiptasia pulchella (Carlgren, 1943) was studied in the context of energy budgets determined under a variety of light and feeding conditions. Continuous darkness significantly increased rates of pedal laceration (the method of asexual reproduction), while different feeding rates had no significant effect. Digestive assimilation efficiency averaged 63% for whole brine shrimp, and conversion efficiencies (assimilated energy into biomass) averaged 31%. There were no significant differences between the conversion efficiencies of energy obtained from light or food. The index of reproductive effort (RE) for pedal laceration was very low, ranging from 0.004 to 0.044. This low RE associated with a substantial rate of asexual reproduction may, in part, explain the widespread success of certain sea anemones.     

Further studies on the anatomy and ecology of opisthobranch molluscs feeding on the scleractinian coral Pontes

Three further species of opisthobranch molluscs are reported to feed on the scleractinian coral Pontes in Tanzania. Further information on Cuthona poritophages Rudman, 1979, is also included. The anatomy of the aeolid Phestilla lugubris {Bergh, 1870, = P. sibogae Bergh, 1905) and a new species of Phestilla is described, as is the anatomy of the arminacean Pinufius rebus. The new species of Phestilla , and Pinufius , are, for the first time, reported to feed on Porites. Notes on the anatomy of the type-species of Phestilla, P. melanobrachia Bergh, 1874, are included to make possible a definition of the genus Phestilla.
Aspects of the feeding biology, life history, defence mechanisms and habitat specificity of the four Porites-feeding opisthobranchs are described and discussed. The four species are shown to have evolved radular teeth of remarkably similar shape. Each species utilizes a different part of the coral tissue as food. The three aeolids have replaced functional cnidosacs at the tip of their cerata with batteries of large secretory cells.
Phestilla lugubris and Pinufius rebus are also reported for the first time from the Great Barrier Reef, Queensland and the new species of Phestilla is reported from Queensland and Hawaii.     

PHYLOGENETIC POSITION OF SYMBIODINIUM (DINOPHYCEAE) ISOLATES FROM TRIDACNIDS (BIVALVIA), CARDIIDS (BIVALVIA), A SPONGE (PORIFERA), A SOFT CORAL (ANTHOZOA), AND A FREE-LIVING STRAIN

The genus Symbiodinium is the commonly observed symbiotic dinoflagellate (zooxanthellae) that forms mutual associations with various marine invertebrates. Numerous studies have revealed that the genus is comprised of a group of diverse taxa, and information on the phylogenetic relationships among the genus’ members is increasing. In this study, small subunit (SSU) ribosomal RNA (ssrRNA) gene sequences were determined for 15 more Symbiodinium strains from 12 relatively unstudied host taxa (Indo-Pacific tridacnids, cardiids, sponge, and soft coral), 1 hitherto unreported free-living Symbiodinium strain, and 4 other Symbiodinium strains from four other host taxa (Indo-Pacific zoanthid, foraminifer, jellyfish, and mid-Pacific hard coral). Their respective phylogenetic positions were inferred, and strains that are either closely related to or distinct from previously reported Symbiodinium taxa were revealed. The cultured Symbiodinium strains isolated from individuals of six species of tridacnids and three species of cardiids all had identical ssrRNA gene sequences, are closely related to S. microadriaticum Freudenthal, and are indistinguishable from the RFLP Type A strain previously reported. However, the ssrRNA gene sequences of clam symbionts that were obtained via gene cloning were different from those of the cultured isolates and represent strains that are close to the RFLP Type C strains. The Symbiodinium-like dinoflagellate from the Indo-Pacific sponge Haliclona koremella De Laubenfels is distinct from any of the Symbiodinium taxa studied and may be similar to the symbiont previously isolated from the stony coral Montipora patula Quelch. The isolates from the soft coral Sarcophyton glaucum Quoy et Gaimard and from the zoanthid Zoanthus sp. are both very closely related to S. pilosum Trench et Blank. The free-living Symbiodinium isolate is very closely related to the symbiont isolated from the Indo-Pacific foraminifer Amphisorus hemprichii Ehrenberg, which in turn is distinct from the Red Sea strain isolated from a similar host. Theisolate from Cassiopeia sp. is different from S. microadriaticum F., the type species harbored by Cassiopeia xamachana Bigelow, and is instead very closely related to S. pulchrorum Trench isolated from a sea anemone. The symbiont from the stony coral M. verrucosa Lamarck is a sister taxon to the symbionts isolated from the foraminifera Marginopora kudakajimensis Gudmundsson and Sorites orbiculus Forskål. These data suggest that polymorphic symbioses extend from cnidarians to some bivalve, foraminifer, and jellyfish host species.