Coral Reef Science:  Development Highlights

Eric Borneman

Lesser Michael P., Mazel Charles H., Gorbunov Maxim Y., and Falkowski Paul G. 2004. Discovery of symbiotic nitrogen-fixing cyanobacteria in corals. Science 305: 997-1000.

Abstract:

Colonies of the Caribbean coral Montastraea cavernosa exhibit a solar stimulated orange-red fluorescence that is spectrally similar to a variety of fluorescent proteins expressed by corals. The source of this fluorescence is phycoerythrin in unicellular, nonheterocystis, symbiotic cyanobacteria within the host cells of the coral. The cyanobacteria coexist with the symbiotic dinoflagellates (zooxanthellae) of the coral and express the nitrogen-fixing enzyme nitrogenase. The presence of this prokaryotic symbiont in a nitrogen-limited zooxanthellate coral suggests that nitrogen fixation may be an important source of this limiting element for the symbiotic association.

Comments:

For many years, the presence of orange fluorescent morphs of M. cavernosa has interested divers and researchers alike. The colonies are generally found in moderate depth water, and they are fluorescent orange during the day. Similarly, a number of Indo-Pacific corals are fluorescent orange by day, such as various fungiids like some Diaseris and Cycloseris, and these too are often found in deeper water. At least in M. cavernosa, the fluorescence is not due to the fluorescing proteins that are responsible for most bright coloration in zooxanthellate corals, nor are they due to the golden brown zooxanthellae. Instead, these colonies harbor other intracellular symbionts besides zooxanthellae, and they are cyanobacteria. Cyanobacteria are able to fix nitrogen, generally considered to be a limiting nutrient for both corals and zooxanthellae and present at very low levels in seawater. Nitrogen needs of corals, required for tissue growth, reproduction, and protein synthesis, are often acquired largely by feeding on particulate material and zooplankton. A primary question will be why these morphs harbor high densities of cyanobacteria while others do not, or perhaps host lower numbers that do not result in the orange fluorescence. Another question will be how widespread this type of symbiosis might be in other species. The presence of symbiotic bacteria, algae, and now cyanobacteria highlights the importance of such associations in species diverse coral reefs and adds another level of complexity to the ecology and biology of corals.

The Tenth International Coral Reef Symposium, Okinawa, Japan - June 28-July 2, 2004

The coral reef conference of the International Coral Reef Society, the largest of its kind, is held every four years. For those who have ever attended, it is a wealth of information and a very exciting event to learn the most recent research and thoughts regarding all aspects of coral reefs. This year, the abstracts for the conference presentation are available, so I need not summarize the event. They are available for download as a .pdf file at http://www.plando.co.jp/icrs2004/

There were several major areas that represented a great number of topics. There was a great deal of research on the symbiosis between corals and their diverse zooxanthellae, and many on the roles of restoration, disease and global warming/global change on coral reefs. I was, unfortunately, unable to attend as many interesting topics as I would have liked, as I was extremely busy during this conference in various sessions.

This year, I chaired a mini-symposium. "Coral Reef Aquarium Husbandry: A Tool for Science," and co-chaired a mini-symposium with Andy Bruckner, "Aquarium Trade Issues: Addressing Sustainability of the Ornamental Coral Reef Species Trade through Improved Management of Wild Harvest and Environmentally-Friendly Coral Farming and Aquaculture Approaches." Dana Riddle was scheduled to present a topic on coral farming during the latter symposium, but apparently was unable to attend. I had looked forward to seeing another person with ties to the reef aquarium hobby at the conference. I will be discussing aspects of these symposia in upcoming articles for Reefkeeping Magazine. I also presented the following five topics in various sessions:

• "Reproduction in Aquarium Corals," in which I summarized the novel and known asexual and sexual reproductive events known from corals in aquaria.

• "Apoptosis in Diseased Reef Corals: A First Look," in which I described the presence of apoptosis as a mode of cell death in corals with white band disease and shut-down reaction, and the ability to trigger apoptosis with known inducing agents.

• "Pathologies Affecting Reef Corals at the Flower Garden Banks, Northwest Gulf of Mexico," in which I described disease incidence and several new pathologies, based on work I have done on these reefs over the past two years.

• "Pathologies Affecting Reef Corals in Captivity," in which I described diseases that occur in coral in aquaria, and

• "Coral Reef Guinea Pigs: Culture of Research Clonal Lines for the Coral Disease and Health Consortium," in which I presented the status of the coral culture facility in which clonal lines are being developed for disease researchers.

The conference proceedings will not be available for quite some time, but should be more affordable to interested persons than in years past as there will be a CD version. I will announce to members of Reef Central when they become available.

Ronald L. Shimek, Ph. D.

K. B. Heidelberg, K. B., K. P. Sebens and J. E. Purcell. 2004. Composition and sources of near reef zooplankton on a Jamaican forereef along with implications for coral feeding. Coral Reefs (2004) 23: 263-276.

Abstract:

Nocturnal near-reef zooplankton from the forereef of Discovery Bay, Jamaica, were sampled during winter and summer 1994 using a diver-operated plankton pump with an intake head positioned within centimeters of benthic zooplanktivores. The pump collected zooplankton not effectively sampled by conventional net tows or demersal traps. We found consistently greater densities of zooplankton than did earlier studies that used other sampling methods in similar locations. There was no significant difference between winter (3491 ± 578 per m³) and summer (2853 ± 293 per m³) zooplankton densities. Both oceanic- and reef-associated forms were found at temporal and spatial scales relevant to benthic suspension feeders. Copepods were always the most abundant group, averaging 89% of the total zooplankton, and most were not of demersal origin. The cyclopoids, Oithona spp., were the numerically dominant organisms, with an average density of 1684 ± 260 per m³. Other zooplankton (e.g., shrimp larvae, crab larvae, polychaetes, chaetognaths, amphipods, and isopods) were highly variable and much less abundant. Near-reef zooplankton abundances were high throughout the night sampling period, not just after sunset and before sunrise as previously described. Mean biomass was 4.5 mg C per m³, with values ranging from 1.0 to 15.6 mg C per m³. This work has important implications for evaluating which zooplankton types are available to benthic suspension feeders, including corals.

Comments:

One more of a series of papers showing how numerous available zooplankton are for coral consumption and how important it is that the corals have this food available to them. The reader is referred to Eric Borneman's series on feeding the reef in Reefkeeping.com in 2002 and 2003 for some earlier data about feeding.