Scleractinian corals with photoprotective host pigments are hypersensitive to thermal bleaching

Recent episodes of mass coral bleaching, the loss of symbiotic dinoflagellates or photosynthetic pigment from hermatypic corals, have been triggered by elevated sea temperatures. Photosynthetic irradiance is an important secondary factor. Host based pigments (pocilloporins or Green Fluorescent Protein homologues) have been proposed to reduce the impact of elevated temperature by shading the dinoflagellate symbionts of corals, thereby reducing light stress. This study investigates this phenomenon in the reef-building coral Acropora aspera from Heron Island Research Station (Great Barrier Reef, Australia), which occurs as 3 distinct colour morphs. Experimental data showed that the host pigments are photoprotective at normal temperatures or

Storm cycles in the last millennium recorded in Yongshu Reef, southern South China Sea

Large storm-relocated Porites coral blocks are widespread on the reef flats of Nansha area, southern South China Sea. Detailed investigations of coral reef ecology, geomorphology and sedimentation on Yongshu Reef indicate that such storm-relocated blocks originated from large Porites lutea corals growing on the spurs within the reef-front living coral zone. Because the coral reef has experienced sustained subsidence and reef development during the Holocene, dead corals were continuously covered by newly growing coral colonies. For this reason, the coral blocks must have been relocated by storms from the living sites and therefore the ages of these storm-relocated corals should approximate the times when the storms occurred. Rapid emplacement of these blocks is also evidenced by the lack of coral overgrowth, encrustation or subtidal alteration. U-series dating of the storm-relocated blocks as well as of in situ reef flat corals suggests that, during the last 1000 years, at least six strong storms occurred in 1064 +/- 30, 1210 +/- 5-1201 +/- 4, 1336 +/- 9, 1443 +/- 9, 1685 +/- 8-1680 +/- 6, 1872 +/- 15 AD, respectively, with an average 160-year cycle (110-240 years). The last storm, which occurred in 1872 15 AD, also led to mortality of the reef flat corals dated at similar to 130 years ago. Thus, the storm had significant impacts on coral reef ecology and morphology. (C) 2004 Elsevier B.V. All rights reserved.

The effect of temperature on the size and population density of dinoflagellates in larvae of the reef coral Porites astreoides

Pre-settlement events play an important role in determining larval success in marine invertebrates with bentho-pelagic life histories, yet the consequences of these events typically are not well understood. The purpose of this study was to examine the pre-settlement impacts of different seawater temperatures on the size and population density of dinoflagellate symbionts in brooded larvae of the Caribbean coral Porites astreoides. Larvae were collected from P. astreoides at 14-20 m depth on Conch Reef (Florida) in June 2002, and incubated for 24 h at 15 temperatures spanning the range 25.1 degrees-30.0 degrees C in mean increments of 0.4 +/- 0.1 degrees C (+/- SD). The most striking feature of the larval responses was the magnitude of change in both parameters across this 5 degrees C temperature range within 24 h. In general, larvae were largest and had the highest population densities of Symbiodinium sp. between 26.4 degrees-27.7 degrees C, and were smallest and had the lowest population densities at 25.8 degrees C and 28.8 degrees C. Larval size and symbiont population density were elevated slightly (relative to the minimal values) at the temperature extremes of 25.1 degrees C and 30 degrees C. These data demonstrate that coral larvae are highly sensitive to seawater temperature during their pelagic phase, and respond through changes in size and the population densities of Symbiodinium sp. to ecologically relevant temperature signals within 24 h. The extent to which these changes are biologically meaningful will depend on the duration and frequency of exposure of coral larvae to spatio-temporal variability in seawater temperature, and whether the responses have cascading effects on larval success and their entry to the post-settlement and recruitment phase.

Diurnal polyp expansion behavior in stony corals may enhance carbon availability for symbionts photosynthesis

Photosynthesis of zooxanthellate stony corals may be limited by inorganic carbon at high irradiances. We demonstrated that oxygen consumption of expanded corals is higher than that of contracted corals in both night-expanding and day-expanding corals. It is assumed that at the single-polyp level, the expansion of tentacles increases the surface area for solute exchange with the surrounding water, which may alleviate potential carbon limitation and excess oxygen levels in the tissue under high irradiance. We investigated this hypothesis using stable carbon isotope (613 C) analysis of coral species from the Red Sea exhibiting different morphologies. delta C-13 ratios in zooxanthellae of branched coral colonies with small polyp size that extend their tentacles during daytime (diurnal morphs) showed lower delta C-13 values in their zooxanthellae - 13.83 +/- 1.45 parts per thousand, compared to corals from the same depth with large polyps, which are usually massive and expand their tentacles only at night (nocturnal morphs). Their algae delta C-13 was significantly higher, averaging - 11.33 +/- 0.59 parts per thousand. Carbon isotope budget of the coral tissue suggests that branched corals are more autotrophic, i.e., that they depend on their symbionts for nutrition compared to massive species, which are more heterotrophic and depend on plankton predation. (c) 2005 Elsevier B.V. All rights reserved.

Ecology - Corals fail a test of neutrality

Ecologists continue to wrestle with a central question in biodiversity studies — the prediction of species’ distributions in various environments. A merger of different theories is the long-term prospect.

Are corals colorful?

Using in situ spectrometry data and visual system modeling, we investigate whether the colors conferred to the reef-building corals by GFP-like proteins would look colorful not only to humans, but also to fish occupying different ecological niches on the reef. Some GFP-like proteins, most notably fluorescent greens and nonfluorescent chromoproteins, indeed generate intense color signals. An unexpected finding was that fluorescent proteins might also make corals appear less colorful to fish, counterbalancing the effect of absorption by the photosynthetic pigments of the endosymbiotic algae, which might be a form of protection against herbivores. We conclude that GFP-determined coloration of corals may be an important factor in visual ecology of the reef fishes.

Black band disease of corals: Ecology and physiology of Phormidium corallyticum

Black band disease of corals consists of a microbial community dominated by the cyanobacteriurn Phormidium corallyticum. The disease primarily affects reef-framework coral species, Active black band disease continually opens up new substrate in reef environments by destroying coral tissue as the disease line advances across the surface of infected colonies. A field study was carried out to determine the abundance and distribution of black band disease on the reef building corals in the Florida Keys. During July of 1992 and 1993, up to 0.72% of coral colonies were infected with black band disease. Analysis of the distribution showed that the disease was clumped. Seasonal patters varied, with some coral colonies infected year round, others exhibiting reinfection from summer 1992 to summer 1993, and some colonies infected for one year only. Statistical analysis of black band disease incidence in relation to various environmental parameters revealed that black band disease was associated with relatively shallow water depths, higher temperatures, elevated nitrite levels, and decreased ortho-phosphate levels. Additional field studies determined recovery of scleractinian coral colonies damaged or killed through the activities of black band disease over a five-year period. These studies determined if the newly exposed substrate was recolonized through scleractinian recruitment, if there was overgrowth of the damaged areas by the formerly diseased colony, or if coral tissue destruction continued after the cessation of black band disease activity. Tissue loss continued on all coral colonies with only one colony exhibiting new tissue growth. The majority of recolonization was by non-reef-framework corals and octocorallians, limited recruitment by framework species was observed. Physiological studies of P. corallyticum were carried out to investigate the photosynthetic capacity of this cyanobacterium, and to determine if this species has the ability to fix dinitrogen. The results of this research demonstrated that P. corallyticum reaches maximum photosynthetic rates at very low light intensities (27.9 μE/m/sec), and that P. corallyticum is able to carry out oxygenic photosynthesis in the presence of sulfide, an ability that is uncommon in prokaryotic organisms. ^