Rapid phase-shift reversal on a Jamaican coral reef

Many Caribbean reefs have experienced a phase-shift in community structure, the principle features being a decline in coral cover and an increase in macroalgal biomass. However, one Jamaican reef—Dairy Bull on the north shore near Discovery Bay—is once again dominated by scleractinian corals and several key species have returned. Living coral cover at 6–8 m depth at Dairy Bull has doubled over the past 9 years and is now ~54%. The absolute cover of Acropora cervicornis was <1% in 1995, but increased to ~11% by January 2004. During this time the cover of macroalgae decreased by 90%, from 45 to 6%. We speculate that long-lived colonies of Montastraea annularis may have facilitated the recovery of this reef by providing structural refugia.     

Densitometry from digitized images of X-radiographs: Methodology for measurement of coral skeletal density

Skeletons of massive coral colonies contain annual density bands that are revealed by X-radiography of slices cut along growth axes. These bands allow measurement of skeletal growth parameters such as annual extension rate and annual calcification rate. Such measurements have been important in understanding coral growth, in assessing environmental impacts and in recovering proxy environmental information. Measurements of coral calcification rate from annual density banding require measurements of skeletal density along tracks across skeletal slices and, until now, such density measurements have depended upon specialized and expensive equipment. Here, we describe a straightforward, inexpensive and accurate technique for measuring skeletal density from digitized images of X-radiographs of coral skeletal slices. An aragonitic step-wedge was included in each X-radiograph of a coral slice together with two aluminium bars positioned along the anode-cathode axis. Optical density was measured along tracks across the X-ray images of these different objects. The aragonite step-wedge provided a standard for converting optical density to skeletal density. The aluminium bars were used to correct for the heel effect—a variation in the intensity of the X-ray beam along the anode-cathode axis that would, otherwise, introduce large errors into measurements of skeletal density. Exposure was found to vary from X-radiographs to X-radiograph, necessitating the inclusion of the calibration standards in each X-radiograph of a coral slice. Results obtained using this technique compared well with results obtained by direct gamma densitometry of skeletal slices.     

White-band disease and the changing face of Caribbean coral reefs

In recent decades, the cover of fleshy macroalgae has increased and coral cover has decreased on most Caribbean reefs. Coral mortality precipitated this transition, and the accumulation of macroalgal biomass has been enhanced by decreased herbivory and increased nutrient input. Populations of Acropora palmata (elkhorn coral) and A. cervicornis (staghorn coral), two of the most important framework-building species, have died throughout the Caribbean, substantially reducing coral cover and providing substratum for algal growth. Hurricanes have devastated local populations of Acropora spp. over the past 20–25 years, but white-band disease, a putative bacterial syndrome specific to the genus Acropora, has been a more significant source of mortality over large areas of the Caribbean region.Paleontological data suggest that the regional Acropora kill is without precedent in the late Holocene. In Belize, A. cervicornis was the primary ecological and geological constituent of reefs in the central shelf lagoon until the mid-1980s. After constructing reef framework for thousands of years, A. cervicornis was virtually eliminated from the area over a ten-year period. Evidence from other parts of the Caribbean supports the hypothesis of continuous Holocene accumulation and recent mass mortality of Acropora spp. Prospects are poor for the rapid recovery of A. cervicornis, because its reproductive strategy emphasizes asexual fragmentation at the expense of dispersive sexual reproduction. A. palmata also relies on fragmentation, but this species has a higher rate of sexual recruitment than A. cervicornis. If the Acropora spp. do not recover, macroalgae will continue to dominate Caribbean reefs, accompanied by increased abundances of brooding corals, particularly Agaricia spp. and Porites spp. The outbreak of white-band disease has been coincident with increased human activity, and the possibility of a causal connection should be further investigated.     

Cellular reactions to sedimentation and temperature stress in the Caribbean coral Montastraea cavernosa

We present evidence of cellular responses to increased sedimentation and temperature in Montastraea cavernosa collected off Broward County, Florida. We sampled corals from six different sites approximately, 500-1000 m off shore, 10-15m depth. Six samples were collected from four sites adjacent to areas of underwater marine dredging (project sites), while the remaining two samples were obtained far away from the influence of the marine dredging (control sites). SSTs around collection time ranged 0.6-0.9 degrees C over the 40-year monthly mean. All specimens collected at project sites exhibited histopathological evidence of mild to moderate sedimentation stress including changes in size and number of mucocytes in epidermis and gastrodermis, attenuation of the epidermal and gastrodermal tissues, presence of cellular debris, and changes in number of zooxanthellae. These findings corroborate results of laboratory-based, sand-application experiments. In addition to the above-noted changes, one specimen exhibited multiple lesions consisting of unusual gastrodermal detachment with infiltration of amoebocytes into the adjacent mesoglea. Tissues surrounding detachment injuries exhibited marked to severe cellular changes. Accumulations of amoebocytes at lesion sites are seldom observed in wild corals. This response may be part of an organized reaction to injury and infection, as has been documented in sea anemones and gorgonians; however, further research is needed on the nature and role(s) of the scleractinian amoebocytes.     

Major colour patterns of reef-building corals are due to a family of GFP-like proteins

Reef-building corals are renowned for their brilliant colours yet the biochemical basis for the pigmentation of corals is unknown. Here, we show that these colours are due to a family of GFP-like proteins that fluoresce under ultraviolet (UV) or visible light. Pigments from ten coral species were almost identical to pocilloporin (Dove et al. 1995) being dimers or trimers with approximately 28-kDa subunits. Degenerative primers made to common N-terminal sequences yielded a complete sequence from reef-building coral cDNA, which had 19.6% amino acid identity with green fluorescent protein (GFP). Molecular modelling revealed a `β-can' structure, like GFP, with 11 β-strands and a completely solvent-inaccessible fluorophore composed of the modified residues Gln-61, Tyr-62 and Gly-63. The molecular properties of pocilloporins indicate a range of functions from the conversion of high-intensity UV radiation into photosynthetically active radiation (PAR) that can be regulated by the dinoflagellate peridinin-chlorophyll-protein (PCP) complex, to the shielding of the Soret and Q_x bands of chlorophyll a and c from scattered high-intensity light. These properties of pocilloporin support its potential role in protecting the photosynthetic machinery of the symbiotic dinoflagellates of corals under high light conditions and in enhancing the availability of photosynthetic light under shade conditions. Accepted: 29 May 2000     

造礁石珊瑚共生虫黄藻离体培养方法的优化

【目的】开发一种高效地从造礁石珊瑚中分离、培养共生虫黄藻的技术方法,为珊瑚共生虫黄藻藻种资源储备和生理功能研究积累基础。【方法】首先采用微孔滤网过滤法和密度梯度离心法从造礁石珊瑚组织中直接分离或富集共生虫黄藻细胞,然后用改良的L1培养基在96孔板上对所得细胞进行离体培养,最后进行单细胞分离、培养和(或)平板划线培养获得单克隆虫黄藻细胞系。对所得虫黄藻单克隆藻株进行聚合酶链式反应-限制性内切酶片段长度多态性(polymerase chainreaction-restrictionfragmentlengthpolymorphism,PCR-RFLP)分析,结合内转录间隔区2(internal transcribed spacer2,ITS2)和大亚基(large subunit,LSU)测序进行物种鉴定及系统发育分析。【结果】采用上述方法从涠洲岛的霜鹿角珊瑚(Acropora pruinose)和西沙群岛的丛生盔形珊瑚(Galaxea fascicularis)及柔枝鹿角珊瑚(Acropora tenuis)中分离、培养得到3个虫黄藻株系,编号分别为AP21C1、GF21D1和AT21A...     

Diversity and dynamics of bacterial communities in early life stages of the Caribbean coral Porites astreoides

In this study, we examine microbial communities of early developmental stages of the coral Porites astreoides by sequence analysis of cloned 16S rRNA genes, terminal restriction fragment length polymorphism (TRFLP), and fluorescence in situ hybridization (FISH) imaging. Bacteria are associated with the ectoderm layer in newly released planula larvae, in 4-day-old planulae, and on the newly forming mesenteries surrounding developing septa in juvenile polyps after settlement. Roseobacter clade-associated (RCA) bacteria and Marinobacter sp. are consistently detected in specimens of P. astreoides spanning three early developmental stages, two locations in the Caribbean and 3 years of collection. Multi-response permutation procedures analysis on the TRFLP results do not support significant variation in the bacterial communities associated with P. astreoides larvae across collection location, collection year or developmental stage. The results are the first evidence of vertical transmission (from parent to offspring) of bacteria in corals. The results also show that at least two groups of bacterial taxa, the RCA bacteria and Marinobacter, are consistently associated with juvenile P. astreoides against a complex background of microbial associations, indicating that some components of the microbial community are long-term associates of the corals and may impact host health and survival.     

Multimodal Optical Microscopy Methods Reveal Polyp Tissue Morphology and Structure in Caribbean Reef Building Corals

An integrated suite of imaging techniques has been applied to determine the three-dimensional (3D) morphology and cellular structure of polyp tissues comprising the Caribbean reef building corals Montastraeaannularis and M. faveolata. These approaches include fluorescence microscopy (FM), serial block face imaging (SBFI), and two-photon confocal laser scanning microscopy (TPLSM). SBFI provides deep tissue imaging after physical sectioning; it details the tissue surface texture and 3D visualization to tissue depths of more than 2 mm. Complementary FM and TPLSM yield ultra-high resolution images of tissue cellular structure. Results have: (1) identified previously unreported lobate tissue morphologies on the outer wall of individual coral polyps and (2) created the first surface maps of the 3D distribution and tissue density of chromatophores and algae-like dinoflagellate zooxanthellae endosymbionts. Spectral absorption peaks of 500 nm and 675 nm, respectively, suggest that M. annularis and M. faveolata contain similar types of chlorophyll and chromatophores. However, M. annularis and M. faveolata exhibit significant differences in the tissue density and 3D distribution of these key cellular components. This study focusing on imaging methods indicates that SBFI is extremely useful for analysis of large mm-scale samples of decalcified coral tissues. Complimentary FM and TPLSM reveal subtle submillimeter scale changes in cellular distribution and density in nondecalcified coral tissue samples. The TPLSM technique affords: (1) minimally invasive sample preparation, (2) superior optical sectioning ability, and (3) minimal light absorption and scattering, while still permitting deep tissue imaging.     

Observations of a new source of coral mortality along the Kenyan coast

In early 2002 coral mortality occurred along 600 km of coastline from Tanzania to Kenya. Astreopora, Echinopora , and Montipora species were severely affected, with Montipora being nearly eliminated from Kenyan reefs. Acropora , Platygyra , Goniopora , and massive Porites were also affected; however, Porites and Goniopora rarely died and often recovered, whereas death for most other species occurred within 2 weeks. In Echinopora and Montipora , a dull ashy tissue color and brittle skeletons characterized the early stages of this event with a mucus layer on the tissue surface in intermediate stages. Mucus and embedded debris then disappeared and surfaces were left covered in a white calcareous dust that sometimes capped a black layer. Astreopora tissues became dull and pale, and seldom produced mucus; eventually the skeleton became bare and white. Either a colorless translucent or brownish thin margin of tissue was visible between living tissue and bare skeleton, depending on species. Scanning electron micrographs of affected corals revealed the presence of fungi. Histology and staining showed that the fungi were mostly in the three genera that died from the syndrome and it may be that fungi invaded and killed corals weakened by another unidentified pathogen.     

Grazing resistance in nutrient-stressed phytoplankton

Grazing experiments were performed with the zooplankters Daphnia pulex and Daphnia magna, feeding on phosphorus-saturated and phosphorus-limited cells of two green algae (Scenedesmus subspicatus and Selenastrum capricornutum). P-limited algal cells passed largely intact through the gut and were thus spared from heavy grazing pressure. P-saturated algal cells, in contrast, were efficiently assimilated. Structural and morphological changes in the P-limited cells most probably reduced their digestibility. This phenomenon may be an important factor in zooplankton production and competition, and may serve as an example of a highly efficient strategy of P-limited algae to resist heavy grazing pressure.     

Coral mass- and split-spawning at a coastal and an offshore Venezuelan reefs,southern Caribbean

This study aimed to evaluate potential differences in coral spawning behavior between a fringing coastal reef and an offshore reef in the southern Caribbean. For this, scleractinian and gorgonian colonies (N = 324) of 21 species were mapped along eight transects, each 10-m long, at two study sites located in Morrocoy and Los Roques National Parks, Venezuela. Observations were made between 19:30 and 23:00 from August 23 to 30 and from September 26 to 30, 2002. Ninety one colonies belonging to six hard coral and seven octocoral species spawned or planulated during this period. We were unable to observe any signs of reproductive activity in 95 colonies of nine species different from those that reproduced. Despite the differences in environmental conditions between the two sites, we observed high synchrony in the spawning behavior of seven coral species common to both reefs. The most striking result was the ability of colonies of Montastraea faveolata and Eusmilia fastigiata to split spawn up to three times, either in consecutive nights or in different months.     

The reef-building coral Siderastrea siderea exhibits parabolic responses to ocean acidification and warming

Anthropogenic increases in atmospheric CO₂ over this century are predicted to cause global average surface ocean pH to decline by 0.1–0.3 pH units and sea surface temperature to increase by 1–4°C. We conducted controlled laboratory experiments to investigate the impacts of CO₂-induced ocean acidification (pCO₂ = 324, 477, 604, 2553 µatm) and warming (25, 28, 32°C) on the calcification rate of the zooxanthellate scleractinian coral Siderastrea siderea, a widespread, abundant and keystone reef-builder in the Caribbean Sea. We show that both acidification and warming cause a parabolic response in the calcification rate within this coral species. Moderate increases in pCO₂ and warming, relative to near-present-day values, enhanced coral calcification, with calcification rates declining under the highest pCO₂ and thermal conditions. Equivalent responses to acidification and warming were exhibited by colonies across reef zones and the parabolic nature of the corals'' response to these stressors was evident across all three of the experiment''s 30-day observational intervals. Furthermore, the warming projected by the Intergovernmental Panel on Climate Change for the end of the twenty-first century caused a fivefold decrease in the rate of coral calcification, while the acidification projected for the same interval had no statistically significant impact on the calcification rate—suggesting that ocean warming poses a more immediate threat than acidification for this important coral species.     

Complex interactions in the control of coral zonation on a Caribbean reef flat

Summary This study uses short-term assays and long-term transplant experiments to document the potential importance of fish predation and herbivory to the distribution and abundance of reef-building corals in a Caribbean back-reef system. Experimental manipulations of fish access reveal that the zonal patterns of the two reef-building corals Porites astreoides and P. porites f. furcata, dominant on shallow back-reef habitats, are strongly associated with the feeding intensity of parrotfishes. Differential palatability of the two corals to parrotfishes, the proximity of protective cover for large grazers and the availability of small refugia to harbor a cryptic grazer fauna are suggested as major features contributing to the observed patterns. A model predicting the interactions of various algivore/corallivore guilds on the relative dominance of Porites and algal populations is presented.     

Grazing activity of Pfiesteria piscicida (Dinophyceae) and susceptibility to ciliate predation vary with toxicity status

Variability has been reported in the toxicity potential of Pfiesteria piscicida that is partly a function of the history of exposure to live fish. Grazing properties of P. piscicida and its susceptibility to ciliate predation were compared in three functional types or toxicity states of this species: actively toxic cultures, cultures with temporary loss of demonstrable toxicity, and cultures with no demonstrable toxicity. Pronounced differences in predator–prey interactions were found between actively toxic cultures and cultures with reduced toxicity. When grown with Rhodomonas sp. (Cryptophyceae) prey, specific growth rates were relatively low in actively toxic cultures under both relatively high and low irradiances. In the cultures with reduced toxicity, prey chloroplast material was apparent in nearly 100% of dinoflagellate cells 3 h after feeding, while chloroplast inclusions were found in <40% of actively toxic cells for ≤16 h (high light) and ≤23 h (low light). These results suggest a relatively high reliance on phagotrophic carbon assimilation and more rapid response to algal prey availability in Pfiesteria cells with lower toxicity. Grazing by two euplotid benthic ciliates (Euplotes vannus and E. woodruffi) on P. piscicida also varied among functional types. Grazing on actively toxic P. piscicida cells did not occur, whereas net positive ingestion rates were calculated for the other prey cultures. These results support concurrent experimental findings that a natural assemblage of microzooplankton displayed lower grazing potential on actively toxic P. piscicida than on cultures with reduced toxicity. In summary, pronounced differences in trophic interactions were found between actively toxic cultures and those with reduced or undetectable toxicity, providing additional evidence of the importance of cellular toxicity in the trophic ecology of Pfiesteria.     

Structure of a unique inland mangrove forest assemblage in fossil lagoons on the Caribbean Coast of Mexico

Scrub mangrove wetlands colonize the intertidal zone of fossil lagoons located in carbonate continental margins along the Yucatan Peninsula of Mexico. These unique ecological types were investigated in October, 1994, by locating transects in several mangrove forests along the Caribbean coast of the peninsula. Four species of mangrove occurred at these sites including Rhizophora mangle, Avicennia germinans, Laguncularia racemosa, Conocarpus erecta. This is one of the first examples of a species rich scrub forest. The mangroves fell into three height categories: short scrub less than 1.5 m, tall scrub to 3.0 m, and basin forests between 4.5 and 6 m. Average height, diameter (dbh), basal area, and complexity index generally increased from short scrub to basin forests. Basal area, ranged from 0.16 m² ha^–1 in a short scrub forest intermixed with Cladium jamaicense to 12.9 m² ha^–1 in a basin forest. Density ranged from 1520 trees ha^–1 to over 25,000 trees ha^–1 in a short scrub forest dominated by R. mangle. The complexity index ranged from 0.01 to 8.3. Height, dbh, basal area, and complexity index were positively related. A number of trees were growing as sprouts from larger downed trunks, suggesting that hurricanes, such as Gilbert that occurred in 1988, are important in controlling the structure of these forests. These forests appear isolated from the sea, but are influenced by groundwater exchange occurring at the land-margin zone.     

Grazing rates of Elysia tomentosa on native and introduced Caulerpa taxifolia

The marine alga Caulerpa taxifolia Vahl (C. Agardh), recognized globally as one of the most prolific non-native species introductions, has been introduced to several temperate locations from where it has since rapidly expanded. C. taxifolia is protected by a toxin (terpenoid) in its tissues that limits grazing by native herbivores. Sacoglossan molluscs of the genus Elysia are among the few organisms that graze C. taxifolia; however, little is known about their feeding ecology. In the current study, we quantified the grazing rates of Elysia tomentosa on native C. taxifolia (Moreton Bay, Queensland) and introduced C. taxifolia (Botany Bay and Lake Conjola, New South Wales). Grazing rates were similar at Moreton Bay sites and Botany Bay; however, they were significantly lower in Lake Conjola. At the maximum observed grazing rate, slugs ate their body weight in C. taxifolia (dry weight) every 18–24 h. Differences in grazing rates between locations may be explained by differences in C. taxifolia morphology rather than native or introduced origin. Handling editor: J. Padisak     

Grazing by a small fish affects the early stages of a post-settlement stony coral

Short-term experiments were used to isolate the detrimental effects of grazer disturbance on young corals, and determine the stage of development at which recruits are no longer susceptible to this disturbance. Artificial substrata containing an algal matrix and coral recruits of different life stages were exposed to grazing by epilithic algal matrix (EAM) feeding combtoothed blennies, Salarias fasciatus. Single polyp recruits were vulnerable to grazer disturbance, while multi-polyp recruits (ca. 6–8 polyps) survived with evidence of minor damage in the form of tissue and polyp loss. The result indicates that blennies, although small and possessing weak dentition, can negatively influence the survival of young coral recruits. The protruding structure of micro-nubbins, representing juvenile corals were not damaged, suggesting that coral achieving that size and form can escape such damage. Communicated by Ecology Editor Prof. Peter Mumby     

A model for wave control on coral breakage and species distribution in the Hawaiian Islands

The fringing reef off southern Molokai, Hawaii, is currently being studied as part of a multi-disciplinary project led by the US Geological Survey. As part of this study, modeling and field observations were utilized to help understand the physical controls on reef morphology and the distribution of different coral species. A model was developed that calculates wave-induced hydrodynamic forces on corals of a specific form and mechanical strength. From these calculations, the wave conditions under which specific species of corals would either be stable or would break due to the imposed wave-induced forces were determined. By combining this hydrodynamic force-balance model with various wave model output for different oceanographic conditions experienced in the study area, we were able to map the locations where specific coral species should be stable (not subject to frequent breakage) in the study area. The combined model output was then compared with data on coral species distribution and coral cover at 12 sites along Molokais south shore. Observations and modeling suggest that the transition from one coral species to another may occur when the ratio of the coral colonys mechanical strengths to the applied (wave-induced) forces may be as great as 5:1, and not less than 1:1 when corals would break. This implies that coral colonys mechanical strength and wave-induced forces may be important in defining gross coral community structure over large (orders of 10s of meters) spatial scales.     

Trace elements found to be variable in two coral reef species,Heliofungia actiniformis andGalaxea fascicularis, collected from the ryukyu islands

Biominerals and metals of intertidal corals of two species (Heliofungia actiniformis, Quoy and Gaimard;Galaxea fascicularis, Linnaeus), collected from the Iriomote Island of Ryukyu, were examined with an inductively coupled plasma atomic emission spectrometer (ICP-AES). Twelve elements were detectable in the coralline skeletons dissected radially along the growth axis. The relative content (RC) of Hg periodically fluctuated and was minimum at the hollow sites of the coralline slab ofHeliofungia sp., corresponding to the cyclic growth. There were two types of elements: constant elements and variable elements along the growth axis. RCs of Ca, Mg, A1, Si, and P were nearly constant. RCs of Fe, Mn, Cu, and Ba were variable, but not as regularly changed as Hg. There were positive mass correlations of Hg to Mn, Cu and Zn, but not to Ba and Fe. In contrast, these relationships were not prominent and were likely degraded by aging in the skeleton ofGalaxea sp., suggesting a different mode from that of theHeliofungia sp.