Reefs from space: Satellite imagery,marine ecology,and ethnography in the Dominican Republic

Coral reef bleaching is an obvious indication that coastal marine ecosystems are being stressed. However, bleached reefs alone are poor indicators because they reflect the final stages of stress. This research project used multidate satellite imagery to look for coral reef changes as indicators of stress. Findings suggest that (1) satellite imagery can be used to identify small-scale changes in coastal marine ecosystems, including coral reefs; (2) remote sensing, marine ecology, and ethnographic data can be integrated to suggest potential causes of coral reef stress; and (3) changes in reef, seagrass, and mangrove ecozones are more closely tied to fishing, tourism, and land use practices than to global warming.     

Coral-virus interactions: A double-edged sword?

Marine viruses were little studied until 1989, when they were discovered to be extremely abundant in the sea. Virology is now a growing field of science in coral reef research, largely related to an increase in the frequency of coral bleaching events and other coral diseases. Because viruses are obligate symbionts, they are generally perceived as parasitic and harmful to their hosts. However, evidence that viruses confer benefits to their hosts is growing and their role as mutualists is emerging. Here we review both the detrimental and beneficial aspects of viral infections and argue that as the field of coral virology expands, in addition to their pathogenicity, the idea that viruses represent functionally beneficial components of the coral holobiont be considered.     

Discriminating causes from consequences of persistent parrotfish corallivory

A detailed understanding of the dual role of parrotfish as both key herbivores and potentially important corallivores is essential to the study of coral health and reef trophodynamics. Some Caribbean parrotfish regularly consume live coral, and discriminate both among coral species and among colonies within a particular species. While they prefer Montastraea spp. corals, which are dominant Caribbean reef builders, causes of selective and persistent grazing of certain colonies remain unknown. We manipulated coral exposure to parrotfish grazing through a long-term cage exclusion experiment in Belize, comparing initially grazed vs. intact (non-grazed) Montastraea spp. colonies. We measured nutrition-related characteristics (C:N ratio, %C, and %N) as well as defensive characteristics (nematocyst density and skeletal hardness) to determine if any of these variables accurately predicted parrotfish grazing. There were substantial reductions in coral nutritional quality (C:N) associated with parrotfish grazing, although these changes appear to be a consequence rather than a cause of parrotfish selectivity. Likewise, nematocyst densities were suppressed in grazed corals, also likely a result of chronic grazing stress. We found no intraspecific differences in skeletal hardness related to grazing. These results provide further demonstration of the physiological consequences of grazing, but the cause of preferential grazing by parrotfishes on certain Montastraea spp. colonies still requires further investigation.     

海南三亚鹿回头造礁石珊瑚生长变化与人类活动的影响

采用全球珊瑚礁监测网络(GCRMN)推荐的永久样方法首次在国内开展珊瑚礁生长的监测和研究。在海南三亚鹿回头岸礁区建立了10个珊瑚礁永久样方,分别于2003年12月、2004年4月、2004年9月和2005年4月开展了4次造礁石珊瑚生长的现场监测,并对周边人类活动进行了相关调查。研究发现,鹿回头东北部岸礁区4个样方的珊瑚覆盖率稳定增长,珊瑚生长良好,监测期间的珊瑚生长覆盖率平均为3.1%,珊瑚死亡覆盖率平均为1.3%;中部和南部岸礁区5个样方的珊瑚覆盖率明显下降,珊瑚出现衰退,衰退范围有明显扩大,珊瑚生长覆盖率平均为2.2%,珊瑚死亡覆盖率平均达到7.9%。珊瑚新个体的繁殖数量极少,平均新生珊瑚数量近1个/m2,新生珊瑚覆盖率对珊瑚生长覆盖率的贡献较低。人类活动对鹿回头岸礁区珊瑚生长的影响主要有两类:一是捕捞、炸鱼、船只抛锚、潜水等物理破坏;二是沿岸养殖场和旅游餐馆污水排放产生的水质污染,导致珊瑚生长机理的破坏。其中,水质污染是造成中部和南部岸礁区样方珊瑚死亡的主要原因,与沿岸养殖场和餐馆的分布、排污时间以及排污量有密切关系。     

Contrasting effects of crustose coralline algae from exposed and subcryptic habitats on coral recruits

Coral recruitment is important in sustaining coral reef ecosystems and contributing to their recovery after disturbances. Despite widespread acceptance that crustose coralline algae (CCA) positively influence coral recruitment success, especially by enhancing coral settlement and early post-settlement stages, there are no experimental data on the effects of CCA species on late post-settlement survival and growth of corals. This study tested the impact of four common, thick-crusted CCA species from two habitats (exposed and subcryptic) on the survival and growth of two recruit size categories of the coral genus Pocillopora. Coral recruits and CCA were transplanted adjacent to each other using epoxy in Petri dishes directly attached to the reef substratum on the forereef of Moorea (French Polynesia) in a 1-year field experiment. In the subcryptic habitat, survival of small-sized recruits adjacent to subcryptic CCA (0–5%) was lower than adjacent to dead CCA (35%), while in the exposed habitat, survival of small-sized recruits adjacent to exposed CCA (20–25%) was higher than adjacent to dead CCA (5%). None of the CCA species affected the survival of large-sized recruits within exposed or subcryptic habitats. However, the growth of large-sized recruits adjacent to subcryptic CCA was lower than adjacent to dead CCA. Recruits adjacent to exposed CCA died less from competition with turf algae relative to dead CCA, while recruits adjacent to subcryptic CCA frequently died from overgrowth by CCA. These results suggest that, in subcryptic habitats, CCA can reduce the survival and/or growth of coral recruits via direct competitive overgrowth, while in exposed habitats, they can enhance coral recruit survival by alleviating competition with turf algae. Importantly, our study demonstrates that not all CCA species are beneficial to the survival and growth of coral recruits and that there is considerable variability in both the outcome and process of competition between CCA and corals.

     

An intertidal Rhabdopleura (Hemichordata, Pterobranchia) from Fiji

Rhabdopleura has been discovered living in coral rubble on reefs in Fiji. The habitat is unusual, being the underside of coral boulders in the intertidal zone. Some features of the environment and the fauna associated with the Rhabdopleura are briefly described. The Rhabdopleura zooids exhibit other modes of tube building besides the regular cylindrical horizontal and erect tubes. The colony ramifies through interstices in the dead coral and the zooids can line larger cavities within the coral with coenecial tissue. It is probably these cavities, together with the overall porosity of coral, that retain enough water to keep the zooids alive while the intertidal reef flat is exposed to the air. Within the depths of the coral the black stolons are frequently naked. The species is probably R. normani Allman.     

Orientation behavior of butterflyfishes (family Chaetodontidae) on coral reefs: spatial learning of route specific landmarks and cognitive maps

Synopsis Foraging butterflyfishes follow predictable paths as they swim from one food patch to another within their territories and home ranges. The pattern is repeated throughout the day. The behavior is described in species belonging to the coral feeding guild. Habit formation and spatial learning are implicated. Foraging paths are based on learned locations of route specific landmarks. When a coral head is removed the fish look for it in its former location. If pairs of foraging fish are deflected from the path, they resume their routine pattern at the first landmark they encounter. Periodically, fish make excursions of 30 m or more to distant parts of the reef. Usually they follow different paths on the outbound and homeward legs of these excursions. The critical question is: Are the paths novel? If they are, it is evidence for the use of cognitive maps. Certainly fishes living in the highly structured coral reef environment are prime candidates to use cognitive maps in their orientation behavior.     

Indirect effects of algae on coral: algae-mediated, microbe-induced coral mortality

Declines in coral cover are generally associated with increases in the abundance of fleshy algae. In many cases, it remains unclear whether algae are responsible, directly or indirectly, for coral death or whether they simply settle on dead coral surfaces. Here, we show that algae can indirectly cause coral mortality by enhancing microbial activity via the release of dissolved compounds. When coral and algae were placed in chambers together but separated by a 0.02  μ m filter, corals suffered 100% mortality. With the addition of the broad-spectrum antibiotic ampicillin, mortality was completely prevented. Physiological measurements showed complementary patterns of increasing coral stress with proximity to algae. Our results suggest that as human impacts increase and algae become more abundant on reefs a positive feedback loop may be created whereby compounds released by algae enhance microbial activity on live coral surfaces causing mortality of corals and further algal growth.     

Degraded Environments Alter Prey Risk Assessment

Elevated water temperatures, a decrease in ocean pH, and an increasing prevalence of severe storms have lead to bleaching and death of the hard corals that underpin coral reef ecosystems. As coral cover declines, fish diversity and abundance declines. How degradation of coral reefs affects behavior of reef inhabitants is unknown. Here, we demonstrate that risk assessment behaviors of prey are severely affected by coral degradation. Juvenile damselfish were exposed to visual and olfactory indicators of predation risk in healthy live, thermally bleached, and dead coral in a series of laboratory and field experiments. While fish still responded to visual cues in all habitats, they did not respond to olfactory indicators of risk in dead coral habitats, likely as a result of alteration or degradation of chemical cues. These cues are critical for learning and avoiding predators, and a failure to respond can have dramatic repercussions for survival and recruitment.     

Coral larvae conservation: physiology and reproduction

Coral species throughout the world's oceans are facing severe environmental pressures. We are interested in conserving coral larvae by means of cryopreservation, but little is known about their cellular physiology or cryobiology. These experiments examined cryoprotectant toxicity, dry weight, water and cryoprotectant permeability using cold and radiolabeled glycerol, spontaneous ice nucleation temperatures, chilling sensitivity, and settlement of coral larvae. Our two test species of coral larvae, Pocillopora damicornis (lace coral), and Fungia scutaria (mushroom coral) demonstrated a wide tolerance to cryoprotectants. Computer-aided morphometry determined that F. scutaria larvae were smaller than P. damicornis larvae. The average dry weight for P. damicornis was 24.5%, while that for F. scutaria was 17%, yielding osmotically inactive volumes (V(b)) of 0.22 and 0.15, respectively. The larvae from both species demonstrated radiolabeled glycerol uptake over time, suggesting they were permeable to the glycerol. Parameter fitting of the F. scutaria larvae data yielded a water permeability 2 microm/min/atm and a cryoprotectant permeability = 2.3 x 10(-4) cm/min while modeling indicated that glycerol reached 90% of final concentration in the larvae within 25 min. The spontaneous ice nucleation temperature for F. scutaria larvae in filtered seawater was -37.8+/-1.4 degrees C. However, when F. scutaria larvae were chilled from room temperature to -11 degrees C at various rates, they exhibited 100% mortality. When instantly cooled from room temperature to test temperatures, they showed damage below 10 degrees C. These data suggest that they are sensitive to both the rate of chilling and the absolute temperature, and indicate that vitrification may be the only means to successfully cryopreserve these organisms. Without prior cryopreservation, both species of coral settled under laboratory conditions.     

Uranium in scleractinian coral skeletons

Accurate determinations have been made of the distribution of uranium in fresh and diagenetically altered coral skeletons occurring both naturally and grown under a variety of experimental conditions. Whereas live coral skeletons are homogeneous in uranium distribution, dead skeletons show heterogeneities relating to lithothamnioid algal encrustations and endolithic sponges. In the analyses of over 100 live coral skeletons, no zonal uranium distributions, described by previous workers, were found. In skeletons, free from organic material, uranium was found to exchange readily with the coral skeleton and/or to be precipitated along trabecular axes and skeletal margins. Bioeroded specimens contained higher uranium concentrations than freshly formed aragonite; they were similar to fossil coral skeletons used by previous researchers for uranium scrics dating.     

Prudent sessile feeding by the corallivore snail,Coralliophila violacea on coral energy sinks

Convergence of form and function has accompanied the evolution of modular growth in terrestrial plants and colonial marine invertebrates. Part of this convergence is related to the optimal exploitation of resources (space and light) and the ability to translocate energy products from sources to sink sites. Feeding on the energy pathways and energy sinks of terrestrial plants is a well-known phenomenon. Hermatypic corals, the major organisms constructing tropical reef environments, contain photosynthetic algae (zooxanthellae), energetic products of which are translocated towards sink sites located at the corals'' growing tips and regenerating areas. Despite the plant–coral convergence in energy pathways and sinks, there has been no evidence to date that coral energy sinks are exploited by coral predators. Gastropods of the genus Coralliophila are found feeding on coral margins, causing small and localized tissue damage. However, the ability of these snails to continue to feed without moving over a long period remains puzzling. Using a ¹⁴C labelling technique, we found that colony margins of the stony coral Porites function as major energy sinks. When snails inhabited these sites they incorporated significant amounts of ¹⁴C, indicating that they had fed on photosynthetic products translocated from the interior of the colony. Furthermore, when snails aggregate in the interior of the colony, thereby causing large surface injuries, they induce the development of significant new sink sites. This mode of prudent sessile feeding maximizes the efficiency of energy exploitation by the predatory snail, while minimizing tissue damage to the coral. The fact that energy sink sites occur in many coral species suggests that the strategy of sink exploitation for nutrition could also occur in many other marine host–symbiont relationships.     

Metabolism of estrogens and androgens by scleractinian corals

Estrogens and androgens are steroids that act as reproductive hormones in vertebrates. These compounds have also been detected in reef-building corals and other invertebrates, where they are hypothesized to act as bioregulatory molecules. Experiments were conducted using labeled steroid substrates to evaluate metabolism of estrogens and androgens by coral homogenates. GC-MS analysis of 13C-labeled steroids showed that Montipora capitata coral homogenates or fragments could convert estradiol to estrone and testosterone to androstenedione and androstanedione, evidence that M. capitata contains 17beta-hydroxysteroid dehydrogenase and 5alpha-reductase. When homogenates from three coral species and symbiotic dinoflagellates (zooxanthellae) were incubated with tritiated steroid substrates, metabolites separated by thin-layer chromatography confirmed that 17beta-hydroxysteroid dehydrogenase activity occurred in all species tested. NADP+ was the preferred cofactor in dehydrogenation reactions with coral homogenates. Reduction of estrone and androstenedione occurred at lower rates and aromatization of androgens was not observed. It is unclear whether estrogens detected previously in coral tissues are produced endogenously or sequestered in coral tissue from dietary or environmental sources. Previous studies have demonstrated that corals can take up estrogens from the water column overlying coral reefs. Considered in total, these observations suggest corals could alter the concentration or form of steroids available to reef organisms.     

Coral reefs promote the evolution of morphological diversity and ecological novelty in labrid fishes

Although coral reefs are renowned biodiversity hotspots it is not known whether they also promote the evolution of exceptional ecomorphological diversity. We investigated this question by analysing a large functional morphological dataset of trophic characters within Labridae, a highly diverse group of fishes. Using an analysis that accounts for species relationships, the time available for diversification and model uncertainty we show that coral reef species have evolved functional morphological diversity twice as fast as non-reef species. In addition, coral reef species occupy 68.6% more trophic morphospace than non-reef species. Our results suggest that coral reef habitats promote the evolution of both trophic novelty and morphological diversity within fishes. Thus, the preservation of coral reefs is necessary, not only to safeguard current biological diversity but also to conserve the underlying mechanisms that can produce functional diversity in future.     

The threat to coral reefs from more intense cyclones under climate change

Ocean warming under climate change threatens coral reefs directly, through fatal heat stress to corals and indirectly, by boosting the energy of cyclones that cause coral destruction and loss of associated organisms. Although cyclone frequency is unlikely to rise, cyclone intensity is predicted to increase globally, causing more frequent occurrences of the most destructive cyclones with potentially severe consequences for coral reef ecosystems. While increasing heat stress is considered a pervasive risk to coral reefs, quantitative estimates of threats from cyclone intensification are lacking due to limited data on cyclone impacts to inform projections. Here, using extensive data from Australia's Great Barrier Reef (GBR), we show that increases in cyclone intensity predicted for this century are sufficient to greatly accelerate coral reef degradation. Coral losses on the outer GBR were small, localized and offset by gains on undisturbed reefs for more than a decade, despite numerous cyclones and periods of record heat stress, until three unusually intense cyclones over 5 years drove coral cover to record lows over >1500 km. Ecological damage was particularly severe in the central‐southern region where 68% of coral cover was destroyed over >1000 km, forcing record declines in the species richness and abundance of associated fish communities, with many local extirpations. Four years later, recovery of average coral cover was relatively slow and there were further declines in fish species richness and abundance. Slow recovery of community diversity appears likely from such a degraded starting point. Highly unusual characteristics of two of the cyclones, aside from high intensity, inflated the extent of severe ecological damage that would more typically have occurred over 100s of km. Modelling published predictions of future cyclone activity, the likelihood of more intense cyclones within time frames of coral recovery by mid‐century poses a global threat to coral reefs and dependent societies.     

Culture and identification of Desulfovibrio spp. from corals infected by black band disease on Dominican and Florida Keys reefs

Black band disease (BBD) of corals is characterized as a pathogenic microbial consortium composed of a wide variety of microorganisms. Together, many of these microorganisms contribute to an active sulfur cycle that produces anoxia and high levels of sulfide adjacent to the coral surface, conditions that are lethal to coral tissue. Sulfate-reducing bacteria, as sulfide producers, are an important component of the sulfur cycle and the black band community. Previous molecular survey studies have shown multiple Desulfovibrio species present in BBD but with limited consistency between bacterial species and infections. In this study we compared 16S rRNA gene sequences of sulfate-reducing bacteria selectively cultured from 6 BBD bands on 4 coral species, Diploria clivosa, D. strigosa, D. labyrinthiformes, and Siderastrea siderea, in the Florida Keys and Dominica. The 16S rRNA gene sequences were obtained through direct sequencing of PCR products or by cloning. A BLAST search revealed that 8 out of 10 cultures sequenced were highly homologous to Desulfovibrio sp. strain TBP-1, a strain originally isolated from marine sediment. Although the remaining 2 sequences were less homologous to Desulfovibrio sp. strain TBP-1, they did not match any other sulfate-reducing (or other) species in GenBank.     

Coral mortality versus structural collapse as drivers of corallivorous butterflyfish decline

As climate change increasingly threatens biodiversity, identifying specific drivers of species loss as well as the attributes of species most vulnerable to climatic disturbances is a key challenge to ecologists and conservationists. Here we assess the effects of coral loss versus declines in structural complexity on obligate and facultative coral feeding butterflyfishes on coral reefs in the central and western Indian Ocean. In the inner Seychelles, the abundance of the obligate coral feeding group declined markedly in response to live coral mortality (r ² = 0.48), but showed no further decline with respect to erosion of the physical matrix of the reef. Conversely, the facultative feeding group showed no decline in response to live coral loss, reflecting their feeding versatility; however they did decline in response to structural erosion of the reef framework (r ² = 0.26). There were no significant changes in either obligate or facultative corallivore abundances at a reference location (Chagos archipelago), highlighting that butterflyfish populations are stable in the absence of habitat disturbance. While specialised coral dependant fishes are highly vulnerable to coral loss caused by climate-induced coral bleaching, the structural collapse of dead coral colonies may have significant, but more variable, impacts across a wide range of fishes. If conservation and mitigation planning are to be effective, there is a clear need to better understand the mechanisms of reef structural collapse and the dynamics of system recovery following large-scale disturbance.     

Density-associated recruitment mediates coral population dynamics on a coral reef

Theory suggests that density-associated processes can modulate community resilience following declines in population size. Here, we demonstrate density-associated processes in two scleractinian populations on the outer reef of Moorea, French Polynesia, that are rapidly increasing in size following the effects of two catastrophic disturbances. Between 2006 and 2010, predation by the corallivorous crown-of-thorns sea star reduced coral cover by 93 %; in 2010, the dead coral skeletons were removed by a cyclone, and in 2011 and 2012, high coral recruitment initiated population recovery. Coral recruitment was associated with coral cover, but the relationship differed between two coral genera that are almost exclusively broadcast spawners in Moorea. Acroporids recruited at low densities, and the density of recruits was positively associated with cover of Acropora, whereas pocilloporids recruited at high densities, and densities of their recruits were negatively associated with cover of Pocillopora. Together, our results suggest that associations between adult cover and density of both juveniles and recruits can mediate rapid coral community recovery after large disturbances. The difference between taxa in sign of the relationships between recruit density and coral cover indicate that they reflect contrasting mechanisms with the potential to mediate temporal shifts in taxonomic composition of coral communities.     

Late Holocene sea level indicators from twelve atolls in the central and eastern Tuamotus (Pacific Ocean)

New sea-level data for the late Holocene period are reported from twelve atolls of the Tuamotu archipelago: Faaite, Hikueru, Marokau, Hao, Amanu, Tatakoto, Pukarua, Nukutavake, Vairaatea, Tureia, Nukutipipi, and Hereheretue. The data come from coral conglomerate outcrops, coral colonies in growth position, in situ reef framework and marine notches; they give consistent results, and their ages are controlled by 29 radiocarbon datings. The Holocene MSL remained 0.8±0.2 m higher than at present, from before 4000 years BP until at least 1500 years BP, then dropped gradually to the present level. This pattern is very similar to that reported from the northwest Tuamotus, suggesting the absence of measurable differential vertical movements over a distance greater than 1300 km during the late Holocene. Effects of the 1983 cyclones on reef morphology are reported from some atolls and radiocarbon dates of some storm-generated reef blocks are given.     

Mycosporine-like amino acids from coral dinoflagellates

Coral reefs are one of the most important marine ecosystems, providing habitat for approximately a quarter of all marine organisms. Within the foundation of this ecosystem, reef-building corals form mutualistic symbioses with unicellular photosynthetic dinoflagellates of the genus Symbiodinium. Exposure to UV radiation (UVR) (280 to 400 nm) especially when combined with thermal stress has been recognized as an important abiotic factor leading to the loss of algal symbionts from coral tissue and/or a reduction in their pigment concentration and coral bleaching. UVR may damage biological macromolecules, increase the level of mutagenesis in cells, and destabilize the symbiosis between the coral host and their dinoflagellate symbionts. In nature, corals and other marine organisms are protected from harmful UVR through several important photoprotective mechanisms that include the synthesis of UV-absorbing compounds such as mycosporine-like amino acids (MAAs). MAAs are small (<400-Da), colorless, water-soluble compounds made of a cyclohexenone or cyclohexenimine chromophore that is bound to an amino acid residue or its imino alcohol. These secondary metabolites are natural biological sunscreens characterized by a maximum absorbance in the UVA and UVB ranges of 310 to 362 nm. In addition to their photoprotective role, MAAs act as antioxidants scavenging reactive oxygen species (ROS) and suppressing singlet oxygen-induced damage. It has been proposed that MAAs are synthesized during the first part of the shikimate pathway, and recently, it has been suggested that they are synthesized in the pentose phosphate pathway. The shikimate pathway is not found in animals, but in plants and microbes, it connects the metabolism of carbohydrates to the biosynthesis of aromatic compounds. However, both the complete enzymatic pathway of MAA synthesis and the extent of their regulation by environmental conditions are not known. This minireview discusses the current knowledge of MAA synthesis, illustrates the diversity of MAA functions, and opens new perspectives for future applications of MAAs in biotechnology.