Cell death and degeneration in the symbiotic dinoflagellates of the coral Stylophora pistillata during bleaching

Rising sea temperatures are increasing the incidences of mass coral bleaching (the dissociation of the coral-algal symbiosis) and coral mortality. In this study, the effects of bleaching (induced by elevated light and temperature) on the condition of symbiotic dinoflagellates (Symbiodinium sp.) within the tissue of the hard coral Stylophora pistillata (Esper) were assessed using a suite of techniques. Bleaching of S. pistillata was accompanied by declines in the maximum potential quantum yield of photosynthesis (F-v/F-m, measured using pulse amplitude modulated [PAM] fluorometry), an increase in the number of Sytox-green-stained algae (indicating compromised algal membrane integrity and cell death), an increase in 2',7'-dichlorodihydrofluroscein diacetate (H(2)DCFDA)stained algae (indicating increased oxidative stress), as well as ultrastructural changes (vacuolisation, losses of chlorophyll, and an increase in accumulation bodies). Algae expelled from S. pistillata exhibited a complete disorganisation of cellular contents; expelled cells contained only amorphous material. In situ samples taken during a natural mass coral bleaching event on the Great Barrier Reef in February 2002 also revealed a high number of Sytox-labelled algae cells in symbio. Dinoflagellate degeneration during bleaching seems to be similar to the changes resulting from senescence-phase cell death in cultured algae. These data support a role for oxidative stress in the mechanism of coral bleaching and highlight the importance of algal degeneration during the bleaching of a reef coral.

Effect of early marine diagenesis on coral reconstructions of surface-ocean 13C/12C and carbonate saturation state

Recent research suggests that future decreases in the carbonate saturation state of surface seawater associated with the projected build-up of atmospheric CO2 could cause a global decline in coral reef-building capacity. Whether significant reductions in coral calcification are underway is a matter of considerable debate. Multicentury records of skeletal calcification extracted from massive corals have the potential to reconstruct the progressive effect of anthropogenic changes in carbonate saturation on coral reefs. However, early marine aragonite cements are commonly precipitated from pore waters in the basal portions of massive coral skeletons and, if undetected, could result in apparent nonlinear reductions in coral calcification toward the present. To address this issue, we present records of coral skeletal density, extension rate, calcification rate, δ13C, and δ18O for well preserved and diagenetically altered coral cores spanning ∼1830-1994 A.D. at Ningaloo Reef Marine Park, Western Australia. The record for the pristine coral shows no significant decrease in skeletal density or δ13C indicative of anthropogenic changes in carbonate saturation state or δ13C of surface seawater (oceanic Suess effect). In contrast, progressive addition of early marine inorganic aragonite toward the base of the altered coral produces an apparent ∼25% decrease in skeletal density toward the present, which misleadingly matches the nonlinear twentieth century decrease in coral calcification predicted by recent modeling and experimental studies. In addition, the diagenetic aragonite is enriched in 13C, relative to coral aragonite, resulting in a nonlinear decrease in δ13C toward the present that mimics the decrease in δ13C expected from the oceanic Suess effect. Taken together, these diagenetic changes in skeletal density and δ13C could be misinterpreted to reflect changes in surface-ocean carbonate saturation state driven by the twentieth century build-up of atmospheric CO2. Copyright 2004 by the American Geophysical Union.

The ecological significance of the combtoothed blenny in a coral reef ecosystem

At Heron Island reef, Great Barrier Reef Australia, biomass densities and mean wet mass of Ward's damselfish Pomacentrus wardi and the jewelled blenny Salarias fasciatus were not significantly different at 2-37 v. 2-95 g m(-2) and 8-7 v. 7-9 g, respectively. Whereas S. fasciatus significantly exceeded P. wardi in (1) total number of bites per day (3427 v. 1155), (2) the mass of epilithic algal community consumed per bite (2-19 1,. 0-14mg) and (3) total organic carbon consumed per day (487-31 v. 35-46 mg C m(-2) day(-1)). Territorial behaviour differed also between the two species. Pomacentrus wardi chased from their territories a smaller proportion of blennies than roving grazers (i.e. scarids, acanthurids, siganids and pomacentrids) relative to S. fasciatus. Salarias fasciatus chased c. 90% of other blennies from their territories, while chasing only c. 20% of all damsels that entered. Both P. wardi and S. fasciatus rarely chased non-grazers. The chasing behaviour of S. fascialus was size dependent, with resident fish chasing only individuals of its own family (i.e. Blenniidae) that were the same or smaller size. Pomacentrus wardi may have tolerated S. fasciatus grazing within its territory, as it contributes to territory defence from other blennies. The possibility that the interaction between the two species is facilitative, rather than competitive, is discussed. It was concluded that salariine blennies play an important, and previously underestimated role in coral reef trophodynamics. (C) 2004 The Fisheries Society of the British Isles.

Testing the 'photoinhibition' model of coral bleaching using chemical inhibitors

Explants of the hard coral Seriatopora hystrix were exposed to sublethal concentrations of the herbicide diuron DCMU (N'-(3,4-dichlorophenyl,-N,N-dimethylurea)) and the heavy metal copper. Pulse amplitude modulated (PAM) chlorophyll fluorescence techniques were used to assess the effects on the photosynthetic efficiency of the algal symbionts in the tissue (in Symbio), and chlorophyll fluorescence and counts of symbiotic algae (normalised to surface area) were used to assess the extent of coral bleaching. At 30 mug DCMU l(-1), there was a reduction in both the maximum effective quantum yield (DeltaF/F-m') and maximum potential quantum yield (F-v/F-m) of the algal symbionts in symbio. Corals subsequently lost their algal symbionts and discoloured (bleached), especially on their upper sunlight-exposed surfaces. At the same DCMU concentration but under low light (5% of growth irradiance), there was a marked reduction in DeltaF/F-m' but only a slight reduction in F-v/F-m and slight loss of algae. Loss of algal symbionts was also noted after a 7 d exposure to concentrations as low as 10 mug DCMU l(-1) under normal growth irradiance, and after 14 d exposure to 10 mug DCMU l(-1) under reduced irradiance. Collectively the results indicate that DCMU-induced bleaching is caused by a light-dependent photoinactivation of algal symbionts, and that bleaching occurs when F-v/F-n, (measured 2 h after sunset) is reduced to a value of less than or equal to 0.6. Elevated copper concentrations (60 mug Cu l(-1) for 10 h) also induced a rapid bleaching in S. hystrix but without affecting the quantum yield of the algae in symbio. Tests with isolated algae indicated that substantially higher concentrations (300 mug Cu l(-1) for 8 h) were needed to significantly reduce the quantum yield. Thus, copper-induced bleaching occurs without affecting the algal photosynthesis and may be related to effects on the host (animal). It is argued that warm-water bleaching of corals resembles both types of chemically induced bleaching, suggesting the need for an integrated model of coral bleaching involving the effect of temperature on both host (coral) and algal symbionts.

High-frequency winter cooling and reef coral mortality during the Holocene climatic optimum

A detailed ecological, micro-structural and skeletal Sr/Ca study of a 3.42 m thick Goniopora reef profile from an emerged Holocene reef terrace at the northern South China Sea reveals at least nine abrupt massive Goniopora stress and mortality events occurred in winter during the 7.0-7.5 thousand calendar years before present (cal. ka BP) (within the Holocene climatic optimum). Whilst calculated Sr/Ca-SST (sea surface temperature) maxima during this period are comparable to those in the 1990s, Sr/Ca-SST minima are significantly lower, probably due to stronger winter monsoons. Such generally cooler winters, superimposed by further exceptional winter cooling on inter-annual to decadal scales, may have caused stress and mortality of the corals about every 50 years. Sea level rose by similar to 3.42 m during this period, with present sea-level reached at similar to 7.3 ka BP and a sea-level highstand of at least similar to 1.8 m occurred at similar to 7.0 ka. The results show that it took about 20-25 years for a killed Goniopora coral reef to recover. (C) 2004 Elsevier B.V. All rights reserved.

Endolithic algae photoacclimate to increased irradiance during coral bleaching

The photoacclimation of endolithic algae ( of the genus Ostreobium) inhabiting the skeleton of the Mediterranean coral Oculina patagonica during a bleaching event was examined. Pulse amplitude modulated (PAM) chlorophyll fluorescence techniques in situ were used to assess the photosynthetic efficiency of endolithic algae in the coral skeleton and the symbiotic dinoflagellates (zooxanthellae) in the coral tissue. Relative photosynthetic electron transport rates (ETRs) of the endolithic algae under bleached areas of the colony were significantly higher than those of endolithic algae from a healthy section of the colony and those of zooxanthellae isolated from the same section. Endolithic algae under healthy parts of the colony demonstrated an ETRmax of 16.5% that of zooxanthellae from tissue in the same section whereas endolithic algae under bleached sections showed ETRmax values that were 39% of those found for healthy zooxanthellae. The study demonstrates that endolithic algae undergo photoacclimation with increased irradiance reaching the skeleton. As PAM fluorometry has become a major tool for assessing levels of stress and bleaching in corals, the importance of considering the contribution of the endolithic algae to the overall chlorophyll fluorescence measured is highlighted.

Dynamics of a temperature-related coral disease outbreak

During the austral summer of 2001/2002, a coral epizootic occurred almost simultaneously with a bleaching event on the fringing reefs of Magnetic Island (Great Barrier Reef region), Australia. This resulted in a 3- to 4-fold increase in the mean percentage of partial mortality rate in a population of the hard coral Montipora aequituberculata. The putative disease state, ‘atramentous necrosis’, was observed on both bleached and normally-pigmented M. aequituberculata, and presented blackened lesions that spread within days across the colony surface and throughout the population. Diseased portions of the corals were only visible for 3 to 4 wk, with diseased tissues becoming covered in sediment and algae, which rapidly obscured evidence of the outbreak. Diseased colonies were again observed in the summer of 2002/2003 after being absent over the 2002 winter. Analysis of when diseased and bleached corals were first observed, and when and where the mortality occurred on individual colonies, indicated virtually all the mortality over the summer could be attributed to the disease and not to the bleaching. Fluorescence in situ hybridisation (FISH) techniques and cloning, and analysis of the 16S rRNA genes from diseased coral tissue, identified a mixed microbial assemblage in the diseased tissues particularly within the Alphaproteobacteria, Firmicutes and Bacteroidetes. While it is not possible in this study to distinguish between a disease-causing microbial community versus secondary invaders, the bacterial 16S rDNA sequences identified within the blackened lesions demonstrated high similarity to sequences from black band disease and white plague infected corals, suggesting either common aetiological agents or development of a bacterial community that is specific to degrading coral tissues. Temperature-induced coral disease outbreaks, with the potential for elevated levels of mortality, may represent an added problem for corals during the warmer summer months and an added dimension to predicted increases in water temperature from climate change.

Use of X-radiographs to distinguish members of the Montastraea annularis reef-coral species complex

Recent work suggests the Montastraea annularis species complex consists of at least three species, which can be distinguished qualitatively in the field using features related to colony growth (e.g. overall growth form. bumpiness, growth along the colony edge). However, when whole colonies are not available and surfaces are eroded, identification becomes problematic when relying on such characteristics. Characters based on internal skeletal structures are less prone to loss due to taphonomic processes. Previous work has shown that internal corallite architectural features measured in transverse thin sections can be used to distinguish species. To determine whether internal colony-level features measured on X-radiographs can be used. eight characters related to corallite budding and accretionary growth were measured on specimens representing three modern members of the M. annularis species complex (M. annularis, M. flaveolata and M. franksi), as well as two fossil forms (columnar and organ-pipe). All eight characters showed significant differences among species. Discriminant function analysis using seven of these characters resulted in distinct species groupings In canonical scores plots and a 100% classification success for specimens from Panama. These results suggest that measurements made on X-radiographs provide a useful tool for quantitatively distinguishing members of the M. annularis complex as well as between other massive reef corals.

Overlapping species boundaries and hybridization within the Monastraea "annularis" reef coral complex in the Pleistocene of the Bahama Islands

Recent molecular analyses indicate that many reef coral species belong to hybridizing species complexes or "syngameons." Such complexes consist of numerous genetically distinct-species or lineages, which periodically split and/or fuse as they extend through time. During splitting and fusion, morphologic intermediates form and species overlap. Here we focus on processes associated with lineage fusion, specifically introgressive hybridization, and the recognition of such hybridization in the fossil record. Our approach involves comparing patterns of ecologic and morphologic overlap in genetically characterized modern species with fossil representatives of the same or closely related species. We similarly consider the long-term consequences of past hybridization on the structure of modern-day species boundaries. Our study involves the species complex Montastraea annularis s.l. and is based in the Bahamas, where, unlike other Caribbean locations, two of the three members of the complex today are not genetically distinct. We measured and collected colonies along linear transects across Pleistocene reef terraces of last interglacial age (approximately 125 Ka) on the islands of San Salvador, Andros, and Great Inagua. We performed quantitative ecologic and morphologic analyses of the fossil data, and compared patterns of overlap among species with data from modern localities where species are and are not genetically distinct. Ecologic and morphologic analyses reveal "moderate" overlap (>10%, but statistically significant differences) and sometimes "high" overlap (no statistically significant differences) among Pleistocene growth forms (= "species"). Ecologic analyses show that three species (massive, column, organ-pipe) co-occurred. Although organ-pipes had higher abundances in patch reef environments, columnar and massive species exhibited broad, completely overlapping distributions and had abundances that were not related to reef environment. For morphometric analyses, we used multivariate discriminant analysis on landmark data and linear measurements. The results show that columnar species overlap "moderately" with organ-pipe and massive species. Comparisons with genetically characterized colonies from Panama show that the Pleistocene Bahamas species have intermediate morphologies, and that the observed "moderate" overlap differs from the morphologic separation among the three modern species. In contrast, massive and columnar species from the Pleistocene of the Dominican Republic comprise distinct morphologic clusters, similar to the modern species; organ-pipe species exhibit "low" overlap (

Communication in coral reef fish: the role of ultraviolet colour patterns in damselfish territorial behaviour

Many coral reef fish possess ultraviolet (UV) colour patterns. The behavioural significance of these patterns is poorly understood and experiments on this issue have not been reported for free-living reef fish in their natural environment. The damselfish Pomacentrus amboinensis has UV facial patterns, and spectroradiometric ocular media measurements show that it has the potential for UV vision. To test the potential behavioural significance of the UV patterns, I studied the response of males, in natural territories on the reef and in aquaria, to two conspecific intruders, one presented in a UV-transmitting (UV+) container and the other in a UV-absorbing (UV-) one. Territory owners attacked intruders viewed through UV+ filters significantly more often and for longer than intruders viewed through the UV- filter. In general, the results of the field experiment confirmed those of the laboratory experiment. The results support the hypothesis that P. amboinensis males are sensitive to UV light and that reflectance patterns, which appear in high contrast only in UV, modulate the level of aggressive behaviour. A recent survey showed that many predatory fish may not have UV vision and the use of UV colours in select species of reef fish may therefore serve as a 'private communication channel'. (C) 2004 The Association for the Study of Animal Behaviour. Published by Elsevier Ltd. All rights reserved.

Coral mortality increases wave energy reaching shores protected by reef flats: Examples from the Seychelles

In the granitic Seychelles, many shores and beaches are fringed by coral reef flats which provide protection to shores from erosion by waves. The surfaces of these reef flats support a complex ecology. About 10 years ago their seaward zones were extensively covered by a rich coral growth, which reached approximately to mean low water level, but in 1998 this was largely killed by seawater warming. The resulting large expanses of dead coral skeletons in these locations are now disintegrating, and much of the subsequent modest recovery by new coral recruitment was set back by further mortalities. A mathematical model of wave energy reaching shorelines protected by coral reef flats has been applied to 14 Seychelles reefs. It is derived from equations which predict: (1) the raised water level, or wave set-up, on reef flats resulting from wave breaking, which depends upon offshore wave height and period, depth of still water over the reef flat and the reef crest profile, and (2) the decay of energy from reef edge to shoreline that is affected by width of reef flat, surface roughness, sea level rise and 'pseudo-sea level rise' created by increased depth resulting from disintegration of coral colonies. The model treats each reef as one entity, but because biota and zonation on reef flats are not homogenous, all reefs are divided into four zones. In each, cover by both living and dead biota was estimated for calculation of parameters, and then averaged to obtain input data for the model. All possible biological factors were taken into account, such as the ability of seagrass beds to grow upwards to match expected sea level rise, reduction in height of the reef flat in relation to sea level as zones of dead corals decay, and the observed 'rounding' of reef crests as erosion removes corals from those areas. Estimates were also made of all these factors for a time approximately a decade ago, representing a time before the mass coral mortality, and for approximately a decade in the future when the observed rapid state of dead coral colony disintegration is assumed to have reached an end point. Results of increased energy over the past decade explain observations of erosion in some sites in the Seychelles. Most importantly, it is estimated that the rise in energy reaching shores protected by fringing reefs will now accelerate more rapidly, such that the increase expected over the next decade will be approximately double than that seen over the past decade. (c) 2005 Elsevier Ltd. All rights reserved.

Wave-generated flow on coral reefs - an analysis for two-dimensional horizontal reef-tops with steep faces

Waves breaking on the seaward rim of a coral reef generate a flow of water from the exposed side of the reef to the sheltered side and/or to either channels through the reef-rim or lower sections of the latter. This wave-generated flow is driven by the water surface gradient resulting from the wave set-up created by the breaking waves. This paper reviews previous approaches to modelling wave-generated flows across coral reefs and discusses the influence of reef morphology and roughness upon these flows. Laboratory measurements upon a two-dimensional horizontal reef platform with a steep reef face provide the basis for extending a previous theoretical analysis for wave set-up on a reef in the absence of a flow [Gourlay, M.R., 1996b. Wave set-up on coral reefs. 2. Set-up on reefs with various profiles. Coastal Engineering 28, 1755] to include the interaction between a unidirectional flow and the wave set-up. The laboratory model results are then used to demonstrate that there are two basic reef-top flow regimes-reef-top control and reef-rim control. Using open channel flow theory, analytical relationships are derived for the reef-top current velocity in terms of the offreef wave conditions, the reef-top water depth and the physical characteristics of the reef-top topography. The wave set-up and wave-generated flow relationships are found to predict experimental values with reasonable accuracy in most cases. The analytical relationships are used to investigate wave-generated flows into a boat harbour channel on Heron Reef in the southern Great Barrier Reef. (c) 2005 Elsevier B.V. All rights reserved.

Effects of the herbicide diuron on the early life history stages of coral

The effects of the herbicide diuron on the early life history stages of broadcast spawning and brooding corals were examined in laboratory experiments. Fertilisation of Acropora millepora and Montipora aequituberculata oocytes were not inhibited at diuron concentrations of up to 1000 mu gl(-1). Metamorphosis of symbiont-free A. millepora larvae was only significantly inhibited at 300 mu gl(-1) diuron. Pocillopora damicornis larvae, which contain symbiotic dinoflagellates, were able to undergo metamorphosis after 24h exposure to diuron at 1000 mu gl(-1). Two-week old P. damicornis recruits on the other hand were as susceptible to diuron as adult colonies, with expulsion of symbiotic dinoflagellates (bleaching) evident at 10 mu gl(-1) diuron after 96 h exposure. Reversible metamorphosis was observed at high diuron concentrations, with fully bleached polyps escaping from their skeletons. Pulse amplitude modulation (PAM) chlorophyll fluorescence techniques demonstrated a reduction in photosynthetic efficiency (Delta F/F'(m)) in illuminated P. dami- cornis recruits after a 2h exposure to 1 mu gl(-1) diuron. The dark-adapted quantum yields (F-v/F-m also declined, indicating chronic photoinhibition and damage to photosystem H. Crown Copyright (c) 2004 Published by Elsevier Ltd. All rights reserved.

A Site Description of the CARICOMP Mangrove, Seagrass and Coral Reef Sites in Bocas del Toro, Panama

Bocas del Toro is located in the western region of the Republic of Panama. It is part of a province of approximately 8917 km(2) with an estimated 68% of its area covered by tropical rainforest. The area receives 2870 mm/year of rainfall. The dry and rainy seasons are not clearly defined. There are two periods each of low and high rainfall, March and September-October, and July and December, respectively. Mangrove forests, seagrass meadows and coral reefs are vast, covering large areas in the shallow waters surrounding the islands of the archipelago and along the mainland coast. The CARICOMP sites were established in 1998-99 and are periodically monitored following Level I protocol. Herein we describe the sites in a regional context and present the baseline data for each site. This paper fulfills the requirements of the formal site description for CARICOMP monitoring sites.