Holocene coral reef accretion in Hawaii: a function of wave exposure and sea level history

 In the high Hawaiian Islands, significant accretion due to coral reef growth is limited by wave exposure and sea level. Holocene coral growth and reef accretion was measured at four stations off Oahu, Hawaii, chosen along a gradient in wave energy from minimum to maximum exposures. The results show that coral growth of living colonies (linear extension) at optimal depths is comparable at all stations (7.7–10.1 mm/y), but significant reef accretion occurs only at wave sheltered stations. At wave sheltered stations in Hanauma Bay and Kaneohe Bay, rates of long term reef accretion are about 2.0 mm/y. At wave exposed stations, off Mamala Bay and Sunset Beach, reef accretion rates are virtually zero in both shallow (1 m) and deeper (optimal) depths (12 m). At wave sheltered stations, such as Kaneohe Bay and Hanauma Bay, Holocene reef accretion is on the order of 10–15 m thick. At wave exposed stations, Holocene accretion is represented by only a thin veneer of living corals resting on antecedent Pleistocene limestone foundations. Modern coral communities in wave exposed environments undergo constant turnover associated with mortality and recruitment or re-growth of fragmented colonies and are rarely thicker than a single living colony. Breakage, scour, and abrasion of living corals during high wave events appears to be the major source of mortality and ultimately limits accretion to wave sheltered environments. Depth is particularly important as a modulator of wave energy. The lack of coral reef accretion along shallow open ocean coastlines may explain the absence of mature barrier reefs in the high Hawaiian Islands. Accepted: 14 May 1998     

Effects of habitat,wave exposure,and marine protected area status on coral reef fish assemblages in the Hawaiian archipelago

The relationships between fish assemblages, their associated habitat, and degree of protection from fishing were evaluated over a broad spatial scale throughout the main Hawaiian islands. Most fish assemblage characteristics showed positive responses to protection whether it was physical (e.g. habitat complexity), biological (e.g. coral cover growth forms), or human-induced (e.g. marine reserves). Fish biomass was lowest in areas of direct wave exposure and highest in areas partially sheltered from swells. Higher values for fish species richness, number of individuals, biomass, and diversity were observed in locations with higher substrate complexity. Areas completely protected from fishing had distinct fish assemblages with higher standing stock and diversity than areas where fishing was permitted or areas that were partially protected from fishing. Locations influenced by customary stewardship harbored fish biomass that was equal to or greater than that of no-take protected areas. Marine protected areas in the main Hawaiian islands with high habitat complexity, moderate wave disturbance, a high percentage of branching and/or lobate coral coupled with legal protection from fishing pressure had higher values for most fish assemblage characteristics.     

Associations between climate stress and coral reef diversity in the western Indian Ocean

Climatic–oceanographic stress and coral reef diversity were mapped in the western Indian Ocean (WIO) in order to determine if there were associations between high diversity coral reefs and regions with low‐to‐moderate climate stress. A multivariate stress model developed to estimate environmental exposure to stress, an empirical index of the coral community's susceptibility to stress, and field data on numbers of fish and corals taxa from 197 WIO sites were overlain to evaluate these associations. Exposure to stress was modeled from satellite data based on nine geophysical–biological oceanographic characteristics known to influence coral bleaching (i.e. temperature, light, and current variables). The environmental stress model and the coral community's susceptibility index were moderately correlated (r=?0.51) with southern and eastern parts of the WIO identified as areas with low environmental stress and coral communities with greater dominance of bleaching stress‐sensitive taxa. Numbers of coral and fish taxa were positive and moderately correlated (r=0.47) but high diversity regions for fish were in the north and west while diversity was highest for corals in central regions from Tanzania to northwestern Madagascar. Combining three and four of these variables into composite maps identified a region from southern Kenya to northern Mozambique across to northern–eastern Madagascar and the Mascarene Islands and the Mozambique–South Africa border as areas where low‐moderate environmental exposure overlaps with moderate‐high taxonomic diversity. In these areas management efforts aimed at maintaining high‐diversity and intact ecosystems are considered least likely to be undermined by climate disturbances in the near term. Reducing additional human disturbances, such as fishing and pollution, in these areas is expected to improve the chances for their persistence. These reefs are considered a high priority for increased local, national, and international management efforts aimed at establishing coral reef refugia for climate change impacts.     

Spatial and temporal patterns in the coral assemblage at Clipperton Atoll: a sentinel reef in the Eastern Tropical Pacific

Coral Reefs - Isolated coral reef habitats are unique systems to study the natural dynamics of coral traits and their natural acclimatization, adaptation, and recovery from global-scale stressors...     

Beyond corals and fish: the effects of climate change on noncoral benthic invertebrates of tropical reefs

Climate change is threatening tropical reefs across the world, with most scientists agreeing that the current changes in climate conditions are occurring at a much faster rate than in the past and are potentially beyond the capacity of reefs to adapt and recover. Current research in tropical ecosystems focuses largely on corals and fishes, although other benthic marine invertebrates provide crucial services to reef systems, with roles in nutrient cycling, water quality regulation, and herbivory. We review available information on the effects of environmental conditions associated with climate change on noncoral tropical benthic invertebrates, including inferences from modern and fossil records. Increasing sea surface temperatures may decrease survivorship and increase the developmental rate, as well as alter the timing of gonad development, spawning, and food availability. The broad latitudinal distribution and associated temperature ranges of several pantropical taxa suggest that some reef communities may have an in‐built adaptive capacity. Tropical benthic invertebrates will also show species‐specific sublethal and lethal responses to sea‐level rise, ocean acidification, physical disturbance, runoff, turbidity, sedimentation, and changes in ocean circulation. In order to accurately predict a species' response to these stressors, we must consider the magnitude and duration of exposure to each stressor, as well as the physiology, mobility, and habitat requirements of the species. Stressors will not act independently, and many organisms will be exposed to multiple stressors concurrently, including anthropogenic stressors. Environmental changes associated with climate change are linked to larger ecological processes, including changes in larval dispersal and recruitment success, shifts in community structure and range extensions, and the establishment and spread of invasive species. Loss of some species will trigger economic losses and negative effects on ecosystem function. Our review is intended to create a framework with which to predict the vulnerability of benthic invertebrates to the stressors associated with climate change, as well as their adaptive capacity. We anticipate that this review will assist scientists, managers, and policy‐makers to better develop and implement regional research and management strategies, based on observed and predicted changes in environmental conditions.     

Reef fish and habitat relationships in a Caribbean seascape: the importance of reef context

Marine protected area (MPA) effectiveness is contingent on understanding key ecological patterns and processes at appropriate spatial scales and may depend upon maintaining critical linkages among essential habitat patches to conserve reef-fish communities. Hypotheses were tested to investigate the importance of habitat linkages in the US Virgin Islands. As expected, reef context (the spatial pattern of surrounding habitat patches) was a strong predictor of reef fish assemblage structure. Specific relationships were functionally consistent with the ecology of the fishes of interest. For example, reefs with large amounts of seagrass nearby harbored the greatest numerical abundance of fishes, particularly mobile invertebrate feeders and the exploited fish families of Haemulidae (grunts) and Lutjanidae (snappers). Species richness for the entire fish community and within these fish groups was also strongly associated with reef context. Furthermore, reef fish mobility influenced how fishes related to reef context. Fish-habitat relationships were detected as far as 1 km from study reefs, suggesting that fish movements result in habitat encounter rates that may influence their patterns of distribution. Consequently, functional habitat connectivity of habitat patches appears important in structuring reef-fish assemblages, and suggests that landscape-scale metrics may provide insights useful to managers in the design of MPAs.     

A comparison of the 1998 and 2002 coral bleaching events on the Great Barrier Reef: spatial correlation,patterns, and predictions

Detailed mapping of coral bleaching events provides an opportunity to examine spatial patterns in bleaching over scales of 10 s to 1,000 s of km and the spatial correlation between sea surface temperature (SST) and bleaching. We present data for two large-scale (2,000 km) bleaching events on the Great Barrier Reef (GBR): one from 1998 and another from 2002, both mapped by aerial survey methods. We examined a wide range of satellite-derived SST variables to determine which one best correlated with the observed bleaching patterns. We found that the maximum SST occurring over any 3-day period (max3d) during the bleaching season predicted bleaching better than anomaly-based SST variables and that short averaging periods (3–6 days) predicted bleaching better than longer averaging periods. Short periods of high temperature are therefore highly stressful to corals and result in highly predictable bleaching patterns. Max3d SST predicted the presence/absence of bleaching with an accuracy of 73.2%. Large-scale (GBR-wide) spatial patterns of bleaching were similar between 1998 and 2002 with more inshore reefs bleached compared to offshore reefs. Spatial change in patterns of bleaching occurred at scales of ~10 s km, indicating that reefs bleach (or not) in spatial clusters, possibly due to local weather patterns, oceanographic conditions, or both. Approximately 42% of reefs bleached to some extent in 1998 with ~18% strongly bleached, while in 2002, ~54% of reefs bleached to some extent with ~18% strongly bleached. These statistics and the fact that nearly twice as many offshore reefs bleached in 2002 compared to 1998 (41 vs. 21%, respectively) makes the 2002 event the worst bleaching event on record for the GBR. Modeling of the relationship between bleaching and max3d SST indicates that a 1 °C increase would increase the bleaching occurrence of reefs from 50% (approximate occurrence in 1998 and 2002) to 82%, while a 2 °C increase would increase the occurrence to 97% and a 3 °C increase to 100%. These results suggest that coral reefs are profoundly sensitive to even modest increases in temperature and, in the absence of acclimatization/adaptation, are likely to suffer large declines under mid-range International Panel for Climate Change predictions by 2050.

Estimation of photosynthesis and calcification rates at a fringing reef by accounting for diurnal variations and the zonation of coral reef communities on reef flat and slope: a case study for the Shiraho reef, Ishigaki Island, southwest Japan

Seven coral reef communities were defined on Shiraho fringing reef, Ishigaki Island, Japan. Net photosynthesis and calcification rates were measured by in situ incubations at 10 sites that included six of the defined communities, and which occupied most of the area on the reef flat and slope. Net photosynthesis on the reef flat was positive overall, but the reef flat acts as a source for atmospheric CO₂, because the measured calcification/photosynthesis ratio of 2.5 is greater than the critical ratio of 1.67. Net photosynthesis on the reef slope was negative. Almost all excess organic production from the reef flat is expected to be effused to the outer reef and consumed by the communities there. Therefore, the total net organic production of the whole reef system is probably almost zero and the whole reef system also acts as a source for atmospheric CO₂. Net calcification rates of the reef slope corals were much lower than those of the branching corals. The accumulation rate of the former was approximately 0.5 m kyr⁻¹ and of the latter was ~0.7–5 m kyr⁻¹. Consequently, reef slope corals could not grow fast enough to keep up with or catch up to rising sea levels during the Holocene. On the other hand, the branching corals grow fast enough to keep up with this rising sea level. Therefore, a transition between early Holocene and present-day reef communities is expected. Branching coral communities would have dominated while reef growth kept pace with sea level rise, and the reef was constructed with a branching coral framework. Then, the outside of this framework was covered and built up by reef slope corals and present-day reefs were constructed.     

Diurnal variation in the abundance of juvenile parasitic gnathiid isopods on coral reef fish: implications for parasite-cleaner fish interactions

 The dynamics of parasitic gnathiid isopod infestation on the fish Hemigymnus melapterus were examined at Heron Island, Great Barrier Reef, by measuring the abundance and feeding state of gnathiids on fish collected between dawn and sunset and by estimating the time required for gnathiids to become engorged on host fluids. A model was developed to estimate gnathiid abundance on fish for any given time of day and host size. Fish at dawn had 2.4 times as many gnathiids compared with fish at sunset, indicating that some gnathiids infest fish overnight. Most gnathiids had engorged guts (72–86%); the proportion of empty guts and engorged guts did not differ in three time periods of collection (<0800 h, 0800 to 1100 h, and >1100 h). In the laboratory, gnathiids fed quickly with 75% of gnathiids exposed to fish for 4 h having engorged guts. The short time required for gnathiids to become engorged and the presence of gnathiids with empty guts throughout the day suggests that gnathiids also infest fish during the day. Thus gnathiids eaten by cleaner fish during the day may be replaced by other gnathiids during the day or night suggesting that interactions between gnathiids and cleaner fish are highly dynamic. Accepted: 15 April 1999     

The effects of spatial habitat configuration on recruitment, growth and population structure in arctic Collembola

The population density and demography of five species of arctic Collembola were studied in a naturally patchy habitat, consisting of Carex ursinae tussocks with varying degrees of isolation. Focal predictor variables were those describing the spatial configuration of tussocks, including tussock size and isolation and the amount of habitat (cover) at a 1-m² scale surrounding each tussock population. The Collembola populations were heavily influenced by environmental stochasticity in the form of winter mortality and summer drought, and the influence of patchiness on population characteristics was evaluated in this context. The five species showed very different responses to the structuring effect of the habitat, depending on life history characteristics, mobility and habitat requirements. Population density was highly variable in both time and space. Spring densities indicated larger winter mortality compared to observations from a previous study, and the snow- and ice-free season from June to August only resulted in population growth for Folsomia sexoculata. In the other species, adult mortality must have been high as there was no net population growth despite observed reproduction. The exception was Hypogastrura viatica, whose population decline was more likely to have been the result of migration out of the study area. Cover was the most important variable explaining density. No pure area or isolation effects at the tussock level were detected, even in areas with very low habitat cover. Drought was probably an important mortality factor, as July was particularly warm and dry. Due to qualitative differences in the tussocks and the matrix substrate, desiccation risk would be higher during dispersal between tussocks. We suggest that increased dispersal mortality gave the observed pattern of increased density in relation to cover, both in general and in F. quadrioculata, an opportunistic species otherwise known for rapid population growth. Onychiurus groenlandicus, which had a similar density response to cover, may also be influenced by a rescue effect sustaining densities in areas with high cover. The cover effect can be viewed as a large-scale factor which encompasses the general spatial neighbourhood of each tussock, where inter-population processes are important, as opposed to internal patch dynamics. Received: 15 March 1999 / Accepted: 22 March 2000     

Temporal and spatial variability of the oxygen isotopic composition of massive corals from the South China Sea: Influence of the Asian monsoon

Coral colonies of Porites lutea and P. lobata were collected from areas to the east and south offshore of Hainan Island, South China Sea. Oxygen isotope ratios, ¹⁸O/¹⁶O, were analyzed along the major axis of growth at a resolution of 25–28 samples within an annual band from three colonies, giving data series lengths of 15, 20 and 30 years. Coral δ¹⁸O correlates well with sea surface temperature (SST) throughout most years, particularly when the Asian winter monsoon prevails over the region. Due to the same seasonal phases of SST and sea surface salinity (SSS), it is estimated that most of the seasonal features of coral δ¹⁸O are controlled by changes in SST with a significant contribution of SSS. This indicates the importance of temperature, as determined by the Asian winter monsoon, as a control on seasonal coral δ¹⁸O variations in the South China Sea. Given the fact that annual SSS maxima show minor inter-annual changes, the inter-annual change of annual coral δ¹⁸O maximum mainly reflects the SST induced by the winter monsoon. While the coral δ¹⁸O is mainly controlled by SST, deviations of the δ¹⁸O from SST correlate statistically with sea surface salinity, particularly for summer extreme events when SST reaches its annual maximum with minor inter-annual change. Therefore, we suggest that the inter-annual variation of the annual coral δ¹⁸O minima is mainly controlled by seawater composition. Seawater composition analysis indicates that its δ¹⁸O and salinity are simultaneously affected by freshwater inputs primarily from precipitation, which is mainly supplied by the Asian summer monsoon. Thus seasonal alternations of the winter and summer monsoon mainly control the coral δ¹⁸O, thereby allowing reconstruction of these monsoonal variables. The three coral records consistently reveal clear inter-decadal trends in δ¹⁸O — a gradual increase from 1968 to 1987, and a subsequent decrease from 1987 to 2003. These inter-decadal trends are roughly consistent with salinity changes — but not with temperature and precipitation, suggesting that seawater composition controlled by freshwater inputs from distant source areas, rather than from local precipitation, is responsible for the trends in seawater composition and coral δ¹⁸O over the last 30 years. Comparison of the three coral records indicates that spatial variations in coral δ¹⁸O coincide with variations in seawater salinity and local precipitation, but not with temperature. This confirms the dominant role of seawater composition, mainly controlled by monsoonal precipitation, on the spatial variability of coral δ¹⁸O in the South China Sea.     

Natural selection and climate change: temperature-linked spatial and temporal trends in gene frequency in Fagus sylvatica

Rapid increases in global temperature are likely to impose strong directional selection on many plant populations, which must therefore adapt if they are to survive. Within populations, microgeographic genetic differentiation of individuals with respect to climate suggests that some populations may adapt to changing temperatures in the short-term through rapid changes in gene frequency. We used a genome scan to identify temperature-related adaptive differentiation of individuals of the tree species Fagus sylvatica. By combining molecular marker and dendrochronological data we assessed spatial and temporal variation in gene frequency at the locus identified as being under selection. We show that gene frequency at this locus varies predictably with temperature. The probability of the presence of the dominant marker allele shows a declining trend over the latter half of the 20th century, in parallel with rising temperatures in the region. Our results show that F. sylvatica populations may show some capacity for an in situ adaptive response to climate change. However as reported ongoing distributional changes demonstrate, this response is not enough to allow all populations of this species to persist in all of their current locations.     

Environmental gradients and grassland trait variation: Insight into the effects of climate change

The research aim was to understand how variation of temperature and water availability drives trait assemblage of seminatural grasslands in sub-Mediterranean climate, where climate change is expected to intensify summer aridity. In the central Italy, we recorded species abundance and elevation, slope aspect and angle in 129 plots. The traits we analysed were life span, growth form, clonality, belowground organs, leaf traits, plant height, seed mass, and palatability. We used Ellenberg's indicators as a proxy to assess air temperature and soil moisture gradients. From productive to harsh conditions, we observed a shift from tolerance to avoidance strategies, and a change in resource allocation strategies to face competition and stress or that maximize exploitation of patchily distributed soil resource niches. In addition, we found that the increase of temperature and water scarcity leads to the establishment of regeneration strategies that enable plants to cope with the unpredictability of changes in stress intensity and duration. Since the dry habitats of higher elevations are also constrained by winter cold stress, we argue that, within the sub-Mediterranean bioclimate, climate change will likely lead to a variation in dominance inside plant communities rather than a shift upwards of species ranges. At higher elevations, drought-adaptive traits might become more abundant on south-facing slopes that are less stressed by winter low temperatures; traits related to productive conditions and cold stress would be replaced on north-facing slopes by those adapted to overcome both the drought and the cold stresses.     

Long-term persistence of low coral cover and abundance on a disturbed coral reef flat in the northern Red Sea

Levels of coral cover and abundance on a coral reef flat in Eilat (Israeli Red Sea) were estimated in 2001 by surveying nineteen 10-m transects, and compared to the levels reported in the same area between 1966 and 1973. Lower values compared to 1966 levels are evident, and there has been only a modest recovery following a catastrophic low tide that killed a large proportion of the corals in 1970. Percent cover of soft and stony corals (16.1%) was less than half of that reported for 1969 (35%), when a sharp decrease in coral abundance had already been observed. The total number of soft and stony coral colonies observed was 300, compared to 541 in 1966. In contrast to 1966, when half of the transects surveyed contained more than 30 coral colonies, no transects with this number of corals were observed. The cover of seven of the most common stony coral species was 841 cm, which is twice the coral cover of that in 1973, but only 22% of the 1969 level. Millepora dichotoma, an abundant species before 1970, has almost disappeared, and the soft coral Litophyton, abundant in 1972, was not observed. Anthropogenic nutrient enrichment is apparently among the causes for the lack of coral recovery in the studied reef flat. Reefs located further away from sources of pollution have recovered quickly after natural and anthropogenic disturbances and have retained their coral abundance and diversity.     

Adaptation to climate change: contrasting patterns of thermal-reaction-norm evolution in Pacific versus Atlantic silversides

How organisms may adapt to rising global temperatures is uncertain, but concepts can emerge from studying adaptive physiological trait variations across existing spatial climate gradients. Many ectotherms, particularly fish, have evolved increasing genetic growth capacities with latitude (i.e. countergradient variation (CnGV) in growth), which are thought to be an adaptation primarily to strong gradients in seasonality. In contrast, evolutionary responses to gradients in mean temperature are often assumed to involve an alternative mode, 'thermal adaptation'. We measured thermal growth reaction norms in Pacific silverside populations (Atherinops affinis) occurring across a weak latitudinal temperature gradient with invariant seasonality along the North American Pacific coast. Instead of thermal adaptation, we found novel evidence for CnGV in growth, suggesting that CnGV is a ubiquitous mode of reaction-norm evolution in ectotherms even in response to weak spatial and, by inference, temporal climate gradients. A novel, large-scale comparison between ecologically equivalent Pacific versus Atlantic silversides (Menidia menidia) revealed how closely growth CnGV patterns reflect their respective climate gradients. While steep growth reaction norms and increasing growth plasticity with latitude in M. menidia mimicked the strong, highly seasonal Atlantic coastal gradient, shallow reaction norms and much smaller, latitude-independent growth plasticity in A. affinis resembled the weak Pacific latitudinal temperature gradient.     

Negative effects of habitat drying and prior exploitation on the detritus resource in an ephemeral aquatic habitat

Ephemeral aquatic habitats are characterized by cycles of drying and subsequent inundation, and by production of sequential non-overlapping cohorts of organisms. Both processes may alter the quantity or quality of resources, and may therefore affect survival and development of cohorts that subsequently colonize ephemeral habitats. We examined these effects of habitat drying and non-overlapping cohorts on experimental cohorts of the tree hole mosquito Aedes triseriatus, testing specifically whether the value of leaf litter as a food resource is altered by cycles of inundation and drying, or by exploitation by a prior non-overlapping cohort. We created four treatments of leaf litter: (1) no prior cohort, continuously wet; (2) no prior cohort, one␣wet/dry cycle; (3) prior cohort, continuously wet, and (4) prior cohort, one wet/dry cycle, and tested for effects on individual fitness components (survivorship, mean dry mass at, and median days to eclosion) and on population growth (estimated finite rate of increase –λ′). Both resource drying and the presence of a prior cohort negatively affected individual fitness components in tires, increasing days to eclosion, and decreasing mean dry mass at eclosion for both sexes. Resource drying also negatively affected estimated rates of increase (λ′) in tree holes. A prior cohort had no significant effects on λ′. These results indicate that intraspecific interactions among mosquito larvae may include amensalistic effects of earlier, non-overlapping cohorts, and that resource drying reduces resource quality. The latter effect indicates that enhanced production of A. triseriatus from recently filled containers is not due to resource drying per se, and may result from more complex community-level effects of habitat drying. Extreme cycles of drying and inundation seem likely to increase intraspecific resource competition among drought-adapted species like A. triseriatus. Received: 5 May 1997 / Accepted: 20 January 1998     

Coast of change: habitat loss and transformations in the Wadden Sea

In the southern North Sea, coastal people commenced with habitat conversions 1,000 years ago. Partly interrupted in late medieval times by large-scale inundations of marshland, progressive embankments transformed the landward half of the amphibic transition zone between a limno-terrestric and a brackish-marine ecosystem into arable land and freshwater lakes. Sea walls rigidly separated the land from the sea. Dynamic transitional habitats have vanished. Areal loss has diminished the capacity of the Wadden Sea to dissipate wave and tidal energy. A coastal ecosystem once rich in marsh plants, seagrass and diatoms on mud flats became transformed into one with less autochthonous phototroph production, dominated by sandy tidal flats, and dependent primarily on allochthonous plankton supply. The large estuaries have been dredged to serve as shipping canals, and have lost most of their former retention and filter capacity. Riverine loads are now flushed right into the North Sea. Symptoms of a syndromatic coastal habitat degradation are diagnosed, leading to a decline in natural habitat diversity. The conventional on-line coastal protection may not achieve a sustainable coastal habitat configuration. At sedimentary coasts immobilised by dikes and petrified shores, a more flexible response to sea level rise is recommended.     

Alien vascular plants in Iceland: Diversity,spatial patterns,temporal trends,and the impact of climate change

The present study provides first comprehensive and up-to-date results on alien plant taxa in Iceland since 1967. We evidenced the presence of 336 alien vascular plant taxa, including 277 casuals and 59 naturalised taxa, two being invasive. The distribution of the alien flora exhibits a clear spatial pattern showing hotspots of occurrence and diversity within areas of major settlement centres. Altitude above sea level and temperature-related variables proved to be the most important factors shaping alien plant distribution in Iceland. Predictive modelling evidenced that arctic areas of Iceland and the Central Highlands are under serious risk of alien plant invasion due to climate change. The results provide crucial information for alien and invasive plant management and contribute data for meta-analyses of invasion processes worldwide.     

Intrageneric variation in antipredator responses of coral reef fishes affected by ocean acidification: implications for climate change projections on marine communities

Our planet is experiencing an increase in the concentration of atmospheric carbon dioxide (CO₂) unprecedented in the past 800 000 years. About 30% of excess atmospheric CO₂ is absorbed by the oceans, thus increasing the concentration of carbonic acid and reducing the ocean's pH. Species able to survive the physiological stress imposed by ocean acidification may still suffer strong indirect negative consequences. Comparing the tolerance of different species to dissolved CO₂ is a necessary first step towards predicting the ecological impacts of rising CO₂ levels on marine communities. While it is intuitive that not all aquatic species will be affected the same way by CO₂, one could predict that closely related species, sharing similar life histories and ecology, may show similar tolerance levels to CO₂. Our ability to create functional groups of species according to their CO₂ tolerance may be crucial in our ability to predict community change in the future. Here, we tested the effects of CO₂ exposure on the antipredator responses of four damselfish species (Pomacentrus chrysurus, Pomacentrus moluccensis, Pomacentrus amboinensis and Pomacentrus nagasakiensis). Although being sympatric and sharing the same ecology and life history, the four congeneric species showed striking and unexpected variation in CO₂ tolerance, with CO₂‐induced loss of response to predation risk ranging from 30% to 95%. Using P. chrysurus as a model species, we further tested if these behavioural differences translated into differential ability to survive predators under natural conditions. Our results indicate that P. chrysurus larvae raised under CO₂ levels predicted by 2070 and 2100 showed decreased antipredator responses to risk, leading to a five‐ to sevenfold increase in predation‐related mortality in the first few hours of settlement. Examining ocean acidification, along with other environmental variables, will be a critical step in further evaluating ecological responses to predicted climatic change.