Isabelle M. Côté

HURRICANES AND CARIBBEAN CORAL REEFS: IMPACTS, RECOVERY PATTERNS, AND ROLE IN LONG-TERM DECLINE

The decline of corals on tropical reefs is usually ascribed to a combination of natural and anthropogenic factors, but the relative importance of these causes remains unclear. In this paper, we attempt to quantify the contribution of hurricanes to Caribbean coral cover decline over the past two decades using meta-analyses. Our study included published and unpublished data from 286 coral reef sites monitored for variable lengths of time between 1980 and 2001. Of these, 177 sites had experienced hurricane impacts during their period of survey. Across the Caribbean, coral cover is reduced by ∼17%, on average, in the year following a hurricane impact. The magnitude of this immediate loss increases with hurricane intensity and with the time elapsed since the last impact. In the following year, no further loss is discernible, but the decline in cover then resumes on impacted sites at a rate similar to the regional background rate of decline for nonimpacted sites. There is no evidence of recovery to a pre-storm state for at least eight years after impact. Overall, coral cover at sites impacted by a hurricane has declined at a significantly faster rate (6% per annum) than nonimpacted sites (2% per annum), due almost exclusively to higher rates of loss in the year after impact in the 1980s. While hurricanes, through their immediate impacts, appear to have contributed to changing coral cover on many Caribbean reefs in the 1980s, the similar decline in coral cover at impacted and nonimpacted sites in the 1990s suggests that other stressors are now relatively more important in driving the overall pattern of change in coral cover in this region. The overall lack of post-hurricane recovery points to a general impairment of the regeneration potential of Caribbean coral reefs.

ACCELERATING IMPACTS OF TEMPERATURE-INDUCED CORAL BLEACHING IN THE CARIBBEAN

Coral bleaching is a stress-related response that can be triggered by elevated sea surface temperatures (SST). Recent increases in the frequency of coral bleaching have led to concerns that increases in marine temperatures may threaten entire coral reef regions. We report exponential increases in the geographical extent and intensity of coral bleaching in the Caribbean with increasing SST anomalies. A rise in regional SST of 0.1°C results in 35% and 42% increases in the geographic extent and intensity of coral bleaching, respectively. Maximum bleaching extent and intensity are predicted to occur at regional SST anomalies of less than +1°C, which coincides with the most conservative projections for warming in the Caribbean by the end of the 21st century. Coral bleaching is therefore likely to become a chronic source of stress for Caribbean reefs in the near future.

Island-specific preferences of tourists for environmental features: implications of climate change for tourism-dependent states

Climate change may affect important environmental components of holiday destinations, which might have repercussions for tourism-dependent economies. This study documents the importance of environmental attributes in determining the choice and holiday enjoyment of tourists visiting Bonaire and Barbados, two Caribbean islands with markedly different tourism markets and infrastructure. Three hundred and sixteen and 338 participants from Bonaire and Barbados, respectively, completed standardized questionnaires. Warm temperatures, clear waters and low health risks were the most important environmental features determining holiday destination choice. However, tourists in Bonaire thereafter prioritized marine wildlife attributes (i.e. coral and fish diversity and abundance) over other environmental features, whereas tourists in Barbados exhibited stronger preferences for terrestrial features, particularly beach characteristics. The willingness of tourists to revisit these islands was strongly linked to the state of the preferred environmental attributes. More than 80% of tourists in Bonaire and Barbados would be unwilling to return for the same holiday price in the event, respectively, of coral bleaching as a result of elevated sea surface temperatures and reduced beach area as a result of sea level rise. Climate change might have a significant impact on Caribbean tourism economy through alteration of environmental features important to destination selection. Island-specific management strategies, such as focusing resources on the protection of key marine or terrestrial features, may provide a means of reducing the environmental and economic impacts of climate change.

Predator-induced clumping behaviour in mussels (Mytilus edulis Linnaeus)

This study examined the aggregation behaviour of blue mussels, Mytilus edulis, under threat of predation by European lobster, Homarus gammarus Linnaeus. Risk of predation was simulated using water in which a hungry lobster had been for 24 h, and mussels were initially set in experimental containers either near (0.5 body length apart) or far (1.5 body length apart) from each other. We found that mussels exposed to lobster effluent formed more clumps, more rapidly than mussels in control conditions. The initial distance separating the mussels had no effect on their aggregation tendencies. Overall, a greater proportion of mussels were aggregated in the lobster treatment at the end of the 22-h experiment. This was not simply the result of increased locomotion. Although mussels in lobster effluent did exhibit greater crawling speed in the first hour of the experiment, mussels initially set far apart also showed enhanced locomotion in both lobster and control treatments. Yet, of the mussels initially far from each other, those in lobster effluent formed clumps on average 5 h sooner than mussels in control water. This suggests that chemotaxis may be involved. Although mussels do aggregate under risk of predation in the laboratory, it is not yet known whether predation plays a significant role in the formation of natural mussel beds.

Effects of predatory crab effluent on byssus production in mussels

This study investigated the effects of effluent of edible crab (Cancer pagurus) on byssus production by blue mussels (Mytilus edulis). Mussels held in the laboratory secreted more, shorter, and thicker byssus threads when placed in water in which an edible crab had been than in control seawater. The cumulative length of byssus produced by individual mussels was not affected by predatory crab effluent, but byssus volume increased by 72% in crab water compared with control seawater after a 6-h period. This difference in thread volume was still great (45%) but disappeared statistically after 22 h of exposure to crab effluent. By contrast, byssus number, length and diameter were not affected by maintaining mussels in water that had contained non-predatory, herbivorous common sea urchins (Echinus esculentus). Blue mussels can therefore alter byssus production selectively in the presence of potential predators.

European colonization by the spined loach (Cobitis taenia) from Ponto-Caspian refugia based on mitochondrial DNA variation.

In the last 20 years, new species, asexual reproduction, polyploidy and hybridization have all been reported within the genus Cobitis. An understanding of the current distribution and baseline phylogeographical history of ‘true’ nonhybrid Cobitis species is crucial in order to unravel these discoveries. In the present work, we investigated the phylogeography of the spined loach, Cobitis taenia, using 1126 bp of the mitochondrial cytochrome b gene from 174 individuals collected at 47 sites. In total, 51 haplotypes that differed at 49 positions (4.35%) were detected. We deduce that C. taenia survived European glaciations in at least three refuges in the Ponto‐Caspian area. Two of these refuges each provided a major lineage that recolonized Europe in separate directions: one westward to England and the other spreading north into Russia before moving west. A third (minor) lineage that contributed little to the recolonization of Europe was also revealed — remaining near its Black Sea refuge. However, more recent history was difficult to resolve with colonization from a more western refugium during the last glacial maximum (LGM) a distinct possibility. Nested clade analysis indicates a pattern of restricted gene flow with isolation by distance at the first two levels and overall. Unlike many other European freshwater fish species, the Danube is not part of the current distribution of C. taenia, nor was it used as either a refuge or a source of colonization of Europe. Low genetic diversity within C. taenia suggests that its colonization of Europe is relatively recent. Demographic analyses revealed a history of recent expansion and isolation by distance.

Dominance hierarchies in group-living cleaning gobies: causes and foraging consequences

In species living in social groups, aggression among individuals to gain access to limiting resources can lead to the formation of stable social hierarchies. We tested whether dominance rank in social groups of sponge-dwelling cleaning gobies Elacatinus prochilos in Barbados was determined by physical attributes of individuals or by prior experience of dominance, and examined the foraging consequences of dominance rank. Intraspecific aggression within groups resulted in stable dominance hierarchies that were strongly correlated with fish length. Dominant individuals maintained exclusive territories while subordinate fish occupied broader home ranges. Larger, competitively dominant fish were able to monopolize areas inside the sponge lumen with the highest abundance of the polychaete Haplosyllis spp., a favoured prey item, and achieved the highest foraging rates. The removal of a territorial individual from large groups resulted in a domino-like effect in territory relocation of the remaining fish as individuals moved to the territory previously occupied by the individual just above them in the group hierarchy. Individuals added to existing groups generally failed to gain access to territories, despite being formerly dominant in their original groups. When given the opportunity to choose a location in the absence of larger competitors, gobies frequently preferred positions that were previously defended and that had abundant food. These results suggest that intraspecific competition for resources creates the observed dominance structures and provides support for the role of individual physical attributes in the formation and maintenance of dominance hierarchies.

In situ evidence for ectoparasites as a proximate cause of cleaning interactions in reef fish

Although cleaning interactions are deemed a textbook example of mutualism, there is limited evidence that clients benefit from cleaning in terms of reduced ectoparasite loads. The proximate causes of cleaning behaviour are also contentious. We examined the effect of ectoparasite load (i.e. the number of larval gnathiid isopods) on client behaviour under natural conditions. Diel variation in gnathiid loads of longfin damselfish, Stegastes diencaeus, a common coral reef fish client of cleaning gobies (Elacatinus spp.), was correlated with variation in gnathiid emergence from the substratum at sites in both Puerto Rico and St John, northeastern Caribbean. Both benthic emergence of gnathiids and their infestation on damselfish peaked in the morning. Concomitantly, clients spent significantly more time posing for and being inspected by cleaners in the morning than at other times of day. Our results corroborate recent experimental results on captive clients and are consistent with the mutualistic interpretation of cleaning symbioses.

Why clean and be cleaned? The importance of client ectoparasites and mucus in a marine cleaning symbiosis

Abstract. The preferences exhibited by cleaner fishes for particular client species and the high variability in rates at which various clients visit cleaning stations have remained largely unexplained. In this study, we assessed the relative importance of client ectoparasite load and mucus characteristics for the behaviour of cleaning gobies, Elacatinus spp, and their fish clients on a Barbadian fringing reef. Client species with high ectoparasite loads visited cleaning stations more often than less parasitised species. This effect was independent of body size. Frequency of visits to cleaning stations was not related to client mucus characteristics. These results suggest that the main motivation for clients to interact with cleaners is ectoparasite removal. Cleaners did not preferentially clean clients with higher ectoparasite load or better mucus, nor did they spend more time inspecting such clients. The interests of cleaners and clients therefore appear to be inconsistent. This may be due to the generally low rate of ectoparasitism on Barbadian fish compared to fish of other regions. Cleaning gobies fed at a lower rate on client species with higher loads of gnathiid isopod larvae, which may be explained if cleaners switch from eating ectoparasites to other items, such as mucus, on clients with few ectoparasites. Our estimates of caloric and protein content of fish mucus suggest that it may be as valuable a food source per unit weight as ectoparasites. However, no data are available to compare the value of each item per unit feeding time. The fact that clients with few ectoparasites still visit cleaners, albeit at a low rate, suggests that the cost of mucus removal may be low, compared to the benefit of incidental parasite removal. Thus, the outcome of cleaning interactions may remain positive, even in areas characterised by naturally low parasitism on clients.

Cleaner-client interactions on a Caribbean reef: influence of correlates of parasitism

Abstractu2002We investigated the influence of known correlates of parasitism, namely fish density, body size and social behaviour, on three highly variable aspects of the interactions between cleaning gobies (Elacatinus spp.) and their clients, on a Barbadian coral reef. We specifically considered (1) variability in client visit rate to cleaning stations, (2) cleaning goby preference for specific clients and (3) variation in the time spent cleaning by cleaners. Using phylogenetically independent contrasts, we found that client species that were abundant on the reef visited cleaning stations more often than rarer client species. This could be due to the positive relationship between ectoparasite load and client density, or alternatively may simply reflect the frequency of contact between cleaners and clients. Cleaning gobies spent more time cleaning large-bodied clients, which usually have higher ectoparasite loads, although cleaning goby preference for clients was influenced by none of the correlates of client parasitism. Overall, factors assumed to correlate with ectoparasite load had a limited influence on the variability observed in the interactions between cleaning gobies and their clients.