Yves Letourneur

Global human footprint on the linkage between biodiversity and ecosystem functioning in reef fishes.

A global survey of reef fishes shows that the consequences of biodiversity loss are greater than previously anticipated as ecosystem functioning remained unsaturated with the addition of new species. Additionally, reefs worldwide, particularly those most diverse, are highly vulnerable to human impacts that are widespread and likely to worsen due to ongoing coastal overpopulation.

Climate Warming, Marine Protected Areas and the Ocean-Scale Integrity of Coral Reef Ecosystems

Coral reefs have emerged as one of the ecosystems most vulnerable to climate variation and change. While the contribution of a warming climate to the loss of live coral cover has been well documented across large spatial and temporal scales, the associated effects on fish have not. Here, we respond to recent and repeated calls to assess the importance of local management in conserving coral reefs in the context of global climate change. Such information is important, as coral reef fish assemblages are the most species dense vertebrate communities on earth, contributing critical ecosystem functions and providing crucial ecosystem services to human societies in tropical countries. Our assessment of the impacts of the 1998 mass bleaching event on coral cover, reef structural complexity, and reef associated fishes spans 7 countries, 66 sites and 26 degrees of latitude in the Indian Ocean. Using Bayesian meta-analysis we show that changes in the size structure, diversity and trophic composition of the reef fish community have followed coral declines. Although the ocean scale integrity of these coral reef ecosystems has been lost, it is positive to see the effects are spatially variable at multiple scales, with impacts and vulnerability affected by geography but not management regime. Existing no-take marine protected areas still support high biomass of fish, however they had no positive affect on the ecosystem response to large-scale disturbance. This suggests a need for future conservation and management efforts to identify and protect regional refugia, which should be integrated into existing management frameworks and combined with policies to improve system-wide resilience to climate variation and change.

Extinction vulnerability of coral reef fishes

With rapidly increasing rates of contemporary extinction, predicting extinction vulnerability and identifying how multiple stressors drive non-random species loss have become key challenges in ecology. These assessments are crucial for avoiding the loss of key functional groups that sustain ecosystem processes and services. We developed a novel predictive framework of species extinction vulnerability and applied it to coral reef fishes. Although relatively few coral reef fishes are at risk of global extinction from climate disturbances, a negative convex relationship between fish species locally vulnerable to climate change vs. fisheries exploitation indicates that the entire community is vulnerable on the many reefs where both stressors co-occur. Fishes involved in maintaining key ecosystem functions are more at risk from fishing than climate disturbances. This finding is encouraging as local and regional commitment to fisheries management action can maintain reef ecosystem functions pending progress towards the more complex global problem of stabilizing the climate.

The humphead wrasse, Cheilinus undulatus: Synopsis of a threatened and poorly known giant coral reef fish

The humphead wrasse, Cheilinus undulatus, is the largest living member of the family Labridae, with a maximum size exceeding 2 m and 190 kg. Its geographic range covers much of the Indo-Pacific. The species is not common, recorded maximum adult densities rarely exceeding 20 fish/10,000 m2. Small individuals are typically associated with high coral cover; larger fish are found mainly on outer or deep reefs, steep slopes and passes, singly or in small groups and seagrasses. However, for reproduction the species forms small spawning aggregations of tens to more than one hundred fish. The diet of the humphead wrasse includes large invertebrates and small fishes. The species attains at least 30 years and reaches sexual maturation at about 35–50 cm total length and <5 years of age. Most small adults are female while mainly males exceed 1 m and there is evidence of female to male sex change. The humphead wrasse is of considerable cultural value in some Pacific countries and is among the most prized in the live reef food fish export trade, for which it is often taken in its juvenile size range, either directly for sale or, increasingly, for grow-out to market size. It is also marketed chilled. The species is particularly sensitive to fishing pressure. In most fished areas, density and body size have dropped substantially. It appears to be particularly heavily targeted and depleted in SE Asia and in some places faces extirpation. The humphead wrasse is often taken by night spearfishing and by cyanide, with protection typically weak or non-existent, despite regulations and by a ‘vulnerable’ assessment on the 1996 IUCN Red List. The humphead wrasse has not been reared successfully in hatcheries. Other giant reef fish share many similar problems and detailed study of the humphead wrasse contributes to a better understanding and conservation of all such species. This review examines and evaluates published and gray literature, original unpublished research and correspondence with almost 50 knowledgeable workers. It examines the value of such sources for quickly, but adequately, assessing the conservation and management status and key data gaps in species that are little known, vulnerable, difficult and expensive to study and may require urgent management or conservation action.

Crucial knowledge gaps in current understanding of climate change impacts on coral reef fishes

SUMMARY Expert opinion was canvassed to identify crucial knowledge gaps in current understanding of climate change impacts on coral reef fishes. Scientists that had published three or more papers on the effects of climate and environmental factors on reef fishes were invited to submit five questions that, if addressed, would improve our understanding of climate change effects on coral reef fishes. Thirty-three scientists provided 155 questions, and 32 scientists scored these questions in terms of: (i) identifying a knowledge gap, (ii) achievability, (iii) applicability to a broad spectrum of species and reef habitats, and (iv) priority. Forty-two per cent of the questions related to habitat associations and community dynamics of fish, reflecting the established effects and immediate concern relating to climate-induced coral loss and habitat degradation. However, there were also questions on fish demographics, physiology, behaviour and management, all of which could be potentially affected by climate change. Irrespective of their individual expertise and background, scientists scored questions from different topics similarly, suggesting limited bias and recognition of a need for greater interdisciplinary and collaborative research. Presented here are the 53 highest-scoring unique questions. These questions should act as a guide for future research, providing a basis for better assessment and management of climate change impacts on coral reefs and associated fish communities.

Temporal Fluctuations and Settlement Patterns of Native and Lessepsian Herbivorous Fishes on the Lebanese Coast (Eastern Mediterranean)

We provide here the first information on the abundance, settlement patterns and microhabitat use of settlers of two Lessepsian siganid species, Siganus rivulatus and S. luridus, in comparison with the two main native herbivores, Sparisoma cretense (Scaridae) and Sarpa salpa (Sparidae). S. rivulatus was the most abundant species (72%), followed by S. cretense (20%) and S. luridus (8%), whereas S. salpa was rare (<1%). A clear pattern of settlement could be established for S. rivulatus and S. cretense, with similar timing in 1999 and 2000. S. cretense settled in schools late June, while S. rivulatus settled mid-July. A few solitary settlers of S. luridus were observed in July and August, but none of S. salpa. All these herbivorous fish species settled in protected shallow areas offering hard substrates and algal communities. S. rivulatus was the most tolerant and adaptable species, able to settle on a large range of substrates and habitats, including rock pools, muddy harbours and sea grass beds. In the eastern Mediterranean Sea, S. rivulatus might have benefited from a release of competition pressure due to the low diversity and abundance of native herbivores. It has probably replaced S. salpa on the coast of Lebanon, being more competitive than the native sparid.

DYNAMICS OF FISH COMMUNITIES ON REUNION FRINGING REEFS, INDIAN OCEAN. I. PATTERNS OF SPATIAL DISTRIBUTION

Abstract This work describes the distribution of fish communitites, including species richness, abundance of individuals and trophic structures on the four main fringing reefs of Reunion Island. Patterns are quantified on several spatial scales: an intra-reef scale and an interreefs scale which includes within-reefs, between-reefs, and between-reefs and zones scales. The total ichthyofauna (217 species) is structured into three main communities — back-reef, inner reef flat and outer reef flat communities — which are influenced by the wave exposure and topographic relief. These communities are organized in a spatial continuum rather than into three totally separate communities. Herbivorous (mainly acanthurids) and omnivorous fishes (mainly pomacentrids) are the most numerous on the inner and outer reef flats. Diurnal carnivorous (mainly mullids) and herbivorous fishes (mainly schooling juveniles) are the dominant fishes in the back-reef zones. The low abundance of carnivorous fishes on the reef flat, irrespective of diet, is most likely due to alterations of benthic communities (e.g. coral damage, increase in algae populations) as a result of anthropogenic activities. The ichthyofauna of each of the four reefs is organized into the same three fish communities. There is a north-south gradient of decreasing distribution of species and abundance of individuals in these communities. However, fish communities are more clearly separated on the northern reefs compared with those of the southern reefs. This pattern is probably due to differences in coral vitality, habitat complexity and width of the reefs. Hydrodynamic conditions, more pronounced in the south of the island, might also lead to a higher flux of recruitment of fish larvae on the northern reefs.

Spatial and temporal variability in territoriality of a tropical benthic damselfish on a coral reef (Réunion Island)

The relationship between length of individual Stegastes nigricans and size of the territory that they defend, and both the spatial and temporal variation in territoriality were investigated monthly on a fringing coral reef of Réunion Island over the course of one year. Length of individual S. nigricans was correlated positively with size of the territory. Most small individuals were found separate from adults, in areas with low algal turf cover. This is probably due to strong intra-specific competition for access to algal food resources and shelter availability, and/or differences in habitat preference. Both abundance of individuals and surface defended showed seasonal fluctuations. Densities were slightly higher in austral summer than in winter, and the surface defended by individuals larger than 8 cm increased in winter. A permanent redistribution of territories also occured between individuals over time.

Difference of mercury bioaccumulation in red mullets from the north- western Mediterranean and Black seas

The relationships between total mercury (Hg) concentration and stable nitrogen isotope ratio (delta(15)N) were evaluated in Mullus barbatus barbatus and M. surmuletus from the Mediterranean Sea and M. barbatus ponticus from the Black Sea. Mercury concentration in fish muscle was six times higher in the two Mediterranean species than in the Black Sea one for similar sized animals. A positive correlation between Hg concentration and delta(15)N occurred in all species. Increase in Hg concentration with delta(15)N was high and similar in the two Mediterranean fishes and much lower in the Black Sea species. Since this was neither related to trophic level difference between species nor to methylmercury (MeHg) concentration differences between the north-western Mediterranean and the Black Sea waters, we suggested that the higher primary production of the Black Sea induced a dilution of MeHg concentration at the base of the food webs.

Temporal variations in the diet of the damselfish Stegastes nigricans (Lacepède) on a Réunion fringing reef

Copyright (c) 1997 Elsevier Science B.V. All rights reserved. The diet of the territorial damselfish Stegastes nigricans (Pomacentridae) was studied on a shallow coral reef flat of Reunion Island, S.W. Indian Ocean. Fishes were collected monthly from November 1989 to August 1990 in order to examine their stomach and gut contents. The temporal variability of the diet of S. nigricans was investigated on (1) a seasonal scale for the various size-classes and (2) a daily scale within two seasons. On average, algae accounted for 69.4% of the total weight of the stomach contents, all sizes combined. The total weight of all prey, and both the weight and the percentage of algae in stomach contents decreased in winter. This pattern was more pronounced for large (>8 cm total length) and medium (4-8 cm) than for small individuals (<4 cm). Small S. nigricans also fed on invertebrates such as polychaetes, ascidians and copepods, whereas medium and large individuals had a very low invertebrate consumption. Daily variations of diet were recorded, with two maxima of food intake in summer: between 0600 and 0930 and between 1430 and 1900. In winter, only one peak of consumption was observed between 1200 and 1700. An estimate of food intake of 2488 g.m −2 .year −1 (dry weight) for the S. nigricans population was determined from stomach and intestine contents. The seasonal variation in the diet of S. nigricans may be related to several interacting factors, such as availability of food resources, high rate of consumption of food in summer for energy storage to offset the lean winter period, and high energetic needs for summer reproductive activities. The ontogenic shift in diet appeared to be a response of small individuals to both a transition phase between larval and benthic phases, and a need for protein-rich prey in order to promote their growth. The daily variation in the diet is probably due to diurnal variations in the nutritional value and/or palatability of algal food.