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

Copyright: © 2011 Mora et al. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.Difficulties in scaling up theoretical and experimental results have raised controversy over the consequences of biodiversity loss for the functioning of natural ecosystems. Using a global survey of reef fish assemblages, we show that in contrast to previous theoretical and experimental studies, ecosystem functioning (as measured by standing biomass) scales in a non-saturating manner with biodiversity (as measured by species and functional richness) in this ecosystem. Our field study also shows a significant and negative interaction between human population density and biodiversity on ecosystem functioning (i.e., for the same human density there were larger reductions in standing biomass at more diverse reefs). Human effects were found to be related to fishing, coastal development, and land use stressors, and currently affect over 75% of the world's coral reefs. Our results indicate that the consequences of biodiversity loss in coral reefs have been considerably underestimated based on existing knowledge and that reef fish assemblages, particularly the most diverse, are greatly vulnerable to the expansion and intensity of anthropogenic stressors in coastal areas

Human impacts on Caribbean coral reef ecosystems

Fishing is one of the oldest anthropogenic disturbances in the ocean, differing from other impacts in its direct removal of biomass from the ecosystem. Despite the centuries of fishing activities, there is much we still do not understand regarding the effects of fish removal on the benthic community. I use an interdisciplinary approach to investigate the affect of human disturbance, primarily the alteration of fish communities, on major functional groups of coral reefs, over extended temporal and spatial scales. In Chapter 2, historical analyses reveal that relatively small human populations and simple fishing technologies can negatively impact reef fish communities. Significant declines are evident in Pre Columbian times and by the mid 19th C. Declines were exacerbated by simple innovations of gear, such as chicken wire, and government subsidies, which expanded degradation to offshore and deeper reefs. In Chapter 3, I identify six major ecological guilds of common Caribbean coral species and show that changes in the abundance of these guilds from the Pleistocene to the present day can be understood in terms of recent human disturbance events. Formerly advantageous life history strategies no longer apply. Instead, guilds with the ability to withstand physical disturbance from storms, sedimentation, and pollution remain present on reefs, while strategies for high recruitment and rapid space colonization increase the relative abundance of another guild. Overall, no guild successfully competes with macroalgae for space and all corals have declined. In Chapter 4, I show that benthic and fish communities across the northwestern Caribbean are largely homogenized as a result of human disturbance. The exception is fish communities in large, no-take marine reserves, which resemble relatively healthy communities of low-impacted reefs in the Pacific. A negative correlation between fish and algal biomass indicate that reserves may facilitate coral recovery, although corals have not yet increased. Chapter 5 describes a novel method for calculating the wet and dry animal tissue mass per unit area of corals. Chapter 6 integrates these findings and demonstrates the importance of increased temporal, spatial, and ecosystem scale in effective research and management of degraded Caribbean coral reef

Tissue biomass trades off with growth but not reproduction in corals

Many life history traits relate to trade-offs among an organism's energy investments in growth, reproduction, and maintenance, as well as to fundamental physiological processes or body size. Other traits reflect affordances, or possibilities enabled by an investment strategy. In scleractinian corals, growth and reproduction have been studied to a much greater extent than maintenance. Species traits likely to correlate or trade off with maintenance investments include those relating to colony growth, reproduction, and susceptibility to bleaching. Here, we measure tissue biomass per cm(2) for 29 Caribbean reef corals and evaluate whether the more easily measured corallite diameter is a proxy for tissue biomass as is often assumed. We examine hypotheses concerning corallite size and tissue biomass on the one hand, and growth rate, reproduction, competitive ability, and bleaching susceptibility on the other. Our results indicate that biomass per unit area ranges from one to two orders of magnitude across species, that corallite size is a weak predictor of tissue biomass per cm(2), and that tissue biomass is strongly correlated with growth rate and competitive ability. Relationships between biomass or module size and reproductive characteristics or bleaching susceptibility are not evident in this set of Caribbean corals. These findings expand our understanding about energy investment strategies in colonial corals and suggest that biomass may be an important metric to consider in cross-species comparisons, especially among corals from different families. Finally, this work can help inform predictions of reef response to continued threats

Trends, current understanding and future research priorities for artisanal coral reef fisheries research

Artisanal coral reef fisheries provide food and employment to hundreds of millions of people in developing countries, making their sustainability a high priority. However, many of these fisheries are degraded and not yielding their maximum socioeconomic returns. We present a literature review that evaluates foci and trends in research effort on coral reef fisheries. We describe the types of data and categories of management recommendations presented in the 464 peer-reviewed articles returned. Identified trends include a decline in articles reporting time-series data, fish catch biomass and catch-per-unit effort, and an increase in articles containing bycatch and stakeholder interview data. Management implications were discussed in 80% of articles, with increasing frequency over time, but only 22% of articles made management recommendations based on the research presented in the article, as opposed to more general recommendations. Key future research priorities, which we deem underrepresented in the literature at present, are: (i) effectiveness of management approaches, (ii) ecological thresholds, trade-offs and sustainable levels of extraction, (iii) effects of climate change, (iv) food security, (v) the role of aquaculture, (vi) access to and control of fishery resources, (vii) relationships between economic development and fishery exploitation, (viii) alternative livelihoods and (ix) integration of ecological and socioeconomic research

Bright spots among the world's coral reefs

Ongoing declines in the structure and function of the world’s coral reefs require novel approaches to sustain these ecosystems and the millions of people who depend on them. A presently unexplored approach that draws on theory and practice in human health and rural development is to systematically identify and learn from the ‘outliers’—places where ecosystems are substantially better (‘bright spots’) or worse (‘dark spots’) than expected, given the environmental conditions and socioeconomic drivers they are exposed to. Here we compile data from more than 2,500 reefs worldwide and develop a Bayesian hierarchical model to generate expectations of how standing stocks of reef fish biomass are related to 18 socioeconomic drivers and environmental conditions. We identify 15 bright spots and 35 dark spots among our global survey of coral reefs, defined as sites that have biomass levels more than two standard deviations from expectations. Importantly, bright spots are not simply comprised of remote areas with low fishing pressure; they include localities where human populations and use of ecosystem resources is high, potentially providing insights into how communities have successfully confronted strong drivers of change. Conversely, dark spots are not necessarily the sites with the lowest absolute biomass and even include some remote, uninhabited locations often considered near pristine. We surveyed local experts about social, institutional, and environmental conditions at these sites to reveal that bright spots are characterized by strong sociocultural institutions such as customary taboos and marine tenure, high levels of local engagement in management, high dependence on marine resources, and beneficial environmental conditions such as deep-water refuges. Alternatively, dark spots are characterized by intensive capture and storage technology and a recent history of environmental shocks. Our results suggest that investments in strengthening fisheries governance, particularly aspects such as participation and property rights, could facilitate innovative conservation actions that help communities defy expectations of global reef degradation.4 page(s