• Energy Research

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.

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.

Global climate change has the potential to substantially alter the production and community structure of marine fisheries and modify the ongoing impacts of fishing. Fish community composition is already changing in some tropical, temperate and polar ecosystems, where local combinations of warming trends and higher environmental variation anticipate the changes likely to occur more widely over coming decades. Using case studies from the Western Indian Ocean, the North Sea and the Bering Sea, we contextualize the direct and indirect effects of climate change on production and biodiversity and, in turn, on the social and economic aspects of marine fisheries. Climate warming is expected to lead to (i) yield and species losses in tropical reef fisheries, driven primarily by habitat loss; (ii) community turnover in temperate fisheries, owing to the arrival and increasing dominance of warm-water species as well as the reduced dominance and departure of cold-water species; and (iii) increased diversity and yield in Arctic fisheries, arising from invasions of southern species and increased primary production resulting from ice-free summer conditions. How societies deal with such changes will depend largely on their capacity to adapt—to plan and implement effective responses to change—a process heavily influenced by social, economic, political and cultural conditions.

Fishing affects patterns of energy use in fish populations, as demonstrated by changes in population energy consumption and the size and age when energy demands are greatest. We compare theoretical predictions and observed patterns of energy use (expressed as the primary production required to support fish production) by North Sea fish, based on simple and widely applicable theory that links life history parameters, fishing mortality (F), trophic transfer efficiency and relationships between size and trophic level (as determined using nitrogen stable isotope analysis). For the demersal species that dominate total biomass, relationships between size and trophic level were quite consistent among years. There were large decreases in relative energy requirements of all exploited demersal populations except plaice Pleuronectes platessa during the last 3 to 4 decades. Relative energy requirements of plaice were more stable because smaller plaice, which now dominate the exploited population, feed at higher trophic levels than larger plaice. The sizes and ages when population energy demands were greatest fell with increasing fishing mortality and differences between the predicted (F = 0) and observed ages at maximum energy demand were greater in larger species. Currently, the energy demands of most species peak early in life (1¿3 years) and largely reflect patterns of recruitment, leading to a homogenisation of the trophodynamics of the fish community. The fate of energy that is no longer used by commercially exploited species is not clear, partly because of the infrequent and untargeted monitoring of species that are more resilient to fishing. However, we conducted a preliminary assessment of the energy demands of solenette Buglossidium luteum, a very abundant small flatfish in the central North Sea that has increased in abundance in recent years. The solenette's high abundance and resilience to fishing, suggests that it now requires 35% of primary production in part of the central North Sea, energy that may have supported larger species in a less heavily fished ecosystem.

Climate change is one of the greatest threats to the long-term maintenance of coral-dominated tropical ecosystems, and has received considerable attention over the past two decades. Coral bleaching and associated mortality events, which are predicted to become more frequent and intense, can alter the balance of different elements that are responsible for coral reef growth and maintenance. The geomorphic impacts of coral mass mortality have received relatively little attention, particularly questions concerning temporal recovery of reef carbonate production and the factors that promote resilience of reef growth potential. Here, we track the biological carbonate budgets of inner Seychelles reefs from 1994 to 2014, spanning the 1998 global bleaching event when these reefs lost more than 90% of coral cover. All 21 reefs had positive budgets in 1994, but in 2005 budgets were predominantly negative. By 2014, carbonate budgets on seven reefs were comparable with 1994, but on all reefs where an ecological regime shift to macroalgal dominance occurred, budgets remained negative through 2014. Reefs with higher massive coral cover, lower macroalgae cover and lower excavating parrotfish biomass in 1994 were more likely to have positive budgets post-bleaching. If mortality of corals from the 2016 bleaching event is as severe as that of 1998, our predictions based on past trends would suggest that six of eight reefs with positive budgets in 2014 would still have positive budgets by 2030. Our results highlight that reef accretion and framework maintenance cannot be assumed from the ecological state alone, and that managers should focus on conserving aspects of coral reefs that support resilient carbonate budgets.

Abundance-body size relationships are widely observed macroecological patterns in complete food webs and in taxonomically or functionally defined subsets of those webs. Observed abundance-body size relationships have frequently been compared with predictions based on the energetic equivalence hypothesis and, more recently, with predictions based on energy availability to different body size classes. Here, we consider the ways in which working with taxonomically or functionally defined subsets of food webs affected the relationship between the predicted and observed scaling of biomass and body mass in sediment dwelling benthic invertebrate communities at three sites in the North Sea. At each site, the energy available to body size classes in the "whole" community (community defined as all animals of 0.03125-32.0 g shell-free wet weight) and in three subsets was predicted from estimates of trophic level based on nitrogen stable isotope analysis. The observed and predicted scalings of biomass and body size were not significantly different for the whole community, and reflected an increase in energy availability with body size. However, the results for subsets showed that energy availability could increase or decrease with body size, and that individuals in the subsets were likely to be competing with individuals outside the subsets for energy. We conclude that the study of abundance-body mass relationships in functionally or taxonomically defined subsets of food webs is unlikely to provide an adequate test of the energetic equivalence hypothesis or other relationships between energy availability and scaling. To consistently and reliably interpret the results of these tests, it is necessary to know about energy availability as a function of body size both within and outside the subset considered.