Coral Reefs: Fishing for Sustainability

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Jan 23, 2017 - levels are also naturally more vulnerable to overexploitation, and have typically slow life histories and smaller population sizes, which can slow ...
Current Biology

Dispatches occasionally go ‘off-line’ to allow for more vivid memory retrieval. Determining how the hippocampus, and in particular sharp wave-ripples, contribute to the detection of the target requires future investigations in at least two directions. First, on-line suppression of ripples is expected to impair animal performance specifically on repeated trials. Second, to establish a link between exploratory-sharp wave-ripples and retrieval, it will be necessary to record large neuronal ensembles in the hippocampus during execution of the task. Neuronal activity concomitant with sharp wave-ripples should code for the configuration of the objects in the scene. The neuronal mechanisms underlying memory formation and retrieval in the brain have only recently started to be unveiled. Many questions remain largely open as to how sharp wave-ripples are generated and transmitted to cortical and sub-cortical structures. Investigation of brain signals at multiple scales, from dendrites to whole brain scans, across animal species, will eventually enable us to draw a global picture of the role of sharp wave-ripples in memory.

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Coral Reefs: Fishing for Sustainability Emily S. Darling1,2,* and Stephanie D’agata1 1Wildlife

Conservation Society, Marine Programs, Bronx, NY, USA of Ecology and Evolutionary Biology, University of Toronto, Toronto, ON, Canada *Correspondence: [email protected] http://dx.doi.org/10.1016/j.cub.2016.12.005 2Department

Sustainable fisheries must ultimately reduce poverty while maintaining ecosystem productivity. On coral reefs, managing for ‘concave’ trophic pyramids might be a win–win for people and ecosystems, by providing higher-value fisheries and maintaining important ecological functions. Over the coming decades, governments and societies must rise to the challenge of creating a sustainable future for both

people and nature. Reducing poverty and strengthening both food security and environmental sustainability are landmark

targets for the UN Sustainable Development Goals [1]. With human populations projected to reach 9.7 billion

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Current Biology

Dispatches A

B

Trophic position

30-90 kg ha-1

Top predators (4 - 4.5) Carnivores (3.5 - 4) Mixed-diet (3 - 3.5) Invertivores (2.5 - 3) Herbivores (2 - 2.5)

1800-5000 kg ha-1

Figure 1. Trophic pyramids revealed on coral reefs. Across gradients of reef fish biomass and human exploitation, the organization of food webs can provide an important reference point for fisheries management. Rebuilding exploited reefs (A) towards ‘concave’ trophic pyramids (B) might have win–wins for ecosystem functioning and fishing livelihoods. Photos: E. Darling and S. D’agata / WCS.

by 2050, there is a continued urgency for the sustainable use and management of agriculture, forests, and fisheries that can meet human needs and maintain ecological integrity in the Anthropocene. Coral reefs provide livelihoods, food security, cultural practices and ecosystem services for millions of people worldwide, for example by supporting one-quarter of the world’s small-scale fishers [2]. But with increasing human pressure, valuable ecological functions can be unexpectedly lost [3,4]. Managing sustainable coral reef fisheries requires rebuilding reef resources and ecosystem functioning, while also strengthening livelihoods and governance in reefdependent societies [5,6]. However, management decisions are often missing simple indicators and reference points, such as how many fish or how much habitat is required to maintain fisheries yields over the long-term. A new study by Nick Graham and colleagues [7] in this issue of Current Biology evaluates how humans alter trophic pyramids on coral reefs to show a path towards win–win management, where intact trophic pyramids can support ecological functions and, in turn, higher-value livelihoods for resource users (Figure 1).

Fishing Through the Food Web Ecological communities can be described in many ways: by their pattern of the abundance and identity of species, by the type of functional traits or amount of evolutionary history they contain, or by the ways in which energy and productivity flow through their food webs. A classic approach to describing food webs is with trophic pyramids, which are simple diagrams of complex processes that show how biomass is distributed from the lower trophic level — prey at the base of the pyramid — to higher trophic levels, with predators at the top [8]. In the real world, trophic pyramids are bottomheavy with more biomass at lower trophic levels due to metabolic and size-based constraints on how energy is transferred upwards through consumers and top predators [9]. Different patterns of fishing should alter trophic pyramids in predictable ways. One such pattern, ‘fishing down the food web’, implies that fishing starts at the highest-value species at the top of the pyramid and then moves down the pyramid as predators collapse with exploitation [10]. For coral reefs, fishing through entire trophic pyramids [11] may be common practice as all trophic levels have market value. The

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highest trophic levels are the most valuable — snappers, groupers and trevallies are sold at high prices to regional markets and hotels — but mesopredators (mid-trophic-species) and small invertivores and herbivores (low-trophic-species) are also sold for affordable prices to local traders and households [12]. Understanding how fisheries and market forces shape the ecological structure of coral reefs is a key step towards ecosystem- and evidence-based management. In their study, Graham et al. [7] present the first demonstration of human alterations to coral reef trophic pyramids across an extensive empirical dataset in the Indian Ocean. Here, the total biomass of reef fish (i.e., the total wet weight of fish on a reef) is a useful indicator for human gradients of fisheries exploitation: heavily fished reefs had very low reef fish biomass (