Ecosystem regime shifts disrupt trophic structure

Hempson, Tessa N.; Graham, Nicholas A. J.; MacNeil, M. Aaron; Hoey, Andrew S.; Wilson, Shaun K.

doi:10.1002/eap.1639

Cited by 49 publications

(38 citation statements)

References 73 publications

(148 reference statements)

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“…Regime‐shifted fish communities were most distinct from their coral‐dominated baselines. These patterns build on previous observations from Seychelles demonstrating that macroalgal overgrowth has resulted in bottom‐heavy fish biomass pyramids and reduced functional diversity (Graham et al, ; Hempson, Graham, MacNeil, Hoey, & Wilson, ). Declines in coral cover and flattening of habitat structure likely prevented coral‐associated species from relocating or recruiting to macroalgal reefs, despite these fish being present on nearby recovering reefs.…”

Section: Discussionsupporting

confidence: 83%

Thermal stress induces persistently altered coral reef fish assemblages

Robinson

Wilson

Jennings

et al. 2019

Global Change Biology

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Ecological communities are reorganizing in response to warming temperatures. For continuous ocean habitats this reorganization is characterized by large‐scale species redistribution, but for tropical discontinuous habitats such as coral reefs, spatial isolation coupled with strong habitat dependence of fish species imply that turnover and local extinctions are more significant mechanisms. In these systems, transient marine heatwaves are causing coral bleaching and profoundly altering habitat structure, yet despite severe bleaching events becoming more frequent and projections indicating annual severe bleaching by the 2050s at most reefs, long‐term effects on the diversity and structure of fish assemblages remain unclear. Using a 23‐year time series spanning a thermal stress event, we describe and model structural changes and recovery trajectories of fish communities after mass bleaching. Communities changed fundamentally, with the new emergent communities dominated by herbivores and persisting for >15 years, a period exceeding realized and projected intervals between thermal stress events on coral reefs. Reefs which shifted to macroalgal states had the lowest species richness and highest compositional dissimilarity, whereas reefs where live coral recovered exceeded prebleaching fish richness, but remained dissimilar to prebleaching compositions. Given realized and projected frequencies of bleaching events, our results show that fish communities historically associated with coral reefs will not re‐establish, requiring substantial adaptation by managers and resource users.

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Section: Discussionsupporting

confidence: 83%

Thermal stress induces persistently altered coral reef fish assemblages

Robinson

Wilson

Jennings

et al. 2019

Global Change Biology

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“…In this case, the rapid downslope increase in water depth can likely be implicated as nearvertical morphology is challenging to image because of light attenuation and shadowing (Jay et al 2017). Ways to more routinely separate live coral from macroalgae in multispectral imagery are of heightening importance given the large-scale regime shift of reefs to algal-dominated states (Graham et al 2015;Hughes et al 2017;Hempson et al 2018).…”

Section: Discussionmentioning

confidence: 99%

High-resolution habitat and bathymetry maps for 65,000 sq. km of Earth’s remotest coral reefs

Purkis

Gleason

Purkis³

et al. 2019

Coral Reefs

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With compelling evidence that half the world's coral reefs have been lost over the last four decades, there is urgent motivation to understand where reefs are located and their health. Without such basic baseline information, it is challenging to mount a response to the reef crisis on the global scale at which it is occurring. To combat this lack of baseline data, the Khaled bin Sultan Living Oceans Foundation embarked on a 10-yr survey of a broad selection of Earth's remotest reef sites-the Global Reef Expedition. This paper focuses on one output of this expedition, which is meter-resolution seafloor habitat and bathymetry maps developed from DigitalGlobe satellite imagery and calibrated by field observations. Distributed on an equatorial transect across 11 countries, these maps cover 65,000 sq. km of shallow-water reef-dominated habitat. The study represents an order of magnitude greater area than has been mapped previously at high resolution. We present a workflow demonstrating that DigitalGlobe imagery can be processed to useful products for reef conservation at regional to global scale. We further emphasize that the performance of our mapping workflow does not deteriorate with increasing size of the site mapped. Whereas our workflow can produce regional-scale benthic habitat maps for the morphologically diverse reefs of the Pacific and Indian oceans, as well as the more depauperate reefs of the Atlantic, accuracies are substantially higher for the former than the latter. It is our hope that the map products delivered to the community by the Living Oceans Foundation will be utilized for conservation and act to catalyze new initiatives to chart the status of coral reefs globally.

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“…Effects of habitat degradation can also migrate up the food web, altering the composition and size structure of prey fish assemblages Hempson, Graham, MacNeil, Hoey, & Wilson 2017), and indirectly impacting piscivorous reef-associated predators .…”

Section: Introductionmentioning

confidence: 99%

Regime shifts shorten food chains for mesopredators with potential sublethal effects

et al. 2018

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Predator populations are in decline globally. Exploitation, as well as habitat degradation and associated changes in prey availability are key drivers of this process of trophic downgrading. In the short term, longevity and dietary adaptability of large‐bodied consumers can mask potential sublethal effects of a changing prey base, producing a delayed effect that may be difficult to detect. In coral reef ecosystems, regime shifts from coral‐ to algae‐dominated states caused by coral bleaching significantly alter the assemblage of small‐bodied reef fish associated with a reef. The effects of this changing prey community on reef‐associated mesopredators remains poorly understood. This study found that the total diversity, abundance and biomass of piscivorous mesopredators was lower on regime‐shifted reefs than recovering reefs, 16 years after the 1998 mass coral bleaching event. We used stable isotope analyses to test for habitat‐driven changes in the trophic niche occupied by a key piscivorous fishery target species on reefs that had regime‐shifted or recovered following climatic disturbance. Using morphometric indices, histology, and lipid analyses, we also investigated whether there were sublethal costs for fish on regime‐shifted reefs. Stable isotopes demonstrated that fish from regime‐shifted reefs fed further down the food chain, compared to recovering reefs. Lower densities of hepatocyte vacuoles in fish from regime‐shifted reefs, and reduced lipid concentrations in spawning females from these reefs, indicated a reduction in energy stores, constituting a sublethal and potential delayed effect on populations. Reduced energy reserves in mesopredators could lead to energy allocation trade‐offs, and decreased growth rates, fecundity and survivorship, resulting in potential population declines in the longer term. A http://onlinelibrary.wiley.com/doi/10.1111/1365-2435.13012/suppinfo is available for this article.

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Ecosystem regime shifts disrupt trophic structure

Cited by 49 publications

References 73 publications

Thermal stress induces persistently altered coral reef fish assemblages

Thermal stress induces persistently altered coral reef fish assemblages

High-resolution habitat and bathymetry maps for 65,000 sq. km of Earth’s remotest coral reefs

Regime shifts shorten food chains for mesopredators with potential sublethal effects

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