Overthrowing a regime shift: displacement of sea urchins by abalone in a kelp forest ecosystem

Wing, Stephen R.; Jack, Lucy; Fujita, Yuki

doi:10.1890/es15-00179.1

Cited by 6 publications

(6 citation statements)

References 50 publications

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“…One of the clear consequences of losses in kelp forests is a reduction in availability of biogenic habitat (e.g. Wing et al 2015). A more cryptic consequence is how losses in production of organic matter from kelp forests influence food web connectivity and trophodynamics at the regional scale (e.g.…”

Section: Discussionmentioning

confidence: 99%

“…Changes of this nature are especially apparent in kelp forest systems, where environmental changes wrought from coastal eutrophication, marine heat waves and proliferation of sea urchins have dramatically modified the distribution and abundance of kelp forests in many parts of the world (Dayton et al 1998, Wernberg et al 2016. As a consequence, elucidating the trophic structure of marine communities, and the sources of basal organic matter required to support them, is a vital component of effective ecosystem-based models for fisheries management and for predicting how changes to critical habitats such as kelp forests may affect the functioning of marine ecosystems (Persson et al 2014, Wing & Jack 2014, Wing et al 2015.…”

Section: Introductionmentioning

confidence: 99%

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Regional differences in supply of organic matter from kelp forests drive trophodynamics of temperate reef fish

Udy¹,

Wing²,

O’Connell-Milne³

et al. 2019

Mar. Ecol. Prog. Ser.

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Regional differences in trophic structure and availability of alternate sources of basal organic matter to food webs can affect the volume of organic matter converted into fish biomass. The present study combined stable isotope analyses (δ 13 C and δ 15 N) with estimates of biomass density of 22 common reef fishes to compare supply of organic matter derived from macroalgae versus phytoplankton to reef fish communities among 30 sites distributed across Fiordland and the Marlborough Sounds, 2 contrasting regions in terms of land-based stressors on the South Island, New Zealand. Fish communities in the Marlborough Sounds were supported by food webs that incorporated less organic matter derived from macroalgae compared to those in Fiordland. Contribution of organic matter derived from macroalgae to fish biomass decreased with trophic level in the Marlborough Sounds, while fishes in Fiordland were supported by a more equal mixture of organic matter derived from phytoplankton and macroalgae among trophic levels. Total fish biomass density was 1.72 times higher in Fiordland, yet the fish community converted 2.91 times more organ ic matter to fish biomass, as a result of a higher proportion of biomass at high trophic levels. The observed patterns were consistent with limitation in supply of organic matter derived from macroalgae in the Marlborough Sounds, where extensive losses of kelp forest habitat linked to land-based stressors have been reported. The results highlight the importance of considering regional variability in basal organic matter source pools, particularly those produced from sensitive kelp forest habitats, when applying ecosystem-based approaches to managing coastal resources.

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Section: Discussionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Regional differences in supply of organic matter from kelp forests drive trophodynamics of temperate reef fish

Udy¹,

Wing²,

O’Connell-Milne³

et al. 2019

Mar. Ecol. Prog. Ser.

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“…However, this relationship has not been as extensively studied in southern New Zealand, primarily because of a scarcity of marine reserves, with the exception of studies in Stewart Island and Fiordland, where there is a network of marine reserves (Schiel , Wing and Jack , Wing et al. ).…”

Section: Introductionmentioning

confidence: 99%

Regional differences in kelp forest interaction chains are influenced by both diffuse and localized stressors

et al. 2019

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On temperate rocky reefs, overexploitation of high‐trophic‐level omnivores can result in the decimation of kelp forest habitats by releasing sea urchin population networks from top‐down control. However, the local dynamics of the resulting trophic cascades are context‐dependent. Here, we investigate the community‐wide patterns associated with both diffuse stressors and localized protection of high‐trophic‐level omnivores in kelp forest ecosystems by comparing communities among marine reserves and fished areas in two contrasting regions in terms of fishing intensity and land‐based stressors, Fiordland and the Marlborough Sounds, New Zealand. We find higher densities of the potential sea urchin predators, red rock lobsters (Jasus edwardsii) and banded wrasse (Notolabrus fucicola), in the Fiordland region, and larger effect sizes of fishing on the exploited fish communities in the Marlborough Sounds. Patterns in sea urchin density were consistent with the idea that high‐trophic‐level species, such as large fish and rock lobsters, regulate sea urchin population density, with lower densities of Evechinus chloroticus observed inside marine reserves, in both regions. Nevertheless, densities of E. chloroticus were generally high (>3 m2) in the Marlborough Sounds, likely above a grazing threshold in both fished and reserve sites. The proportion of habitat where sea urchins were absent was 29% in Marlborough Sounds and 90% in Fiordland. Consequently, we observe 49% barren habitat in Fiordland vs. 70%, and a larger effect of fishing on kelp community structure, in the Marlborough Sounds, where fishing effect sizes and land‐based stressors were more severe. We propose that a combination of diffuse stressors including regional overexploitation of important sea urchin predators, sedimentation, and warming of coastal waters likely contributed to regional differences in the responses of trophic interaction chains to localized reductions in fishing within marine reserves. The present study highlights how physiologically stressed and modified kelp forest ecosystems are more susceptible to detrimental phase shifts at a regional spatial scale.

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“…Nevertheless, state changes typically have multiple causalities in ecological systems, and the predator–sea urchin–kelp interaction chain alone is often insufficient to explain all of the dynamics observed in these systems as they degrade (Dayton et al, 1998; Foster & Schiel, 2010; Sala et al, 1998; Shears et al, 2008). For example, the legacy of overexploitation in kelp forest systems has also removed dense concentrations of abalone in many areas around the world (Hobday et al, 2001) including in New Zealand (Wing et al, 2015). There is some evidence of competition for space between sea urchins ( Evechinus chloroticus ) and abalone ( Haliotis iris ), suggesting that in the absence of exploitation, abalone can effectively reinvade and maintain patches free of sea urchin grazing in the shallow wave‐washed zone, thereby preventing overgrazing of kelps by sea urchins (Wing et al, 2015).…”

Section: Introductionmentioning

confidence: 99%

“…For example, the legacy of overexploitation in kelp forest systems has also removed dense concentrations of abalone in many areas around the world (Hobday et al, 2001) including in New Zealand (Wing et al, 2015). There is some evidence of competition for space between sea urchins ( Evechinus chloroticus ) and abalone ( Haliotis iris ), suggesting that in the absence of exploitation, abalone can effectively reinvade and maintain patches free of sea urchin grazing in the shallow wave‐washed zone, thereby preventing overgrazing of kelps by sea urchins (Wing et al, 2015). Each of these patterns indicates possible long‐term legacy effects of changes in the trophic structure of kelp forest systems with unknown direct and indirect effects on community, and grazer–kelp dynamics.…”

Section: Introductionmentioning

confidence: 99%

The legacies of land clearance and trophic downgrading accumulate to affect structure and function of kelp forests

et al. 2022

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Aotearoa New Zealand is the last major landmass settled by people, and therefore provides a recent record of ecological legacy effects in the coastal zone. Large-scale land clearances of forests accelerated over the last century, affecting the concentration of suspended sediments, light environment, and nutrient composition on rocky reefs, and consequently the distribution, abundance, and composition of algal forests. The environmental effects were compounded in many places by overfishing and long-term declines of large predatory species, often leading to proliferation and extensive grazing by sea urchins. In this study, we examine these processes in three biogeographic regions that have been differentially affected by ecological legacy effects. The study was based on the depth-specific associations between sea urchins (Evechinus chloroticus) and the common kelp (Ecklonia radiata) from multiple sites within each region, some of which were sampled over two decades within no-take marine reserves and in actively fished areas. Satellite-derived estimates of water-column properties were used as proxies for the relative effects of coastal sedimentation on kelp forest habitats. We then used an information-theoretic framework to assess the relative factor weightings of marine reserve effects on urchin density, total suspended solids (TSS), and regional urchin density on the depth-specific density of Ecklonia radiata. The fishing effects were significant within and outside of reserves in the northern and central regions, but the effect sizes were by far strongest in the northern region. In the central region characterized by extensive land clearance and forestry combined with high coastal retention of water, the concentration of TSS had a major influence on the depth distribution of kelp, confining it to shallow water (<10-m depth) in small patches where urchins did not overgraze. These patterns are in sharp contrast to the small marine reserve effects and deep distribution of Ecklonia radiata in the southern region, which has intact native forested catchments, comparatively low fishing pressure, and a large regional network of marine reserves. The results highlight important differences in how centuries-old legacies of land clearance and exploitation affect regional-scale

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Overthrowing a regime shift: displacement of sea urchins by abalone in a kelp forest ecosystem

Cited by 6 publications

References 50 publications

Regional differences in supply of organic matter from kelp forests drive trophodynamics of temperate reef fish

Regional differences in supply of organic matter from kelp forests drive trophodynamics of temperate reef fish

Regional differences in kelp forest interaction chains are influenced by both diffuse and localized stressors

The legacies of land clearance and trophic downgrading accumulate to affect structure and function of kelp forests

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