Cascade effects and sea-urchin overgrazing: An analysis of drivers behind the exploitation of sea urchin predators for management improvement

Wallner-Hahn, Sieglind; Torre‐Castro, Maricela de la; Eklöf, Johan; Gullström, Martin; Muthiga, Nyawira A.; Uku, Jacqueline

doi:10.1016/j.ocecoaman.2015.01.010

Cited by 22 publications

(8 citation statements)

References 64 publications

(104 reference statements)

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“…Given the potential for wide variations in canopy quality and biomass turnover, and the functional consequences for the role of macroalgal reefs in tropical marine ecosystems, there is a need to identify and protect high‐quality patches from local threats. The latter include increases in turbidity, habitat destruction from anchoring, sediment smothering from poor catchment management and dredging (Umar, McCook, & Price, ), as well as overfishing‐induced trophic cascades that drive the ecological release of herbivores (e.g., urchins; Wallner‐Hahn et al, ).…”

Section: Research and Management Prioritiesmentioning

confidence: 99%

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Form and function of tropical macroalgal reefs in the Anthropocene

et al. 2019

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Tropical reefs have been subjected to a range of anthropogenic pressures such as global climate change, overfishing and eutrophication that have raised questions about the prominence of macroalgae on tropical reefs, whether they pose a threat to biodiversity, and how they may influence the function of tropical marine ecosystems. We synthesise current understanding of the structure and function of tropical macroalgal reefs and how they may support various ecosystem goods and services. We then forecast how key stressors may alter the role of macroalgal reefs in tropical seascapes of the Anthropocene. High levels of primary productivity from tropical canopy macroalgae, which rivals that of other key producers (e.g., corals and turf algae), can be widely dispersed across tropical seascapes to provide a boost of secondary productivity in a range of biomes that include coral reefs, and support periodic harvests of macroalgal biomass for industrial and agricultural uses. Complex macroalgal reefs that comprise a mixture of canopy and understorey taxa can also provide key habitats for a diverse community of epifauna, as well as juvenile and adult fishes that are the basis for important tropical fisheries. Key macroalgal taxa (e.g., Sargassum) that form complex macroalgal reefs are likely to be sensitive to future climate change. Increases in maximum sea temperature, in particular, could depress biomass production and/or drive phenological shifts in canopy formation that will affect their capacity to support tropical marine ecosystems. Macroalgal reefs can support a suite of tropical marine ecosystem functions when embedded within an interconnected mosaic of habitat types. Habitat connectivity is, therefore, essential if we are to maintain tropical marine biodiversity alongside key ecosystem goods and services. Consequently, complex macroalgal reefs should be treated as a key ecological asset in strategies for the conservation and management of diverse tropical seascapes. A plain language summary is available for this article.

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Section: Research and Management Prioritiesmentioning

confidence: 99%

“…The latter include increases in turbidity, habitat destruction from anchoring, sediment smothering from poor catchment management and dredging (Umar, McCook, & Price, 1998), as well as overfishinginduced trophic cascades that drive the ecological release of herbivores (e.g., urchins; Wallner-Hahn et al, 2015).…”

Section: Re S E Arch and Manag Ement Prioritie Smentioning

confidence: 99%

Form and function of tropical macroalgal reefs in the Anthropocene

et al. 2019

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“…Large predatory fish and blacktip sharks were frequently observed in the seagrass meadows at all sites and all times of year throughout the duration of the experiment and on the video footage collected during the study (e.g., video S1). A lack of top-down control due to overfishing of herbivore predators has been shown to contribute to overgrazing by macroherbivores in other locations [69] and presence of predators can control macroherbivore populations [61,66]. The presence of predators can also modify the feeding behaviours of megaherbivores over space and time, based on their perceived risk of predation [68,70,71] and it is possible the macroherbivores at Green Island are also attempting to avoid predators while foraging.…”

Section: Discussionmentioning

confidence: 99%

Spatial and Temporal Patterns in Macroherbivore Grazing in a Multi-Species Tropical Seagrass Meadow of the Great Barrier Reef

2021

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Macroherbivory is an important process in seagrass meadows worldwide; however, the impact of macroherbivores on seagrasses in the Great Barrier Reef (GBR) has received little attention. We used exclusion cages and seagrass tethering assays to understand how the intensity of macroherbivory varies over space and time in the seagrass meadows around Green Island (Queensland), and what impact this has on overall meadow structure. Rates of macroherbivory were comparatively low, between 0.25–44% of daily seagrass productivity; however, rates were highly variable over a one-year period, and among sites. Loss of seagrass material to macroherbivory was predominantly due to fish; however, urchin herbivory was also taking place. Macroherbivory rates were of insufficient intensity to impact overall meadow structure. No macroherbivory events were identified on video cameras that filmed in the day, indicating that feeding may be occurring infrequently in large shoals, or at night. While relatively low compared to some meadows, seagrass macroherbivory was still an important process at this site. We suggest that in this highly protected area of the GBR, where the ecosystem and food webs remain largely intact, macroherbivory was maintained at a low level and was unlikely to cause the large-scale meadow structuring influence that can be seen in more modified seagrass systems.

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“…Paracentrotus lividus is one of the most important herbivores of Mediterranean benthic ecosystems ( Hereu et al, 2005 ; Prado et al, 2012 ). The impact of overfishing through the impairment of predatory control on P. lividus determines a significant loss of macroalgal communities and biodiversity ( Micheli et al, 2005 ; Giakoumi et al, 2012 ; Sala et al, 2012 ; Wallner-Hahn et al, 2015 ). For this reason, in the Mediterranean Sea it is widely accepted that P. lividus harvesting may be a potentially effective method for mitigating overgrazing in areas of severe overfishing (e.g.…”

Section: Introductionmentioning

confidence: 99%

The challenge of managing the commercial harvesting of the sea urchin Paracentrotus lividus: advanced approaches are required

Farina

Baroli

Brundu³

et al. 2020

PeerJ

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Sea urchins act as a keystone herbivore in marine coastal ecosystems, regulating macrophyte density, which offers refuge for multiple species. In the Mediterranean Sea, both the sea urchin Paracentrotus lividus and fish preying on it are highly valuable target species for artisanal fisheries. As a consequence of the interactions between fish, sea urchins and macrophyte, fishing leads to trophic disorders with detrimental consequences for biodiversity and fisheries. In Sardinia (Western Mediterranean Sea), regulations for sea urchin harvesting have been in place since the mid 90s. However, given the important ecological role of P. lividus, the single-species fishery management may fail to take into account important ecosystem interactions. Hence, a deeper understanding of population dynamics, their dependance on environmental constraints and multispecies interactions may help to achieve long-term sustainable use of this resource. This work aims to highlight how sea urchin population structure varies spatially in relation to local environmental constraints and species interactions, with implications for their management. The study area (Sinis Peninsula, West Sardinia, Italy) that includes a Marine Reserve was divided into five sectors. These display combinations of the environmental constraints influencing sea urchin population dynamics, namely type of habitat (calcareous rock, granite, basalt, patchy and continuous meadows of Posidonia oceanica), average bottom current speed and predatory fish abundance. Size-frequency distribution of sea urchins under commercial size (<5 cm diameter size) assessed during the period from 2004 to 2007, before the population collapse in 2010, were compared for sectors and types of habitat. Specific correlations between recruits (0–1 cm diameter size) and bottom current speeds and between middle-sized sea urchins (2–5 cm diameter size) and predatory fish abundance were assessed. Parameters representing habitat spatial configuration (patch density, perimeter-to-area ratio, mean patch size, largest patch index, interspersion/juxtaposition index) were calculated and their influence on sea urchin density assessed. The density of sea urchins under commercial size was significantly higher in calcareous rock and was positively and significantly influenced by the density and average size of the rocky habitat patches. Recruits were significantly abundant in rocky habitats, while they were almost absent in P. oceanica meadows. The density of middle-sized sea urchins was more abundant in calcareous rock than in basalt, granite or P. oceanica. High densities of recruits resulted significantly correlated to low values of average bottom current speed, while a negative trend between the abundance of middle-sized sea urchins and predatory fish was found. Our results point out the need to account for the environmental constraints influencing local sea urchin density in fisheries management.

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Cascade effects and sea-urchin overgrazing: An analysis of drivers behind the exploitation of sea urchin predators for management improvement

Cited by 22 publications

References 64 publications

Form and function of tropical macroalgal reefs in the Anthropocene

Form and function of tropical macroalgal reefs in the Anthropocene

Spatial and Temporal Patterns in Macroherbivore Grazing in a Multi-Species Tropical Seagrass Meadow of the Great Barrier Reef

The challenge of managing the commercial harvesting of the sea urchin Paracentrotus lividus: advanced approaches are required

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