Bottom-up and top-down control of seagrass overgrazing by the sea urchin Tripneustes gratilla

Agustin Moreira-Saporiti; Dieuwke Hoeijmakers; Hauke ReuterFlower E. MsuyaKatrin GeseMirta Teichberg

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Bottom-up and top-down control of seagrass overgrazing by the sea urchin Tripneustes gratilla

机译：Bottom-up and top-down control of seagrass overgrazing by the sea urchin Tripneustes gratilla

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The lack of top-down control on Tripneustes gratilla, a sea urchin commonly known to graze on seagrass, and the bottom-up control of its feeding preference, led to the overgrazing of seagrass meadows of the species Thalassodendron ciliatum in Changuu Island (Zanzibar Archipelago). The impact of overgrazing on seagrasses was assessed by mapping the presence of grazed versus non-grazed seagrass patches in the study site, while the top-down control on T. gratilla was assessed by measuring the abundance of its fish predators. The feeding preference and distribution of T. gratilla were characterized by calculating the electivity indexes for each seagrass species and measuring sea urchin density, respectively. Approximately half of the patches of T. ciliatum were overgrazed, while predatory fishes of T. gratilla were absent from the site. The Vanderploeg and Scavia's Relativized Electivity Index indicated that T. gratilla had a feeding preference for T. ciliatum, which was also supported by higher urchin densities within T. ciliatum dominated patches. Bottom-up control of grazing activity was observed by quantifying and analyzing morphological, nutritional, and the chemical defense traits of the seagrass in relation to feeding preference and urchin density. Feeding was positively correlated to the seagrass tissue C:P ratio (ρ = 0.9), whereas urchin density showed no correlations. The bottom-up control of the feeding preference and agglomeration of T. gratilla in T. ciliatum meadows, together with the lack of evidence of substantial top-down control and the long recovery time of T. ciliatum led to the overgrazing of this species at this site. Overgrazing, therefore, was shown to be the result of multiple factors ranging from the traits of the seagrass and feeding preference of T. gratilla, to the abundance of predators in this area.

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《Marine ecology》 |2023年第1期|e12734.1-e12734.14|共14页
作者
Agustin Moreira-Saporiti; Dieuwke Hoeijmakers; Hauke ReuterFlower E. MsuyaKatrin GeseMirta Teichberg;
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作者单位

Leibniz Centre for Tropical Marine Research, Bremen, Germany,University of Bremen, Faculty for Biology and Chemistry, Bremen, Germany;

Leibniz Centre for Tropical Marine Research, Bremen, Germany;

University of Dar es Salaam, Dar es Salaam, TanzaniaUniversity of Oldenburg, Oldenburg, Germany;

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正文语种英语
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C:P ratio; electivity index; feeding preference; seagrass traits; Thalassodendron ciliatum; tropical seagrass;

Bottom-up and top-down control of seagrass overgrazing by the sea urchin Tripneustes gratilla

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