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MEPS prepress abstract   -  DOI: https://doi.org/10.3354/meps14809

Broad dietary niche of irrupting subtropical sea urchin exacerbates threats to multiple temperate reef habitats

Celia A Balemi*, Shunqi Pan, Nick T Shears

*Corresponding author:

ABSTRACT: Climate change is modifying species distributions and abundances, with flow-on impacts to trophic dynamics and the surrounding environment. Climate-induced increases in the subtropical sea urchin Centrostephanus rodgersii are occurring in northeastern New Zealand, yet the ecological impact of this species relative to that of the more common sea urchin Evechinus chloroticus is unknown. While the impacts of both species on kelp forests are well documented, C. rodgersii also commonly occur on vertical rock walls, in caves and archways, which are typically dominated by diverse sessile invertebrate assemblages. We used gut content analysis, stable isotope analysis, as well as choice and no choice feeding assays, to test for differences in feeding preferences and trophic levels between E. chloroticus and C. rodgersii across 3 different habitats: kelp forest, urchin barren and invertebrate-dominated walls. E. chloroticus preferred kelp and other seaweeds but consumed invertebrates when seaweeds were unavailable. In contrast, C. rodgersii exhibited more nonselective feeding behaviour, consumed greater quantities of invertebrates, and consistently fed at higher trophic levels across all habitats. These findings highlight that the expanding C. rodgersii population will have a more profound impact than E. chloroticus, significantly threatening both kelp forest and sessile invertebrate-dominated reef habitats across the region.