The effects of the nonnative brittle star Ophiothela mirabilis Verrill, 1867 on the feeding performance of an octocoral host in a southwestern Atlantic rocky shore

Abstract

The Pacific epizoic brittle star Ophiothela mirabilis Verrill, 1867 has widely spread and colonized hosts at high densities along the Western Atlantic. We assessed the impacts of O. mirabilis on the feeding performance of the preferred host Leptogorgia punicea (Milne Edwards and Haime, 1857) through in situ experiments using incubation chambers and estimated its putative effects on the benthic-pelagic coupling processes of a rocky shore system. The feeding rates and heterotrophic carbon inputs of L. punicea treatments with high colonization by O. mirabilis (5.4 ± 0.6 individuals cm−2 of host area; mean ± standard deviation) were compared to host controls naturally without brittle stars. No significant differences in host feeding performance were observed between the control and treatments. Overall, L. punicea ingested 3,047,118 ± 1,843,183 particles g DW (dry weight)−1 h−1, corresponding to 116.1 ± 159.0 µg of carbon (C) g DW−1 h−1. Therefore, although octocorals hosting O. mirabilis may have impaired polyp opening and extension, their feeding performance remains similar. In this sense, the impact of O. mirabilis on the carbon flux of the rocky shore system driven by octocoral ingestion is minimal. The grazing rate of 49.9 ± 68.3 mg C m−2 day−1 highlights the significant role of L. punicea in such benthic-pelagic coupling processes. Notwithstanding, further laboratory and field experimental studies assessing the effects on host taxa with distinct morphological and functional features are needed to better understand the responses of the recipient hard-bottom systems along the Western Atlantic to increasing densities of O. mirabilis.