Invertebrate communities on shipwrecks in Stellwagen Bank National Marine Sanctuary

Abstract

Shipwrecks serve as island-like habitats on the seafloor and can be conceptualized as unplanned, unprepared, and unintentional artificial reefs. Most artificial reef studies have been restricted in scope and duration, but we have leveraged a dataset of 18 shipwrecks ranging from 15 to 155 yr old and at 24 to 140 m depth in Stellwagen Bank National Marine Sanctuary (SBNMS; Massachusetts, USA) to investigate the factors influencing benthic invertebrate communities on shipwrecks. Classical ecological relationships between species richness and composition and shipwreck size and age (e.g. a log-linear relationship between species richness and shipwreck size) were not observed. Our hypotheses for turnover in species composition with shipwreck age and a significant influence of shipwreck material (i.e. metal, wood) on species composition were also not supported. Rather, our results showed turnover in species composition with shipwreck size, as larger shipwrecks supported dense populations of sessile species such as sponges and anemones. We also observed a high level of patchiness and a significant influence of depth on shipwreck invertebrate communities. These results highlight the importance of shipwrecks as habitats in SBNMS. High-profile shipwrecks in particular support dense invertebrate populations, but the degradation of wooden shipwrecks reduces this effect over time. Our study has implications for future artificial reef management, showing that larger shipwrecks are more valuable habitats, and that reef placement has a strong influence on the resulting species composition.