MEPS 752:69-82 (2025)  -  DOI: https://doi.org/10.3354/meps14754

ABSTRACT: Biogenic habitats influence biodiversity through both direct and indirect mechanisms. Direct influences result in changes to abiotic conditions or trophic support, while indirect influences result in changes in associated communities and species interactions. Seagrass forms a marine biogenic habitat that slows water flow, modifies water chemistry, provides food to grazers, and offers refuge. In this study, we examined how seagrass directly and indirectly influences invertebrate communities. Using sessile filter feeding invertebrate communities, also known as fouling communities, as a study system, we deployed experiments with bare settlement plates and predator exclosures inside and outside of seagrass over the summer of 2018. We also conducted a predator exposure experiment in 2020 by removing exclosures following community development to better understand predator effects and how they change temporally. We found that seagrass reduced abundance, diversity, and richness of fouling species in a high recruitment year (2018). Predators influenced communities by reducing the abundance of competitively dominant solitary ascidians, allowing for an increase in the abundance of other morphotypes. The effect of predation appeared to be greater outside of seagrass than inside in 2018 for some community responses, although this statistical interaction was small relative to the main predator effect and was likely influenced by variable recruitment of fouling species. While we caution against the overgeneralization of effects of biogenic habitat on biodiversity, our study provides evidence that seagrass ecosystems alter fouling communities through direct effects on abundance and that indirect effects of seagrass on fouling communities are less important than predicted.

KEY WORDS: Seagrass · Invertebrates · Predation · Habitat structure · Biogenic habitats · Biodiversity · Fouling communities · Zostera marina