Sand dynamics drive kelp forest biodiversity and community structureLong-term Temporal Trends

Ethan Kadiyala¹, Jonathan Walter², Max Castorani¹

¹University of Virginia, USA, ²UC Davis Center for Watershed Sciences, USA

In this study, we leveraged spatially replicated annual survey data spanning more than two decades in coastal southern California, USA, to investigate the effects of sediment dynamics on subtidal reef communities. We applied statistical models to quantify the response of abundance, diversity, and composition to the amount of hard substrate. We examined the effect of substrate type on recruitment and the influence of spatial variation in substrate on spatial patterns in community structure. Lastly, we investigated the oceanographic and landscape characteristics that contribute to substrate variability over time at a reef. Abundance and diversity were positively associated with hard substrate cover, however diversity saturated at higher cover of rock. Species composition exhibited significant changes from sandy to rocky conditions, reflecting morphological differences among taxa. Community dissimilarity increased with greater differences in the amount of hard substrate between two reefs. Finally, temporal variation in substrate at a reef was negatively associated with reef rugosity, indicating the importance of reef complexity in providing stable habitat for benthic organisms. Together, these results provide insight into the role of substrate dynamics in mediating abundance, diversity, composition, and recruitment in reef communities, the consequences of spatial variation of substrate in these systems, and the drivers of substrate variability in subtidal reef environments.