Marine macrophytes form biogenic habitats that maintain the biodiversity of coastal systems such as seagrass beds and sandy beaches. These habitats are used by small invertebrate fauna that provide ecosystem functions and trophic links between macrophytes and secondary consumers. These systems were also challenged with periodic influxes of pelagic sargasso, a region-wide issue affecting the Caribbean since 2011. Very little is known about how these sargasso influxes affected the macrophyte and invertebrate faunal communities. This research investigated the macrophyte habitat characteristics that drive invertebrate faunal communities and how those communities were affected by pelagic sargasso inundations. Initial assessments of habitat types were conducted in South Florida to characterize assemblages of macrophytes composing these habitats and associated fauna. Six unique habitat types were compared, of which red macroalgal mats contained higher faunal richness and abundance than other habitats. This variation of faunal diversity was further investigated by quantifying macrophyte diversity, biomass, and architecture as habitat metrics. These three metrics were further synthesized into a structural complexity index. However, biomass itself explained variation in faunal diversity as well as the structural complexity index. This finding interrogated the use of an index as an accurate predictor of species diversity patterns. These macrophytes can be transported onto intertidal zones and used by terrestrial invertebrate fauna. Thus, seasonal sargasso influxes was hypothesized to be a major contributor to invertebrate faunal resource use. Temperature in sargasso-dominant wrack was lower and more stable than the surrounding beach. There also was evidence of trophic resource use of sargasso by invertebrates, particularly with terrestrial amphipods. The regional scope of pelagic sargasso inundations called for monitoring efforts to investigate spatiotemporal variation in sargasso accumulation levels and species composition. This was accomplished using community-contributed data, where seasonality in sargasso accumulations between 2019 and 2021 was detected, and the Mexican Caribbean had longer seasons and higher accumulation levels than South Florida. This research synthesizes the role of macrophytes providing resources for invertebrate faunal communities in coastal systems that encompassed submerged benthic vegetation and intertidal sandy beaches. These findings could be applicable to investigate further changes of these systems under periodic sargasso inundations.
