Characterizing potential resource use of sargasso-dominant sea wrack by terrestrial invertebrate fauna during sargasso influxes in South Florida

Abstract

Marine-derived macrophytes primarily compose beach-cast sea wrack that can be used by terrestrial invertebrate fauna in sandy beach system. Since 2011, the inundations of pelagic sargasso would accumulate and decompose at local, nearshore systems across the Tropical Atlantic. While ecological effects of pelagic sargasso influxes were considerably studied on tropical Atlantic nearshore coastal systems, not much has been known about their effects on the intertidal interface or terrestrial faunal communities. This study aims to investigate terrestrial invertebrate communities associated with landed sargasso and the sargasso's potential as habitat or food for these invertebrates. Surveys, sample collection of flora and fauna, and trials of a temperature experiment were conducted at Crandon Park and MJ State Park along Southeast Florida during the 2020 and 2021 sargasso seasons. Invertebrate communities were primarily composed of talitrid amphipods, coleopterans, and dipterans. The quantity of sargasso, dependent on year of sampling session, seemed to have a more discernible effect on invertebrate composition than location. HOBO logger microhabitat experiment trials showed treatments with sargasso-dominant wrack having lower temperatures than treatments with exposed or buried sand. Many invertebrate consumers showed δ13C and δ15N signatures closer to marine macrophytes than terrestrial plants. However, mixing models reveal amphipods and oligochaete worms having a trophic link with pelagic sargasso, while insect fauna had their resource use sourced from other marine macrophytes. However, any consumption of sargasso would likely be attributed to generalist resource use rather than a specific preference to sargasso. The potential uses of sargasso depend on the amount of biomass accumulated on the beach surface and the habitat requirements of specific invertebrate species.