Role of Seagrass as a Food Source for Benthos in Tidal Flats: Toward Conservation and Restoration of Resilient Ecosystems.

Abstract

Seagrass is a key primary producer in coastal ecosystems; however, most studies on seagrass-benthos interactions have focused on subtidal zones. Some species such as <i>Zostera japonica</i> grow in intertidal flats; however, their ecological functions remain unclear. Understanding whether intertidal seagrass beds contribute to benthic abundance and diversity can provide insights that facilitate tidal flat conservation. The present study clarifies the role of intertidal <i>Z. japonica</i> as a food source for benthos. Field surveys were conducted in an intertidal flat in Matsushima Bay, Japan. Five benthic species (<i>Batillaria cumingii</i>, <i>Umbonium costatum</i>, <i>Phacosoma japonicum</i>, Nereididae, and Paguroidea) were identified. Carbon and nitrogen stable isotope ratios (δ¹³C, δ¹⁵N) and fatty acid compositions of sediment organic matter, seawater, and target benthos were analyzed to determine food sources. The results showed that <i>B. cumingii</i> actively consumed <i>Z. japonica</i>-derived organic matter present in both seagrass and sandy sediments. <i>Z. japonica</i> also influenced bacterial community structure, providing a favorable habitat for Nereididae. Filter feeders (<i>U. costatum</i> and <i>P. japonicum</i>) exhibited minimal reliance on <i>Z. japonica</i>-derived organic matter. The findings suggest that, similar to subtidal seagrass ecosystems, intertidal seagrass meadows support benthic communities by supplying organic matter and enhancing bacterial production.