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

## TL;DR

This study shows that intertidal seagrass supports benthic animals like mud snails and worms by providing food and improving their habitat.

## Contribution

The study reveals that intertidal seagrass, specifically Zostera japonica, serves as a food source and habitat enhancer for certain benthic species in tidal flats.

## Key findings

- Mud snails (Batillaria cumingii) and marine worms (Nereididae) rely on organic matter from Zostera japonica.
- Bivalves like Umbonium costatum and Phacosoma japonicum show minimal reliance on seagrass-derived organic matter.
- Zostera japonica influences sediment bacterial communities, benefiting marine worms.

## Abstract

Seagrass plays an important role in coastal ecosystems by providing food and habitats for many marine animals. While most research has focused on seagrass growing in the subtidal zone, some species, such as Zostera japonica, grow in tidal flats that are exposed at low tide. However, their roles in supporting marine life are not well understood. This study investigated whether intertidal seagrass beds provide food for small animals inhabiting tidal flats. Field surveys were conducted in Matsushima Bay, Japan, where sediment, seawater, and five benthic species, including a mud snail (Batillaria cumingii), two types of bivalve (Umbonium costatum and Phacosoma japonicum), a marine worm (Nereididae), and small hermit crabs (Paguroidea) were collected. Dietary analyses revealed that mud snails and marine worms relied on organic matter from Z. japonica, whereas bivalves did not. Seagrass also influences bacterial communities in the sediment, establishing a favorable environment for marine worms. The results suggest that intertidal seagrass beds support marine life by supplying food and improving habitat conditions, similar to seagrass beds in the subtidal zone. Understanding the role of seagrasses could guide conservation and restoration efforts in tidal flat ecosystems.

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 Zostera japonica 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 Z. japonica as a food source for benthos. Field surveys were conducted in an intertidal flat in Matsushima Bay, Japan. Five benthic species (Batillaria cumingii, Umbonium costatum, Phacosoma japonicum, 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 B. cumingii actively consumed Z. japonica-derived organic matter present in both seagrass and sandy sediments. Z. japonica also influenced bacterial community structure, providing a favorable habitat for Nereididae. Filter feeders (U. costatum and P. japonicum) exhibited minimal reliance on Z. japonica-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.