# Comparison of Environmental DNA Metabarcoding and Underwater Visual Census for Assessing Macrobenthic Diversity

## TL;DR

This study compares eDNA and visual surveys for assessing marine life in the Nanji Islands, showing that combining methods gives a more complete picture of biodiversity.

## Contribution

The study demonstrates the complementary strengths of sediment eDNA and UVC for benthic diversity assessment in subtidal ecosystems.

## Key findings

- Sediment eDNA detected higher species richness and key phyla like Annelida and Arthropoda.
- UVC was more effective for large and active organisms, such as Bryozoa.
- Combining methods revealed distinct species profiles with low overlap, emphasizing their complementary nature.

## Abstract

This study evaluates the efficacy of environmental DNA (eDNA) metabarcoding and underwater visual census (UVC) in assessing the diversity of subtidal macrobenthic communities. We compared water eDNA, sediment eDNA, and traditional UVC methods in the Nanji Islands, China. Sediment eDNA demonstrated superior performance in detecting key benthic phyla such as Annelida and Arthropoda, whereas UVC was more effective for large and active organisms. Integrating these methods provides a more comprehensive biodiversity assessment, highlighting the importance of combining molecular and traditional techniques for effective conservation and management strategies in marine ecosystems.

The rapid advancement of environmental DNA (eDNA) technology has transformed ecological research, particularly in aquatic ecosystems. However, the optimal sampling matrix (e.g., water or sediment) and the potential for eDNA to replace or complement traditional underwater visual census (UVC) remain unclear. Here, we integrate water eDNA, sediment eDNA, and UVC approaches to systematically compare the diversity of benthic macrofauna in the subtidal zones of the Nanji Islands, China. Our results show that sediment eDNA samples exhibited the highest species richness, while UVC had the lowest. Each method revealed distinct species profiles, with relatively few shared taxa at the order level and below. Environmental eDNA showed significant advantages in detecting key phyla such as Annelida and Arthropoda. In contrast, traditional UVC was crucial for identifying certain taxa, such as Bryozoa, which were undetectable by eDNA methods. The low overlap in species detected by these methods underscores their complementary nature, highlighting the necessity of integrating multiple approaches to achieve a more comprehensive and accurate biodiversity assessment. Future research should focus on refining eDNA techniques, such as developing more universal primers, to further enhance their applicability in biodiversity monitoring.