Distribution and biodiversity of benthic macroalgae in the Nanji Islands, China

Xin Wang ¹ Qijun Luo ¹ Wantao Xu ¹ Shangwei Xie ² Wandong Chen ² Xiaopin Ni ² Haimin Chen ^1*

• ¹ Ningbo University, Ningbo, China
• ² Nanji Islands National Marine Nature Reserve Administration, Wenzhou, China

We conducted a comprehensive qualitative and quantitative survey of benthic macroalgae in the Nanji Islands, China, evaluating species diversity and biomass using historical data. Our findings reveal significant variations in biodiversity and biomass across different seasons and tidal zones. The study identified 127 species with Rhodophyta (57.48%) as the dominant group, showing superior ecological adaptability through year-round prevalence. Seasonal analysis revealed peak biomass in spring (1344.31 g•m⁻²) and minimum in autumn (428.78 g•m⁻²), with distinct intertidal zonation showing mid/low-tide zones sustaining 2.6-fold higher biomass than high-tide zones. Co-occurrence network analysis demonstrated southern communities' enhanced stability through complex species interactions (129 nodes, 999 edges), indicating greater ecosystem resilience. Crucially, the establishment of protected areas since 1990 has effectively reversed biodiversity loss, evidenced by 61.14% biomass recovery at key monitoring sites since 2006 and sustained species diversity maintenance. These findings highlight the critical role of marine reserves in conserving marine biodiversity and offers insights into the distribution patterns of benthic macroalgae, which are crucial for understanding marine ecosystems and guiding conservation efforts.