Seasonal patterns of juvenile fish assemblages in the surf zones of tropical sandy beaches along Gaolong Bay, Hainan Island, China

Aim

Surf zones are crucial nursery habitats for the early life stages of fish species associated with typical coastal ecosystems. However, little is known about the temporal patterns and drivers of fish assemblages in tropical surf zones. This study aimed to assess the (1) main changes in fish community structure throughout 1 year, (2) seasonal dynamic patterns in fish assemblages, and (3) key factors influencing fish assemblages in the tropical surf zones.

Location

Gaolong Bay, Wenchang City, Hainan Island, China.

Methods

Fish sampling was conducted monthly from June 2021 to May 2022 using a beach seine net. Fish species were identified using both morphological and molecular analyses. Kruskal–Wallis test, analysis of similarity, non-metric multidimensional scaling analysis, and similarity percentage analysis were used to investigate the temporal fish assemblage patterns. Generalised additive models and canonical correspondence analysis were used to assess how environmental variables influence fish assemblages.

Results

We identified 83 fish species, which were grouped into three ecotypes based on their primary habitat: coral reef-seagrass-associated species (CS) (35), mangrove-estuarine-associated species (ME) (30), and common coastal-estuarine-associated species (CE) (18). Most captured individuals were juveniles, and fish abundance and diversity were highest in May. Most CS species were abundant between March and May. ME and most CE species were dominant from June to August, and Mugilidae (CE) was abundant between October and February. Furthermore, surf fish assemblages were substantially influenced by tidal level, water temperature, conductivity, pH, turbidity, and dissolved oxygen.

Conclusions

Juvenile fish were abundant in May and fish species with three ecotypes alternate in the surf zones throughout the year. Counter to much current thinking, March maybe the spawn peak of most fish species in the studied area, and we suggest that the fishing ban period could start from March instead of May in the inshore areas of Hainan Island.