Changes in Functional and Species Diversity of Seagrass - Associated Fish Due to Anthropogenic Disturbance: A Case Study in Tanjung Merah, North Sulawesi, Indonesia

Seagrass meadows are crucial for supporting fish diversity and abundance, thereby enhancing fisheries resources. However, these ecosystems are increasingly threatened by anthropogenic activities that directly impact fish populations. This study aimed to investigate the patterns of fish species utilizing seagrass habitats at Tanjung Merah, North Sulawesi, by comparing data collected during the pre-disturbance period (2004-2005) and the post-disturbance period (2014-2022). The objective was to assess the effects of anthropogenic pressures on both the seagrass meadows and their associated fish communities. This study employed the swept area method with beach seine and  analyzed seagrass coverage changes through satellite data. Our findings revealed a significant decrease in species richness and fish abundance in Tanjung Merah (P<0.01) following the onset of anthropogenic pressures. A decline in beta diversity was also observed, with fish assemblages prior to disturbance exhibiting greater heterogeneity compared to those after disturbance, indicating that anthropogenic activities had a considerable impact on species composition. Additionally, the findings indicate a shift in the functional trait composition of fish associated with seagrass meadows. Species possessing traits related to greater adaptability and resilience – such as an omnivorous diet, high swimming ability, wide habitat range (visitor type), and high salinity tolerance became more prominent. Conversely, species with traits indicative of lower adaptability or greater specialization declined in response to increased anthropogenic pressure. Moreover, satellite data showed a progressive seagrass decline over time, with coverage estimated at 47.30, 43.02, 31.66, and 35.19 hectares across the study periods. The fish diversity index were assessed at moderate level, while the dominance fish species varied temporally, presumably influenced by environmental fluctuations. These findings suggest a strong correlation between seagrass loss and the reduction of seagrass-associated fish populations in Tanjung Merah, primarily attributable to anthropogenic disturbances. This study highlights the urgent need for the conservation effort to the vulnerable seagrass ecosystems and associated fish populations in Tanjung Merah.