Effects of Fish Farming Prior to Farm Removal on Macrozoobenthic Crustacean and Molluscan Assemblages in a Major Turkish Aquaculture Gulf: Integrating Historical Data with Literature Insights

Fish farming can significantly impact benthic ecosystems, particularly through alterations in water and sediment quality, potentially disrupting ecosystem functioning and biodiversity. This study investigates the effects of fish-farming on crustacean and molluscan assemblages in Güllük Gulf and Bozburun bay along Turkey’s Aegean coast. Macrozoobenthic samples were collected from fish farm sites and corresponding control sites, representing a baseline prior to the relocation of many farms to offshore areas in the 2010s. A total of 114 crustacean and 54 molluscan species were identified at farm sites, compared to 88 crustaceans and 52 molluscs at control sites. Crustaceans, particularly amphipods, were the most diverse group, while bivalves dominated the molluscan assemblages. Species such as Moerella donacina and Varicorbula gibba (Bivalvia) were most abundant at farm sites, whereas Chondrochelia savignyi (Tanaidacea) and Apseudopsis latreillii (Tanaidacea) were dominant at control sites. Ecological differences between Güllük Gulf and Bozburun bay, as well as between farm and control sites, were evident, with faunal abundance at farm sites showing stronger correlations with environmental variables, including orthophosphate, silicate, and temperature. Biomass emerged as a key indicator for assessing ecological status, alongside abundance and species composition. Fish-farm capacity, as determined by the number of fish cages, played a significant role in shaping faunal patterns, with higher capacity farms exhibiting greater ecological disturbance. This study provides a crucial baseline for future research on the long-term ecological impacts of fish farming, including ecosystem recovery and the role of environmental variables. The findings suggest the importance of incorporating biomass-based indicators and considering farm capacity and site-specific conditions in fish-farming management strategies to mitigate environmental degradation.