Ecological effects of the caged-fish and kelp cultures in semi-enclosed bay: evidence from diatom assemblages and environmental variables

Abstract

Spatial and temporal dynamics of diatom assemblages and their relationships to physico-chemical environmental variables were studied in Sansha Bay, a semi-enclosed bay. A total of 51 taxa were found belonging to the orders Discoidales, Rhizosoleniales, Biddulohiales, Araphidiales, Monoraphidinales, Biraphidinales and Aulonoraphidinales. CCA analysis revealed that physical and chemical parameters were important environmental factors that would influence the diatom community. Based on their seasonal occurrence, most of the species had different relationships with environmental factors. Furthermore, the concentrations of DIN and PO₄^3- in caged-fish culture zone were significantly higher than those in kelp culture and control zones. The abundance of diatoms in the caged-fish culture zone was significantly higher than that in kelp culture and control zones in some seasons, especially in spring. Therefore, the large-scale caged-fish and kelp cultures play key roles in the spatial and temporal dynamics of the diatom community and environmental quality in semi-enclosed coastal bay.