Assessment of water quality and phytoplankton community of Limpenaeus vannamei pond in intertidal zone of Hangzhou Bay, China

This study was conducted to understand the associations between water quality and the phytoplankton community in intertidal mudflat pond of Limpenaeus vannamei, in the region around Hangzhou Bay. The water parameters at each sampling site were measured monthly including temperature, pH, dissolved oxygen, salinity, ammonia, natrite, nitrite, total nitrogen, total phosphateand CODMn. The cultivation water met or exceeded the class V surface water quality standard. Total nitrogen, phosphate and CODMnwere the main exceeding standard factors. The Principal component analysis (PCA) result showed that total phosphorus (0.743), total nitrogen (0.728), ammonia (0.417) and nitrate (0.691) were the main factors. A total of 84 phytoplankton species were isolated, which were comprised of 59 genera of 8 phyla.Tianhe site recorded the highest phytoplankton abundance (942.5 × 105 in./L, July) and biomass (12.46 mg/L, July). The major peaks in phytoplankton abundance were mostly associated with the proliferation of certain Chlorophyta (Merismopediatenuissima, Microcystisaeruginosa and Phormidiumtenus). The Margalef richness index classified the sampled water as being mildly or moderately polluted. Pielou evenness index (0.59-0.82) and Shannon-Wiener diversity index (1.93-2.49) also demonstrated a slight or moderate pollution. Canonical correlation analyses (CCA) results revealed that CODMn, followed by total nitrogen, total phosphorus, ammonia, temperature, salinity, pH, dissolved oxygen, nitrate and nitrite exhibited a close relation with dominant species. In particular, most species in this study showed significant correlation with temperature, pH and dissolved oxygen. While CODMn and ammonia distributed on the opposite direction. Phytoplankton such as Merismopedia, Schroederia and Closterium showed positive relationships with total nitrogen and total phosphorus.