Seasonal Changes of Microphytoplankton Community in Prince William Sound, Alaska in 2019

Prince William Sound (PWS) is a large estuarine-fjord system connected with the northern Gulf of Alaska. Many ecologically and economically important predators, such as juvenile herring and pink salmon, benefit from seasonally abundant and structured plankton prey fields. Past studies on primary production in PWS were based mostly on chlorophyll measurements, which lacked information about food quality and seasonal changes. In 2019, oceanographic data and phytoplankton samples were collected seasonally from the open waters and four nearshore bays in PWS. Laboratory microscopic identification and enumeration of phytoplankton samples provided taxonomic composition and abundance of the larger-celled diatoms and dinoflagellates. Both the total species abundance and community structure cluster analysis showed statistically significant seasonality and subregional differences within the Sound. Diatoms were numerically the most dominant group through spring and summer while dinoflagellates became more abundant in late autumn season. The spring diatom bloom continued in influence through June. High chlorophyll concentrations measured at Whale and Eaglek Bays in early March imply a late winter bloom in these locations. Correlation analysis revealed several influential variables on year-round community patterns including stratification, average temperature of the mixed layer, downwelling condition, nitrate, and silicate. Although this 1-year seasonality study is limited in its representation of other specific years, the findings suggest an appropriate direction for future studies, such as earlier sampling from late winter through spring months, and confirming of the presence of late summer and early autumn blooms.