Abstract
Salt marsh ponds (SMPs) form a vital component of coastal wetlands. We investigated microalgal assemblages in SMPs located on Sheepshead Meadows peninsula in New Jersey, in three types of marshes: open marsh water managed, ditched, and unaltered. Monthly samples were collected from six SMPs between May 2022 and June 2023. Microalgae composition showed high dynamic temporal changes within each pond and was spatially heterogeneous among different ponds. The study revealed, for the first time in this area, highly diverse and abundant harmful algal blooms (HABs) in the SMPs. The detected HAB species cover several taxonomic classes, including dinoflagellates Akashiwo sanguinea, Amphidinium carterae, Gymnodinium aureolum, Prorocentrum lima and Alexandrium, raphidophytes Chattonella subsalsa and Heterosigma akashiwo, haptophyte Prymnesium parvum, and cyanobacteria Planktothrix agardhii, Lyngbya aestuarii. In many cases, the HABs accounted for > 60% of total algal abundance and reached as high as 98% with cell density of 103 to 104 cell/mL for dinoflagellates, and 100% with 105 cells/mL for P. parvum. Environmental parameters, temperature, salinity, pH and dissolved oxygen, accounted for about 6.9% of the algal community variance, suggesting other factors could have affected the temporal and spatial variability of HABs in the SMPs. It is possible that the enclosed and semi-enclosed shallow, small water bodies of the SMPs provide unique microhabitat conditions favoring these HAB species. The SMPs are subject to frequent tides and flooding during which the HAB species can be transported, thus potentially function as HAB reservoirs and sources for NJ wetlands and coastal waters.