A Decade of Time Series Sampling Reveals Thermal Variation and Shifts in Pseudo-nitzschia Species Composition That Contribute to Harmful Algal Blooms in an Eastern US Estuary

Abstract

In 2016-17, shellfish harvesting closed for the first time in Narragansett Bay, Rhode Island, USA, from domoic acid (DA), a neurotoxin produced by diatoms of the Pseudo-nitzschia genus. Pseudo-nitzschia have occurred frequently for over 60 years in Narragansett Bay’s Long-Term Plankton Time Series (NBPTS), therefore it is surprising that the first closure only recently occurred. Pseudo-nitzschia species are known to vary in their toxin production, thus species identification is critical for understanding the underlying ecological causes of these harmful algal blooms (HABs). DNA in plankton biomass can be preserved for many years, so molecular barcoding of archived samples is useful for delineation of taxa over time. This study used amplification of the Pseudo-nitzschia-specific 18S-5.8S rDNA internal transcribed spacer region 1 (ITS1) in plankton samples and high throughput sequencing to characterize Pseudo-nitzschia species composition over a decade in Narragansett Bay, including eight years before the 2016-17 closures and two years following. This metabarcoding method can discriminate nearly all known Pseudo-nitzschia species. Several species recur as year-round residents in Narragansett Bay (P. pungens var. pungens, P. americana, P. multiseries, and P. calliantha). Various other species increased in frequency after 2015, and some appeared for the first time during the closure period. Notably, P. australis, a species prevalent in US West Coast HABs and known for high DA production, was not observed in Narragansett Bay until the 2017 closure but has been present in several years after the closures. Annual differences in Pseudo-nitzschia composition were correlated with physical and chemical conditions, predominantly water temperature. The long-term composition trends of Pseudo-nitzschia in Narragansett Bay serve as a baseline for identifying the introduction of new species, understanding shifting assemblages that contributed to the 2016-17 closures, and monitoring species that may be cause for future concern.

Multi‐year time series reveals temporally synchronous diatom communities with annual frequency of recurrence in a temperate estuary

“…Of the environmental factors we examined, temperature and light data were correlated ( r = 0.62) and thus could not both be included in the tb‐RDA. We chose to include temperature because it has been observed as a more important filter of phytoplankton composition than light in NBay (Karentz and Smayda 1984; Rynearson et al 2020; Roche et al 2022). The ordination analysis indicated that 80% of the variability in diatom ASV occurrence was constrained by axes one (64%) and two (16%) (Fig.…”

Changes in the Composition of Bloom-Forming Toxic Pseudo-nitzschia Diatoms in Surface Waters in Ussuri Bay, Northwestern Sea of Japan, during the Autumn Seasons of 2017–2022

“…In addition to the mass poisoning of wild marine animals, DA can cause significant economic damage to aquaculture farms [5,6]. Studies of the temporal dynamics of the Pseudo-nitzschia species associated with environmental or biotic factors or climate change events are carried out in highly productive waters or areas adjacent to aquaculture farms and recreational zones worldwide [7][8][9][10][11]. Such studies are crucial not only for interpreting the temporal patterns of the population dynamics of Pseudo-nitzschia but also for understanding the toxic events and their economic and social effects.…”