Co-occurrence of freshwater and marine phycotoxins: A record of microcystins and domoic acid in Bogue Sound, North Carolina (2015 to 2020)

• Published in: Harmful algae Vol. 125; p. 102412
• Main Authors: Anderson, Madeline, Valera, Marco, Schnetzer, Astrid
• Format: Journal Article
• Language: English
• Published: Netherlands Elsevier B.V 01.06.2023
• Subjects: Animals; Domoic acid; Ecosystem; Fresh Water; Humans; Land-sea interface; Microcystins; North Carolina; North Carolina; North Carolina; Domoic acid; Land-sea interface; Microcystins
• ISSN: 1568-9883; 1878-1470
• DOI: 10.1016/j.hal.2023.102412

•Year-round, monthly sampling showed the consistent presence and co-occurrence of domoic acid and microcystins in Bogue Sound, NC.•Pseudo-nitzschia spp. contributed 0–19% to the microplankton assemblage.•The producers of microcystins could not be identified in this study but toxin presence in the marine sound was likely associated with transport from upriver.•Low algal biomass and toxin concentrations were attributed to Bogue Sound's short water residence time (∼2 days).•The prevalence of low-level concentrations of domoic acid and microcystin warrant investigation of potential food web contamination and human exposure risks. Harmful algal blooms (HABs) create issues both environmentally and economically in coastal regions, especially if algal growth is linked to the production of toxins which can affect ecosystems, wildlife, and humans. This study is the first to confirm near year-round presence and co-occurrence of microcystins (MCs) and domoic acid (DA) within the outskirts of the largest lagoonal US estuary, the Pamlico-Albemarle Sound System (PASS). Monthly sampling at a time-series location in Bogue Sound, located within the eastern part of the PASS, showed DA and MCs were commonly present and detected together 50% of the time based on an in situ toxin tracking approach over a 6-year time period (2015–2020). Particulate toxin concentrations based on monthly grab sampling remained well below regulatory thresholds for MCs and below DA concentrations associated with animal sickness and mortality elsewhere. Time-integrated levels for dissolved MCs and DA, however, indicated a continuous presence of both toxins within Bogue Sound where high flushing rates (∼2-day average residence time) presumably alleviate potential issues linked to nutrient inputs, subsequent algal growth, or toxin accumulation. Pseudo-nitzschia spp. contributed 0 to 19% to the resident microplankton community. Light microscopy analyses did not reveal the source of MCs production in the sound but suggested potential downstream transport and/or autochthonous production due to taxa not accounted for in this study (e.g., picocyanobacteria). Nitrate+nitrite (NOx) concentrations, wind speed, and water temperature explained a third of the variations in accumulated dissolved MCs, but no relationship was seen for DA concentrations based on monthly sampling within this highly dynamic system. This study emphasizes the importance of continued algal toxin monitoring in systems like Bogue Sound which might experience decreases in water quality similar to adjacent, nutrient-impaired regions within the PASS.