Dynamics of Alexandrium fundyense blooms and shellfish toxicity in the Nauset Marsh System of Cape Cod (Massachusetts, USA)

Abstract

Paralytic Shellfish Poisoning (PSP) toxins are annually recurrent along the Massachusetts coastline (USA), which includes many small embayments and salt ponds. Among these is the Nauset Marsh System (NMS), which has a long history of PSP toxicity. Little is known, however, about the bloom dynamics of the causative organism Alexandrium fundyense within that economically and socially important system. The overall goal of this work was to characterize the distribution and dynamics of A. fundyense blooms within the NMS and adjacent coastal waters by documenting the distribution and abundance of resting cysts and vegetative cells. Cysts were found predominantly in three drowned kettle holes or salt ponds at the distal ends of the NMS – Salt Pond, Mill Pond, and Town Cove. The central region of the NMS had a much lower concentration of cysts. Two types of A. fundyense blooms were observed. One originated entirely within the estuary, seeded by cysts in the three seedbeds. These blooms developed independently of each other and of the A. fundyense population observed in adjacent coastal waters outside the NMS. The temporal development of the blooms was different in the three salt ponds, with initiation differing by as much as 30 days. These differences do not appear to reflect the initial cyst abundances in these locations, and may simply result from higher cell retention and higher nutrient concentrations in Mill Pond, the first site to bloom. Germination of cysts accounted for a small percentage of the peak cell densities in the ponds, so population size was influenced more by the factors affecting growth than by cyst abundance. Subsurface cell aggregation (surface avoidance) limited advection of the vegetative A. fundyense cells out of the salt ponds through the shallow inlet channels. Thus, the upper reaches of the NMS are at the greatest risk for PSP since the highest cyst abundances and cell concentrations were found there. After these localized blooms in the salt ponds peaked and declined, a second, late season bloom occurred within the central portions of the NMS. The timing of this second bloom relative to those within the salt ponds and the coastal circulation patterns at that time strongly suggest that those cells originated from a regional A. fundyense bloom in the Gulf of Maine, delivered to the central marsh from coastal waters outside the NMS through Nauset Inlet. These results will guide policy decisions about water quality as well as shellfish monitoring and utilization within the NMS and highlight the potential for “surgical” closures of shellfish during PSP events, leaving some areas open for harvesting while others are closed.

Temperature dependence of an estuarine harmful algal bloom: Resolving interannual variability in bloom dynamics using a degree‐day approach

“…One example is Nauset estuary on Cape Cod, Massachusetts, where A. fundyense blooms occur annually (Anderson et al 1983; Crespo et al 2011). The blooms in Nauset caused shellfishing closures due to PSP toxin in 20 of 21 years from 1992 to 2012.…”

“…The blooms in Nauset caused shellfishing closures due to PSP toxin in 20 of 21 years from 1992 to 2012. The blooms most likely originate within the estuary rather than coming from the Gulf of Maine because Nauset blooms occur earlier in the year and are concentrated in the upper reaches of the estuary rather than near the inlet (Anderson 1997; Crespo et al 2011). The potential for cells to be exported from Nauset and transported downcoast to seed HABs in other nearby embayments remains uncertain.…”

“…A. fundyense blooms were first investigated in Nauset and a similar Cape Cod estuary over 30 years ago (Anderson et al 1983; Crespo et al 2011), and after a long interval with little study, detailed examination of the bloom dynamics resumed recently (Crespo et al 2011). A. fundyense has the ability to migrate vertically, and observations in Salt Pond, a subembayment in the northwest of the Nauset estuary, found that retention of cells within the pond was enhanced by a combination of the cells’ vertical migration and tidally asymmetric flows (Anderson and Stolzenbach 1985).…”

“…Surface avoidance during the day and downward migration at night reduces cell concentrations in the near-surface layer and limits the rate of tidal flushing from the salt ponds. This selective retention enhances cell accumulation in the ponds and cyst deposition in the estuary at the end of blooms, perpetuating self-seeding A. fundyense populations (Anderson et al 1983; Crespo et al 2011). In this way, A. fundyense life history and behavior seem well matched to the estuary, consistent with the recurrence of localized blooms in the ponds of the Nauset system.…”

Harmful Algal Blooms in Fjords, Coastal Embayments, and Stratified Systems: Recent Progress and Future Research

“…blooms in inshore bays apparently does not depend on cyst distribution or abundance (Cosgrove et al, 2014;Ralston et al, 2014). These blooms are determined by a combination of retention of vegetative cells behind bathymetric barriers (shallow sills), daily vertical migration, and temperature that controls cell division rates (Crespo et al, 2011). In the case of the tropical and subtropical dinoflagellate Pyrodinium bahamense, the most common cause of PSP in the Philippines and in Southeast Asia, blooms are inoculated by cyst germination in small tropical bays but not in open coastal waters.…”