title: Temperature dependence of an estuarine harmful algal bloom: Resolving interannual variability in bloom dynamics using a degree day approach.
abstract: Observations of harmful algal blooms (HABs) of the dinoflagellateAlexandrium fundyensein an estuary over multiple years were used to assess drivers of their spatial and temporal variability. Nauset Estuary on Cape Cod, Massachusetts has a recurrent, self-seedingA. fundyensepopulation that produces paralytic shellfish poisoning toxins and leads to nearly annual closure to shellfishing. Weekly surveys of the entire estuary were made in 3 of 4 consecutive years, with surveys of a subembayment during the intervening year. MajorA. fundyenseblooms were observed all 4 years, with maximum concentrations >106cells L-1. Concentrations were greatest in three salt ponds at the distal edges of the estuary. The bloom timing varied among the salt ponds and among years, although the blooms had similar durations and maximum cell concentrations. Nutrient concentrations did not correlate with the growth of the bloom, but differences in water temperature among years and ponds were significant. Net growth rates inferred from the surveys were similar to those from laboratory experiments, and increased linearly with temperature. A growing degree day calculation was used to account for effects of interannual variability and spatial gradients in water temperature on population development. The approach collapsed variability in the timing of bloom onset, development, and termination across years and among ponds, suggesting that this relatively simple metric could be used as an early-warning indicator for HABs in Nauset and similar areas with localized, self-seeding blooms.
authors.affiliation: Woods Hole Oceanographic Institution, Applied Ocean Physics and Engineering Department, Woods Hole, Massachusetts.
authors.forename: David K
authors.initials: DK
authors.lastname: Ralston
authors.affiliation: Woods Hole Oceanographic Institution, Biology Department, Woods Hole, Massachusetts.
authors.forename: Bruce A
authors.initials: BA
authors.lastname: Keafer
authors.affiliation: Woods Hole Oceanographic Institution, Biology Department, Woods Hole, Massachusetts.
authors.forename: Michael L
authors.initials: ML
authors.lastname: Brosnahan
authors.affiliation: Woods Hole Oceanographic Institution, Biology Department, Woods Hole, Massachusetts.
authors.forename: Donald M
authors.initials: DM
authors.lastname: Anderson