A biogeochemical investigation of Aureococcus anophagefferens blooms: Interactions with organic nutrients and trace metals.

摘要

During the past several decades, coastal ecosystems around the world have experienced notable increases in the frequency, intensity and diversity of Harmful Algal Blooms. Since 1985, Brown Tides of the pelagophyte Aureococcus anophagefferens have plagued multiple mid-Atlantic estuaries and have decimated the commercial scallop industry on Long Island. Therefore, this study used a combined approach of laboratory experiments, field experiments and field measurements to evaluate the role of organic, inorganic and trace metal nutrients in the initiation, persistence and demise of Aureococcus anophagefferens blooms within Long Island embayments.; During a two-year study of Brown Tides at West Neck Bay (WNB) on Shelter Island, it was found that groundwater seepage supplied 83% of dissolved inorganic nitrogen entering the bay. During 1997 and 1998, elevated levels of nitrate (1--25 muM) were measured in WNB during the annual peaks in groundwater flow. Peak nitrate inputs were followed by mixed assemblage phytoplankton blooms that were succeeded by monospecific Brown Tides with densities >5 x 105 cells mL-1.; To evaluate the ability of nutrients to enhance Aureococcus growth during blooms, a series of nutrient enrichment experiments were conducted over the course of a two-month Brown Tide bloom at West Neck Bay (WNB), Long Island. The nutrient stimulating Brown Tide growth was a function of ambient nutrient levels, as the bloom shifted from organic carbon to N-limitation when nitrate levels in WNB decreased from elevated (2 to 20 muM) to low (0.5 muM) levels. Despite occasional growth enhancement by additions of nitrate or urea, these additions either had no effect or significantly decreased the relative abundance of Brown Tide among the algal community during experiments.; To evaluate the role of iron in the occurrence of Brown Tide blooms, we investigated its physicochemical speciation in the Peconic Estuary. Across the Brown Tide-prone, high salinity portion of the estuary, dissolved Fe varied from 9 to 240 nM, which is within the range (100 nM) reported to cause physiological Fe stress in this species. Iron speciation results indicated that dissolved Fe in the more saline portions of the Peconics was, on average, 87% organically complexed and 76% high molecular weight (HMW).; Since bloom densities of Aureococcus anophagefferens can repress benthic and pelagic grazing, viral lysis may be the primary removal mechanism for Brown Tide blooms on Long Island. A laboratory investigation was designed to understand the biogeochemical cycling of C, N, P, Fe and Se following the viral demise of Aureococcus blooms. (Abstract shortened by UMI.)