Effect of the northern quahog Mercenaria mercenaria on the development of blooms of the brown tide alga Aureococcus anophagefferens

Abstract

Three experiments were carried out in 300 l mesocosms using natural seawater from the Peconic Bays ecosystem, Long Island, New York, to examine the ability of the northern quahog Mercenaria mercenaria to prevent blooms of the brown tide alga Aureococcus anophagefferens. Nutrient enrichment and mixing of the mesocosms was conducted according to previous methods that we have employed to induce brown tides. Treatments with and without clams were examined. Abundances of A. anophagefferens increased dramatically during 8 to 9 d experiments in mesocosms without bivalves (average peak abundances > 600 000 cells ml -1). The brown tide alga constituted > 50% of the total phytoplankton biomass in these mesocosms by the end of the experiment. In contrast, algae in mesocosms with high abundances of clams did not develop brown tides and A. anophagefferens abundances in these mesocosms were 2 orders of magnitude lower. Bivalves not only prevented a buildup of total phytoplankton biomass but also prevented the shift in phytoplankton species composition to dominance by A. anophagefferens observed in treatments without clams. Experiments to test the efficacy of different abundances of clams for preventing blooms of A. anophagefferens demonstrated that population clearance rates by clams of approximately 40% of the mesocosm volume d -1 were sufficient to prevent the buildup of phytoplankton biomass and net population growth of the brown tide alga under the environmental conditions and nutrient enrichment that we employed. This turnover rate by suspension-feeding bivalves is similar to the same magnitude of bivalve filtration pressure estimated for Great South Bay, Long Island more than 2 decades ago, prior to the outbreak of brown tides. We conclude that the feeding activities of northern quahogs in shallow bays can exert considerable control on total phytoplankton biomass in the overlying water column, and specifically on the ability of A. anophagefferens to dominate the phytoplankton assemblage and form brown tides.

Resource-restricted growth of eelgrass in New York estuaries: light limitation, and alleviation of nutrient stress by hard clams

“…2). There was no correlation between the presence of hard clams and sediment characteristics, perhaps due to low overall abundances of hard clams, which were a fraction of those found in this system decades ago (Cerrato et al 2004). Sediment characteristics within the eelgrass beds were significantly different from those outside.…”

“…One individual (~5 cm valve length) was added to the center of each plot. This yielded a clam density of 16 m -2 , which is higher than current clam densities in LISSE, but considerably lower than historical densities (Cerrato et al 2004). Another 10 plots were randomly assigned to the fertilized treat-ments and received a single Miracle-Gro ® Tree & Shrub Fertilizer spike to the center.…”

“…Eelgrass coverage decreased dramatically during the late 1980s with the annual occurrence of algal blooms, which decreased light levels reaching eelgrass beds (Dennison et al 1989). Since that time, levels of suspended algal biomass have remained high (Suffolk County Department of Health Services, SCDHS 1976-2005, likely due in part to the low current abundances of hard clams and other filter feeders (Cerrato et al 2004). As such, the majority of eelgrass beds in LISSE currently subsist under subsaturating light (Cosper et al 1987).…”

Effects of Coverage by Benthic Seaweed Mats on (Northern Quahog = Hard Clam) Mercenaria Mercenaria in a Eutrophic Estuary

“…Mesocosm experiments have shown that filtration of A. anophagefferens cells at low densities by hard clams may prevent the development of brown tide outbreaks (Cerrato et al, 2004), which reduce eelgrass production via light attenuation. Nutrient enrichment of sediments by bivalve biodeposits can facilitate eelgrass productivity, given that Z. marina absorb most of their nutrients from sediments via their roots rather than from the water column (Peterson and Heck, 1999).…”

Responses of loggerhead sponges Spechiospongia vesparium during harmful cyanobacterial blooms in a sub-tropical lagoon

“…Many of these algal blooms can be linked to eutrophication (Anderson et al 2008, Heisler et al 2008 or loss of benthic filtration (Newell 1988, Lotze et al 2006. Benthic suspension feeders can filter the water column quickly enough to suppress blooms of phytoplankton in some systems (Officer et al 1982, Cerrato et al 2004, Wall et al 2008, and such top-down control should be more prevalent in ecosystems that are shallow and have a high density of consumers (Smaal & Prins 1993, Heck & Valentine 2007, such as shallow coastal lagoons. Since coastal lagoon systems often have extended physical turnover times, which makes them more vulnerable to harmful micro-algal blooms (Cloern 2001), the loss of benthic suspension feeders from such a system likely represents a more significant loss of top-down control than for deeper, well-flushed ecosystems.…”