Does flow speed also have a direct effect on growth of active suspension‐feeders: An experimental test on oysters

Abstract

The direct effects of flow velocity on growth of juvenile American oysters Crassostrea virginica (Gmelin) were tested without confounding by indirect effects of vertical mixing by measuring growth inside pipes, varying average flow over five levels (0, 0.5, 2.5, 4, and 7 cm s‒1) at each of two food concentrations. Growth increased with food concentration and increased monotonically with flow velocity over all flows tested for both food treatments. In this experiment, food concentration and flow velocity acted independently in their effects on growth, with a multiplicative term (flux) not making any significant contribution beyond the independent, additive contributions of food and flow. Thus, the apparent positive response of growth in this active suspension‐feeder to external flux of food is best interpreted as a coincidental by‐product of the action of two separate responses to the terms that comprise flux.

The influence of multiple environmental stressors on susceptibility to parasites: An experimental determination with oysters

“…Temperature, salinity, and dissolved oxygen concentration are abiotic factors that most profoundly influence the development, feeding, growth, reproduction, and survival of oysters (Shumway 1996) because they control their physiological condition. When parasitic infection is absent, growth rate, physiological condition, and survival of oysters increase with flow speed (Lenihan et al 1996) and salinity (Shumway 1996) and decrease with sedimentation and burial (Ali 1981).…”

“…In addition, when harvest-degraded reefs are located in deep water subject to density stratification and bottom water hypoxia-anoxia, exposure to low oxygen stress increases in frequency and duration. Oysters exposed to the combined effect of low flow speed (and associated high sediment deposition) and prolonged hypoxia on harvest-degraded reefs suffer poorer growth, physiological condition, and survival (Lenihan 1999). Thus, the structure and location of oysters reefs may control exposure to environmental stressors with subsequent effects on the prevalence and intensity of Perkinsus infection in oysters.…”

“…In turn, these environmental factors influence the recruitment, growth, physiological condition, and survival of oysters (Lenihan and Peterson 1998;Lenihan 1999). Experiments with restored oyster reef habitat show that destructive harvesting practices reduce the height of reefs by removing not only oysters, but the shell matrix on which oysters are attached (Lenihan and Peterson 1998). The reduction in reef height causes local flow speed to decrease and rates of sedimentation and reef burial to increase (Lenihan 1999).…”

“…Experiments with restored oyster reef habitat show that destructive harvesting practices reduce the height of reefs by removing not only oysters, but the shell matrix on which oysters are attached (Lenihan and Peterson 1998). The reduction in reef height causes local flow speed to decrease and rates of sedimentation and reef burial to increase (Lenihan 1999). In addition, when harvest-degraded reefs are located in deep water subject to density stratification and bottom water hypoxia-anoxia, exposure to low oxygen stress increases in frequency and duration.…”

“…The physical structure and location of oyster reefs regulate environmental conditions for oysters, including flow speed, sediment deposition and accumulation, and exposure to hydrographic conditions, including temperature, salinity, and dissolved oxygen concentrations. In turn, these environmental factors influence the recruitment, growth, physiological condition, and survival of oysters (Lenihan and Peterson 1998;Lenihan 1999). Experiments with restored oyster reef habitat show that destructive harvesting practices reduce the height of reefs by removing not only oysters, but the shell matrix on which oysters are attached (Lenihan and Peterson 1998).…”