The impact of oyster aquaculture on the estuarine carbonate system

Abstract

Many studies have examined the vulnerability of calcifying organisms, such as the eastern oyster (Crassostrea virginica), to externally forced ocean acidification, but the opposite interaction whereby oysters alter their local carbonate conditions has received far less attention. We present an exploratory model for isolating the impact that net calcification and respiration of aquacultured eastern oysters can have on calcite and aragonite saturation states, in the context of varying temperature, ocean-estuary mixing, and air-sea gas exchange. We apply the model to the Damariscotta River Estuary in Maine which has experienced rapid expansion of oyster aquaculture in the last decade. Our model uses oyster shell growth over the summer season and a previously derived relationship between net calcification and respiration to quantify impacts of net oyster calcification and gross metabolism on carbonate saturation states in open tidal waters. Under 2018 industry size and climate conditions, we estimate that oysters can lower carbonate saturation states by up to 5% (i.e., 0.17 and 0.11 units on calcite and aragonite saturation states, respectively) per day in late summer, with an average of 3% over the growing season. Perturbations from temperature and air-sea exchange are similar in magnitude. Under 2050 climate conditions and 2018 industry size, calcite saturation state will decrease by up to an additional 0.54 units. If the industry expands 3-fold by 2050, the calcite and aragonite saturation states may decrease by 0.73 and 0.47 units, respectively, on average for the latter half of the growing season when compared to 2018 climate conditions and industry size. Collectively, our results indicate that dense aggregations of oysters can have a significant role on estuarine carbonate chemistry.

Oyster Aquaculture Site Selection Using High-Resolution Remote Sensing: A Case Study in the Gulf of Maine, United States

“…Hillyer et al (2021) also recently calculated residence times for the Medomak River estuary on the order of days. Conversely, the mouths of these same estuaries tend to have residence times on the order of one to two tidal cycles (Liberti et al, 2021). Clearly, our transects reflect the spatial change in residence time of these long narrow estuarine systems where bottom and side friction retains water and particulates at the upper end of the estuaries and flushes relatively rapidly at the mouth.…”

“…There are relatively few published estimates of residence time for these systems; however, it has been examined in some of the study estuaries. Geomorphological features in the upper Damariscotta result in long residence times (>7 days, Liberti et al, 2021). Hillyer et al (2021) also recently calculated residence times for the Medomak River estuary on the order of days.…”

“…Although these estuaries are similar in freshwater input, they vary in geomorphology, existing aquaculture intensity, and catchment basin characteristics. Due to a large tidal range (>2 m) and narrow shape, the residence time of these estuaries is on the order of multiple days in the upper estuary and roughly two tidal cycles closer to the mouths of the systems (Hillyer et al, 2021;Liberti et al, 2021).…”