Local Scale Gradients

Coastal oceanography and resource gradients for oysters in CA

Upwelling along coastlines has the dual effect of increasing nutrients and phytoplankton production, while also decreasing temperature and advecting phytoplankton offshore. For filter-feeding invertebrates along open coastlines (such as oysters), the advection of food and low temperatures associated with high upwelling are thought to lower growth and metabolic rates. I worked with Dr. Largier and Dr. Grosholz in California to test the effects of upwelling on Olympia oyster growth in a tidal estuary (Tomales Bay), to see if this generalization applies in estuarine environments. We demonstrated that a gradient in tidal-exchange along the length of this estuary interacts with intense upwelling to create inversely related spatial gradients. Water at the mouth of the bay had the lowest residence time and lowest temperature, but the highest concentration of upwelled nutrients. Water at the head of the bay had the highest residence time and highest temperature, but the lowest concentration of upwelled nutrients. As a result, seasonal phytoplankton blooms tended to occur in the middle of the bay, where conditions were optimal for their growth and retention. Furthermore, we found that the growth and size of oysters was highest in the middle of the bay – the location of the phytoplankton maximum. Because of the physical processes occuring within low-inflow estuaries, high phytoplankton levels (and high bivalve growth) may be obtained even under intense upwelling conditions.

Kimbro, D. L., J. Largier, and E. D. Grosholz. 2009. Coastal oceanographic processes influence the growth and size of a key estuarine species, the Olympia oyster. Limnology and Oceanography 54(5): 1425-1437.

Tomales Bay, CA

David sampling water column in Tomales Bay, CA

Effect of multiple parasites in the Gulf of Mexico

As oyster populations decline globally, it’s important to understand how parasites may affect these ecologically important and economically valuable species across the dominant environmental gradients of estuaries. While it is common to study the effects of one parasite on one host, it’s rare to find a host infected with only a single parasite. In this study, Hanley et al. looked at patterns of parasite species diversity across the two main environmental gradients of an estuary in the northern Gulf of Mexico, a region that has experienced dramatic decreases in oyster populations, with devastating impacts on the oyster fishery. Hanley et al. sampled oyster reefs at distances close to and far from the river input (freshwater) in order to sample parasites across a salinity gradient. In addition, Hanley et al. sampled oyster reefs that are always submerged by water and reefs that are periodically submerged by water and exposed to the air (intertidal reefs). They found that almost 70% of oysters were infected with multiple parasites. While the diversity of parasites did not vary across each of the environmental gradients, parasite identity did. In addition, a variety of different environmental (salinity, tidal height) and biotic (host density and size) factors best predicted the prevalence of each parasite species. Consequently, predicting disease outbreaks and long-term health of oyster populations requires consideration of multiple environmental contexts and multiple parasites.

Photos of oyster shells damaged by two different parasites: mud blister worms (left) and boring sponge (right).

Hanley, T.C., J.W. White, C.D. Stallings, D.L. Kimbro. 2019. Environmental gradients shape the combined effects of multiple parasites on oyster hosts in the northern Gulf of Mexico. Marine Ecology Progress Series 612, 111-125.