Biology subjects

Seitz, R. D.

Publications and source records attributed to Seitz, R. D..

3 recordsLinked to original sources

bioRxiv2017

Habitat complexity mediates benthic predator-prey interactions in Chesapeake Bay

In Chesapeake Bay, the soft-shell clam Mya arenaria (thin-shelled, deep-burrowing) exhibits population declines when predators are active and persists at low densities. In contrast, the hard clam Mercenaria mercenaria (thick-shelled, shallow-burrowing) has a stable population and age distribution. We examined the potential for habitat and predators to control densities and distributions of bivalves in a field caging experiment (Mya only) and laboratory mesocosm experiments (both species). In the field, clams exposed to predators experienced 76.3% greater mortality as compared to caged individuals, and blue crabs were likely responsible for most of the mortality of juvenile Mya. In mesocosm experiments, Mya had lower survival in sand and seagrass than in shell hash or oyster shell habitats. However, crabs often missed one or more prey in seagrass, shell, and oyster shell habitats. Predator search times and encounter rates declined when prey were at low densities, likely due to the added cost of inefficient foraging; however, this effect was more pronounced for Mya than for Mercenaria. Mercenaria had higher survival than Mya in mesocosm experiments, likely because predators feeding on Mercenaria spent less time foraging than those feeding on Mya. Mya may retain a low-density refuge from predation even with the loss of structurally complex habitats, though a loss of habitat refuge may result in clam densities that are not sustainable. A better understanding of density-dependent predator-prey interactions is necessary to prevent loss of food-web integrity and to conserve marine resources.

ecology↗

bioRxiv2017

Impacts of predators, habitat, recruitment, and disease on soft-shell clams Mya arenaria and stout razor clams Tagelus plebeius in Chesapeake Bay

Soft-shell clams, Mya arenaria, and razor clams, Tagelus plebeius, in Chesapeake Bay have declined since the 1970s, with severe declines since the 1990s. These declines are likely caused by multiple factors including warming, predation, habitat loss, recruitment limitation, disease, and harvesting. A bivalve survey in Chesapeake Bay examined influential factors on bivalve populations, focusing on predation (crabs, fish, and cownose rays), habitat (mud, sand, gravel, shell, or seagrass), environment (temperature, salinity, and dissolved oxygen), recruitment, and disease. M. arenaria and T. plebeius were found more often in habitats with complex physical structures (seagrass, shell) than any other habitat. Pulses in bivalve density associated with recruitment were attenuated through the summer and fall when predators are most active, indicating that predators likely influence temporal dynamics in these species. Presence of Mya arenaria, which is near the southern extent of its range in Chesapeake Bay, was negatively correlated with water temperature. Recruitment of M. arenaria in Rhode River, MD, declined between 1980 and 2016. Infection by the parasitic protist Perkinsus sp. was associated with stressful environmental conditions, bivalve size, and environmental preferences of Perkinsus sp, but was not associated with bivalve densities. It is likely that habitat loss, low recruitment, and predators are major factors keeping T. plebeius and M. arenaria at low densities in Chesapeake Bay. Persistence at low densities may be facilitated by habitat complexity (presence of physical structures), whereas further reductions in habitats such as seagrass and shell hash could result in local extinction of these important bivalve species.

ecology↗

bioRxiv2017

The perfect storm: Extreme weather drives and predation maintains phase shift in dominant Chesapeake Bay bivalve

A dynamic systems approach can predict steady states in predator-prey interactions, but there are very few empirical tests of predictions from predator-prey models. Here, we examine the empirical evidence for the low-density steady state predicted by a Lotka-Volterra model of a crab-clam predator-prey system using data from long-term monitoring, a field survey, and a field experiment. We show that Tropical Storm Agnes in 1972 likely resulted in a phase shift to a low-density state for the soft-shell clam Mya arenaria, which was once a biomass dominant in Chesapeake Bay. This storm altered predator-prey dynamics between M. arenaria and the blue crab Callinectes sapidus, shifting from a system controlled from the bottom-up by prey resources, to a system controlled from the top-down by predation pressure on bivalves. Predator-prey models with these two species alone were capable of reproducing observations of clam densities and mortality rates, consistent with the idea that C. sapidus are a major driver of M. arenaria population dynamics. Over 40 y post-storm, M. arenaria densities hover near a low-density steady state predicted from the predator-prey model. Relatively simple models can predict phase shifts and identify alternative stable states, as shown by agreement between model predictions and field data in this system. The preponderance of multispecies interactions exhibiting nonlinear dynamics indicates that this may be a general phenomenon.

ecology↗