Jean-Sebastien Lauzon-Guay

Importance of Spatial Population Characteristics on the Fertilization Rates of Sea Urchins

We show that inclusion of population characteristics in coupled advection-diffusion and fertilization-kinetics models results in higher fertilization rates than those previously reported in theoretical studies. We incorporate parameters related to both individuals and populations by running simulations over a large spatial scale and incorporating sperm contribution from multiple males. We compare predictions for three subpopulations of the sea urchin Strongylocentrotus droebachiensis (those occupying kelp beds, barrens, and grazing fronts) to observations from small-scale experiments, and estimate effects of population size and current velocity in each subpopulation. Model outputs suggest that fertilization rates are low in kelp beds, intermediate in barrens, and high in grazing fronts. In all populations, increasing current velocity has a negative effect on the relationship between fertilization rate and downstream distance of gametes after release, but no effect on the relationship between fertilization rate and elapsed time since gamete release. Our model output was most sensitive to changes in the number of spawning males and the sperm release rate, suggesting that spawning synchrony and high gonadic index could greatly increase the fertilization success in sea urchins.

FORMATION AND PROPAGATION OF FEEDING FRONTS IN BENTHIC MARINE INVERTEBRATES: A MODELING APPROACH

Feeding fronts are a striking pattern of spatial distribution observed in both marine and terrestrial ecological systems. These fronts not only determine the abundance and distribution of prey populations, but on a broader scale they may also affect the structure and dynamics of entire communities. Several mechanisms leading to the formation of feeding fronts have been proposed, and chemotaxis has been suggested as an important component. Here we develop two mathematical models that show front formation can occur with simple kinesis (and without chemotaxis) in two marine invertebrates with different feeding habits: a microphagous sea star (Oreaster reticulatus) that feeds on sediments and an herbivorous sea urchin (Strongylocentrotus droebachiensis) that grazes kelp beds. We utilize a large body of detailed empirical information on movement pattern, foraging behavior, and front dynamics for each species to develop, parameterize, and evaluate our models. We found that our model predictions for the rate of advance of a front and its relationship to the density of consumers at the front were in close agreement with independently collected, empirical observations in both systems. This work shows that simple local interactions between mobile consumers and a stationary resource can result in large-scale heterogeneous patterns of abundance of both species.

FOOD DEPENDENT MOVEMENT OF PERIWINKLES (LITTORINA LITTOREA) ASSOCIATED WITH FEEDING FRONTS

ABSTRACT Consumer aggregations have the potential to drastically change the distribution and availability of resources. One form of aggregation observed in marine benthic invertebrates is the feeding front: a dense band of consumers that travels in a directional manner through a food patch, leaving a cleared area behind it. By artificially creating spatial heterogeneity in the distribution of a filamentous green alga, the formation of a feeding front of periwinkles Littorina littorea was induced on a rocky intertidal shore. The position of the front, the density of snails that comprised it, and the movement of individual snails in and around the front were monitored over a period of 14 days. During that period, the front advanced at an average speed of 2.25 cm d-1 and the density of snails in the front varied between 10 and 24 snails 100 cm-2. Temporal variation in snail density was negatively correlated with wave action. Snails on the trailing edge of the front or on bare rock behind the front exhibited directional movement towards the front, but snails in the front moved shorter distances than those on bare rock. These results support previous findings of resource-dependent movement as a causal mechanism of front formation in marine benthic habitats.

Protective socking material for cultivated mussels: a potential non-disruptive deterrent to reduce losses to diving ducks

Predation of cultivated mussels by diving ducks can threaten the viability of mussel farms. Conventional scaring tactics have had limited success at deterring ducks from feeding on cultivated mussels, because of rapid habituation and 24-h feeding cycles of some waterfowl species. We tested a socking material containing a biodegradable protective layer against predation by diving ducks on experimental blue mussel (Mytilus edulis) aquaculture sites in Prince Edward Island, Canada. We also assessed the effect of this new socking material on mussel growth and survival. Results showed that the protective socking has the potential to reduce losses to ducks, but did not perform well for all mussel seed sizes used by the industry. The protective layer also did not biodegrade fast enough, trapping a portion of mussels inside the sock, affecting growth and survival of these mussels. Improvements are needed to make this solution effective for all mussel sizes used by the industry and to make its production more cost effective.