Our lab has documented a decades-long decline in cover and biomass of
canopy-forming kelps on the Atlantic coast of Nova Scotia. My research
aims at identifying feedbacks and reinforcing process that maintain or elicit
further loss of kelp in favour of turf-forming assemblages that dominate the
seabed in its place. My interests are on mechanisms acting throughout the
life cycle of kelp from the changing role of grazers of the macroscopic stage,
to limits on propagule supply, settlement, and recruitment, to the sources of
mortality of new recruits in recovering kelp beds.
My research has demonstrated that severe thinning of kelp beds due to
large regional disturbances (e.g. hurricanes, the invasive bryozoan
Membranipora membranacea) leads to the disproportionate concentration of
abundant molluscan grazers (Lacuna vincta) and subsequent grazing damage
on remaining individuals. This is expected to augment indirect losses of
kelp biomass through increased blade erosion and fragmentation.
Most recently, I have identified further consequences of heightened grazing owing to a strong feeding preference of L. vincta for spore-producing tissue. This results in extensive grazing of the dark brown, spore-bearing patches (sori) that develop on kelp blades in the fall. Effects of spore supply limitation on recruitment will likely be strongly felt in recovering kelp populations.
O’Brien JM, Scheibling RE, Krumhansl KA In press. Positive feedback between large-scale disturbance and density-dependent grazing decreases resilience of a kelp-bed ecosystem. Mar Ecol Prog Ser [MEPS “Feature Article”]. pdf
O’Brien JM, Krumhansl KA, Scheibling RE 2013. Invasive bryozoan alters interaction between a native grazer and its algal food. J Mar Biol Ass UK 93: 1392-100. pdf