Population Dynamics And Persistence Of An Invasive Species In Kelp Bed Ecosystems In The Northwest Atlantic Ocean

Abstract

The bryozoan Membranipora membranacea is an ecologically significant invasive species in the northwest Atlantic where it has facilitated substantial defoliation of kelp beds and dramatically altered rocky subtidal habitats. The main objectives of this thesis are to 1) identify life-history strategies and quantify critical demographic processes for M. membranacea in relation to physical and biological characteristics of its invaded habitat, and 2) incorporate this information into a population model to examine persistence and population growth in invaded habitats in response to near-future projections of ocean temperature and kelp bed community composition. Larvae of M. membranacea selectively settled within preferred regions of kelp blades, but did not exhibit preference for settling on specific kelp species or within kelp beds. Critical demographic processes were most strongly influenced by biological characteristics of the invaded habitat (algal substrate) or the colonies themselves (colony size). Rates of colony senescence increased with colony size and recovery capacity was related to the location of damage within the colony, while mortality rate varied with loss of kelp biomass and potential colony fecundity depended on the specific host algal substrate. In model simulations, increasing ocean temperature led to increased population growth of M. membranacea; however, temperature-dependent growth and persistence of the population depended on the species composition of invaded kelp bed communities. These results indicate that the persistence and abundance of this invasive bryozoan in the northwest Atlantic will depend on both the direct effects of climate change on its population dynamics, as well as indirect effects mediated though climate-driven changes to kelp bed ecosystems. The results provide evidence that impacts of climate change on ecosystem structure can influence invasion success, further complicating predictions of the ecological impact of invasive species under future climate conditions.