Non-indigenous species are one of the main threats to biodiversity in the world’s oceans, and their impacts are intensifying as a result of climate change. Membranipora membranacea, an invasive epiphytic bryozoan, has been causing damage to ecologically important kelp beds in the northwest Atlantic since its introduction to the area in the late 1980s. Although temperature is considered the main determinant of the abundance of M. membranacea, wave exposure and kelp substrate characteristics (abundance and species composition) may also play significant roles. Most previous research has been conducted at a small number of sites within a limited geographic range, and no study has investigated the relative impacts of these variables on bryozoan abundance. We created a large dataset of data on the abundance of M. membranacea and its predictors by compiling existing data and collecting data from previously unsurveyed sites. We used generalized linear mixed models to investigate the relative impacts of temperature (thermal integral), wave exposure (wind-based relative exposure index), and kelp bed characteristics (species, density, percent cover) on regional patterns in the abundance of M. membranacea (settlers and adult colonies) in the northwest Atlantic.
Results/Conclusions
Preliminary results showed a positive correlation between thermal integral and the abundance of both settlers and adult colonies of M. membranacea. This result is consistent the findings of with past studies and is likely due to the positive effect of temperature on fecundity and colony growth. Contrary to the results of past research, a significant negative relationship was found between wave exposure and the abundance of settlers and adult colonies of M. membranacea; however, in both cases, the effect size of exposure was an order of magnitude lower than the effect of temperature. High wave action may be detrimental to larval attachment to kelp during settlement and to feeding in adult colonies. No significant relationships were found between kelp substrate characteristics and the abundance of the bryozoan. The implications of our preliminary results are that the abundance of M. membranacea is controlled by both temperature and, to a lesser extent, wave exposure, with colder and more exposed areas supporting lower abundances of the bryozoan. Therefore, the bryzoan’s damage to kelp beds can be predicted to be less severe such areas. This knowledge will facilitate the conservation of kelp bed ecosystems by informing marine spatial planning and will also be applicable to management in the kelp aquaculture industry.