Multiple Stressors Make for Complex Impacts
Denley, D., A. Metaxas, and K. Fennel. 2019. Community composition influences the population growth and ecological impact of invasive species in response to climate change. Oecologia 189:537–548. PDF.
Summary
Climate change is having profound impacts on local and global biodiversity in the marine realm. Similarly, biological invasions are considered a major threat to marine biodiversity and introduced species often have broad tolerance to environmental conditions which may benefit them in the face of climate change. Denley et al. (2019) ask “How do these multiple stressors affect marine organisms?” They tested how the introduced bryozoan M. membranacea and invaded kelp communities are affected by increasing ocean temperatures along the shores of Nova Scotia. They found that increasing ocean temperature positively benefited population growth of M. membranacea under all future scenarios of increased temperature. In general, the direct negative impacts to kelp by M. membranacea include the weakening of kelp tissue, reduction in growth, and decrease in survival. Here, these impacts compounded ongoing population declines of kelp species (Saccharina latissima, Laminaria digitata, and Agarum clathratum) due to increasing ocean temperatures. Interestingly, stands with two or fewer kelp species present had lower population growth of the bryozoan compared to more diverse kelp stands. When kelp stands contain multiple species, there are multiple sources for M. membranacea larvae, ensuring near continuous larval supply and positive population growth. Although single-species kelp beds may reduce the overall abundance of M. membranacea, population growth is also maintained by colonization on other algal species on substrates such as jetties, aquaculture gear, and other anthropogenic structures. Thus, both M. membranacea invasion and ocean warming pose a significant threat to Atlantic kelp stands and associated communities.
Take home points
Climate change and introduced species together can have compounding effects on native species and communities.
The invasive bryozoan M. membranacea has greater population growth with increasing ocean temperature.
Kelp species are negatively affected by increasing ocean temperature as well as increasing populations of damaging, encrusting bryozoans such as M. membranacea.
Management implications
Limiting additional sources of propagules (jetties, buoys, aquaculture, other anthropogenic structures) can help reduce M. membranacea population growth.
Some actions to control on anthropogenic structures include scrubbing and cleaning fishing/aquaculture gear, docks, buoys; cleaning with water over 55°C (131°F); and air drying nets and other gear.
Modification of invaded habitat (i.e. changing the placement proximity of anthropogenic gear to kelp beds) can help reduce increased propagules of M. membranacea.
Keywords
Climate Extremes; Range Expansion; Changing Biotic Interactions; Invasive Marine Species; Population Dynamics; Northwest Atlantic