The Response of Marine Fouling Communities and Introduced Species to Increased Water Temperature

Evidence from terrestrial ecosystems suggests that invasive species may have larger latitudinal ranges than native species. This may indicate an ability of invasives to tolerate a broader range of environmental conditions and, as a result, have higher potentials for success with the advent of global warming (Sorte et al. 2010). Previous studies have shown that there is strong evidence that climate change will affect marine species, but responses of marine invaders relative to native species are still largely unknown. In order to test these questions the fouling community of Bodega Harbor, Bodega Bay, California was studied using laboratory mesocosms. Fouling communities colonize human-made structures such as ships, mariculture farms, and seawater pipelines, and are great models for community assembly studies because they can be dominated by nonnative species. The scientists performed two experiments to measure the effects of warmer temperatures on introduced species. First, a temperature tolerance experiment was conducted to address the hypothesis that introduced species are more tolerant than native species to high temperatures. The second experiment measured the survival and growth rate of different native and nonnative species at current and future predicted temperatures. Results showed that responses differed between species, species origins, and demographic processes, which suggest that native species will decrease in abundance, while the abundance of introduced species is likely to increase. Essentially, the effects of climate change will impact both the diversity and abundance of native species, as well as increase the dominance of introduced species. — Patricio Ku
Sorte, C., Williams, S., Zerebecki, R., 2010. Ocean warming increases threat of invasive species in a marine fouling community. Ecology 91, 2198–2204.

Sorte and her team of scientists performed all of their field collections from a floating dock at Spud Point Marina in Bodega Harbor, California. In the first experiment, 10 fouling species (four natives and six invasives) were settled on plastic tiles suspended below the surface in the harbor. After colonization had occurred the tiles were moved to a laboratory where the ambient temperature (12°C) was raised by 1°C every 15 minutes until the treatment temperature was reached. After 24 hours of exposure, individuals were determined to be alive or dead based on the presence of movement after two days of recovery at ambient temperature. For the second experiment, fouling species were collected on PVC plastic plates and then randomly assigned to tanks with different treatment temperatures. The survival and growth on each of the plates was measured after five weeks at which point the experiment was repeated.
The first experiment showed that introduced species were more tolerant of higher temperatures than native species. For the six nonnative species, survival was unrelated to temperature. One of the nonnative species (Watersipora) had a survival rate of almost 100%, while some of the native species (Distaplia) had survival rates of only 2%. The second experiment supported the hypothesis that growth was strongly influenced by temperature with five of the seven species showing responses to warmer temperatures. Out of the five species that showed a response to temperature increase, three of them were introduced and two were native, of which the native Distaplia is predicted to decrease in abundance. The nonnative species, Didemnum, Botrylloides, and Bugula neritina, are predicted to increase 4%, 5%, and 19% respectively. In all, the results suggest that introduced species are likely to become more abundant due their higher survival rate and because of their greater increase in growth relative to native species. Potential changes due to different species distribution may include changes in filtering rates, water clarity, fish species abundances and diversity, and competition with farmed shellfish. These kinds of effects demonstrate the need to begin increasing fouling control practices against two types of climate change effects, direct impacts on native species and also indirect effects that come from the increased dominance of introduced species.

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