Seawater temperature mediates biological erosion by a non-native burrowing crustacean

Background/Question/Methods

Increases in water temperature associated with global climate change are predicted to elicit drastic changes to marine and freshwater ecosystems. Even small changes in water temperature (1-2°C) may alter the rate of biological activity, particularly in poikilotherms, with concomitant effects to communities and ecosystems. The biological erosion of substrata (hereafter: bioerosion) is a rarely considered, yet important biological activity that is likely to be influenced by changing water temperatures. Changes to bioerosion and boring amounts can alter the physical structure of marine habitats (hence communities and ecosystems) and damage human-made structures. We conducted an experiment to test how different seawater temperatures affect the burrowing of a non-native isopod crustacean (Sphaeroma quoianum). Closed aerated saltwater aquaria were maintained at one of thirteen different temperatures (7.5°C-25.2°C) using aquarium chillers and heaters. In each aquarium, twenty isopods were encaged with an expanded polystyrene foam block (800ml) and left to burrow.  Polystyrene foam, used as floats under docks, is often damaged by isopods in the field.

Results/Conclusions

After two months, isopods created the longest burrows in the moderate seawater temperatures (13.8°C-18.3°C) with lower burrow lengths observed for the coldest (7.5°C) and warmest seawater treatments (25.2°C). Bioerosive impact, measured as the total length and volume of burrows created, exhibited convex parabolic relationships across temperature. Millions of plastic particles can be created during the boring process on polystyrene floats; the number of particles created exhibited the same relationship as the bioerosive impact. These results indicate that increasing seawater temperatures can exacerbate the bioerosive impacts and plastic pollution caused by a non-native crustacean until a threshold, after which the impacts diminish. Given ocean temperatures are predicted to raise 1-2°C in the next 90 years, our data suggest that the impacts of this non-native crustacean will increase 5.1-17.1% in some cold central California and Oregon bays where mean water temperatures presently range from 12.7 to 16.4°C. We hypothesize the bioerosion and boring rates of other species will also increase with rising water temperatures with numerous implications for marine and aquatic habitats and human-made structures.