Future ocean acidification and temperature rise alters community structure and diversity in marine benthic communities

Chair: Ken Caldeira

Rachel Hale (1)*, Martin Solan (1), Jasmin Godbold (1)

1 University of Southampton, Ocean and Earth Science, Waterfront Campus, National Oceanography Centre Southampton, SO14 3ZH

Background
Most studies of the synergistic effects of low pH hypercapnia and temperature increase have focused on individual species in isolation and few experiments investigate the effects of either on intact communities. Complex community dynamics and species interactions have the potential to ameliorate or enhance environmental stress related effects through competitive, predatory and positive or negative symbiotic relationships. Single species mesocosm experiments are therefore unlikely to provide results that will be realised in natural environments.

Methods
To determine the effects of the combined stressors of low pH hypercapnia and elevated temperature on the marine benthic habitat whole communities (macrofauna, meiofauna and microbial fauna) were incubated in the laboratory. After medium term exposure species were identified and enumerated to the lowest taxonomic level.

Findings
Communities showed significant changes in structure and diversity in response to the combined stressors of low pH hypercapnia and increased temperature. The calcifying groups molluscs, echinoderms, and copepods were the most vulnerable to the future conditions and many species were absent in the treatments exposed to the highest CO2 levels. Species shown to be vulnerable to low pH or high temperature in other single species based studies, such as nematodes, increased in abundance due to the relief of predation in low pH and high temperature treatments, however nematode species diversity decreased. We also observed a functional shift in the bacterial groups present with a large reduction in the abundance of both bacterial and archaeal ammonium oxidisers and nitrite reducers.

Conclusions
Species interactions observed within these community studies show the importance of considering both direct physiological and indirect ecological and behavioural effects that occur within multispecies assemblages when attempting to predict the consequences of ocean acidification and global warming on marine communities.