ScholarWorks@UNO

Effects of ocean warming and acidification on the rates of suspension feeding for two reef invertebrates in the northern Gulf of Mexico

Ocean acidification and warming often have species-specific consequences on organismal behavior and physiology that in turn can scale to influence ecosystem processes. Suspension-feeding invertebrates couple benthic and pelagic processes and are prominent taxa at artificial reefs throughout the northern Gulf of Mexico (nGoM) - a region where effects of global ocean change are relatively understudied. Our purpose was to evaluate whether predicted ocean changes will impact the feeding rates of two suspension-feeding invertebrates abundant on nGoM reefs, the Leafy jewel box clam (Chama macerophylla) and Titan acorn barnacle (Megabalanus coccopoma). In a laboratory mesocosm, organisms were exposed to single- and multi-stressor treatments. Treatments mimicked current conditions as well as modest and extreme scenarios of warming and acidification predicted for the end of the 21st century. Feeding rates were measured within isolated chambers. Organisms were fed algae and the remaining algae were assessed at set time intervals (5, 20, 40, and 80 minutes) using images slides, analyzed with image-J. Bivalve feeding appeared unaffected yet, barnacles kept at the more extreme acidification scenario (corresponding to pHT of 7.5) had significantly increased feeding rates (p < 0.001) compared to other conditions(pHT of 8.1 and 7.8). This effect, however, was not observed in multi-stressor treatments. Therefore, barnacles may only be able to compensate for moderate stress by taking up more energy. This interpretation is consistent with survivorship measured in the same study and is concerning given suspension feeders improve water clarity and serve to transfer primary productivity from the water column into secondary fish production.