Science Inventory

Ocean acidification but not nutrient enrichment reduces grazing and alters diet preference in Littorina littorea

Citation:

Ober, G., C. Thornber, AND Jason S. Grear. Ocean acidification but not nutrient enrichment reduces grazing and alters diet preference in Littorina littorea. MARINE BIOLOGY. Springer, New York, NY, 169:Article 112, (2022). https://doi.org/10.1007/s00227-022-04099-8

Impact/Purpose:

It is well known that responses of aquatic life to ocean and coastal acidification are variable among species. This means that, although coastal ecosystems are likely to change in response to acidification, the characteristics of this change remain unpredictable. Much of the uncertainty comes from the lack of knowledge about how coastal acidification and its land-based drivers (i.e., nutrients) affect species interactions. This manuscript narrows some of this uncertainty and examines grazer control of macroalgae. These macroalgae are sometimes considered nuisance species by stakeholders but certain species are positively affected by acidification. Results show that some of this increased algal growth may be controlled or modified by the effects of acidification on grazers. This is an important consideration for efforts to predict and address effects of nutrient-enhanced coastal acidification on marine macroalgae.

Description:

Ocean acidification and eutrophication have direct, positive effects on the growth of many marine macroalgae, potentially resulting in macroalgal blooms and shifts in ecosystem structure and function. Enhanced growth of macroalgae, however, may be controlled by the presence of grazers. While grazing under ocean acidification and eutrophication conditions has variable responses, there is evidence of these factors indirectly increasing consumption. We tested whether a common marine herbivorous snail, Littorina littorea, would increase consumption rates of macroalgae (Ulva and Fucus) under ocean acidification (increased pCO2) and/or eutrophication conditions, via feeding trials on live and reconstituted algal thalli. We found that increased pCO2 resulted in reduced grazing rates on live thalli, with snails feeding almost exclusively on Ulva. However, eutrophication did not impact consumption rates of live tissues. In addition, similarity in consumption of reconstituted Ulva and Fucus tissues across all treatments indicated that physical characteristics of algal tissues, rather than tissue chemistry, may drive dietary shifts in a changing climate. In this system, decreased consumption, coupled with increased growth of macroalgae, may ultimately enhance algal growth and spread.