Title

Ocean Acidification Outweighs Nutrient Effects in Structuring Seagrass Epiphyte Communities

Authors

Justin E. Campbell, Smithsonian Marine StationFollow
James W. Fourqurean, Marine Science Program, Department of Biological Sciences and Southeast Environmental Research Center, Florida International UniversityFollow

Abstract

1. Developing a framework for assessing interactions between multiple anthropogenic stressors remains an important goal in environmental research. In coastal ecosystems, the relative effects of aspects of global climate change (e.g. CO₂ concentrations) and localized stressors (e.g. eutrophication), in combination, have received limited attention.
2. Using a long-term (11 month) field experiment, we examine how epiphyte assemblages in a tropical seagrass meadow respond to factorial manipulations of dissolved carbon dioxide (CO_2(aq)) and nutrient enrichment. In situ CO_2(aq) manipulations were conducted using clear, open-top chambers, which replicated carbonate parameter forecasts for the year 2100. Nutrient enrichment consisted of monthly additions of slow-release fertilizer, nitrogen (N) and phosphorus (P), to the sediments at rates equivalent to theoretical maximum rates of anthropogenic loading within the region (1.54 g N m⁻² d⁻¹ and 0.24 g P m⁻² d⁻¹).
3. Epiphyte community structure was assessed on a seasonal basis and revealed declines in the abundance of coralline algae, along with increases in filamentous algae under elevated CO_2(aq). Surprisingly, nutrient enrichment had no effect on epiphyte community structure or overall epiphyte loading. Interactions between CO_2(aq) and nutrient enrichment were not detected. Furthermore, CO_2(aq)-mediated responses in the epiphyte community displayed strong seasonality, suggesting that climate change studies in variable environments should be conducted over extended time-scales.
4. Synthesis. The observed responses indicate that for certain locations, global stressors such as ocean acidification may take precedence over local eutrophication in altering the community structure of seagrass epiphyte assemblages. Given that nutrient-driven algal overgrowth is commonly cited as a widespread cause of seagrass decline, our findings highlight that alternate climate change forces may exert proximate control over epiphyte community structure.

Comments

The definitive publisher-authenticated version is available online at http://dx.doi.org/10.1111/1365-2745.12233

This material is based upon work supported by the National Science Foundation through the Florida Coastal Everglades Long-Term Ecological Research program under Cooperative Agreements #DBI-0620409 and #DEB-9910514. Any opinions, findings, conclusions, or recommendations expressed in the material are those of the author(s) and do not necessarily reflect the views of the National Science Foundation.

Recommended Citation

Campbell, J.E., J.W. Fourqurean. 2014. Ocean acidification outweighs nutrient effects in structuring seagrass epiphyte communities. Journal of Ecology DOI: 10.1111/1365-2745.12233