Impacts of Elevated CO2 and Nutrients on Marine Communities and Trophic Interactions

EPA Grant Number: F13B20383
Title: Impacts of Elevated CO2 and Nutrients on Marine Communities and Trophic Interactions
Investigators: Ober, Gordon Talbot
Institution: University of Rhode Island
EPA Project Officer: Lee, Sonja
Project Period: September 3, 2014 through September 3, 2016
Project Amount: $84,000
RFA: STAR Graduate Fellowships (2013) RFA Text |  Recipients Lists
Research Category: Academic Fellowships , Fellowship - Ecology and Ecosystems


Increases in atmospheric carbon dioxide (CO2) are directly linked to decreasing oceanic pH. More acidic oceans are detrimental to calcifying organisms like corals and shellfish, but for primary producers like algae, CO2 is necessary for photosynthesis. As the base of many coastal marine food webs, algae support diverse and productive communities. Impact
at this level of the food web will likely ripple outward and affect many other species. This research aims to determine how ocean acidification, or increased CO2, in conjunction with increased nutrients, is affecting algae and the species they support. This project takes an ecosystem approach to understanding the impact of climate change, investigating how multiple species at multiple trophic levels are responding to change and how their interactions are changing.


This project focuses on coastal communities found in Narragansett Bay, Rhode Island. In a series of laboratory-based mesocosm experiments
two local species of algae (Gracilaria verimuculophylla, an invasive red alga, and Ulva rigida, a native green alga) are exposed to increased CO2, simulating acidification, and increased nutrients. By measuring growth, tissue quality and productivity the experiments will determine the fitness of both species and their competitive ability. Experiments will be run multiple times using different levels of CO2, based on Intergovernmental Panel on Climate Change projections, to determine the range of responses. In subsequent experiments a common, herbivorous marine snail and omnivorous crab will be added to experimental mesocosms along with the algae. Snail feeding rates, feeding preferences and overall changes in behavior will be monitored over the course of the experiment. Performing experiments using multiple trophic levels will provide insight to how communities will be shaped and will function under future climate conditions.

Expected Results:

Projected ocean acidification will be detrimental to the fitness of calcifying organisms, such as coral and shellfish, but non-calcifying algae should reap the benefits of increased CO2 by maximizing photosynthetic activity. Different algal species will respond differently to increases in CO2, however, due to differences in life history and the presence or absence of a carbon-concentrating mechanism. Both species of algae are expected to see increases in growth, tissue quality and productivity under treatment conditions, but G. vermiculophylla will likely see significantly greater increases due to its ability to access CO2 from the water column. When environmental stressors are combined an addi- tive, if not synergistic, effect is expected on the growth of both species of algae. Due to stress from acidification, herbivores will feed less frequently on algae but their feeding preference will shift from U. rigida to G. vermiculophylla. Herbivores are expected to be more likely to flee under acidification stress and the presence of a predator, therefore further aiding the growth of algae by removing consumer pressure. Communities will see shifts in dominant algal species and reduced effects from herbivores, ultimately leading to less diverse and less productive ecosystems.

Potential to Further Environmental/Human Health Protection

Coastal zones are of great economic importance. Keeping these ecosystems diverse and functioning will be challenged by anthropogenic climate change. Many algal species are expected to thrive under future climate conditions, blooming more frequently and replacing calcifying organisms and leading to oxygen-poor waters, hypoxic events and even fish kills. These blooms are detrimental not only to ecosystem health, but also to local economies. Understanding the response of species within a community is key in understanding how ecosystems will function in the future.

Supplemental Keywords:

algal blooms, community ecology, ocean acidification

Progress and Final Reports:

  • 2015
  • Final