Because species mediate key biogeochemical processes and play unique ecological roles, changes in the diversity and composition of species in an ecosystem can alter how that system functions. A growing body of work has demonstrated that changes in biodiversity can have profound effects on the functioning of marine ecosystems. However, key unresolved issues remain with respect to relationships between marine biodiversity and ecosystem functioning. In particular, few studies have evaluated interactions between producer diversity and herbivore diversity, especially in the field. Furthermore, the vast majority of experiments have evaluated the consequences of biodiversity changes at only one location, so there is very little knowledge of how diversity-function relationships are modified by environmental context. This study will examine, in the field, how environmental context shapes marine diversity-function relationships and particularly the interaction between changes in consumer and producer diversity in intertidal ecosystems at three sites spanning 500 km of the New England coastline. These factorial experiments will manipulate seaweed and grazer diversity at East Point, Massachusetts; Chamberlain Point, Maine; and Quoddy Head, Maine. The research asks the following questions: 1) How does seaweed diversity influence key marine ecosystem processes such as primary and secondary productivity? 2) How does herbivore diversity affect the top-down impacts of molluscan grazers on intertidal seaweed assemblages? 3) What are the feedbacks between grazer and seaweed diversity in driving intertidal community and ecosystem structure and function? And 4) How does environmental context modify the top-down and bottom-up effects of biodiversity change on intertidal ecosystem functioning?
This study will make important intellectual contributions to marine ecology by considering feedbacks between diversity change at two adjacent trophic levels. The work will be conducted at multiple sites which span a range of nearshore oceanographic and climatic conditions, enhancing the generality of the work and allowing for evaluation of the effects of environmental context on diversity-function relationships. Biodiversity is changing at all scales, from local to global, and it is essential to understand the consequences of these changes in order to better predict and ameliorate their impacts on communities and ecosystems. This research will provide a more holistic understanding of the links between diversity, trophic interactions and ecosystem function that will facilitate more effective conservation and management strategies in marine, as well as other, ecosystems. It will provide training and research experience for students at all educational levels. The investigators will involve graduate and undergraduate students in all phases of the research and will also offer a summer research internship each year to a high school student from the Coastal Ocean Science Academy (COSA) that is taught by the Northeastern University Marine Science Center's Outreach staff. COSA students are primarily from under-represented groups in the greater Boston area. Finally, the results of the research will be communicated to the public through the outreach and public education program at the Center.
Biodiversity - the number and variety of life - is changing at both local and global scales, primarily due to human activities such as habitat destruction (on land) and overfishing (in the ocean). Because species provide important goods, services, and functions for us and every other organism on earth, it is critical to understand how these changes in biodiversity will affect how natural systems work. In our research, we addressed that issue, using an easily manipulated group of organisms on New England rocky shorelines. In particular, we were interested in how the effects of biodiversity loss on the system would change depending on the location in which we conducted the work. We therefore set up three identical experiments on three different beaches in each of three regions stretching from Boston, Massachusetts, north to the border between Maine and Canada. This gave us a total of 9 separate - but identically set up - experiments spanning ~300 miles of coastline and an average temperature difference of 10 deg F. Each location was characterized by the same seaweed species growing on the rocks, and we tested how removing seaweed species affected overall seaweed growth. We found that higher seaweed diversity was associated with higher seaweed growth, but only in one of the three regions that we studied. Interestingly, these strong effects of biodiversity occurred in the middle of the gradient, and we also found that seaweeds grow the best there. We think that this location - not too warm, not too cold, but just right - is the ideal location for growth and productivity of seaweeds on the coast. As part of this work we conducted a second experiment to evaluate how the loss of rare species affects organisms higher on the food chain. We surveyed locations on the beach and found that a few species - a mussel, a barnacle, and a rockweed - made up the vast majority of "stuff" growing on the beach. All of the other species represented less than 10% of the growth. We removed these "rare" species and found that their loss resulted in a 40-50% decline in the abundance of animals like snails and crabs. Remeber, the rare species that were lost represented less than 10% of the stuff at the base of the food chain, so their lost had a large and disproportionate impact on the snails and crabs in the system. We call these species "cornerstone species", because they represent only a small fraction of the foundation of the food chain, but their removal has a very large effect. Finally, while we were conducting surveys related to this project, we spotted an unknown seaweed, which we identified as Heterosiphonia japonica. Native to eastern Asia and introduced to the U.S. via Europe, this species had apparently invaded Rhode Island coastal waters in about 2007. It was first described in a 2010 paper - published after our discovery - but early reports limited its distribution to south of Cape Cod, Massachusetts. We initially found this invader just north of Boston, and we subsequently tracked it as far north as Portland, Maine. We have found that it is choking out native seaweed species and reducing biodiversity. We are now studying how these changes in seaweed diversity are affecting how the system works. Collectively, these projects highlight the importance of biodiversity in marine ecosystems.
