Award: OCE-0961364

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. Last Modified: 06/25/2014 Submitted by: Matthew E Bracken