Introduction to the study
As biologists, we have an intuitive understanding that biological diversity is “important.” We see diversity as an integral component in the maintainance of functional ecosystems, and we value high levels of diversity, yet little research in marine ecosystems has addressed how primary producer diversity impacts higher trophic levels. We do not have an informed understanding of how the loss of diversity (for example, due to human activities) may change the ways that marine ecosystems function. This study is designed to examine how the diversity of primary producers affects the diversity, abundance and reproduction of macroalgae and invertebrate animals living in the rocky intertidal system in Northern California.

The macroalgal community in the upper rocky intertidal at the UC Davis Bodga Marine Lab is characterized by a mosaic of four common species: one brown alga (Pelvetiopsis limitata), two red algae (Mastocarpus papillatus and Endocladia muricata) and one green alga (Cladophora columbiana). A pilot study conducted in this community indicated a response of invertebrate diversity to algal diversity (Figure 1, at right). For this project, we have established a series of manipulations of algal diversity to demonstrate (1) the role of algal diversity in maintaining invertebrate diversity and abundance, and (2) the effect of algal diversity on algal productivity, growth, recruitment, and reproduction.

To compare the effect of low algal diversity (i.e. monocultures) with the effect of high algal diversity (i.e. polycultures), we have “weeded” experimental plots (circles with a 1.5-meter diameter) to have either (1) a single species of algae, or (2) all four species of algae. Over the course of the next four years we will monitor the plots and track how changes in algal and invertebrate assemblages reflect the impact of diversity loss.

Volunteers weed algae in the 1.5 m diameter plots on the rocky bench near Bodega Bay, CA

 

Spring 2007 update
Drs. Michael Graham (Moss Landing Marine Labs) and Jay Stachowicz (UC Davis, Bodega Marine Lab), and a team of students and researchers seasonally sample the 72 established plots at Bodega Marine Lab (next trip July 14-17, 2007). To begin to examine.... [read & see more]

This study will further explore the possible mechanisms for any observed “diversity effects.” These projects will include (1) a comparison of algal photosynthesis rates among algal species in air vs. in water by examining O2 evolution (in water) and CO2 uptake (in air), (2) field experiments with algal mimics to assess how the structural complexity of more diverse algal communities affects invertebrate diversity and abundance, and (3) how the algal diet provided by multiple species in poly cultures results in superior growth, survival or fecundity of herbivorous invertebrates in the plots.