Collaborative Research: Biodiversity and Ecosystem Function in Seaweed Communities

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Stachowicz/Graham-0351778/1345Collaborative research: Biodiversity and ecosystem function in intertidal seaweed communities. The relationships between species diversity and ecosystem properties such as stability, resilience, and resistance to perturbation have long been topics of theoretical interest to ecologists. In recent years, however, accelerating loss of biodiversity due to human activities has renewed interest in the functional consequences of biodiversity in ecosystems. Although experimental ecology in marine habitats has a long and productive history, and there is a fair understanding of what maintains diversity in marine benthic assemblages, little is known about the functional consequences of that diversity for the rest of the community. In this regard marine scientists lag far behind their terrestrial colleagues. This project entails a series of lab and field experiments to examine the effects of intertidal macroalgal (seaweed) diversity on primary production and the diversity, abundance, and reproduction of consumer species. The study will begin with a relatively large scale manipulation (2 m diameter plots) of macroalgal diversity on natural rocky intertidal communities at Bodega Bay, California. Five main treatments will consist of a monoculture of each of the 4 algal species that comprise 90% of the algal cover in this system and the the 4-species polyculture. Results of this experiment will be used to examine the relationship between diversity and a variety of ecosystem functions at the producer and consumer level, including the primary productivity and biomass of the macroalgal community; the growth, recruitment and reproduction of individual algal species; and the diversity, and abundance of mobile and sessile invertebrates. For objectives 2 and 3, the mechanisms responsible for any of these effects will be explored. For example, some seaweeds exhibit significantly different rates of photosynthesis in air vs. water, providing a potential mechanism for complementarity among species. Thus, in objective 2, the effects of diversity on shorter term carbon fixation in air and in water will be explored in the lab using O2 evolution (water) and CO2 uptake (air). Similarly, in objective 3, field experiments with algal mimics will be used to assess whether the structural complexity of more diverse algal communities is responsible for enhanced inverterbrate diversity or abundance. For this objective, the possibility that the algal diet provided by multiple species in polycultures results in superior growth, survival or fecundity of herbivorous invertebrates in the plots will also be tested. In all experiments, the experimental design will allow us to (a) determine whether there is a diversity effect and (b) if there is a diversity effect, whether it is simply due to the overwhelming effect of one species (i.e., the sampling effect) or due to complementary roles played by the various macroalgal species. Given the unprecedented rate of extinctions the earth is experiencing, an understanding of the consequences of biodiversity loss is critical to management efforts and this study will allow us to assess the applicability of terrestrial results to the management of marine systems. For example, it is vital that resource managers and designers of Marine Protected Areas understand the degree to which diversity at the producer level is important for enhancing the production and diversity of higher trophic levels and the overall function of coastal ecosystems. This study will provide some of the first data anywhere in marine systems on these issues and the first experimental data for the Pacific marine rocky intertidal. This project will also enhance the experience and training of post-doctoral, Ph.D. and M.S. students, and undergraduate students at two institutions. (edited 15 Jan 04, J. Pawlik)