|PhD student, Oregon State University|
|Bottom Up and Top Down Effects in the Rocky Shores of the Galapagos Archipelago: Implications for Marine Reserve Design and Conservation|
|Location: Galapagos Islands, Ecuador|
|Species: Marine iguanas, fish, crabs, algae, intertidal communities|
|Abstract: The rocky shores of the Galapagos Islands are a diverse but relatively unexplored habitat that harbors a unique array of species, including marine iguanas, flightless cormorants and penguins. Nonetheless, their ecosystems are increasingly threatened by fishing and climate change. I will study 3 key issues for the conservation of rocky shore communities: (1) Evaluate consumer-resource interactions (top-down effects) at sites that experience different temperature and influxes of nutrients (bottom-up effects) (2) Assess if different levels of productivity (bottom-up effects) lead to increasing levels of stability (change little or recover quickly after perturbations). (3) Evaluate how the interactive effect of nutrients, temperature and herbivory regulates algal settlement, biomass and diversity. I will study these processes at three islands that experience different levels of upwelling† intensity (bottom-up effects). Outcomes will supply vital and novel information for the Galapagos National Park Service (GNPS) to support the ongoing evaluation of the zoning scheme (allocation of no-fishing zones) within the Galapagos Marine Reserve.|
Project Report: September 2007
Since January 2006, a series of manipulative experiments were set up to evaluate the interactive effect of herbivory (marine iguanas, fish and crabs), temperature and nutrients on the diversity of marine sessile organisms (i.e. algae and sessile invertebrates). These experiments were conducted on three islands located at three biogeographic regions characterized by different levels of temperature and productivity: Genovesa (North, low productivity), Santa Cruz (Center, mid productivity), and Fernandina (West, high productivity). Experiments will continue to be monitored until June 2008. Initial results show that at Northern, low productive locations any combination of herbivores will reduce the diversity of marine algae to few grazing resistant forms (mainly crustose algae). In areas of intermediate productivity the system was dominated by two types of algae, crustose and Ulva sp., and herbivores also tended to decrease diversity. At sites of high productivity, consumers had the opposite effects to those observed at less productive locations. Herbivores increased the diversity and maintained the system on an early successional and productive stage. Temperature and consumers also had an important effect on biomass, species richness and diversity of the flora and fauna associated with it. Thermal amelioration experienced in white plates facilitated the settlement of algae. Biomass was also higher on white plates.
At all sites grazers modified the canopy structure of Ulva sp. by reducing it to a low algal matt. By keeping the algal matt at a uniform low level, herbivores prevent the settlement of more complex but unpalatable forms of algae that appear to displace palatable forms of algae when grazers are absent. Both grazing and temperature have important effects on community structure. White plots ameliorated thermal stress, below what was experienced by the black plates. Thermal amelioration experienced on white plates favored the settlement of algae. White plates also had a higher biomass of algae, and a higher richness and diversity of fauna associated to the algal canopy. To my knowledge, the use of black and white plates is a new technique that has been developed and refined during the present study. This technique has already called the attention of world experts on marine climate change studies (Dr. Christopher Harley, University of British Columbia) and has a lot of potential for future research on different ecological aspects.
Several students including local Galapagueños, Ecuadorians, and students from other countries, including the United States, Germany and Brazil participated in the project since January 2006. Two students from the United States are doing their thesis honors project using some of the information collected in the present study. Some of the local students are now applying to their own projects the techniques that they have learned. This international and diverse group of students has fostered friendship, technical and cultural exchange, and future collaboration among them.