|Bottom Up and Top Down Effects in the Rocky Shores of the Galapagos Archipelago: Implications for Marine Reserve Design and Conservation|
|Location: The Galapagos Archipelago, Ecuador|
|Abstract: Marine reserves are created with two main purposes: to protect biodiversity and to enhance fisheries by protecting species, habitats and the processes that maintain ecosystems. Therefore, it is crucial to select sites that can maximize this goal. In this context, understanding the processes that affect the dynamics of organisms and communities is crucial, particularly when communities are affected by large-scale natural (i.e. ENSO) or anthropogenic disturbances (i.e. oil spills). In upwelling areas a higher influx of nutrients promotes the growth of algae and sessile invertebrates, which in turn supports a higher biomass of consumers (herbivores and predators). This finding suggests that coastal areas affected by upwelled nutrient rich waters might have the potential to act as sources of larvae or food to supply unproductive sites or sinks; however, little is known about the stability of these systems in response to natural or anthropogenic disturbances. I will use the upwelling ecosystems of the Galapagos Islands to conduct manipulative experiments to study the effect of consumers at different levels of productivity and thermal stress. The presence of three biogeographic regions characterized by different gradients of temperature and productivity, together with the sporadic presence of El Niño events make the Galapagos Archipelago an ideal system to assess the compounded effects of abiotic and biotic factors on community structure and stability and to understand the likely consequences of global climate change. This study will increase our understanding of how tropical rocky shores respond to environmental fluctuations and will have direct implications in the future evaluation of the Galapagos Marine Reserve.|
Between December 2004 and March 2005 preliminary monitoring and experiments were completed in order to:
Strong upwelling sites located to the western part of the Archipelago had the highest diversity. At these locations I found species of tropical, subtropical and temperate affinity. In addition, there was a higher diversity of filter feeder organisms, including sponges, anemones, barnacles and mussels and a higher diversity of secondary and tertiary consumers, including marine iguanas, sea turtles, coastal birds, crabs, snails, among others. At northern locations, the composition of sessile species was dominated by ephemeral species of algae and by grazing resistant forms (encrusting algae).
In the absence of grazers, the diversity of algae increases in the north, while the opposite effect was observed in the west. This pattern suggests that grazers have a site specific effect associated with levels of productivity and local diversity.
Thermal stress limited algal growth in the north, while in the central part of the Archipelago only the effect of grazers reduced algal growth. The size structure and body mass of organisms appear to be correlated with levels of productivity and food availability. This pattern seems to hold for a wide suite of organisms, including marine iguanas, welks, damselfish and others.