Variantes genéticas en las células B

CONCLUSIONS AND FINAL THOUGHTS

This research investigated the role of sponge populations on the ecology of a coral reef ecosystem. Sponges are evolutionarily ancient animals that have come to inhabit nearly every marine (and some aquatic) benthic habitat on Earth. Coral reefs are among the most valuable ecosystems on the planet for the goods and services they provide that influence human welfare. The research findings presented here improve our knowledge of both sponge ecology and coral reef ecology and it is the hope of the author that these data will be built upon and inspire future research in a variety of fields and habitats.

This research found that coral reef sponge populations are capable of rapid and dramatic C and N transformations that impact reef ecosystem water quality. These transformations are the result of complex biogeochemical mechanisms carried out by the sponges and the associated microbial communities commonly found living in their tissues. Interactions between the sponges and other reef components including hard corals and fleshy macroalgae may be altering reef ecosystem structure and function, likely resulting in an increase in sponge and algal dominance at the further expense of hard corals. In the context of global coral reef decline, this research implicates sponge populations in benefiting from, and potentially contributing to, the decline of hard coral populations and an ecosystem phase shift. These results may be unique to the study system of the upper Florida Keys fore-reef community, though the mechanisms involved are potentially occurring in a number of similar systems.

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Much of the data presented in this dissertation was only made possible through the use if novel in situ instrumentation. These devices facilitated investigations of nutrient cycling and benthic metabolism at scales and resolutions otherwise impossible. Creative use of advancing technologies for detecting the chemical and physical dynamics of marine ecosystems is likely to be a major focus of future research in marine science. These technologies are emerging for investigations at multiple scales: from microprobes for sub-millimeter spatial resolution of chemical gradients to instrument arrays, like those used here, for local scale observations to networks of ocean buoy sensors for basin scale parameterization of ocean dynamics to satellite systems for observations of global

productivity and climate change. An important factor for maximizing the benefit of these technologies is the identification of critical interactions within and among ecosystems that operate a large amount of control on the system dynamics. These ―hot-spots‖ and ―hot-moments‖ exist at all scales and may not be obvious, yet their role becomes clear when investigations are conducted with a systems-based approach.

The body of work on sponge ecology provides an interesting example of the revelation of a critical ecosystem component and the utility of systems-based science. Although sponges have always been present on tropical coral reefs, they garnered little attention until the decline of hard coral populations revealed the relative health and abundance of sponges on many reef ecosystems. The historical dogma of sponge ecology expounds their roles as filter feeders working to ―clean‖ the water column to provide a better habitat for the reef-building corals, and their capacity to bind reef rubble and stabilize vital hard substrate on the reef. As their associations with microbial

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explored. It is now known that nearly every reaction in the complex N cycle can be carried out by sponges. Indeed, this biogeochemical faculty coupled with the incredible pumping capacity of these animals likely exerts a powerful regulatory mechanisms on the form and availability of N on the reef.

The discovery of coral reef sponge N processing, while certainly important on the reef, may find greater value when this knowledge is applied to other ecosystems where sponges are abundant. This study examined the Florida Keys coral reef, a fringing barrier reef on the Atlantic ocean side of the Keys archipelago. The reef ecosystem is relatively open and experiences exchange of water and material with the coastal ocean . Across the Keys island chain lies the shallow, largely confined estuary that is Florida Bay. The seagrass beds and mangrove islands that characterize this ecosystem are home abundant and diverse populations of sponges, animals with the same capacity for pumping and biogeochemical transformations as those on the neighboring coral reef. The difference lies in the greater ecosystem dynamics and the potential for autochthonous processes to dominate. Florida bay has far less water mass and hydrologic exchange than the offshore reef, and the relative importance of sponge processing may be greatly amplified in this system relative to the more open reef system. Indeed, the process of sponge-mediated nitrification/denitrification may play a critical role in balancing the N budget for Florida Bay and mediating N inputs from upstream land-based inputs.

This dissertation provides evidence that sponge populations are inheriting the reef from the scleractinian coral that built it. The implications of this shift are not yet known, nor do we have an understanding of the resilience of a sponge-dominated reef ecosystem. There is some evidence that the sponge populations are existing in autocatalytic feedback

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with abundant fleshy macroalgal populations, a phenomena that would support the continued growth and development of these populations while hindering the recovery of hard corals on the reef. The emergence of sponges, algae, and soft corals as providers of reef structure is not an ecosystem capable of persisting in geologic time or surviving conditions of sea-level rise. Indeed, the Florida Keys reef appears to have ―gone soft‖ and since it is unable to accrete significant new carbonate structure to match rising sea- level, it will likely become a drowned reef.

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