Understanding the Role of the Physical Environment on Marine Organisms in Tropical Ecosystems
In an era of biodiversity collapse and climate change, both on land and in the aquatic world, understanding the interactions of marines organisms with the dynamics of their physical environment becomes necessary. In my projects I have chosen to focus on endangered species of coral and fish such as Elkhorn coral and Nassau grouper. I'm particularly interested in the transport of eggs and larvae through motions of oceanic waters. I apply my knowledge and my understanding of the ocean physics to the transport of marine organisms in their moving and changing environment. So far, our research has focused on tropical species in the Caribbean where reef ecosystems are degrading under growing threats... Our long term goal is to understand the response of the marine organisms to a physical environment which carries threats, such as carbon dioxide, warmer temperatures, pathogens, terrestrial sediments and pollutants. Transport itself might become a threat if it changes too much from the usual or past patterns as a result of climate change ...
Understanding the physical environment
Over the past ten years, our physical environment has been changing more than it did over past centuries. Yet we are not fish or marine organisms, our physical environment is the air we breathe, which in some places has become warmer, dryer, or more humid, and polluted; very polluted. The physical environment, which sustains us has become harmful and evasive: ice cap melting, ozone hole extension, more and stronger hurricanes, extreme temperature records, carbon dioxide and the green house effect, etc. We all complain about it! Similarly in the ocean, live beings like coral reef organisms also feel these changes and are more vulnerable than we are. Like the air, the water of the oceans has changed, more gradually than the air of the atmosphere, but enough to cause irreversible damages to shallow water marine ecosystems.My research focuses on the physical mechanisms that are taking place in the water world; such as the motions of the wind from the open ocean, which carries dust from the Sahara desert across the Atlantic Ocean. Under the surface, fish eggs, larvae, pathogens, runoffs, pollutants, etc, are transported by the motions of water "bodies" at the surface as well as at the bottom of the ocean. Motions carrying eggs, larvae, and plankton from the open ocean to the coastal reef can be seen as the arrival of the saving rain in the African savanna! Understanding the underlying mechanisms that drive these motions is essential to determining how they interfere with the living marine organisms.
Motions can be driven by wind, tides, temperature, salinity, earth rotation, and pressure. They take the form of large scale currents like the Gulf Stream, eddies like the North Brazil Current rings, waves that propagate horizontally or vertically in the water, which are driven by gravity, stratification and earth rotation. Motions in the form of currents or eddies can occur anywhere and at any depth in the ocean; the Sea is in fact a swirling world!
Therefore, the different forms of motions interact with each other and also with the solid boundaries of the ocean like the bottom floor. In my research, I've addressed these very important interactions as they result in changes of properties and content transported by current, eddies, or waves. In particular I've acquired an expertise in understanding interactions between current, eddies and topography, and mixing processes. I have studied their instabilities using quasi-geostrophic analytical and numerical models. I use numerical model that simulate the ocean circulation such as MICOM, HyCOM and ROMS to study these interaction in a more realistic framework. To close the loop, I have designed and conducted surveys at sea to observed these processes.
Coupling the physics and the biology
Using my knowledge of the physical environment of the ocean, I've studied the interaction of marine organisms with their environment. In particular, with my biologist colleagues we have focused on the transport of fish eggs and larvae by currents and eddies in the vicinity of reef ecosystems in the Caribbean, Gulf of Mexico, Florida Keys and the Bahamas, all together called the Intra-America Seas (IAS). We have established the role of currents and eddies in the Caribbean Sea in connecting marine populations of different regions of the Caribbean Basin. We have also identified sources and receiving areas. To accomplish this, we built an Individual Based Model (IBM) which couples transport by currents and fish larvae behavior. The IBM is particularly adapted to coral reef ecosystems and incorporates fish and larvae habitat, ontogeny, vertical migration, and mortality. It can be used with any Ocean General Circulation Model (OGCM), such as HyCOM or ROMS, and may be applied in any tropical region if local biological parameters can be provided.Applications
Collapsing ocean biodiversity, overfishing, and ocean resources exploitation all serve as indicators that we need to have tools and models dedicated to the understanding of the underlying mechanisms that initially drive the equilibrium and perturbations of marine ecosystems. Without them we would be unable to make the right decision at the right time and to deploy the conservation efforts necessary to reverse, if not too late such decline. From a marine conservation point of view, population connectivity can be used to establish Marine Protected Area (MPA) as or until sources of replenishment can be identified. From the fisheries point of view, the best productive area can be determined using our knowledge of ocean features that concentrate food. From a coastal development or agricultural point of view, the impact of changes in the landscape can be estimated by observing from space and modeling the transport of terrestrial runoff in coastal and open waters. From the aquaculture point of view, the environmental impact of fish cages can be estimated as well as the water quality of the site where fish will be grown, ensuring the best productivity while limiting the impact on the natural environment.All of this and more can be achieved because we have developed an expertise in coupling the physical environment with its content, which can be pollutant, runoff, nutrients, or livings organisms such as fish, but also any marine organism which, lives in this physical environment.
This initiation of this research has been supported by the National Science Foundation
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