Past Projects

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"N vs P limitation of benthic primary production in Florida Bay: a manipulative experiment"

Freshwater discharge into Florida Bay brings not only freshwater, but Everglades-derived nutrients as well. Recently, it has been suggested that an increase in freshwater flow, as envisioned in the Everglades Restoration Plan, would increase N loading into Florida Bay, and therefore cause increased microalgal growth and loss of seagrass beds. Implicit in this hypothesis is the notion that N limits biomass of primary producers in sections of Florida Bay. This project is manipulating the availability of N and P to seagrass beds in selected regions of Florida Bay and measuring the response of the major primary producers and consumers to this nutrient manipulation.

The goals of this project are to determine the limiting nutrient for benthic primary producers in Florida Bay and to asses the likely impact of increases in N and P availability on seagrass-dominated benthic communities. We will also assess the changes in population structure of small consumer organisms as a function of nutrient availability.

"The role of habitat fragmentation on the structure and function of seagrass ecosystems in the northern Gulf of Mexico"

The result of the global decline in seagrass meadows is the fragmentation of once continuous seagrass beds into smaller functional units. This fragmentation can alter patch size and shape, ultimately altering the perimeter: area (P/A) ratio (i.e. the amount "edge" present), which in turn, may impact faunal abundance, biological interactions, and water flow. Of the few studies examining these trends, there is little agreement on the exact consequences of shifts in patch shape and/or size on seagrass beds.

To better understand how communities are impacted by changes in patch size
and shape, there is a need to isolate and examine the controlling mechanisms at work. To date, most research has done little to separate the role of colonization from the confounding effects of post-settlement processes (i.e. predation). Within seagrass beds, potential changes could be controlled or compensated for by shifts in colonization rates of juveniles and adults, recruitment/settlement of larvae, growth rates, or predation rates.

The goals of my work are to examine how changes in patch size and patch shape influence community structure of macrofaunal organisms in seagrass beds, and to examine the effects of changes in patch size and patch shape on larval settlement rates and post-settlement processes. Specific objectives are to: 1. Evaluate the effects of seagrass bed size, shape and degree of isolation on the composition, abundance and secondary production of macrofaunal seagrass communities, 2. Isolate and evaluate the specific role the patch size and shape plays on settlement, predation/survival, habitat preference, and growth of seagrass associated macrofauna, 3. Determine if seagrass bed size, shape, and degree of isolation can impact the above ground biomass, and leaf characteristics of associated seagrasses.

"Marine reserve effectiveness in restoring coastal food webs: an experimental test using special protection areas and an ecological reserve in the Florida Keys National Marine Sanctuary" (Conducted in the Lower Keys)
 

Funding Agency: NOAA (MARFIN)
PI: John F. Valentine
Co-PI's: Ken Heck

Scientists and conservationists alike are increasingly concerned that the harvesting of large predatory fishes has caused significant alterations in the structure and function of marine ecosystems. Marine reserves are being used as tool to address this problem, but there has been little examination of (i) how fishing has altered food webs on reefs and adjacent habitats or (ii) how landscape-scale considerations should be included in the design of reserves. In addition, most reserves are small, unreplicated, designed around just one habitat type (usually a coral reef),and studies of marine reserves overlook the connectivity between coral reef and adjacent seagrass habitats, as well as the importance of reef structural complexity and geometry on the re-establishment of large predators.

We are taking advantage of the rare opportunity to use replicated "no-take" (predator rich) and unprotected (predator poor) reefs in the Florida Keys National Marine Sanctuary to assess the impact of large piscivorous fishes on food web structure in and around coral reefs, the importance of linkages among seagrass and coral reefs in the reestablishment of these food webs, and the effects of habitat structure (complexity and fragmentation of reefs) on the success of marine reserves. We predict (i) that there will be dramatic increases in the size and density of predatory fishes not just on protected reefs, but also in seagrass habitats adjacent to protected reefs and that this benefit will decrease with distance from protection, (ii) that there will dramatic decreases in both the size and survivorship of many marine invertebrates in seagrass habitats adjacent to protected reefs, as reef predators transfer productivity from seagrasses to reefs, and (iii) that more structurally complex reefs that are less fragmented will show greater densities and diversities of reef fish. This research will help inform scientists, managers, and conservationists about the importance of linkages among habitats and landscape-scale considerations in the design of tropical marine reserves.

"Predicting Seagrass Survival in Nutrient Enriched Waters: Toward a New View of An Existing Paradigm"
 

Funding Agency: Alabama Center for Estuarine Studies (Environmental Protection Agency)
PI: Ken Heck   
Co-PI's: Jonathan Pennock (UNH), John F. Valentine (DISL), Patricia M. Spitzer

The goal of this project is to test the generality of previous experimental studies, including our own, that found that consumption by small herbivores could greatly reduce the incidence of algal overgrowth in eutrophic coastal waters. We are focusing on seagrass-dominated ecosystems because they are well-documented to serve as nursery habitats for a broad variety of economically valuable finfish and shellfish (see Heck et al. 1997 and Williams and Heck 2001 for reviews), and because eutrophication is strongly implicated in the disappearance of these critically important habitats in the Gulf of Mexico, and the nation as a whole (e.g., Howarth et al. 2000; Bricker et al. 1999). We are testing the ability of different types of small grazers (both individually and collectively) to buffer the effects of eutrophication by conducting field studies at small spatial scales that will allow us to sustain elevated nutrient concentrations at levels that will mimic those of up to the most highly eutrophic of coastal waters. Therefore, we will test the degree to which different types and abundances of herbivores can explain the observed variation in algal responses to eutrophication.