Marine Sciences Programs Faculty Research news and Events Contact Us Links Home USA Home


Dr. Kenneth L. Heck, Jr.                                                                                               
Senior Marine Scientist and
Professor, University of South Alabama 
Ph.D., 1976, Florida State University                                                                                          

Associate Director Alabama Center for Estuarine Studies (ACES) 

Plant/animal interactions in seagrass-dominated ecosystems

Research Interests: 
Efforts focus on ecological studies of seagrasses and seagrass-associated macrofauna, especially shrimps, crabs and fishes.
Current studies include assessments of seagrass nursery value, investigations of herbivory, and the direct and indirect effects of nutrients and predator removal as they influence seagrass meadows.

Seagrass ecosystems serve as essential nursery areas for a wide variety of species in coastal waters, including many economically important finfish and shellfish. They are also among the most productive environments known, and support abundances of animals that are frequently 100 times those of nearby unvegetated bottoms.

During the past two decades there have been unprecedented declines in seagrass ecosystems along the Atlantic, Gulf and Pacific coastlines. Despite the recognized importance of seagrasses, the critical environmental factors limiting the seagrasses meadows are poorly understood, as are the biological interactions that directly and indirectly affect the health of seagrass ecosystems.

We are carrying out both laboratory and field studies of seagrass-dominated ecosystems at the population and community levels, and employ a team approach to problem solving. Our goals are to better understand the relative importance of physical-chemical and biological factors as they influence the health of seagrass meadows, as well as an increased understanding of how such high levels of plant and animal productivity are sustained in seagrass ecosystems. 

Ongoing projects include:
Relative Role of Top-down and Bottom-up Effects in Seagrass Ecosystems

Faculty colleagues, research associates, graduate students and I are conducting field tests of the interacting effects of large predator reductions and nutrient additions at a biologically relevant scale in marine systems. We expect these studies, being carried out in St. Joseph Bay, Florida, Perdido Bay, Florida, Mobile Bay, Alabama, and the northern Florida Keys to provide fresh insight into how to maintain the "health" of seagrass ecosystems.

Specifically, we expect to gain a better understanding of the degree to which "top down" and "bottom up" factors influence the structure of seagrass beds in coastal waters, and the factors that might promote a shift from a seagrass-dominated system to a unvegetated system.

Because nutrient enrichment and overfishing are occurring at an advancing rate along the Gulf coast, and indeed throughout the world, it is urgent that we understand the direct and indirect consequences of altering large predator abundance and concomitantly increasing nutrient supply.

Trophic Cascades and Spatial Subsidies in a Coral Reef Ecosystem: A Field-test using No-take Areas in the Florida Keys National Marine Sanctuary

It has been known since the 1960's that feeding in nearby vegetated (seagrass) habitats can subsidize coral reef consumers and may allow them to be more abundant than would otherwise be the case if they were supported solely by in situ productivity.

To date, most of what we know about the flow of energy within coral reefs comes from locations that have experienced heavy fishing pressure. Since fishing has been intense for centuries in most coastal areas, it is difficult to know what natural unharvested systems might have been like.

In this study, we will determine the impact of the removal of large fish predators from coral reef food webs, by quantifying the amount of trophic transfer from nearby seagrass foraging grounds on both no take and unprotected reefs.

Our specific objectives are to determine:

The effects of the projected increases in large piscivorous fish density and biomass within no-take reserves on the rates at which production in adjoining seagrass habitats is consumed by reef associated marine herbivores

The impacts of increased piscivorous fish density on herbivore abundance

Habitat Fragmentation
In marine environments, many habitats are comprised of discrete patches of varying size and geometry. For example, in habitats dominated by submerged aquatic vegetation (SAV), the SAV bed is actually more often a mosaic of vegetated patches interspersed with patches of unvegetated substrate (Larkum and den Hartog 1989; Robbins and Bell 1994; Bell et al 1995). While SAV cover may approach 100% in some areas, numerous natural disturbances such as wave energy and episodic storms prevent continuous SAV coverage of the substrate (reviewed by Fonseca et al. 1998). 

In addition, human-induced SAV habitat loss has increased dramatically in recent decades, with activities such as dredging, eutrophication, disease and damage from boating being major factors (Onuf 1994; Duarte 1995; Sargent et al 1995). Because SAV habitats are critical "nursery habitats" for numerous commercially and recreationally important species, (Orth et al. 1984, Heck et al 1997 and Fonseca et al. 1998) we must asses the potential impacts, as well as the overall susceptibility, of these habitats to an increasing number of anthropogenic disruptions. In addition, we need to gain an understanding how SAV habitat fragmentation influences the productivity of SAV-associated fisheries and delineate among large-scale negative effects which may be taking place on populations of economically and ecologically valuable species. 

Specifically, the objectives of this project are to 1) evaluate the effects of SAV bed size, shape and degree of isolation on the composition, abundance and secondary production of decapod crustaceans and fishes and 2) develop an understanding of the potential impacts of SAV fragmentation on the biological functioning of associated SAV fauna.


Selected Publications: 
Williams, S. W. and K. L. Heck, Jr. 2001. 'Seagrass Communities', Pp. 317-337 In: M. Bertness, S. Gaines and M. Hay (Eds.), Marine Community Ecology. Sinauer Press, Sunderland, Mass.

Valentine, J. F., K. L. Heck, Jr., K. K. Kirsch and D. Webb. 2001. The role of leaf nitrogen content in determining turtlegrass (Thalassia testudinum) grazing by a generalist herbivore in the northeastern Gulf of Mexico. J. Exp. Mar. Biol. Ecol. 258: 65-86.

Peterson, B. J. and K. L. Heck, Jr. 2001. Interactions between suspension feeding bivalves and seagrass assemblages - a facultative mutualism. Mar. Ecol. Prog. Ser. 213: 143-155.

Aronson, R. B., K. L. Heck, Jr. and J. F. Valentine. 2001. Measuring predation with tethering experiments. Mar. Ecol. Prog. Ser. 214: 311-312.

Beck, M. W., K. L. Heck, Jr., K. W. Able, D. L. Childers, D. B. Eggleston, B. M. Gillanders, B. Halpern, C. G. Hays, K. Hoshino, T. J. Minello, R. J. Orth, P. F. Sheridan and M. P. Weinstein. 2001. The identification, conservation and management of estuarine and marine nurseries for fish and invertebrates. Bioscience 51: 633-641.

Heck, K. L., Jr., L. D. Coen and S. G. Morgan. 2001. Pre- and post-settlement factors as determinants of juvenile blue crab abundance: results from the north-central Gulf of Mexico. Mar. Ecol. Prog. Ser, 222: 163-176.,

Heck, K. L., Jr., and P.M. Spitzer. 2001. Post Settlement Mortality of Juvenile Blue Crabs: Patterns and Processes. Proc. of the Blue Crab Mortality Symposium. Pgs. 18-27.

Spitzer, P. M., K. L. Heck, Jr. and J. Mattila. 2000. The effects of vegetation density on the relative growth rates of juvenile pinfish, Lagodon rhomboides, in Big Lagoon, Florida. J. Exp. Mar. Biol.
Ecol. 244:67-86

Heck, K. L., Jr., J. R. Pennock, J. F. Valentine, L. D. Coen and S. S. Sklenar. 2000. Effects of nutrient enriched and large predator removal on seagrass nursery habitats: an experimental assessment. Limnology and Oceanography, In Press.

Valentine, J. R. and K. L. Heck, Jr.June 20, 2007y: evidence for the continual grazing of marine grasses. Marine Ecology Progress Series 176:291-302.

Bologna, P. A. X. and K. L. Heck, Jr. 1999. Macrofaunal associations with seagrass epiphytes: relative importance of trophic and structural characteristics. J. Exp. Mar. Biol. Ecol. 242:21-39.

Peterson, B. J. and K. L. Heck, Jr. 1999. The potential for suspension feeding bivalves to increase seagrass productivity. J. Exp. Mar. Biol. Ecol. 240:32-52.

Mattila, J., G. Chaplin, M. R. Eilers, K. L. Heck, Jr., J. P. O'Neal and J. F. Valentine. 1999. Abundance and composition of fish and macroinvertebrates of a Zostera marina bed and nearby unvegetated sediments in Damariscotta River, Maine (USA). J. Sea Research 41:321-332.

Bologna, P. A. X. and K. L. Heck, Jr. 1999. Differential predation and growth rates of bay scallops within a seagrass habitat. J. Exp. Mar. Biol. Ecol. 239:299-314.

Selected Current Research Grants:
Effects of nutrient enrichment and food web alteration on nearshore ecosystems. EPA - $188,000. Period Covered: 1997 - 2000. PI's: Heck, Pennock and Valentine.

Fisheries-induced changes in the structure and function of shallow water nursery habitats: an experimental assessment. EPA (ACES) - $261,000. period Covered: 1999 - 2001. PI's: Heck, Valentine, Cowan and DeVries.

Trophic cascades and spatial subsidies in a coral reef ecosystem: a field test using "not take" areas in the Florida Keys National Marine Sanctuary. NURC - $40,000. Period Covered: 2000 - 2001. PI's: Valentine and Heck.

Evaluation of the nursery role of wetlands and seagrasses for better conservation and management. National Center for Ecological Analysis and Synthesis - $88,000. period Covered: 1999 - 20001. PI's: Beck and Heck.

Shelter bottlenecks and self-regulation in blue crab populations: assessing the roles of nursery habitats and juvenile interactions for shelter dependent organisms. EPA (ACES). $64,000. Period Covered: 2000- 2002. PI's : Heck and Moksnes.

Predicting seagrass survival in nutrient enriched waters: toward a new view of an existing
paradigm. EPA (ACES). $105,000. Period Covered: 2001- 2002. PI's: Heck, Valentine and Pennock.

Shelter bottlenecks and self-regulation in blue crab populations: assessing the roles of nursery habitats and juvenile interactions for shelter dependent organisms. EPA (ACES). $64,000. Period Covered: 2000- 2002. PI's : Heck and Moksnes.

Predicting seagrass survival in nutrient enriched waters: toward a new view of an existing
paradigm. EPA (ACES). $105,000. Period Covered: 2001- 2002. PI's: Heck, Valentine and Pennock.

Human-induced changes in the cross-habitat flow of energy in a subtropical marine ecosystem: experimental assessments using newly created marine reserves in the Florida Keys. Mellon Foundation. $180,000. Period Covered: 2001- 2003. Heck, Valentine and Beck.

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. NOAA (MARFIN) $183,000. Period Covered: 2001-2003. Heck and Valentine.

Post-doctoral Fellow
Per Moksnes (January 2001 - December 2002)

Research Associate
Patricia Spitzer 
M.S., Marine Science 1997. University of South Alabama. Thesis Title: "The Effects of Vegetation
Density on the relative growth rates and foraging behavior of juvenile pinfish, Lagodon
rhomboides, in Big Lagoon Florida"
B.S. Ecology & Evolutionary Biology. 1994 University of West Florida

Current Graduate Students
Stacey Harter, M.S. Candidate
Thesis Title: "Growth rates of juvenile pinfish (Lagodon rhomboides): effects of 
habitat and predation risk"
B.S. Biology 1999. Florida State University

Deborah Kilbane, M.S. Candidate
Thesis Title: "Intra-year class cannibalism in early juvenile blue crabs (Calinectes sapidus)"
B.A. Biology 2000. Wittenberg University

Meg Goecker, M.S. Candidate
Thesis Title: "The effects of nitrogen content of turtlegrass, Thalassiastestudinum, on the rates of
herbivory by the bucktooth parrotfish, Sparisoma radians."


University of South Alabama - Mobile Alabama 36688-0002 / 1 (251) 460-6101
For questions or comments Contact Us
Last date changed: June 20, 2012 3:50 PM