Welcome to the Marine Community & Behavioral Ecology Lab!

 

 

 

 

 

 

 

Tiger sharks cause grazers to change habitats, but how does this affect seagrass communities?

 

Dugongs can modify the structure of seagrass beds through their foraging.

 

A Himantura fai ray over a Shark Bay seagrass bed.

 

Pied cormorant.

 

 

 

 

An alligator captured during studies in the Florida Coastal Everglades. We are using a variety of techniques to identify drivers of consumer movements and trophic interactions in the estuary.

Contact information

Dr. Michael Heithaus
Executive Director, School of Environment, Arts and Society
Florida International University
3000 NE 151 St
North Miami, FL 33181
(305) 919-5234 voice
(305) 919-4030 fax
Mike Heithaus CV

Understanding the dynamics of a relatively undistrurbed marine ecosystem

One of the lab's major research sites is Shark Bay, Western Australia where we have initiated the Shark Bay Ecosystem Research Project (SBERP). As perhaps the most pristine remaining seagrass ecosystem in the world that can easily be accessed by scientists, Shark Bay allows us to answer questions about the intricicies of behavioral decisions by large marine vertebrates and the ecological role of top predators in marine ecosystems that would be almost impossible to address elsewhere. Since1997 we have been quanttifying the seasonal abundance, habitat use, and trophic relationships of tiger sharks and how their presence influences habitat use decisions by their prey, including Indo-Pacific bottlenose dolphins, dugongs, green and loggerhead turtles, sea snakes, and cormorants. Currently, we are investigating whether the "risk" effects of tiger sharks are transmitted to the wider food web and whether the effects of tiger shark predation risk is context-dependent. For information on all of these projects visit the SBERP website (www.sberp.org)

 

 

Some current projects in Shark Bay

1. Behaviorally mediated indirect species interactions in a subtropical seagrass ecosystem

In this project, we are testing whether tiger sharks indirectly influence seagrass communities through predation-sensitive habitat use and foraging behavior of megagrazers (dugongs and green sea turtles). We have found that dugongs shift their use of deep and shallow habitats, microhabitats within shallow banks, and foraging tactics in response to tiger shark predation risk. In addition, green turtles in good body condition give up foraging opportunities in order to be safe from tiger sharks. To test whether these shifts in the spatial pattern of grazer abundance are transmitted to seagrass communities, we have constructed exclosures that will allow us to quantify grazer impacts in habitats that vary in the level of risk that turtles and dugongs face from tiger sharks. In addition, we are using stable isotopes to determine the relative contributions of seagrass, algae, and jellyfish to the diets of green sea turtles. This project also investigates spatial and temporal variation in seagrass community composition and nutrient content within our study site and across Shark Bay. We are currently expanding this project to determine whether the indirect effect of tiger sharks on seagrassess in amplified or attenuated by parallel trophic and behavioral pathways. Namely, we are investigating the role of mesograzers (fishes) on seagrass communities and how the spatiotemporal pattern of fish herbivory is influenced by habitat use patterns of piscivores that are sensitive to spatial and temporal variation in tiger shark abundance. These studies are supported by the National Science Foundation.

 

2. Spatiotemporal variation in ray communities and trophic interactions

Rays - like the Himantura fai pictured crusing over a Shark Bay seagrass bed on the left - are large conspicuous predators in soft bottom communities and may play a significant role in structuring these communities through predation and bioturbation. In fact, it has been suggested that increases in ray populations following the decline of their large shark predators led to collapses in populations of shellfish. Despite their potential importance, surprisingly little research has focused on the ecology of rays. The goals of this project are to determine how rays respond to spatial and temporal variation in prey availability and the physical environment (e.g. water depth and temperature) and risk from predators like tiger and hammerhead sharks. We are assessing ray habitat use with a combination of visual surveys and acoustic tracking and their trophic interactions using stable isotope analysis. We also are trying to determine how rays partition their habitats and food resources in a location where there are intact predator populations and rays also have not been affected by human expoitation. This research is supported by the National Geographic Expeditions Council.

 

3. The influence of predation risk on diving behavior of air-breathing aquatic foragers

Our lab is working on theoretical, experimental, and field studies to determine the role of predation risk in shaping diving behavior. Current projects include a laboratory study of red-eared slider turtles to test theoretical predictions and field studies of dugongs, green and loggerhead turtles, and pied cormorants that are under spaially and temporally variable risk of tiger shark predation. Pied cormorants - like the one pictured to the left - decrease the total amount of time they spend at the surfece, where they are the greatest risk of shark predation, as the number of sharks increases in the bay. However, this only occurs in the most dangerous habitats. Field studies are being carried out in collaboration with Dr. Lawrence M. Dill (Simon Fraser University), PhD student Jordan Thomson (SFU), and Dr. Aaron Wirsing (University of Washington).

 

4. Trophic structure of a pristine seagrass community.

We are using stable isotopes to determine the trophic structure of sand-bottom and seagrass communities in Shark Bay, Western Australia. These data will be useful in comparisons of trophic structure with similar, but more heavily impacted, ecosystems. Ultimately, we hope to construct energy-flow models of the Shark Bay community that can be used to test the relative predictive power of traditional food web models with those that incorporate non-lethal predator effects. We also are investigating the factors associated with the degree of individual specialization in foraging within species.

 

 

Biotic and abiotic drivers of habitat use and trophic interactions of estuarine predators in the Florida Coastal Everglades (FCE)

The second major field site for our research is the coastal Everglades, where we are part of the NSF-funded FCE LTER. The coastal Everglades estuary is relatively oligotrophic and limiting nutrients (primarily phosphorus) in are derived from the Gulf of Mexico. The hydrology of the coastal Everglades has been radically altered by humans, but there are ongoing efforts to restore waterflow to more natural dynamics. How these proposed changes will impact the consumers in the coastal Everglades is largely unknown. We have initiated studies, using a combination of acoustic tracking, stable isotopic analysis, and sampling of biological communities to understand the drivers of habitat use, movements, and trophic interactions of juvenile bull sharks, American alligators, snook, and Florida gar. We have become particularly interested in factors associated with individual specialization in movements and foraging patterns of alligators and bull sharks as well as their potential to be vectors for upstream transport of phosphorus. A site dedicated to these studies is currently under development.

 

 

 

All photographs copyrighted; Images may be used for educational purposes. For use in other forms contact Mike Heithaus

 

Please address questions or comments about this website to: heithaus@fiu.edu