Michael Heithaus
Florida International University, Biological Sciences, Faculty Member
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A global survey of coral reefs reveals that overfishing is driving resident shark species toward extinction, causing diversity deficits in reef elasmobranch (shark and ray) assemblages. Our species-level analysis revealed global declines... more
A global survey of coral reefs reveals that overfishing is driving resident shark species toward extinction, causing diversity deficits in reef elasmobranch (shark and ray) assemblages. Our species-level analysis revealed global declines of 60 to 73% for five common resident reef shark species and that individual shark species were not detected at 34 to 47% of surveyed reefs. As reefs become more shark-depleted, rays begin to dominate assemblages. Shark-dominated assemblages persist in wealthy nations with strong governance and in highly protected areas, whereas poverty, weak governance, and a lack of shark management are associated with depauperate assemblages mainly composed of rays. Without action to address these diversity deficits, loss of ecological function and ecosystem services will increasingly affect human communities.
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Determining the drivers of prey selection in marine predators is critical when investigating ecosystem structure and function. The newly recognized Rice’s whale (Balaenoptera ricei) is one of the most critically endangered large whales in... more
Determining the drivers of prey selection in marine predators is critical when investigating ecosystem structure and function. The newly recognized Rice’s whale (Balaenoptera ricei) is one of the most critically endangered large whales in the world and endemic to the industrialized Gulf of Mexico. Here, we investigated the drivers of resource selection by Rice’s whales in relation to prey availability and energy density. Bayesian stable isotope (δ13C, δ15N) mixing models suggest that Rice’s whales feed primarily on a schooling fish, Ariomma bondi (66.8% relative contribution). Prey selection using the Chesson’s index revealed that active prey selection was found to be positive for three out of the four potential prey identified in the mixing model. A low degree of overlap between prey availability and diet inferred from the mixing model (Pianka Index: 0.333) suggests that prey abundance is not the primary driver of prey selection. Energy density data suggest that prey selection may ...
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Small cetaceans (dolphins, porpoises, and small toothed whales) occur from the poles to the tropics, and from freshwater habitats to the open ocean. Most ecological research has focused on the influence of abiotic factors on the... more
Small cetaceans (dolphins, porpoises, and small toothed whales) occur from the poles to the tropics, and from freshwater habitats to the open ocean. Most ecological research has focused on the influence of abiotic factors on the abundance, distribution, and behavior of these species. The ecological impacts of small cetaceans on communities and ecosystems remain poorly quantified. Their movement patterns, often high local and regional abundances across a range of ecosystems, and high metabolic rates suggest that small cetaceans could have large effects on ecosystem structure, dynamics, and function through a variety of mechanisms. These include top-down (e.g., direct predation and risk effects) and bottom-up effects (e.g., translocation of nutrients within and across ecosystems), but also behavior-mediated processes where these predators can facilitate access to resources to other predators or modify the physical properties of habitat (e.g., bioturbation). Most small cetaceans can be...
Research Interests: Biology, Ecology, Population, Habitat, Predation, and 3 moreEcosystem, Marine ecosystem, and Apex Predator
Sharks are a diverse group of mobile predators that forage across varied spatial scales and have the potential to influence food web dynamics. The ecological consequences of recent declines in shark biomass may extend across broader... more
Sharks are a diverse group of mobile predators that forage across varied spatial scales and have the potential to influence food web dynamics. The ecological consequences of recent declines in shark biomass may extend across broader geographic ranges if shark taxa display common behavioural traits. By tracking the original site of photosynthetic fixation of carbon atoms that were ultimately assimilated into muscle tissues of 5,394 sharks from 114 species, we identify globally consistent biogeographic traits in trophic interactions between sharks found in different habitats. We show that populations of shelf-dwelling sharks derive a substantial proportion of their carbon from regional pelagic sources, but contain individuals that forage within additional isotopically diverse local food webs, such as those supported by terrestrial plant sources, benthic production and macrophytes. In contrast, oceanic sharks seem to use carbon derived from between 30° and 50° of latitude. Global-scale compilations of stable isotope data combined with biogeochemical modelling generate hypotheses regarding animal behaviours that can be tested with other methodological approaches
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Seagrass ecosystems were traditionally assumed to be structured by competition as well as by “bottom up forces” such as resource availability and disturbance. However, a wealth of new evidence demonstrates that exertion of “top down... more
Seagrass ecosystems were traditionally assumed to be structured by competition as well as by “bottom up forces” such as resource availability and disturbance. However, a wealth of new evidence demonstrates that exertion of “top down control” by animals may be widespread. The strength and direction of top down control is context dependent, however, and varies with properties of organisms, the community, and the physical environment. Consumers can facilitate, consume, or destroy primary producers, aid or inhibit seagrass reproduction, or alter bottom up processes with implications for the properties and persistence of seagrass ecosystems. Studies in Australian ecosystems have been critical in helping to elucidate the role of consumers in seagrass ecosystems. Specifically, work investigating the roles of megaherbivores and apex predators and the pioneering of novel experimental approaches which allow for cage-free manipulations of mesograzers have substantially furthered our understanding of top-down control. At the broadest scale, megagrazers are likely to dominate grazing pathways in Australian tropical and subtropical seagrass ecosystems, while macrograzers and mesograzers do so in temperate seagrass ecosystems. However, while we have learned much about mechanisms through which top-down control can operate and its effects on seagrass ecosystems, predicting which grazing pathways dominate at smaller spatial scales, and net herbivore effects on seagrasses in specific ecosystems remains challenging due to context dependence and the highly complex nature of species interactions. Anthropogenic impacts further complicate these relationships. Australian seagrass habitats possess unusual properties, including relatively intact populations of megafauna, remote and pristine locations, and distinctive oceanographic features which allow these habitats to provide unique insights of top down control in seagrass ecosystems.
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Research Interests: Geography, Medicine, Multidisciplinary, Nature, Coral Reef Fishes, and 4 moreSharks, Coral Reef, Fishery, and Reef
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Background Hurricanes can have catastrophic effects on coastal ecosystems. To minimize negative impacts of storms, animals may seek shelter in place, move to a nearby refuge, or evacuate long-distances. Crocodilians can be important... more
Background Hurricanes can have catastrophic effects on coastal ecosystems. To minimize negative impacts of storms, animals may seek shelter in place, move to a nearby refuge, or evacuate long-distances. Crocodilians can be important predators in estuarine habitats, but little is known about how they respond to extreme weather events. We investigated the movement behaviors of eight acoustically tracked American alligators (Alligator mississippiensis) before, during, and after Hurricane Irma in 2017 within the Shark River Estuary of Everglades National Park, USA. Using tracking data, we compared their movements and habitat use before and after the hurricane to similar timeframes in other years without major storms. Results We observed considerable variation in movement tactics and responses to the hurricane. Of eight animals that we tracked, two showed no changes in movement or habitat use throughout the study. Two animals ceased upstream excursions that they were regularly making bef...
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Stable‐isotope analysis supplemented with stomach contents data from published sources was used to quantify the trophic niches, trophic niche overlaps and potential trophic redundancy for the most commonly caught fish species from an East... more
Stable‐isotope analysis supplemented with stomach contents data from published sources was used to quantify the trophic niches, trophic niche overlaps and potential trophic redundancy for the most commonly caught fish species from an East African nearshore seagrass community. This assessment is an important first step in quantifying food‐web structure in a region subject to intense fishing activities. Nearshore food webs were driven by at least two isotopically distinct trophic pathways, algal and seagrass, with a greater proportion of the sampled species feeding within the seagrass food web (57%) compared with the algal food web (33%). There was considerable isotopic niche overlap among species (92% of species overlapped with at least one other species). Narrow isotopic niche widths of most (83%) species sampled, low isotopic similarity (only 23% of species exhibited no differences in δ13C and δ15N) and low predicted trophic redundancy among fishes most commonly caught by fishermen...
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Iconic ecosystems like the Florida Coastal Everglades can serve as sentinels of environmental change from local to global scales. This characteristic can help inform general theory about how and why ecosystems transform, particularly if... more
Iconic ecosystems like the Florida Coastal Everglades can serve as sentinels of environmental change from local to global scales. This characteristic can help inform general theory about how and why ecosystems transform, particularly if distinctive ecosystem properties are studied over long time scales and compared to those of similar ecosystems elsewhere. Here we review the ways in which long‐term, comparative, international research has provided perspectives on iconic features of the Everglades that have, in turn, informed general ecosystem paradigms. Studies in other comparable wetlands from the Caribbean to Australia have shed light on distinctive and puzzling aspects such as the “upside‐down estuary” and “productivity paradox” for which the Everglades is known. These studies suggest that coastal wetlands on carbonate (karstic) platforms have: (1) hydrological and biogeochemical properties that reflect “hidden” groundwater sources of water and nutrients, (2) very productive, mat...
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Research Interests: Marine Biology, Zoology, Oceanography, Biology, Ecology, and 5 moreSeagrass, Nutrient Limitation, Bay, Subtropics, and Shark Bay
This special issue on ‘Science for the management of subtropical embayments: examples from Shark Bay and Florida Bay’ is a valuable compilation of individual research outcomes from Florida Bay and Shark Bay from the past decade and... more
This special issue on ‘Science for the management of subtropical embayments: examples from Shark Bay and Florida Bay’ is a valuable compilation of individual research outcomes from Florida Bay and Shark Bay from the past decade and addresses gaps in our scientific knowledge base in Shark Bay especially. Yet the compilation also demonstrates excellent research that is poorly integrated, and driven by interests and issues that do not necessarily lead to a more integrated stewardship of the marine natural values of either Shark Bay or Florida Bay. Here we describe the status of our current knowledge, introduce the valuable extension of the current knowledge through the papers in this issue and then suggest some future directions. For management, there is a need for a multidisciplinary international science program that focusses research on the ecological resilience of Shark Bay and Florida Bay, the effect of interactions between physical environmental drivers and biological control thr...
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Transect Data (over 27,000 animals over more than 14,000 km of transect surveys over 17 years) used for all transect analyses and for creation of Figure 4. File includes Standardized Data, a Column Key, and a Readme tab
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This dataset provides information on the catches of sharks in the Shark River Slough in relation to physical factors including dissolved oxygen, water temperature, salinity, and distance upstream. Analysis of data collected suggest that... more
This dataset provides information on the catches of sharks in the Shark River Slough in relation to physical factors including dissolved oxygen, water temperature, salinity, and distance upstream. Analysis of data collected suggest that distance from the Gulf of Mexico and dissolved have the largest effects on shark catch rates, with most juvenile bull sharks being caught in Tarpon Bay. This dataset includes all sharks caught on longline gear.
This dataset provides information on stationary video cameras set within the study area from 2011 to 2012, including animals viewed along with relevent environmental and camera data. These data provide insight into teleost communities... more
This dataset provides information on stationary video cameras set within the study area from 2011 to 2012, including animals viewed along with relevent environmental and camera data. These data provide insight into teleost communities that utilize various habitats within Shark Bay.
Carbon isotope data compiled from muscle tissues of 5394 sharks from 114 species. Data provided include d13C values, latitude of capture, designation as shelf, slope or oceanic shark, length, depth of capture (where available), C/N ratios... more
Carbon isotope data compiled from muscle tissues of 5394 sharks from 114 species. Data provided include d13C values, latitude of capture, designation as shelf, slope or oceanic shark, length, depth of capture (where available), C/N ratios of muscle, and lipid extraction method if used. Also included are phytoplankton d13C data modelled from Magozzi et al 2016 (Ecosphere 8(5):e01763. 10.1002/ecs2.1763). Model data expressed as the median and standard deviation d13C value for the Longhurst Biogeographic province corresponding to the location of shark captur
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Here, we identify the extant species of marine megafauna (>45 kg maximum reported mass), provide a conceptual template for the ways in which these species influence the structure and function of ocean ecosystems, and review the... more
Here, we identify the extant species of marine megafauna (>45 kg maximum reported mass), provide a conceptual template for the ways in which these species influence the structure and function of ocean ecosystems, and review the published evidence for such influences. Ecological influences of more than 90% of the 338 known species of extant ocean megafauna are unstudied and thus unknown. The most widely known effect of those few species that have been studied is direct prey limitation, which occurs through consumption and risk avoidance behavior. Consumer-prey interactions result in indirect effects that extend through marine ecosystems to other species and ecological processes. Marine megafauna transport energy, nutrients, and other materials vertically and horizontally through the oceans, often over long distances. The functional relationships between these various ecological impacts and megafauna population densities, in the few well-studied cases, are characterized by phase sh...
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Individual niche specialization (INS) is increasingly recognized as an important component of ecological and evolutionary dynamics. However, most studies that have investigated INS have focused on the effects of niche width and inter- and... more
Individual niche specialization (INS) is increasingly recognized as an important component of ecological and evolutionary dynamics. However, most studies that have investigated INS have focused on the effects of niche width and inter- and intraspecific competition on INS in small-bodied species for short time periods, with less attention paid to INS in large-bodied reptilian predators and the effects of available prey types on INS. We investigated the prevalence, causes, and consequences of INS in foraging behaviors across different populations of American alligators (Alligator mississippiensis), the dominant aquatic apex predator across the southeast US, using stomach contents and stable isotopes. Gut contents revealed that, over the short term, although alligator populations occupied wide ranges of the INS spectrum, general patterns were apparent. Alligator populations inhabiting lakes exhibited lower INS than coastal populations, likely driven by variation in habitat type and ava...
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In Shark Bay, wild bottlenose dolphins ( Tursiops sp.) apparently use marine sponges as foraging tools. We demonstrate that genetic and ecological explanations for this behavior are inadequate; thus, “sponging” classifies as the first... more
In Shark Bay, wild bottlenose dolphins ( Tursiops sp.) apparently use marine sponges as foraging tools. We demonstrate that genetic and ecological explanations for this behavior are inadequate; thus, “sponging” classifies as the first case of an existing material culture in a marine mammal species. Using mitochondrial DNA analyses, we show that sponging shows an almost exclusive vertical social transmission within a single matriline from mother to female offspring. Moreover, significant genetic relatedness among all adult spongers at the nuclear level indicates very recent coancestry, suggesting that all spongers are descendents of one recent “Sponging Eve.” Unlike in apes, tool use in this population is almost exclusively limited to a single matriline that is part of a large albeit open social network of frequently interacting individuals, adding a new dimension to charting cultural phenomena among animals.
Research Interests: Genetics, Design Research, Biology, Social learning, Medicine, and 15 moreMultidisciplinary, Material Culture, Mammal, Foraging, Mitochondrial DNA, Dolphins, Female, Animals, Male, Cultural transmission, Bottlenose dolphin, Feeding Behavior, Marine Mammal, Genetic Relatedness, and Cooperative Behavior
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CHONDRICHTHYAN BIODIVERSITY: ECOSYSTEMS AND DISTRIBUTION OF FAUNA Epipelagic Oceanic Elasmobranchs John D. Stevens Deepwater Chondrichthyans Peter M. Kyne and Colin A. Simpfendorfer Chondrichthyans of High Latitude Seas David A. Ebert and... more
CHONDRICHTHYAN BIODIVERSITY: ECOSYSTEMS AND DISTRIBUTION OF FAUNA Epipelagic Oceanic Elasmobranchs John D. Stevens Deepwater Chondrichthyans Peter M. Kyne and Colin A. Simpfendorfer Chondrichthyans of High Latitude Seas David A. Ebert and Megan V. Winton Elasmobranchs of Tropical Marine Ecosystems William T. White and Emma Sommerville Biology of the South American Potamotrygonid Stingrays Ricardo S. Rosa, Patricia Charvet-Almeida, and Carla Christie Diban Quijada Life History Strategies of Batoids Michael G. Frisk ADAPTIVE PHYSIOLOGY Ontogenetic Shifts in Movements and Habitat Use R. Dean Grubbs Tracking and Analysis Techniques for Understanding Free-Ranging Shark Movements and Behavior David W. Sims Sensory Adaptations to the Environment: Electroreceptors as a Case Study Stephen M. Kajiura, Anthony D. Cornett, and Kara E. Yopak Molecular Insights into Elasmobranch Reproductive Behavior for Conservation and Management David S. Portnoy Physiological Responses to Stress in Sharks Gregory Skomal and Diego Bernal Pollutant Exposure and Effects in Sharks and Their Relatives James Gelsleichter and Christina J. Walker CONSERVATION Factors Contributing to Shark Attacks on Humans: A Volusia County, Florida, Case Study George H. Burgess, Robert H. Buch, Felipe Carvalho, Brittany A. Garner, and Christina J. Walker Shark Control: Methods, Efficacy, and Ecological Impact Sheldon F.J. Dudley and Geremy Cliff DNA Forensic Applications in Shark Management and Conservation Mahmood S. Shivji Unraveling the Ecological Importance of Elasmobranchs Michael R. Heithaus, Alejandro Frid, Jeremy J. Vaudo, Boris Worm, and Aaron J. Wirsing Life Histories, Population Dynamics, and Extinction Risks in Chondrichthyans Nicholas K. Dulvy and Robyn E. Forrest