How many turtle species

Of all the sea turtles that nest in the United States, the loggerhead is the one seen most often. The loggerhead was listed in the United States under the Endangered Species Act as threatened in , and is the only sea turtle species not listed as endangered.

The majority of loggerhead nesting is concentrated in two main areas of the world — at Masirah Island, Oman, in the middle east and on the coast of the southeastern United States. The majority of nesting in the southeast U. Green turtles are an endangered species around the world, but they still nest in increasing numbers on the east coast of Florida.

The green sea turtle was listed in the United States under the Endangered Species Act as endangered in While the nesting population may be stable in Suriname, and increasing in Tortuguero, there is insufficient information from other nesting sites to determine a species trend worldwide.

The leatherback is the champion of sea turtles: It grows the largest, dives the deepest, and travels the farthest of all sea turtles. The leatherback was listed in the United States under the Endangered Species Act as endangered in Leatherbacks are seriously declining at all major nesting beaches throughout the Pacific. In contrast, there has been a recent increase in leatherback nesting on the central and south eastern coast of Florida.

It is a solitary nester, and thus, population trends or estimates are difficult to determine. The decline of nesting populations is accepted by most researchers. In , the only known apparently stable populations were in Yemen, northeastern Australia, the Red Sea, and Oman. Another tortoise species endemic to Madagascar, the radiated tortoise Astrochelys radiata , formerly achieved estimated population densities of up to per km 2 Leuteritz et al.

The loss of turtles from an ecosystem can lead to significant environmental consequences. For example, populations of small estuarine diamond-backed terrapins Malaclemys terrapin are members of a guild of top-down predators that regulate grazing species, such as salt-marsh periwinkle snails Littorina irrorata.

Without the effect of these predators, periwinkle snails can convert productive grasslands in salt marshes to barren mudflats in 8 months under experimental conditions Silliman and Bertness Other descriptions of the effects that turtles have on ecosystems are described in the section on ecosystem restoration. Predators e. Turtles assume all the traditional trophic positions of consumers; therefore, the removal or extirpation of turtles could have profound effects on the structure and function of terrestrial, freshwater, and marine communities.

For instance, the removal or diminished role of turtles in the wild can be far-reaching and create trophic cascades, altered biomass structure, loss of community function, and invasive species resilience, all of which are critical to maintaining healthy ecosystems.

Unfortunately, empirical data reporting these top-down effects caused by turtles are scarce in the scientific literature. The top-down effects of sea turtles on seagrass meadows and coral reefs are relatively well known.

Green turtles Chelonia mydas can alter the physical structure and flowering of seagrass meadows by heavy, sustained grazing Lal et al. In addition, green turtles directly alter the vegetation community composition of the seagrass meadows, which indirectly diminishes prey refugia and recruitment see Lal et al.

Furthermore, hawksbill turtles Eretmochelys imbricate often provide top-down indirect effects on coral reef ecosystems. These sea turtles directly consume sponges, which are competitively superior to coral, thus reducing competition for space within the coral reef and increasing coral species richness and health.

The roles of sea turtles are now greatly diminished because of years of global overexploitation Jackson et al. As freshwater predators, aquatic and semiaquatic freshwater turtles may have strong direct effects on prey abundance but also indirect effects that shape communities as well.

For example, the presence of a common freshwater species, the slider turtle, significantly altered environmental characteristics e. In addition, the increased nutrient load associated with turtle presence in the experimental ponds drove a significant increase in invertebrate abundance and density in the system. Similarly, in ephemeral freshwater ponds, increased nutrient influx provided by the common snapping turtle Chelydra serpentina positively affected the lowest trophic position of the food web, phytoplankton Wilbur In aquatic ecosystems, in which turtles occupy the highest trophic position, as apex predators, their long-term or temporary presence can have strong effects on ecosystem dynamics.

For example, in freshwater mesocosms, common snapping turtles directly altered amphibian community compositions and body condition of prey Garig Altered dynamics of lower trophic levels in these mesocosms exposed to turtles were documented over several weeks, even though the turtles were introduced and removed over a 4-day period, demonstrating short- and potentially long-term e.

Consequently, the extirpation or a diminished role of turtles in a freshwater community could have cascading effects at multiple trophic levels and environmental conditions, shifting short- and long-term ecosystem processes. The majority of temperate and tropical woody plants depend on vertebrates for seed dispersal Howe and Smallwood Therefore, this ecosystem service is vital for maintenance of terrestrial ecosystems globally Wang and Smith Turtles have long been overlooked as important seed dispersers; however, several species have been identified as important agents for seed dispersal and germination enhancement of plants.

Braun and Brooks fed wild fruits to captive eastern box turtles Terrapene carolina to determine germination potential. Eleven of 15 species germinated, and 5 had higher germination potential following digestion. In fact, the eastern box turtle is the only known seed dispersal agent for the mayapple Podophyllum peltatum. Mayapple seeds eaten by this turtle species germinate faster and have a higher probability of success than noningested seeds Rust and Roth Fecal samples of the leopard tortoise Geochelone pardalis in South Africa contained 75 plant species belonging to 26 families.

Viable seeds were observed for seven plant families on the basis of germination trials, but data were not presented to indicate enhanced germination following digestion Milton The majority of seedlings that germinated were grasses. Similar dispersal and germination enhancement capabilities were documented for the Greek tortoise Testudo graeca ; Cobo and Andreu , with 6.

Rose and Judd conducted one of the most thorough analyses of germination enhancement in a tortoise. Seeds placed in a solution of hydrochloric acid with a pH of 3. The authors suggested that seeds passed in fecal pellets have a selective advantage in that they germinate quickly in the presence of water and have a nitrogen source for early development.

Another interesting example of seed dispersal—and, presumably, germination enhancement—involves the declining tambalacoque trees Sideroxylon sessiliflorum and S. The extinction of the dodo bird Raphus cucullatus has been suggested as an explanation for the declining trees, because dodos may have abraded the thick endocarp of the seed and facilitated germination.

However, Iverson provided sufficient evidence to suggest that the extinct tortoises ate the seeds and facilitated germination. Similar scenarios may have existed between extinct tortoises and an extant baobab tree Adansonia rubrostipa in Madagascar Andriantsaralaza et al. Twenty-eight species of grasses, herbs, and woody plants have been documented to germinate from the feces of Aldabra giant tortoises Hnatiuk The seed dispersal and germination enhancement abilities of turtles and other members of the seed-eating guild can have a strong influence in the composition of plant communities they occupy.

The habit of the black wood turtle Rhinoclemmys funerea to emerge and defecate on river banks may contribute to the establishment of certain riparian plant species, and the foraging activity of the furrowed wood turtle Rhinoclemmys annulata may contribute to the distinctive flora of treefall areas in the forest Moll and Jansen Similar roles can be envisioned for other species of turtles such as alligator snapping turtles Macrochelys temminckii that feed on the fruits of riverine plant species including acorns Elbers and Moll Digging and burrowing animals, including some tortoises, can have an enormous impact on soil processes including its formation, function, and maintenance.

Animals living in the soil body and intimately associated with it are considered part of the soil, and animals living above the soil make contributions to it Hole In a major review of the effects of animals on soil, Hole identified 12 effects: mounding, mixing, forming voids, back-filling voids, forming and destroying peds soil particles , regulating soil erosion, regulating movement of air and water, regulating plant litter, regulating animal litter, regulating nutrient cycling, regulating biota, and producing special constituents.

Turtles have a role in many of these processes. Some turtles are prodigious burrowers, including Agassiz's desert tortoise and the gopher tortoise. Their impressive burrows, sometimes over 10 meters m in length for gopher tortoises, qualify them for the title of ecosystem engineers because of the impact of burrows on soil layers, water and gas diffusion, and surrounding vegetation.

The excavated mounds in front of burrows contribute to environmental heterogeneity and increased plant species diversity Kaczor and Hartnett In addition, their burrows are used by over other species figure 3 as symbiotic occupants Johnson et al.

Given the high densities these tortoises previously achieved and their habit of using more than one burrow per year, they exerted a strong influence on soils before their populations declined Ernst and Lovich Catano and Stout concluded that gopher tortoises were keystone species and ecosystem engineers by virtue of their burrowing habit. Gopher tortoise Gopherus polyphemus burrows provide shelter for over vertebrates and invertebrates Johnson et al.

Included are burrowing owls Athene cunicularia , various species of lizards, gopher frogs Lithobates capito , red foxes Vulpes vulpes , bobcats Lynx rufus , rodents, rabbits, and snakes, including other declining species, such as eastern indigo snakes Drymarchon couperi and diamondback rattlesnakes Crotalus adamanteus.

An example of the degree of soil disturbance that turtles are capable of achieving is shown in nesting green turtles and loggerhead sea turtles on Heron Island, Australia. These species exert a profound effect on the fringing vegetation of the island. Thousands of turtles nest during the period from October to March, affecting a swath of coastal vegetation averaging A single turtle can affect an area of over 2 m in diameter Rogers Loggerhead sea turtles in Moreton Bay, Australia, use an unusual foraging strategy that causes considerable disturbance to the seafloor Preen To gain access to buried food sources, loggerhead sea turtles dig pits up to 1.

Turtles advance through the sediment, eroding the quarry face of the excavation with their front flippers and feeding on invertebrates that are dislocated from their hiding places.

Including the lateral sedimentation of spoils from the excavation activity, 8. Preen concluded that foraging disturbance by loggerhead sea turtles had a substantial impact on the biomass, species composition, and dynamics of some seagrass beds and associated fauna. A similar conclusion was reported by Lazar and colleagues for loggerhead sea turtles in the neritic zone of the northern Adriatic Sea. They stated that foraging behavior by loggerhead sea turtles actively reworks marine sediments and increases the rate of mollusk shell disintegration.

They conservatively estimated that loggerhead sea turtles there bioturbate about 33 metric tons of mollusk shells per year.

In addition, infaunal mining of invertebrate prey by loggerhead sea turtles may be important in nutrient transfer in marine ecosystems. One of the benefits of understanding the functional role of organisms is the potential ability to harness ecological services they provide. For example, failure to recognize the ecological role of turtles in maintaining habitat heterogeneity has resulted in losses of certain habitat features, such as small wetlands, and the extinction or decline of some plant species Iverson , Griffiths et al.

Consider the value of turtles in cleaning rivers polluted with corpses in India or scavenging for carrion, as was discussed previously. The ability of some turtles to thrive in polluted waterways Moll makes them a tangible benefit. Hundreds of thousands of tortoises were removed from the islands over the centuries MacFarland et al. Since then, tortoise reintroduction efforts are having a positive effect on a rare keystone species of tree-like cactus Opuntia megasperma var.

The selection of tortoise species is important for the success of reintroduction for ecological restoration of some plant species, because not all tortoise species have the same effect or food preferences Hunter et al. Similar efforts are underway with giant tortoises in the Indian Ocean Griffiths et al.

Even small tortoise species are potential substitutes for the seed dispersal services formerly provided by extinct larger mammal species in defaunated continental forests Sobral-Souza et al.

The declines and extinctions of turtle populations globally mean that their ecological roles are now greatly diminished from times when turtles were more abundant. The impacts of their lessened roles are poorly appreciated and inadequately understood.

More definitive studies are needed to demonstrate the direct and indirect consequences of removing turtles from ecosystems. Two possible reasons exist for why society tends to overlook the decline of turtles.

The first is what we call the perception of persistence. Turtles of many species have the ability to live a long time, occasionally exceeding years Gibbons , Ernst and Lovich Some species also take a long time to reach sexual maturity and have long reproductive lifespans Congdon et al. Mortimer presented an elegant example of a hypothetical sea turtle population that required 25 years to reach sexual maturity. In Mortimer's scenario, humans began killing every female sea turtle that returned to nest after a certain date.

This is a plausible scenario, because of all reptiles used by humans as a food source, turtles are the most heavily exploited Klemens and Thorbjarnarson , and turtle extinctions from overharvest are well-documented Turtle Extinctions Working Group Because of the success of previous nests prior to overexploitation and the long time it took those turtles to reach sexual maturity, a casual observer on the beach would see turtles return to be slaughtered for over two decades before there were no more sea turtles left to return see figure 4 for an example of another heavily exploited turtle species.

The persistence of adult turtles in a population for years does not necessarily mean that recruitment is taking place that will replace those adults when they die over the course of many years.

Any time the rate of deaths exceeds births, a population will decline. Populations without recruitment are demographically decadent, to borrow a term long used by foresters to describe old trees.

This scenario can also happen because of total nest predation, or destruction of all nesting beaches in an area. If it takes 15 years for females to reach maturity, and no more nests are produced after , by about the year Modified from Mortimer with permission. People born into a world without large numbers of turtles performing important ecosystem functions accept that as the new norm e. A recent example involves a now cosmopolitan species of invasive turtle known as the red-eared slider Trachemys scripta elegans.

The species is introduced and thriving all over the temperate world from their humble origins in southern North America. Sliders often do very well in their new environments, sometimes to the detriment of other native turtles e. As a result of their ubiquity and shifting baselines in Japan, a cultural transition in public awareness may have occurred in the perception of what constitutes a native turtle Lovich and Yamamoto People seeing large numbers of exotic slider turtles in urban or agricultural ponds might be duped into thinking that turtles are doing well, without recognizing that sliders are not native to the area and, in many situations, replace the indigenous turtle species, thus reducing the diversity of native species.

As the only reptiles that are universally liked by people, it would be a sad world indeed to lose more of these iconic and remarkable survivors from the mists of deep evolutionary time. They survived the Cretaceous—Paleogene boundary cataclysm that wiped out the dinosaurs.

Will they survive us in the Anthropocene? George Heinrich, Russ Mittermeier, Shellie Puffer, and Kristy Cummings provided stimulating conversations and comments during the development of this manuscript. We thank Steve Bennett and James Beasley for a review of the manuscript. Special thanks to Karen Estes for preparing figures. This work was supported in part by the Department of Energy under award no. Any use of trade, firm, or product names is for descriptive purposes only and does not imply endorsement by the US Government.

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Humans cause the largest harm to turtle populations, but we have the power to make positive changes toward turtle survival. The largest threats to turtle populations include:. Careful stewardship and conservation action can successfully slow or reduce the declining trend of turtles. Because turtles can respond well to population management and conservation, it is not too late to preserve our turtle heritage. Three basic approaches for species conservation include:.

The months of May through July are the nesting season for many turtles. At this time, egg-bearing females sometimes travel great distances to find the perfect location to dig a nest and lay eggs.

Aquatic turtles also leave the water to travel across land in search of terrestrial nesting sites. Be sure to assist a turtle in the road only when it is safe to do so and do not attempt to stop traffic. Research has shown that aquatic turtle populations across the United States have uncommonly high proportions of males because so many female turtles are being killed on roadways.

Guidance on Assisting Turtles: Always keep the turtle pointed in the direction it is going. If you turn it around in the other direction, the turtle will only make another attempt to cross the road. Turtles have a home range and females often return to the same general area to lay their eggs. Some people use a shovel or a stick to push or skid snapping turtles across the road. Turtles have a long lifespan, take a long time to reach sexual maturity, and have low survivorship when newly hatched.

Because of these attributes, turtle populations cannot compensate for losses due to adult mortality without experiencing long-term consequences. This concern is even greater in recent years because many U. Connecticut Department of Energy and Environmental Protection.

Threats to U. Turtles Humans cause the largest harm to turtle populations, but we have the power to make positive changes toward turtle survival.