TAXONOMY

Species Description

The non-native marine toad, Bufo marinus, is the largest of Florida's frogs and toads. It has a stout body and short legs, with the digits of the forelimbs lacking webbing and those of the hind limbs being webbed. The skin is rough and warty. Skin ranges in color from gray to tan to red-brown, dark brown, olive to dull green, to black above, and cream-colored and often flecked with brown or black on the belly. The tympani (ear membranes) are one-half to two-thirds the diameter of the eyes (Ashton and Ashton 1988)

The most distinguishing feature (other than size) is the presence of two large parotid glands, located at the shoulder behind each eye. These are venom glands capable of producing toxic milky secretions when squeezed. Smaller venom glands ('warts') are distributed all over the surface of the skin (Conant and Collins 1991, Gautherot 2000).

Tadpoles are jet black dorsally and silvery white with black spots ventrally (Ashton and Ashton 1988).

The vocalization of B. marinus is a slow, low-pitched trill and larger males usually have deeper calls (Somma 2004).

Potentially Misidentified Species

The size of the marine toad and the presence of the large parotid glands and webbed hind digits make this species easy to distinguish from other Florida frogs and toads.

HABITAT AND DISTRIBUTION

Regional Occurrence

Bufo marinus is a highly adaptable invader and where it occurs in Florida it is typically found in agricultural and urbanized areas.

The native range of B. marinus extends from northern South America, through Central America and Mexico, and up into southernmost Texas (Conant and Collins 1991, Somma 2004).

The species is established in south Florida and around Tampa on the Gulf coast, and they are also found on Stock Island and Key West (USGS/SEARMI). These populations are probably derived from intentional introductions as well as accidental introductions in agricultural products and from escapes of pets from homes and from the pet trade (Somma 2004).

IRL Distribution

Collection records indicate Bufo marinus occurs in at least three of six IRL watershed counties (Palm Beach, Martin, Indian River, probably St. Lucie as well). It appears to be widely established in Palm Beach and Martin counties. Smaller populations of B. marinus pesist elsewhere in isolated pockets as, for example, an established population reported in Vero Beach near Dodgertown in 2002.

LIFE HISTORY AND POPULATION BIOLOGY

Age, Size, Lifespan

Bufo marinus in Florida can reach sizes of around 10-15 cm (and up to nearly 24 cm elsewhere) and female toads can weigh up to 2.5 kg (Behler 1979, Somma 2004).

Abundance

Bufo marinus is considered to be abundant in Dade and in some areas of Monroe Counties, occurring in lesser numbers elsewhere in south Florida (USGS/SEARMI).

Reproduction

In Florida, Bufo marinus typically breeds in man-made habitats such as drainage canals and ditches, fish ponds, temporary pools and other shallow water bodies (Somma 2004). Breeding in Florida typically occurs during the wet season from early spring into the fall, and typically occurs during or just after rain events (Conant and Collins 1991).

B. marinus exhibits high fecundity with large females capable of producing 20,000 eggs or more (Somma 2004).

Embryology

Egg strings may be free-floating or wrapped around submerged as well as surface material (Somma 2004). Eggs hatch into tadpoles at around three days and the tadpoles metamorphose to juvenile toads around 45-55 days later (Krakauer 1970, Ashton and Ashton 1988).

PHYSICAL TOLERANCES

Temperature

Marine toads are cold intolerant. Krakauer (1970) suggests that cold-sensitivity had thwarted several past attempts to intentionally introduce the species more widely in Florida.

Salinity

Despite the scientific and common names, the marine toad is entirely terrestrial as an adult outside of breeding. Eggs and tadpoles of Bufo marinus do exhibit a degree of salinity tolerance but only to concentrations of around 5 ppt or so, roughly equivalent to 15% the salinity of seawater (Ely 1944, Wright and Wright 1949).

COMMUNITY ECOLOGY

Trophic Mode

Marine toads are voracious predatory omnivores that consume not only insects and other arthropods but also molluscs, vegetation, and any other frogs or toads they encounter. In urbanized settings, they will consume cat or dog food if it is left out and they may also scavenge garbage (Alexander 1964, Cabrera et al. 1996, Somma 2004).

Marine toads are primarily nocturnal and they often congregate around lights to take advantage of the insects that they attract.

Associated Species

None reported.

ADDITIONAL INFORMATION

Invasion History

Marine toads have been repeatedly introduced throughout the world as a potential biological control agent for crop-damaging insects, primarily those that damage sugarcane (Krakauer 1968, 1970). The most infamous introduction is the 1935 intentional release into the canefields of Queensland, Australia in an unsuccessful attempt to control the sugar pest the greyback cane beetle (Dermolepida albohirtum). The marine toads used in the Queensland introduction were from Hawaii where the species had been intentionally introduced just a few years earlier (McKeown 1996, Lever, 2001).

The first attempts at intentional introduction of Bufo marinus into Florida occurred at approximately the same time as the Hawaii and Australia introductions. Specimens imported from Puerto Rico were released into Palm Beach County in 1936 but the species failed to become established on this occasion and in two subsequent attempts as well (Krakauer 1968).

Marine toads finally did become established in Florida after an accidental release by an importer in 1955 from the Miami Airport (Krakauer 1968, Ashton and Ashton 1988). Additional intentional releases into south Florida in 1963 and 1964 facilitated establishment and subsequent explosive population growth. The species was recognized as a nuisance species requiring control as early as 1965 (Krakauer 1968, 1970).

Potential to Compete With Natives

Marine toads likely compete with native species for food, living space and breeding sites and may have, in some parts of the world, been a the principal cause of local extirpation of some native amphibians (Krakauer 1968). Marine toads also eat other species of frogs and toads and practically any other suitably-sized animal they encounter.

Possible Economic Consequences of Invasion

The defensive secretions produced by the parotids and other poison glands are highly toxic and are capable of killing dogs, cats, and other animals that bite into or attempt to consume them (USGS/SEARMI). Effects on native fauna are not fully known but are believed to be similar.

The secretions are also capable of making humans seriously ill, and of causing serious skin and eye irritation Carmichael and Williams 1991, Conant and Collins 1991).

Bufo marinus is listed by ISSG as as among "100 of the Worst" global invasive organisms, and authorities consider it to be the "most introduced amphibian in the world" (Behler 1979, Carmichael and Williams 1991).

REFERENCES

Alexander T.R. 1964. Observations on the feeding behavior of Bufo marinus (Linne). Herpetologica 20:255-259.

Ashton, R.E. and P.S. Ashton. 1988. Handbook Of Reptiles And Amphibians of Florida. Part Three, the Amphibians. Windward Publishing, 191 p.

Behler J.L. 1979. The Audubon Society Field Guide to North American Retiles and Amphibians. Alfred A. Knopf, New York. 743 p.

Cabrera J., Barrantes R., and D. Rodriguez. 1996. Habitos alimentarios de Bufo marinus (Anura Bufonidae) en Costa Rica. Revista de Biologia Tropical 45:702-703.

Carmichael P. and W. Williams. 1991. Florida's Fabulous Reptiles and Amphibians. World Publications. Tampa, FL. 120 p.

Conant R., and J.T. Collins. 1991. Reptiles And Amphibians, Eastern/Central North America. Houghton Mifflin Company. Boston. 450 p.

Ely C.A. 1944. Development of Bufo marinus larvae in dilute sea water. Copeia 56:256.

Krakauer T. 1968. The ecology of the neotropical toad, Bufo marinus, in south Florida. Herpetologica 24:214-221.

Krakauer T. 1970. The invasion of the toads. Florida Naturalist 1970:12-14.

Lever, C. 2001. The Cane Toad. The History and Ecology of a Successful Colonist. Westbury Publishing, England. 230 p.

McKeown S. 1996. A Field Guide to Reptiles and Amphibians in the Hawaiian Islands. Diamond Head Publishing, Inc., California. 172 p.

Somma L.A. 2004. Bufo marinus species profile. USGS Nonindigenous Aquatic Species Database. Gainesville, FL. Available online.

Wright A.H., and A.A. Wright. 1949. Handbook of Frogs and Toads. Comstock Publishing Associates, Ithaca NY. 640 p.