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Home , Jill Heinerth, Subterranean river

BIOLOGY OF UNDERWATER by Tom IlifJe, PhD

Recent speleological investigations in coastal areas have confirmed that anthropogenic pollutants can have potentially devastating effects on the fresh groundwater lenses and adjacent open water marine ecosystems including coral reefs, mangroves and sea grass. Many species ofcave animals are listed as critically endangered. These animals are a barometer ofthe health ofthe environment and virtual missing links that help to explain the evolution oflife in the sea and the evolution oflife on earth.

The subterranean aquatic environment consists of known and studied from freshwater caves, the discov­ interstitial (small, water-filled spaces between uncon­ ery of similar animals from marine caves is a recent solidated ) and (larger voids within event brought to light by explorations. bedrock, either formed by or volcanic action) Anchialine (tidal, water-filled voids near the coast) ecosystems. The water in underground environments caves typically possess a highly stratified water col­ can vary from completely fresh to fully marine sa­ umn with deeper, fully marine waters separated by linities. Such habitats are characteristically lightless, a from overlying fresh or brackish water. environmentally stable and have limited input offood Cave diving technology has been an essential tool to due to the absence ofphotosynthetic plants and barri­ explore and study the deeper waters in such systems. ers to external input. Anchialine caves include the of Mexico's Ecologically, aquatic cave animals can be subdi­ Yucatan Peninsula, the blue holes ofthe Bahamas and vided into stygobites (cave-adapted species restricted Belize, as as numerous limestone and volcanic to subterranean waters), stygophiles (species inhabit­ caves, mostly on islands, around the Caribbean, Med­ ing caves and completing their entire life cycle there, iterranean and Indo-Pacific. Seven of the ten longest obut which also occur in similar open water habitats) underwater caves in the world are anchialine caves stygoxenes (species common in caves, but which from the Caribbean coast ofYucatan. This anchialine must leave the cave to feed or reproduce), and acci­ cave habitat is characterized by the absence oflight, a dentals (species that wander or are washed into caves, salinity and stratified water column, very but which cannot survive there for very long). The limited food resources, low levels of dissolved oxy­ prefix "stygo" refers to the subterranean gen and stable environmental conditions. which from Greek mythology circles through Hades Anchialine and freshwater stygobites are mostly or the underworld. Thus, stygobites are literally the crustaceans, and include several higher groups of "aquatic cave life", stygophiles the "aquatic cave lov­ crustaceans found only or primarily in subterranean ers", and stygoxenes the "aquatic cave guest~". habitats. Such animals include: , • Remipedes - primitive, anchialine, "living fos­ sil" crustaceans with highly segmented bodies, remi­ niscent of the segmented worms from which crusta­ .' ceans are thought to have evolved. Remipedes have paired hollow fangs for capturing prey and are among the top predators in this habitat. They are up to 4.5 cm in length, usually colorless and blind, with elongate, centipede-like bodies. Seventeen species ofremipedes inhabit fully marine, -deficient waters in caves Mictocaris halope, Bermuda. Photo: Tom llifJe in the Bahamas, Caicos Islands, Cuba, Yucatan Pen­ Although cave-adapted animals have long been insula, Canary Islands and Western Australia.

63 • Thermosbaenaceans - small (4 mm or less), • SpeJaeogriphaceans - small (less than 1 cm eyeless or eye-reduced, anchialine and freshwater long) freshwater crustaceans represented by spe­ crustaceans with a dorsal brood pouch in females. cies from caves in South Africa, Brazil and Western Their wide distribution in caves and thermal springs Australia. They are most closely related to the micta­ around the Mediterranean and Caribbean, as well as ceans. This widely separated distribution implies an Australia and Cambodia, suggests an origin along the early origin for the group, at least 200 million years coastline of the Tethys Sea, a shallow sea separating before present in the Tethys Sea. the continents during the early Mesozoic some 200 • Bochusaceans - small (1.2-1.6 mm), semi-trans­ million years ago. They include at least 34 species. parent and eyeless crustaceans that include two an­ chialine species from the Bahamas and Cayman Is­ lands and three deep-sea species. • Copepods - a large and diverse group, compris­ ing the most common animals in marine plankton. Platycopioid, misophrioid, cyclopoid, harapacticoid and epacteriscid calanoid copepods inhabit anchia­ line caves in tropical regions aroung the globe. They are small (typically 1-2 mm long) and have a short, cylindrical body with head and thorax fused Thermosbaenacean. Photo: Tom lliffe into a cephalothorax. Most are planktonic filter-feed­ • Mictaceans - small (3-3.5 mm), eyeless and de­ ers, but some such as the harpacticoids and cyclopoids pigmented, non-predatory crustaceans represented by are benthic. a single species in anchialine caves in Bermuda.

64 • Ostracods - small (approximately 0.5-2 mm), Caribbean, Europe, Galapagos, India, Indonesia, Ja­ benthic or planktonic bivalve crustaceans. Halocyprid pan, Malaysia, NOI1h and Central America and Poly­ ostracods include anchialine species with a distribu­ nesia. Cirolanid isopods have been found in freshwa­ tion and co-occurrence similar to that of remipedes. ter and anchialine caves clustered in Mexico and the More than 300 species of podocopid ostracods have Caribbean as well as in Europe and the Mediterra­ been found in springs, caves and anchialine habitats. nean. • Mysids - small (approximately 3-20 mm), • Amphipods - laterally compressed body (flat­ shrimp-like crustaceans including stygobitic species tened from side to side), occurring in freshwater and found in freshwater and anchialine habitats in Africa, marine habitats. Stygobitic representatives are present the Caribbean, Mediterranean, and India. Their distri­ in the bogidiellid, crangonyctid, hadziid and niphar­ bution suggests that they were stranded in caves by gid families of the amphipod suborder Gammaridea. lowering of sea levels in the Tethys and Mediterra­ They are very widely dispersed with large numbers nean. inhabiting caves in Central and Southern Europe, the Mediterranean, eastern and southern North America, and the Caribbean. • Decapods - possess five pairs of pereiopods or legs (hence the name Decapoda). Anomuran crabs (e.g., hermit, porcelain, mole and sand crabs) inhabit a freshwater cave in Brazil and an anchialine in the Canary Islands. Stygobitic crayfish are pres­ ent in caves in North America and Cuba. Brachyuran crabs (i.e., true crabs) are widely distributed from Stygiomysid. Photo: Tom Iliffe caves in the tropics and subtropics. Caridean shrimp include freshwater and anchialine representatives • Isopods - dorsoventral1y compressed body (flat­ from caves mostly in tropical latitudes. tened from top to bottom); occuring in terrestrial, freshwater and marine habitats. Stygobitic isopods • Fish - nearly 100 species of stygobitic fish are range from several millimeters to several centimeters presently described, primarily from tropical and sub­ in length. tropical regions. They occur principally in freshwater caves, but anchialine fish are present in Caribbean is­ lands and Yucatan. The principle stygobitic fish are cyprinids (carps and minnows), balitorids (river 10­ aches), and siluriform fishes (catfish). Six species of amblyopsid cave fish occur in the southern and east­ ern .

Isopod. Photo: Tom llifJe - Ogilbia persei. Photo: Tom llifJe Anthurid isopods occur in anchialine and freshwa­ ter caves in the Canary Islands, Caribbean and Indian • SaJamanders - Ten species of stygobitic sala­ Ocean islands, Mexico and South America. Asel10t manders are known, including Proteus, the 25-30 cm isopods inhabit anchialine and freshwater caves in the long world-famous blind salamander from caves near the , and nine species from the US (Tex- 65 as, southwestern Ozark Plateau, Tennessee, Alabama, subsequently were dispersed by plate tectonic Georgia and ). as the continents separated and moved to their present Most ofthese animals have lost their eyes and pig­ positions. A number ofother anchialine animals show mentation in response to life in the constant and total close relationships with present deep-sea species im­ darkness of the cave. A number of less-obvious evo­ plying a possible deep-sea origin for cave fauna. Fi­ lutionary modifications have also occurred. In com­ nally, some cave animals are thought to have been parison to their surface relatives, cave animals tend to 'stranded' in their present locations by receding wa­ be longer-lived, produce fewer but larger eggs, have ters of the Tethys Sea. lower rates of , possess more abundant Unfortunately, many of these unique and fascinat­ tactile and chemo-receptors, have longer antennae ing animals are threatened with extinction due to the and long, thin, body forms. actions of man. In Bermuda alone, 25 species ofcave animals are internationally recognized as "critically endangered." This is the highest level of threat and roughly equates to a 50% chance of the species go­ ing extinct if nothing is done. All too frequently, an­ chialine cave animals can be considered endangered since I) they have very limited distributions, com­ monly being known only from a single cave, and 2) environmental conditions in these caves are often de­ teriorating through the effects of water pollution or cave destruction.

Dr. Tom I/iffe and Dr. Wolfgang Sterrer examine a specimen at the Bermuda Zoological Society, Aquarium and Zoo. Photo: Jill Heinerth To date, more than 350 new species of anchialine crustaceans have been collected and described, most­ ly from caves in the Bahamas, Bermuda and Yucatan Peninsula. Other hotspots for anchialine cave species include the Galapagos Islands in the eastern Pacific, Bermuda 5 Church Cave is home to the country 5 largest under­ Cape Range Peninsula in Western Australia, Canary ground lake and many different species ofunique cave adapted Islands in the eastern Atlantic and Balearic Islands animals. Photo: Jill Heinerth in the Mediterranean. Continued exploration is still Threats to caves include and waste dispos­ turning up new discoveries at a high rate. al, deep well injection, quarrying and construction ac­ Despite being limited to caves, many groups of tivities and diver and other human disturbances. As an anchialine organisms are widely separated, e.g., on example, the small oceanic island of Bermuda is the opposite sides of oceans or even opposite sides of the third-most densely populated country in the world and earth, and seemingly isolated from one another on has the largest number of private cesspits per capita. a global scale. One theory attempts to explain such Disposal of sewage and other waste water into cess­ distributions by suggesting that cave organisms origi­ pits or by pumping down is contaminating nated more that 100 million years ago when all con­ the ground and cave water with nitrates, detergents, tinents were combined into one supercontinent and toxic metals and pharmaceuticals; depleting the very 66 limited amounts of dissolved oxygen in cave water; less crustaceans that chance to stray into the beam of and generating toxic levels ofhydrogen sulfide. Some a . Considering the many hundreds to thou­ ocean caves such as the Blue Holes of the Bahamas sands ofcave divers who use these systems each year, have strong tidal currents sweeping through them for it is not surprising that the caves most heavily visited very considerable distances. In one such cave, plastic by tourist divers are now essentially devoid of live. bottles and other trash have been observed littering Even the gas exhaled by divers may have untold the floor of the cave nearly a mile back into virgin and unknown effects ofcaves and cave animals. Since passage. Far too many caves and are viewed anchialine caves waters typically contain extremely as preferred locations for the dumping ofgarbage and low levels of dissolved oxygen in the parts-per-bil­ other waste products. lion range, the exhaust bubbles from open circuit and especially divers could have profound effects on the cave ecosystem. Several anchiaIine caves in Western Australia with unique fauna are currently off-limits to open circuit divers and may only be vis­ ited by those using .

Jill Heinerth examines trash found inside the cave downstream ofRose Creek Swallet, Florida. Photo: Wes Skiles - from the film: Water's Journey, Hidden of Florida. A boardwalk allows easy access through a tourist cave in Ber­ muda. Photo: Jill Heinerth Another serious environmental problem concerns the destruction of caves by limestone quarries or Some anchialine caves in Bermuda, the Canary Is­ construction activities. At least half a dozen or more lands and MaJIorca have been developed into com­ caves have been totally destroyed by Bermuda lime­ mercial tourist attractions. Unfortunately, many ofthe stone quarries which produce crushed aggregate for tourists visiting these sites have viewed the deep clear construction. Untold other caves have been lost to water cave pools as natural wishing in which enormous limestone mines in the Yucatan Peninsula. to throw a coin or two. Copper coins tend to rapidly Many caves have been filled and built over by golf deteriorate and dissolve in salt water, producing high courses, hotels and housing developments in Bermu­ levels of toxic copper ions in the cave waters. In one da. Recently, a series ofluxury town homes were built such cave in the Canary Islands off the coast of West directly on top of the largest cave lake in Bermuda. Africa, an endemic, cave-adapted crab related to deep­ sea species is showing a marked decline in abundance Sometimes even seemingly innocent activities over the last ten years or more, probably in response can threaten caves and cave animals. Along the Ca­ to high levels of copper in the cave water. ribbean coast of the Yucatan Peninsula, many open water pools are inhabited by several species It is time that cave divers in particular begin to rec­ offreshwater fish. Some of these fish have learned to ognize the unique biological resources of caves and follow divers into caves, moving in front of the dive take steps to make sure such systems and organisms team and voraciously darting in to devour any help- are protected for future generations. 67 Unable to rent cars on the island, Dr. Tom I1iffe and Jill Heinerth are using any means available to get to the dive site in Bermuda. Photo: Nate Skiles

CONTACT INFORMATION Dr. Tom Iliffe Dept. ofMarine Biology, Texas A&M University at Galveston· www.cavebiologycom A large quany operation in Bermuda has destroyed unique cave ecosystems. Photo: Tom I1iffe In March 2002, Tom Iliffe and his gradstudent Scott Webb were invited byfilmmaker Wes Skiles to the Yucatan Pen­ REFERENCES AND FURTHER READING insula ofMexico to carry out diving explorations and bio­ Botosaneanu, L., 1986. Mundi. E 1. Brill, Le­ logical investigations of the Ring of Cenotes, a 180 km iden, 740 pp. diameter semi-circle of water-filled caves. The Ring of Culver, D.C. and WB. White (Eds.), 2004. Encyclopedia of Cenotes is the only surface expression ofthe 65 million­ Caves, Elsevier, Burlington, MA, 654 pages. year-old meteorite impact crater which caused the extinc­ tion ofthe dinosaurs. The story ofthis expedition, "Watery Gunn, 1. (Ed.), 2004. Encyclopedia of Caves and Graves ofthe Maya", is recounted in the October 2003 is­ Science, Fitzroy Dearborn, NY, 902 pages. sue ofNational Geographic Magazine andon the National Iliffe, T.M, 2000. Anchialine cave ecology. In: Ecosystems Geographic website. ofthe World. 30. Subterranean Ecosystems, H. Wilkens, D. C. Culver, & WF Humphreys (eds.), Elsevier Science, To read about the expedition, go to: http://magma.nation­ Amsterdam, p. 59-76. algeographic.com/ngm/0310/feature4/index.html Iliffe, T. M, 2004. Anchialine caves, biodiversity in. In: Encyclopedia ofCaves, D.C. Culver and WB. White. eds., Elsevier, Burlington, MA, p. 24-30. luberthie, C. and V Decu, 1994. Encyclopaedia Biospeo­ logica, Societe de Biospeologie, Moulis, France, vol. 1 (1994) p. 1-834, vol. 2 (1998) p. 835-1374, vol. 3 (2001) p.1375-2294.

ABOUT THE AUTHOR ------Tom Iliffe earned degrees in Biochemistry and Ocean­ ography at Penn State, Florida Slate and the University ofTexas Medical Branch. Prior to coming to Texas A&M University at Galveston, Tom workedfor 11 years as a Re­ search Scientist at the Bermuda Biological Station. It was in Bermuda that he became interested in marine cave biol­ ogy. Diving explorations ofBermuda caves resulted in the discovery ofmore than 200 species, 70 ofwhich were new 10 science. Tom has led many expeditions worldwide to study and collect animals from underwater caves. Tom is currently a Professor ofMarine Biology at Texas A&M University Dr. Tom I1iffe using his Megalodon to collect ani­ at Galveston where he teaches courses in , mals inside the cave. and Tropical Marine Ecology. Learn more about identifying cave animals at: www.cavebiofogy.com. 68