Observations on the Biology and Geology of Anchialine Caves
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OBSERVATIONS ON THE BIOLOGY AND GEOLOGY OF ANCHIALINE CAVES Thomas M. Iliffe Bermuda Biological Station for Research Ferry Reach GE 01, Bermuda ABSTRACT METHODS: CAVE DIVING Significant biological and geological Specialized cave diving techniques and discoveries have resulted from the use of equipment have been developed for the safe specialized cave diving techniques for the exploration and study of underwater caves exploration and study of anchialine caves. (Exley, 1981; Exley and Young, 1982). Unique Many new and higher taxa of troglobitic hazards, quite different from those en- organisms have been found, some of which countered by divers in open waters, exist in are relic "living fossils". Marine troglobites underwater caves. When cave diving, the have at least three possible origins: (1) ceiling restricts access to the surface making localized cave colonizations with dispersal by a diver much more dependent upon his ocean currents, (2) Tethyan origin with equipment and its proper function. Should an dispersal by sea floor spreading and con- emergency such as an air failure occur, it is tinental drift, and (3) deep sea origin, necessary to exit the cave the same way it possibly in association with deep water was entered - out and then up. A basic caves. Geological phenomena of interest in premise of cave diving is that any piece of anchialine limestone and volcanic caves equipment can fail, so that redundancy is include submerged stalactites and stalagmites, the key to safe cave diving. Typically, cave cave morphology, mineralogy, and sediments. divers use double tanks connected with a dual valve manifold, two independent INTRODUCTION regulators - one for each tank valve, submersible tank pressure gauge, buoyancy Recent diving explorations of inland compensator with automatic inflator, caves containing marine waters have revealed minimum of three underwater lights of which the presence of a unique environment one must be of a minimum of 30 watts and containing features of special biological and have a burn time of at least 50 minutes, geological significance. Several terms have nylon guideline on reel, watch, depth gauge, been introduced or redefined in order to decompression tables, and knife. more accurately characterize these caves. Special safety precautions are also The term "anchialine" was originally coined required in cave diving. It is necessary to by Holthuis (1973) to describe "pools with no reserve at least 2/3 of the starting air surface connection to the sea, containing supply for the swim out of the cave. A salt or brackish water, which fluctuates with single continuous guideline must be run from the tides". Stock and others (1986) proposed the entrance of the cave throughout the a more exact ecological definition for this route followed on the dive. Stirring up of term: "bodies of haline waters, usually with fine bottom silt, which can reduce under- a restricted exposure to open air, always water visibility to zero, should be avoided by with more or less extensive subterranean proper use of the buoyancy compensator and connections to the sea, and showing by special swimming techniques. A course in noticeable marine and terrestrial influences". cave diving provides the opportunity for Submarine caves are those which are entirely practice and development of these essential filled with sea water, while littoral or sea diving skills. All cave diving done under this caves are shallow erosional features opening study has met standards set by the Cave at sea level and containing air plus sea Diving Section of the U.S. National Speleolo- water. The term "marine cave" is a broad gical Society. one referring to all caves containing haline waters of marine origin and thus includes anchialine, submarine, and littoral caves. ANCHIALINE CAVES Some taxa show even more complex biogeographic relationships. The shrimp Anchialine caves occur in both limestone Procaris is known only from caves and and volcanic rocks. Extensive anchialine anchialine pools on Bermuda, Ascension limestone caves found in Bermuda, the Island, and Hawaii. Equally puzzling is a new Bahamas, and other locations were probably genus of misophrioid copepods which has formed during Pleistocene low sea stands as new species from caves in Palau and the evidenced by their general morphology and Canary Islands on opposite sides of the abundant submerged speleothems (i.e. world. stalactites and stalagmites). The longest such Examination of the fauna from Bermuda anchialine cave is the 10 km long Lucayan and Lanzarote caves indicates that several Caverns on Grand Bahama Island. Lava tubes derivations are likely (Iliffe and others, which extend below sea level can also be 1983; Iliffe and others, 1984). Those species classified as anchialine. The Jameos del Agua such as Remipedia and Mictacea (Fig. lb) lava cave on Lanzarote in the Canary Islands which represent relic "living fossil" taxa is the 2 km long, seaward-most segment of appear to have had a Tethyan origin. the tube that is partially or totally flooded Species, including the shrimp Barbouria with sea water. Other anchialine lava tubes cubensis which is known from Cuba, the are present in the Hawaiian Islands as well. Bahamas, and Bermuda, may have had a localized origin in caves and been subse- ANCHIALINE CAVE FAUNA quently dispersed by ocean currents. Still other species from anchialine caves are A rich and diverse endemic fauna has closely related to deep sea forms and may been found to inhabit anchialine caves. have originated by dispersal from this These include many relic taxa such as habitat. Such deep sea related cave forms Remipedia, a new class of Crustacea (Yager, include the galatheid crab Munidopsis 1981); Mictacea, a new order of peracarid polymorpha (Fig. lc); the polynoid poly- Crustacea (Bowman and Iliffe, 1985); chaetes Gesiella jameensis and Pelagomacel- Platycopioida, a new order of Copepoda licephala ili f fei; the halocyprid ostracods (Fosshagen and Iliffe, 1985); Atlantasellidae, Danielopolina orghidani, D. wilkensi, and a new family of lsopoda (Sket, 1980); and Deeveya spiralis; the amphipods Spelaeonicip- Deeveyinae, a new subfamily of halocyprid pe buchi and S. provo; and six species of Ostracoda (Kornicker and Iliffe, 1985). Over misophrioid copepods. 200 species of marine macro invertebrates In order to explain both the puzzling have been collected from Bermuda's anchia- biogeographic distributions and the deep sea line caves, one-third of which are new (Sket affinities of the anchialine cave fauna, Hart and Iliffe, 1981; Iliffe and others, 1983). and others (1985) have proposed the The biogeography of anchialine faunas existence of systems of caves and crevices shows many striking anomalies. Remipedia, on the steep sides of submerged sea mounts for example, is known only from limestone and along mid-ocean ridges in the deep sea. caves in the Bahamas and the Jameos del Such "crevicular" habitats could provide a Agua volcanic cave in the Canary Islands virtual continuum linking caves on distant (Iliffe and others, 1984). Other troglobitic oceanic islands via the deep sea. taxa including the mysid Heteromysoides, the There is already substantial evidence for anthurid isopod Curassanthura, and the the existence of extensive caves in the deep thermosbaenacean Halosbaena show similar sea. Keating (1985) reports on the discovery amphi-Atlantic distributions. The amphipod of two large, hydrologically active limestone Pseudoniphargus is primarily known from caves containing stalactites and stalagmites groundwaters and caves in the Mediterranean at a depth of 366 m on Johnston Island. The region and the Azores, but two troglobitic presence of abundant sponges on overhanging species from this genus are present in ledges in these caves, but not observed Bermuda (Fig. la). These distributions have elsewhere, indicates that even in deep been interpreted as implying a cave coloni- waters, caves offer a preferred biological zation early in the history of the Atlantic niche for some animals. Fornari and others followed by dispersal by sea floor spreading (1985) have found a lava tube of recent and plate tectonics. origin together with numerous fissures at the la. The amphipod Pseudoniphargus grandimanus (length about 7 mm) from C Bermuda caves belongs to a genus previously I known only from caves and groundwaters in the Mediterranean region, the Azores and I Madeira. + +Fig. lb. Mictocaris halope (length about 3 mm) f~.om Bermuda caves is a member of the new peracarid crustacean order Mictacea I whose only other representative was I described from the deep sea. Fig. Ic. Munidopsis polymorpha (length to 4 cm) from a lava tube in the Can Islands is a member of the Galatheidae, n species of which inhabit the deep sea. + Fig. Id. Submerged stalagmites (Deep Blu~ Cave, Bermuda) form only in air and wen deposited during Pleistocene low sea leve stands when the caves were dry. base of a seamount in 2700 m water depths enclosed Harrington Sound to the more open on the East Pacific Rise. Fornari (pers. North Lagoon (Fig. 3a). The average depth comm.) believes that lava tubes are a of this cave, -18 m, corresponds to that of common feature in the deep sea and are Bermuda's main reef terrace and to the important in lava dispersal around sea floor maximum depth of the North Lagoon extrusive sites. Carew and Mylroie (1984) suggesting that all three features were have found solution conduits on the sides on formed by a long stationary stand of sea San Salvador Island in the Bahamas at 105 level at this position. Indeed, undercut walls to 125 m depths, near the probable low point at sharp bends in the passage and a for Pleistocene sea level. continuous channel along the silt floor of the cave indicate vadose stream flow through GEOLOGICAL OBSERVATIONS the cave at some time in the past. An as yet hypothetical deeper system of The development of specialized cave caves may exist in Bermuda at the interface diving techniques and equipment has provided between the island's volcanic pedestal and a means to gain access to extensive and the overlying eolian limestone about 30 m geologically unique, totally submerged cave below present sea level.