OBSERVATIONS ON THE BIOLOGY AND GEOLOGY OF ANCHIALINE

Thomas M. Iliffe Bermuda Biological Station for Research Ferry Reach GE 01, Bermuda

ABSTRACT METHODS:

Significant biological and geological Specialized 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 , 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 and volcanic caves equipment can fail, so that is include submerged and , 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, tank gauge, Recent diving explorations of inland compensator with automatic inflator, caves containing marine waters have revealed minimum of three underwater 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, , , been introduced or redefined in order to 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 ". 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 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 (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. 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) 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 . 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 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 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 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 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. Such caves could systems. During the course of have formed during Pleistocene low sea biological studies of anchialine caves, several stands by vadose groundwaters flowing along significant geological phenomena have been the top of the impermeable basalts toward noted. the sea. Several lines of evidence point to Submerged stalactites and stalagmites, the existence of such deeper caves in which can form only in air, are common Bermuda. Cave divers have reached break- features of anchialine limestone caves (Fig. down chokes at depths of 24 m indicating Id). These have been observed in all sections that deeper levels must have existed at some of Bermuda's caves to depths of 24 m. time in the past. During a drilling operation Underwater speleothems have been noted in Government Quarry, a large cave was from a in Belize at depths to 122 encountered at a depth of 18 m which m (Dill, 1977). Despite their long immersion, continued until volcanic flows were recov- delicate helectites and "" stalac- ered from -33 m (Peckenham, 1981). A funnel tites in the fully marine waters of Bermuda's shaped depression about 2 m in diameter in caves show no evidence of resolution. the sand floor of Tucker's Town Cave at a However, speleothems close to the fresh depth of 20 m suggests the presence of a water lens in Bahamian caves are often lower level to the cave into which the sand pitted and crumbling. is disappearing (Fig. 3b). Isotopic analyses of submerged speleo- Cave sediments are generally a fine thems can provide insights into sea level grained silt. The origin and rate of deposi- fluctuations and paleo climates. Thorium- tion of sediments in anchialine caves is still uranium dating of speleothems can be used in question. Although moderate to strong to document periods of lowered sea level and tidal currents transporting exogenous can thus be used for generating paleo sea particles into the cave are present along level curves (Harmon and others, 1978, 1981). coastlines, caves farther inland lack notice- In addition, estimates of paleo able currents and have waters devoid of can be made from stable isotope suspended particulates. Sediments in a few ratios of fluid inclusions in speleothems caves contrast sharply with the norm. (Schwarcz and others, 1976). Tucker's Town Cave in Bermuda contains a Exploration and mapping of anchialine 60 m long underwater chamber floored with caves has revealed previously unsuspected sand probably derived from the nearby South morphological features. In contrast to the Shore beaches. Despite the lack of noticeable limited extent, predominant collapse cham- currents in this cave, ripple marks are bers and fissures entrances of Bermuda's dry evident on the sand surface (Fig. 3b). caves, the 2 km long and totally underwater Other unusual features have been noted Green Bay Cave System (Fig. 2) consists of in underwater caves. A horizontal white nearly level, anastomosing passages, probably "bathtub ring" is present on the walls at a of vadose origin, reaching across a narrow depth of 14 m in only one section of the peninsula of land from the almost completely Green Bay Cave, Bermuda (Fig. 3c). This

Fig. 3a. Silhouette of a diver in the . North Shore Passage (Green Bay Bermuda), a long, nearly level, anastomosing passage at 18 m depth, probably of vadose origin.

Fig. 3b. Funnel-shaped depression (below diver) at 20 m depth in Tucker's Town Cave, Bermuda was probably formed by sand dropping through a small hole into a deep cave. Note sand ripples in lower left corner.

Fig. 3c. White "bathtub ring" at 13 m .. depth in the Harrinnton Sound Passane , ,,p, (Green Bay Cave, ~ermida) may be evidence ,'8'. *qk$,i.*w.'t P ', ,:.; of a paleo lens. 'ha.. , . ;.s,q. si". . '%' . .,. 8, , ,,",":L## ,.:, '.. , , ..,

on dark basalts in the Jameos del Agua lava tube (Lanzarote, Canary Islands) may be a n ,- submarine cement. approximately half meter wide band appears peracaridan crustacean from marine caves to be the result of bleaching, possibly by a on Bermuda: Journal of Crustacean paleo fresh water lens, of the normally Biology, v. 5, p. 58-73. darker brown wall coating on exposed bedrock. Carew, J.L., and Mylroie, J.E., 1984, Sub- Anchialine lava tube caves also provide merged evidence of Pleistocene low sea interesting subjects for study. Several of levels on San Salvador, Bahamas: these caves are of apparently recent origin N.O.A.A. Undersea Research Program, v. and thus were probably formed underwater. 2, no. 2, (in press). The sea water flooded sections of the caves both compare and contrast with terrestrial Dill, R.F., 1977, The Blue Holes - geological- tubes. Both may be of comparable size and ly significant submerged sink holes and configuration and share the presence of caves off British Honduras and Andros, lateral benches, lava stalactites and floors of Bahama Islands: Proceedings of the Third solidified lava or breakdown. However, a International Symposium, lithified white carbonate crust, possibly a Miami, , p. 237-242. submarine cement, is common in underwater sections of the Jameos del Agua lava tube Exley, S., 1981, Basic cave diving - A (Fig. 3d), but not in the terrestrial sections blueprint for survival: Jacksonville, of the same cave. Florida, Cave Diving Section of the As diving investigations of marine caves National Speleological Society, 46 p. progress, further biological and geological discoveries will surely result. Caves in vast Exley, S., and Young, I.F., eds., 1982, NSS areas of the Indo-Pacific are just now cave diving manual: Jacksonville, Florida, beginning to be explored and studied. New Cave Diving Section of the National equipment and techniques, such as ultra high Speleological Society, 291 p. pressure diving tanks and underwater scooters, are permitting farther and deeper Fornari, D.J., Ryan, W.B.F., and Fox, P.J., penetrations into underwater caves. The use 1985, Sea-floor lava fields on the East of and remotely operated Pacific Rise: Geology, v. 13, p. 413-416. vehicles (ROV) may provide a means of investigating even those caves in the deep Fosshagen, A., and Iliffe, T.M., 1985, Two sea. new genera of Calanoida and a new order of Copepoda, Platycopioida, from marine ACKNOWLEDGMENTS caves on Bermuda: Sarsia, v. 70, p. 345- 358. This research was supported by grants from the National Science Foundation (DEB- Harmon, R.S., Land, L.S., Mitterer, R.M., 8001836, BSR-82 15672, BSR-8417494), National Garret, P., Schwarcz, H.P., and Larson, Academy of Sciences, Explorers Club, G.J., 1981, Bermuda sea level during the Earthwatch and the National Speleological last interglacial: Nature, v. 289, p. 481- Society. Permission to use Figs. Id and 3a 483. was generously provided by the photo- graphers Laurence Gould and Robert Power, Harmon, R.S., Schwarcz, H.P., and Ford, respectively. All other photos are by the D.C., 1978, Late Pleistocene sea level author. Robert Power also provided the map history of Bermuda: Quaternary Research, of Green Bay Cave (Fig. 2). Assistance of v. 9, p. 205-218. the Bermuda Cave Diving Association is gratefully acknowledged. This paper is Hart, C.W., Jr., Manning, R.B., and Iliffe, Contribution No. 1105 of the Bermuda T.M., 1985, The fauna of Atlantic marine Biological Station for Research. caves: Evidence of dispersal by sea floor spreading while maintaining ties to deep REFERENCES CITED waters: Proceedings of the Biological Society of Washington, v. 98, p. 288-292. Bowman, T.E., and Iliffe, T.M., 1985, Mictocaris halope, a new unusual Holthuis, L.B., 1973, Caridean shrimp found in land locked salt water pools at Yager, J., 1981, Remipedia, a new class of fourIndo-West Pacific localities (Sinai Crustacea from a marine cave in the Peninsula, Funafuti Atoll, Maui and Bahamas: Journal of Crustacean Biology, Hawaii Islands). with the description of v. 1, p. 328-333. one new genus and four new species: Zoologische Verhandelingen, Leiden, v. 128, p. 1-48

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