Typhliasina pearsei (Hubbs, 1938)
Synonyms: Typhlias pearsei Hubbs, 1938; Ogilbia pearsei (Hubbs, 1938); Ogilbia (Typhliasina) pearsei (Hubbs, 1938)
Taxonomic Characterization: Clear white brotulid becoming pinkish along the posterior margins. Total absence of eyes. Appearing white with pink posterior margins. Head large with broad snout. Large and well developed sensory cavities and papilla on head. Longitudinal split at mouth edges, nose opening adjacent to the superior lip. Scaled body. Long dorsal and anal fins not continued with the caudal. Males with claspers (Schmitter-Soto, 1998a).
Ecological Classification: Stygobitic
Size: Up to 9 cm SL
Number of Species in Genus: One
Species Range: Cenotes and groundwater on the Yucatan peninsula, Mexico. This species coexists 43% of the time with Ophisternon infernale (Synbranchidae). Typhliasina also coexists with the catfish Rhamdia about 53% of the time. Endemic crustaceans such as Creaseria morleyi, Typhlatya mitchelli, T. pearsei and Creaseriella anops among others are also found in association with Ogilbia.
Closest Related Genera: Typhliasina resembles Ogilbichthys and Gunterichthys in the broad and robust head and the fused colliculi of the otoliths (Møller et al., 2004).
Habitat: Freshwater limestone caves
Ecology: As the top predator in the Quintana Roo anchialine community (Pohlman et al., 1997), it is likely that the population is small. In freshwater habitats of the Yucatán state, populations are also small, with few specimens observed in each cenote. It seems that it is not widely distributed, recorded in at most 16% of the caves. Considering that most observations are from the surface, it is expected that with additional underwater observations, this proportion of occurrence will increase. Lives in the freshwater aquifer. Temperature range between 22 and 27°C (Schmitter-Soto, 1998a). Various Crustacea are probably the main food supply. Both cave fish are often found together and rarely in sites with the stygophilic Rhamdia guatemalensis (Pimelodidae). This may be due to competitive exclusion.
Life History: Viviparous. Reproduction between December and February. Young animals (size 22-34 mm) are independent from birth. From 2 to 11 young are produced, depending on size of female (Navarro-Mendoza, 1988).
Evolutionary Origins: Derived from marine forms (Wilkens, 1982).
Conservation Status: Endangered (Williams et al., 1989), Endangered (IUCN, 1990; 1994), VU(D2) (IUCN, 1996). The IUCN (1996) criteria describe the following: Population with area of occupancy less than 100 km2, or number of sites less than 5. Population therefore prone to effects of human activities or stochastic events which could result in the severe worsening of the status in a very short time (Proudlove et al., 2001).
The main threats to this species, and to the syntopic Ophisternon infernale (Synbranchidae), are from various sorts of human-induced water pollution, particularly bacterial in the form of fecal coliforms and from excess nitrate. The human population obtains its water from the aquifer underlying the plateau and, until recently, disposed of its waste water into "sumideros" or septic tanks in cities and big towns, often only a few meters from where it was obtained. In Mérida, as well as in other cities, people use piped water. The situation is particularly acute under the largest city, Mérida, but it seems likely that the same situation will exist elsewhere on the peninsula. In rural areas, there is little or no sewage treatment and that industrial and domestic waste is sometimes discarded into caves. A further threat is from excessive freshwater removal that will lead to the incursion saline waters into the normally freshwater zone. The population of the peninsula is growing (censused at 2.9 million in 1995; Mérida estimated at 649,770 in 1995) and this will place greater and greater strain on the water resources of the area. Another important threat is the modification and/or the intensive use of their habitat by humans either for recreational or touristic purposes.
Waste water in some parts of Mérida is now collected and pumped to various treatment plants. The resulting treated product is injected into the saline groundwater 200 m below the surface of the aquifer. The injected water will become saline and remain below the less dense freshwater lens. This action itself may be of detriment to the health of the aquifer. Another concern is that the injection wells sometimes are not properly sealed, causing the waste water to filter to levels above the saline layer. Dissolved oxygen levels are inherently low because there is no photosynthesis and there is no ability for atmospheric exchange. Increased organic input from the waste water will increase bacterial activity which will lead to the consumption of oxygen and to anoxia in areas around the injection point.
Mérida is only one of many growing towns and cities on the Yucatán Peninsula which has also a growing tourist population. The main problems are the increased use of water for the growing population and the government programs that promote intensive use of the aquifer and the use of fertilizers to increase the production in rural areas. These visitors will demand clean water for drinking and washing and will also demand that their waste is removed rapidly and completely. The continued existence of all of the freshwater organisms of the plateau depends wholly on their water supply quality. Human water supply should be augmented by the collection and subsequent treatment of rainfall to supplement that obtained from the aquifer. All wastewater should be collected and properly treated. It should not be injected into the aquifer which contains is a very delicate ecosystem. The best economic solution is probably to pipe it out to sea, although this will of course have its own detrimental effects. An important problem here is that the continental shelf is quite wide and thus, it will be expensive to dispose of waste water far enough out to sea to avoid the immediate effect on the coastal systems. Detailed studies of the aquifer need to be made to monitor its health.
Contributor: Graham Proudlove, University of Manchester, UK; Roger
Medina, Universidad Autónoma de Yucatán, Mérida, Mexico
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