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Crustacean extremophiles in Yucatán’s anchialine caves:

Metabolic adaptations and associated environmental parameters


Lara Hinderstein
Department of Wildlife and Fisheries Sciences, Texas A&M University
College Station, Texas USA


 

Figure 1: Lara and Dr. Iliffe chase an elusive stygobitic shrimp in Cenote Ponderosa

The hydrology of the Yucatán region is distinctive in that there is a subterranean stratification of lighter fresh water over denser marine water.  There are no surface streams or rivers in the Yucatán and thus all fresh water is found underground in a networking system of caves. In order to survive in this extreme environment typically lacking in oxygen and food, cave animals or stygobites have adapted a low metabolism.  Most cave animals are from the subphylum Crustacea and typical adaptations include loss of pigmentation, loss of eyes, and highly developed chemosensory systems.   

 

Figure 2: Cenote Crustacea's remipede city - remipede above diver's right hand

Two types of cave systems located in the state of Quintana Roo were studied to compare and contrast results: one cave with plentiful nutrition was compared to more typical caves with a paucity of food.  Metabolic rates of cave animals were measured and analysis of respiratory enzymes was conducted on representatives of four orders of stygobitic organisms.  Water quality parameters of salinity, temperature, dissolved oxygen, and pH were then compared between the two types of systems to suggest their effect on metabolic rates.   Mass-specific respiration rates were significantly lower than comparable open water crustaceans, but did not differ significantly between caves.  Respiratory enzymes of the stygobites showed an adaptation to anaerobic respiration with higher lactate dehydrogenase activity than citrate synthase.  Malate dehydrogenase activities for most stygobites were also greater suggesting further adaptation to a hypoxic environment.  Hydrological profiles between the two caves were significantly different indicating the influence of habitat on the physiological ecology of these animals.  These results suggest that current nutritional content of the anchialine cave habitat does not influence metabolism, but an evolutionary role cannot be excluded at this time.  More likely influences are low dissolved oxygen and the stable environment with little change over thousands of years found in caves.

 

Figure 3: Dr. Iliffe admires speleothems in Cenote Maya Blue

With the development of the area around the Riviera Maya resort corridor, the marine systems of Quintana Roo are now in danger of losing much of their animal diversity and of becoming a series of fragmented and isolated underground water deposits.  The cave systems also benefit humans by serving as a vital source of freshwater for the region.  Marine caves are a link between many ecosystems: from the interior jungle to coastal coral reefs.  Any pollution or destruction of habitat in the caves will eventually affect all surrounding ecosystems.  It is of extreme importance that we learn more about this unknown underworld so that we can prevent current and future threats.