Ecological physiology of the anchialine shrimp Barbouria cubensis: a comparison of epigean and hypogean populations

Stygobites have morphological, ethological and physiological adaptations for their subterranean existence. Included in the physiological adaptations of hypogean organisms is a reduced metabolism with respect to related epigean organisms. Our objectives were to examine the physiological adaptations of the shrimp, Barbouria cubensis, to the anchialine environment through the use of energetics. Barbouria cubensis were collected from oxic anchialine pools in the Bahamas and from a dysoxic cave system in the Yucatan Peninsula of Mexico. Metabolism was addressed via direct measurement of oxygen consumption using microcathode oxygen electrodes as well as the activities of three primary metabolic enzymes, citrate synthase (CS), lactate dehydrogenase (LDH), and malate dehydrogenase (MDH). Additionally, protein and lipid content were determined. Respiration rates of the B. cubensis from the oxic environment were lower than reported values for other epigean crustaceans but greater than reported values for stygobitic crayfish. The specimens collected from the dysoxic environment in the Yucatan differed significantly (p < 0.01) from the specimens collected in the oxic environment in oxygen consumption, enzyme activities, and lipid concentration. Enzymes of B. cubensis from both sites were anaerobically poised with LDH activities exceeding those of CS in all organisms. But in the Yucatan B. cubensis, LDH activities exceeded MDH activities. Percent protein did not vary significantly between the two systems. Barbouria cubensis provided us with an opportunity to examine the process of cave colonization by looking at the metabolism of specimens in a dysoxic environment and those residing in oxic, surface pools.