The Salt Life of Sea Snakes

Dehydration and lack of fresh water are key problems for vertebrates that have secondarily invaded marine environments. However, recent investigations of 9 species representing the principal clades of sea snakes indicate these reptiles do not drink seawater but will drink fresh water at variable thresholds of dehydration, which these snakes tolerate well. Marine reptiles were previously thought to remain in water balance without consuming fresh water owing to the ability of extrarenal salt glands to excrete excess salts obtained either from prey or from drinking sea water directly. Thus, species of marine snakes which dehydrate at sea and are dependent on environmental sources of fresh water represent a shift of paradigm from previous “textbook” literature. Recent studies also demonstrate that the abundance and diversity of sea snakes correlate with access to fresh water, and that global distributions and evolutionary origins are related to low and variable ocean salinity. Currently available data indicate that sea snakes have relatively high levels of total body water (around 80% of body mass), are comparatively resistant to dehydration, and have diverse thresholds for thirst.