Field and laboratory observations on microhabitat selection in the amphibious red sea rockskipper fish, Alticus kirki (family blenniidae)

The physiological and behavioral characteristics of the intertidal amphibious blenny, Alticus kirki, illustrate an adaptive pattern that could have been important in the invasion of the land by vertebrates during the Devonian period. Field observations show that Alticus are diurnal and spend most of their active time out of water, above but near the tidally varying water line. Their abiotic environment is complex, providing them with many choices of microhabitat. They do not thermoregulate behaviorally and probably never need to contend with evaporative water losses. They voluntarily remain in water temperatures as high as 36°C and water salinities as high as 64 ppt. They prefer high light intensities.

We also performed laboratory experiments testing the preferences of the fish for specific ecologically significant ranges of three variables: land vs water, temperature, and salinity. Preferences for land vs water were strong in given sets of conditions, but changed when experimental conditions changed. The choice of wet rocks vs water (salinity 0–50 ppt) resulted in preferences for the rocks, with no water contact, 90% of the time. Comparable experiments using moist rocks produced the opposite result: preferences for continuous contact with water 90% of the time, including full submersion 62% of the time. Rockskippers have a narrow aquatic thermal preference range near 26°C. A significant difference was observed, however, between individuals and groups of animals, groups choosing slightly lower temperatures. In contrast, salinity preference studies indicated little ability of the animal to discriminate between waters of different salinities. Animals freely entered waters of salinities ranging from 0–60 ppt. They avoided salinities above 70 ppt. They showed a slight preference for entering water in the 30–40 ppt range.

Key words:

• Amphibious fish
• Alticus kirki
• microhabitat selection
• terrestriality
• blennies