Temporal and spatial activity of the key-hole limpet Fissurella crassa (Mollusca : Gastropoda) in the eastern Pacific

An automated photographic technique was used to collect quantitative inform ation on the activity patterns of Fissurella crassa under heavy-exposed sea conditions. The activity of this key-hole limpet was confined to nocturnal low tides. Total length of excursions was significantly greater during spr ing tides than neap tides, as was the maximum distance reached fi,om the re fuge. Total duration of excursions and their average speed did not vary sig nificantly according to the spring/neap cycle. While the direction angle of excursions relative to the refuge was not influenced significantly by the spring/neap cycle, the lowest zone within the intertidal was reached by F. crassa during spring low tides only. Fissurella crassa showed a spatial activity pattern fluctuating intra/inter -individually between a central place foraging and a ranging strategy, with a marked propensity for the former. Looped excursions were characterized b y higher speed for the movements away and toward the limpet's refuge, than the movements at maximum distance front the refuge. As the outward and inwa rd branches of looped excursions often overlapped extensively, trail-follow ing is suggested as the main mechanism of orientation used by F crassa to r elocate the refuge.