Continuous, video-recording assessment of daily activity cycle of the ghost crab Ocypode quadrata Fabricius, 1787 (Brachyura: Ocypodidae) in southeastern Brazil

Several studies have used the abundance of ghost crabs (Ocypodidae) as an indicator of human impacts on sandy beaches. Such studies have used assessment of burrows, even if the ratio between the number of burrows and crabs might not be consistent across beaches over time. The activity period of crabs frequently mentioned in such studies is always assumed to be during daylight. The few published studies on the daily activity of Ocypode Weber, 1795 preclude generalizations. Our study assessed the activity of O. quadrata Fabricius, 1787 over six 24-hour cycles, using the most affordable filming devices on a restricted-access beach, thus excluding the influence of observers and tourists. The number of individual crabs and the time spent outside the burrows were calculated for every ten minutes of filming. These variables were assessed for correlation to each other, tidal height, temperature, and time of day. Both activity variables were significantly related to tide height, regardless of temperature or time of day. Peaks of activity in O. quadrata occurred during both day and night, and were mostly influenced by circatidal rhythms.