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BURROW DYNAMICS OF THE RED LAND CRAB GECARCOIDEA NATALIS (BRACHYURA, GECARCINIDAE) IN RAIN FOREST ON CHRISTMAS ISLAND (INDIAN OCEAN)

Abstract This study quantified the burrow dynamics of the gecarcinid land crab Gercarcoidea natalis (Pockock, 1888), the most common land crab in rain forest on Christmas Island, Indian Ocean. Mean burrow density remained relatively stable over a two-year period, fluctuating between 1.4 and 1.6 burrows/m2. Burrows were long-lived, stable structures, with a mean turnover time estimated at least 4.4 ± 1.6 y, and probably greater than 5 y. Burrow entrances were also highly stable in space. Two thirds of burrow entrances were repositioned within an area of 20 cm2 or less, and 83% of entrances moved within less than 60 cm2. Red crabs accumulate litter around their burrow entrances and create nutrient hotspots in the soil around burrow entrances, whose stability and longevity suggested that germinating seedlings may derive some benefit from germinating in the immediate vicinity of crab burrows. The rate of burrow turnover is slow, causing minimal soil disturbance at the study site with little, if any, impact on above-ground plant productivity. Red crabs plugged their burrows intermittently year-round with loose wads of leaves or with soil. Major plugging peaks were recorded in March of both years of the study, midway through the wet season. At this time 49–59% of burrow entrances were sealed with a deep plug of soil, and many burrows remained plugged long enough for the crabs to molt. These data suggest that most red crabs molted annually at the study site.