Influence of Canopy Gaps on Mangrove vegetation and Crab communities in the Andaman Islands

Abstract

Small-scale, infrequent disturbances enhance habitat heterogeneity in the landscape and promote diversity. Canopy disturbances caused by lightning strikes in mature mangrove stands modify environmental factors such as canopy cover and light intensity. Response of mangrove vegetation and crab communities to such canopy gap formation remains the least investigated aspect among ecologists. The canopy gaps were stratified based on the recent and recovering status of vegetation recruitment along with gap age, and an intact forest plot was sampled as a control treatment. The result shows that canopy opening has a significant effect on water temperature, and it has a profound influence on structuring vegetation and the crab communities in mangroves. Seedling and sapling density was 2-fold higher in canopy gaps than intact forest, and higher sapling survival was witnessed in canopy gaps. 28 species of crabs were recorded collectively from all treatments. Crabs of the family Ocypodidae were found in large proportion in canopy gaps, as the organic matter from microalgae and bacteria is their primary food base. Overall, canopy gaps in contiguous mangrove habitats are a hot spot for crab diversity and serve as a regeneration niche for seedlings and saplings by creating structural heterogeneity in the landscape. It suggests that small-scale natural disturbances, such as canopy gaps, promote habitat complexity and crab diversity.