Impact of Nesting Socotra Cormorants on Terrestrial Invertebrate Communities

SIMPLE SUMMARY: Seabirds that breed on remote islands often form dense nesting colonies. Nesting activities during the course of a breeding season could result in the deposition of large quantities of feces that could influence soil biodiversity. We determined the impact nesting activities of Socotra Cormorants on soil invertebrates using artificial substrate samplers. Nesting activities had variable effects on soil invertebrates. Isopods and spiders declined in due to nesting activities. Beetles and ants seemed to be unaffected by nesting activities. Ticks increased significantly but in non-nesting areas. Our study shows that seabird breeding activities determine long-term community structure of remote islands by affecting different invertebrate taxa in different ways. ABSTRACT: Seabirds and some inland waterbirds nest in densely aggregated colonies. Nesting activities for a duration of months could lead to large quantities of guano deposition that affects the soil chemistry, flora and fauna. We assessed the effects of nesting Socotra Cormorants on soil invertebrates on Siniya Island, United Arab Emirates. Artificial substrate traps were set in nesting and non-nesting areas to sample invertebrates both before and after nesting had occurred. Diversity of soil invertebrate taxa decreased significantly in nesting areas compared to non-nesting areas after the commencement of nesting. This indicated that nesting activities had a negative effect on diversity. Among selected taxa, isopods and spiders decreased significantly in response to nesting activities. In contrast, ants were likely affected by habitat while beetles did not change significantly in response to nesting activities, suggesting that their numbers probably fluctuated in relation to seasonality. Ticks increased significantly but only in non-nesting areas. Thus, the impact of nesting varied between taxa depending on life history and seasonality. Our observations reflect the dynamic nature of invertebrate abundance that is affected by seasonality and the hyper-abundance of nesting seabirds.