The Impact of Nesting Socotra Cormorants on Soil Chemistry and Vegetation in a Large Colony in the United Arab Emirates

Abstract

Socotra Cormorants (Phalacrocorax nigrogularis) are regionally endemic seabirds with restricted distribution. To better understand their nest selection, we assessed vegetation and soil elements in their nesting areas at Siniya Island of United Arab Emirates. Field sampling was done from three areas (2011 nesting area, 2012 nesting area and control area) in February and March in 2013. Sampling consisted of vegetation assessment in the field and close-range photography. Ground cover within quadrats was classified into the percent of (1) living cover, (2) dead cover, (3) droppings, (4) bare ground and (5) other. Soil samples were analyzed for thirteen elements. Multivariate stepwise discriminant analysis was performed to determine the importance of the attributes on nest sites. The contribution of Function 1 to the discriminant model was estimated to be 77.4%, whereas Function 2 contributed 22.6% to the discriminant model (P ≤ 0.05). Sites could not be classified adequately using ground cover alone; however, discriminant analysis using soil attributes could better distinguish sites. We noted that Fe and Mn had high discriminant ability in Function 1, whereas Al and Cr showed high discriminant roles for Function 2. The contribution of Function 1 to the model, using soil attributes, was estimated to be 90.7% (P ≤ 0.05). The combination of ground cover and soil attributes did not improve discrimination of nest sites. Furthermore, some soil variables (Ca, Na, Cd and Cr) were much higher than normal levels in soil, indicating high transport of marine nutrients to nesting sites, which could detrimentally affect surrounding vegetation.Diversity 2015, 7 61

Impact of Nesting Socotra Cormorants on Terrestrial Invertebrate Communities

“…Guano from Socotra cormorants become part of the soil and the impact on the vegetation is visible by the end of the season [ 7 ]. We found that Socotra cormorants significantly influence ground-dwelling invertebrate diversity and the abundance of selected taxa.…”

“…In Chrzypsko Lake, Poland, a breeding population of 155–175 pairs of Great Cormorants ( Phalacrocorax nigrogularis ) caused an increase in the concentration of nitrogen and phosphorus in the ground water as well as an elevation in the E. coli and other coliform bacteria, within the boundaries of the colony [ 6 ]. Similarly, Socotra cormorants elevated concentrations of soil elements through allochthonous transport of nutrients on an island in the United Arab Emirates [ 7 ]. Offshore breeding sites with dense aggregations of cormorants or other seabirds have elevated soil nutrient content that regulates their plant and invertebrate assemblages [ 3 ].…”

Demographic consequences of native fox predation on Socotra cormorants on Siniya Island, United Arab Emirates

“…The initial population size was set at 46 500 individuals (from Jennings 2010, estimated in 1995). The carrying capacity of the island was set at 300 000 individuals based on the observation that additional habitat was present on Siniya Island that could support a significant increase in the population (Ksiksi et al 2015). We modelled the population for 50 years using 1000 simulations.…”