Is faunal diversity on Maltese sandy beaches related to intensity of human use?

Abstract

Sandy beaches are rare in the Maltese Islands where only some 2.4% of the ca 271km coastline is sedimentary; yet such beaches are much sought after for their amenity value by tourists and locals alike. Carrying capacity studies conducted by the Malta tourism authorities have shown that most beaches are under very heavy use while a study by Deidun et al. (2003) has indicated that the fauna of Maltese sandy beaches tends to be impoverished compared to other Mediterranean beaches and has hinted that this may be a result of lack of recruitment due to the relative isolation of these beaches. Therefore human use of Maltese sandy beaches may potentially be a key factor affecting faunal diversity of these beaches. We explored this hypothesis by sampling the faunal assemblages of four Maltese beaches (Gnejna and White Tower Bay on Malta, and Xatt l-Ahmar and Ramla l-Hamra on Gozo) using pitfall traps set up in the wet and dry zones of each beach during the summer, when human use is expected to be highest. Human use of these beaches was assessed by estimating human occupancy of the beaches from standardised photographs. Beach occupancy values of 2400, 5700, 6700, and 12300 persons per square km were estimated for Ramla, White Tower Bay, Xatt l-Ahmar and Gnejna, respectively, establishing a gradient of anthropogenic impact with Gnejna as the most impacted beach and Ramla the least. Three components of faunal diversity were considered: population size (number of individuals), species richness, and taxonomic composition. Faunal population size ranged from 7 individuals/trap/hour for Xatt l-Ahmar to 199 individuals/trap/hour for Ramla in the wet zone, and from 22 individuals/trap/hour for White Tower Bay to 87.33 individuals/trap/hour for Gnejna in the dry zone. The species richness ranged from 7 species (Xatt l-Ahmar) to 17 species (White Tower Bay). Between them, Amphipoda, Isopoda, Coleoptera Dermaptera and Hymenoptera accounted for the bulk of both species and individuals collected. There were no statistically significant correlations between population size, species richness and taxonomic composition. The species collected from the four beaches was categorized into psammophiles, coastal species (occurring in coastal habitats but not restricted to sandy beaches) and euryoecious (ubiquitous) species. Ramla exhibited the highest proportion of psammophiles (98.4% of all species collected at Ramla) and the lowest proportion of ubiquitous ones (1.5% of all species), whilst for Xatt L-Ahmar the equivalent figures were 31.8% and 61.8% for ubiquitous and psammophilic species respectively From the present study it results that there is no trend between any of the three components of faunal diversity analysed and the degree of human occupancy of the beaches, and the only tangible human impact was related to faunal habitat–use specificity. This suggests that human use of the beaches has no direct impact on the faunal assemblages of the mediolittoral and supralittoral zone of the beaches studied but that high levels of human disturbance result in generalists displacing specialist psammophilic species. In spite of these results, intense human use of Maltese sandy beaches is of conservation concern since previous work has indicated a high degree of ‘compartmentalisation’ with different beaches harbouring distinct faunal assemblages either due to natural inter-beach barriers to dispersal, or due to unique environmental conditions present on the different beaches, including the nature and intensity of anthropogenic pressures. In addition, the present study addresses only the direct effect of trampling by beach visitors; indirect negative impacts, such as those of beach cleaning, have been well documented in other studies.