Aspects of the ecology of a sandy beach in Gozo

Abstract

The distribution and abundance ot macrotauna and macroflora along transects on the sandy beach at Ramla, Gozo, and seasonal variations in these parameters were investigated between summer 1992 and summer 1993. Granulometry and physico-chemical parameters of the sediment were measured in order to study any correlation between these and changes in the biota. Ramla is a sheltered beach with medium (M2 = 0.25-0.50mm) sand in the top 30cm up to a distance of 70m from sea level. The sand becomes finer with depth and on moving upshore. The sand was generally well to moderately sorted, except for a few poorly sorted samples where sand was compacted due to traffic. Negatively skewed values of sand samples were mostly obtained at sea level. Cluster analysis of the fauna! abundance data indicated the presence of two zones for the fauna: a high-shore assemblage of air-breathers, and a lower shore one of water-breathers. Floral zonation was similar to that on Mediterranean coastal dunes, starting with a fore-dune characterised by Cakile maritima and other pioneers and proceeding towards a consolidated dune with Tamarix africana. A total of 267 individuals representing 25 species of fauna were collected from a combined volume of l.175m3 of sand by sieving, while 149 individuals representing 28 species of fauna were collected from a combined area of 700m 2 by the standard search method. The polychaete Ophelia bicornis was the only species collected from the wet zone. No molluscs were collected and no empty valves were observed on the surface of the sand. Coleoptera were dominant in both the dry and dune zones. No fauna! group was specific to the dry zone but five groups inhabited specifically the dune: Amphipoda, Araneae, Collembola, Neuroptera and Hymen0ptera. The number of faunal taxa (Hill's NO!, number of abundant taxa (Hill's Nl) and number or very abundant taxa (Hill's N2) collected by sieving and standard search were always higher in winter than in summer for all transects. Evenness values for fauna sampled by the standard search ranged from 1.00 to 0.63, indicating that no single group was dominant in the community. For fauna collected by sieving, evenness values ranged from 0.94 to 0.38, indicating that only a few groups, such as Coleoptera and Polychaeta were becoming more dominant. Faunal diversity and abundance were higher in winter than in summer and decreased with depth. Considering all transects, eight taxa were recorded at a depth of 0 to l0cm, five from 10 to 20cm, and four from 20 to 30cm. Araneae, Collembola and Neuroptera were sampled only from the O to l0cm depth-zone but no group was exclusive to the other depths. From the dunes at Ramla, 21 species of flora were recorded from a combined area of 110m 2. Cluster analysis of the floral data indicated that distinct vegetation assemblages occurred in winter and summer. Hill's NO, Nl, N2 and evenness were higher in the winter sample than in the summer ones. Floral abundance ranged from 522 individuals/m2 in winter to O/m 2 in summer in some quadrats. Bromus rigidus, Cutandia maritima, Elymus farctus, Pancratium maritimum and Sporobulus arenarius were the dominant species in winter and C. maritima and S. arenarius in summer.