Assessing inter-beach differences in semi-terrestrial arthropod assemblages on Maltese pocket sandy beaches (Central Mediterranean)

The distinctiveness of macrofaunal assemblages on different sandy beaches in the Maltese Islands was previously suggested by different single-season studies. A multi-seasonal sampling programme using pitfall trapping was implemented on four Maltese beaches to test the occurrence of this phenomenon. A total of 29,302 individuals belonging to 191 species were collected over a 2-year period, during which the beaches were sampled once per calendar season. A total of 77 species were recorded from single Maltese beaches only, of which nine were psammophiles. Non-metric multidimensional scaling analyses of pitfall trap species-abundance data resulted in a weak separation pattern, with samples grouping mainly in terms of beach and island rather than in terms of season or year of sampling, No physical variable could conclusively explain these patterns. It is concluded that although operating on Maltese beaches, macrofaunal assemblage distinctiveness is weaker than originally thought and can be attributed to the presence/absence or abundance of just a few psammophilic species. It is postulated that this phenomenon may be related to the ‘pocket beach’ nature of Maltese beaches, where headlands on either side of the beach to a large extent prevent the occurrence of longshore currents, resulting in semi-isolation of the populations of psammophilic species. A large number of single-beach records reported in this study highlight the high degree of beta diversity and spatial heterogeneity of Maltese beaches, and the conservation importance of the individual beach macrofaunal assemblages.peer-reviewe

Zonação de comunidade bêntica do entremarés em molhes sob diferente hidrodinamismo na costa norte do estado do Rio de Janeiro, Brasil Zonation of intertidal benthic communities on breakwaters of different hydrodynamics in the north coast of the state of Rio de Janeiro, Brazil

O presente estudo pretende comparar a distribuição vertical da comunidade bêntica na zona entremarés em dois locais compostos por matacões graníticos caracterizados por hidrodinâmica distinta, reflexo da diferença na orientação dos molhes nas praias do Farol de São Tomé (Píer) e na Barra do Furado (Barra), norte do Estado do Rio de Janeiro. Quadrados de 400 cm² foram sobrepostos ao longo de três perfis verticais de ambos os sítios e amostrados através do método de fotoquadrats, desde o nível 0,2 m da maré até o limite superior de Littorina spp. O limite superior dos organismos marinhos foi ampliado na Barra (3,8 m) em relação ao Píer (2,2 m). Quanto à composição taxonômica, nove espécies foram comuns. Chaetomorpha sp., Chondracanthus teedii (Mertens ex Roth) Fredericq e Grateloupia sp. foram exclusivas na Barra, enquanto Tetraclita stalactifera (Lamarck, 1818), Fissurella clench, Gracilaria domingensis (Kützing) Sonder ex Dickie e Hypnea musciformis (Wulfen in Jacqu.) Lamouroux ocorreram somente no Píer. Em ambos os locais, a riqueza e a diversidade de espécies foram superiores nos quadrados intermediários. Os maiores valores foram registrados na Barra. As maiores diferenças nos agrupamentos entre faixas equivalentes de locais distintos ocorreram na faixa eulitorânea superior, seguida pela faixa eulitorânea inferior e franja sublitorânea. Apenas a orla litorânea não revelou diferença significativa entre os locais, mas uma maior extensão desta franja e da faixa eulitorânea superior era bastante evidente. As demais faixas na Barra do Furado foram caracterizadas em grande parte por espécies típicas de ambientes mais expostos como Chaetomorpha sp. na faixa eulitorânea superior e Perna perna (Linnaeus, 1758) na eulitorânea inferior, além de C. teedii e Ulva fasciata Delile, 1813 na franja sublitorânea. No Píer, as diferentes faixas apresentavam distribuição eqüitativa, refletindo um ambiente menos estressante. As diferenças observadas na distribuição vertical dos organismos bênticos, principalmente na extensão das faixas superiores, evidenciam condições de exposição a ondas variáveis.<br>The present study aims to compare the vertical distribution of intertidal benthic communities in two sites composed by granitic boulders with distint hydrodynamics due to different wave swells at Farol de São Tomé (Pier) and Barra do Furado beaches (Barra), both in northern state of Rio de Janeiro. Quadrats of 400 cm² were overlapped along three vertical profiles on each site and were sampled by the photoquadrat method from 0.2 m of the tide level to the upper limit of Littorina spp. The upper limit of the marine organisms was higher at Barra site (3.8 m) than at Píer site (2.2 m). Nine species were common to both sites. Chaetomorpha sp., Chondracanthus teedii (Mertens ex Roth) Fredericq, and Grateloupia sp. were unique to Barra, whereas Tetraclita stalactifera (Lamarck, 1818), Fissurella clench, Gracilaria domingensis (Kützing) Sonder ex Dickie, and Hypnea musciformis (Wulfen in Jacqu.) Lamouroux occurred only at Píer boulders. On both sites species richness and diversity were superior at the intermediate quadrats of the intertidal zone. The highest values were recorded at Barra. The most pronounced assemblage differences between equivalent areas of either site occurred on the lower upper eulittoral band followed by the lower eulittoral and the sub-littoral fringe, respectively. The littoral fringe assemblage was the only one that did not show significant differences among the studied sites, yet a larger range of this fringe and the upper eulittoral band at Barra was quite evident. This site was mostly characterized by species of more exposed areas, such as Chaetomorpha sp. and Perna perna (Linnaeus, 1758) on upper and lower eulittoral bands, and by C. teedii and Ulva fasciata Delile, 1813 on the sub-littoral fringe. At Píer, the intertidal zone showed an even distribution, reflecting a less stressful environment. The differences on vertical distribution of the local benthic, particularly in the extent of the upper bands, indicate the variable conditions of wave exposure