Macrofauna assemblages in a XVIIth century shipwreck: comparison with those on natural reefs and sandy bottoms

BRAZILIAN JOURNAL OF OCEANOGRAPHY, 60(4):447-462, 2012 MACROFAUNA ASSEMBLAGES IN A XVIIth CENTURY SHIPWRECK: COMPARISON WITH THOSE ON NATURAL REEFS AND SANDY BOTTOMS Rui Coelho1,*, Pedro Monteiro1, David Abecasis1, Jean Yves Blot2 and Jorge M. S. Gonçalves1 1 Centro de Ciências do Mar (CCMAR) - Universidade do Algarve (Campus de Gambelas FCT Ed. 7, 8005-139 Faro, Portugal) 2 Centro Nacional de Arqueologia Náutica e Subaquática Instituto de Gestão do Património Arquitectónico e Arqueológico, IP (1300-300 Lisboa, Portugal) *Corresponding author: ABSTRACT The macrofauna assemblages of a XVIIth century shipwreck off southern Portugal were studied and compared with those of nearby natural reefs and sandy bottoms, by underwater visual census. A total of 11 173 specimens of 224 different fauna taxa and 12 phyla were recorded. Natural reefs had the highest density of specimens (35 122 / 1000 m2) followed by the shipwreck (21 392 / 1000 m2) and the sandy bottoms (3771 / 1000 m2). Three biodiversity indices were estimated (Margalef, ShannonWiener and Pielou), with the natural reefs showing the highest values. However, the shipwreck presented values relatively similar to those of the natural reefs for the Shannon-Wiener and Pielou indices. The three habitats were clearly distinguishable by multivariate statistical analysis, with the average dissimilarity between sand and shipwreck, and between sand and natural reefs being much higher than that between the shipwreck and the natural reefs. The shipwreck had higher abundances of some commercially important species, such as the pouting Trisopterus luscus, European conger Conger conger, and common spider crab Maja squinado, as well as some vulnerable and threatened species such as the pink seafan Eunicella verrucosa. The results presented emphasize the importance of this habitat on the southern Portuguese coast. RESUMO As comunidades de macrofauna de um naufrágio do século XVII ocorrido ao largo da costa Sul de Portugal, foram estudadas e comparadas com recifes naturais e fundos de areia através de census visuais subaquáticos. Foram registados 11 173 espécimes pertencentes a 224 taxa faunísticos e 12 phyla. Os recifes naturais apresentaram a maior densidade de espécimes (35 122 / 1000 m2) seguidos do naufrágio (21 392 / 1000 m2) e dos fundos de areia (3771 / 1000 m2). Foram calculados três índices de biodiversidade (Margalef, Shannon-Wiener e Pielou), com os recifes naturais que apresentarem os valores mais elevados. No entanto, o naufrágio mostrou valores relativamente semelhantes aos fundos rochosos nos índices de Shannon-Wiener e Pielou. Os três habitats foram separados por estatística multivariada, com a dissimilaridade média entre areia e naufrágio, e entre areia e recifes naturais sendo muito superior à dissimilaridade entre os recifes naturais e o naufrágio. O naufrágio apresentou elevada abundância de algumas espécies comercialmente importantes, como a faneca Trisopterus luscus, o safio Conger conger e a santola Maja squinado, assim como de espécies vulneráveis e ameaçadas como a gorgonia rosa Eunicella verrucosa. Os resultados apresentados realçam a importância desse habitat para a costa Sul de Portugal. Descriptors: Artificial reefs; Biodiversity, Underwater visual survey, Multivariate analyses; NE Atlantic. Descritores: Recifes artificiais, Biodiversidade, Monitorização visual subaquática, Análise multivariada, Nordeste Atlântico. INTRODUCTION Artificial reefs are defined by the European Artificial Reef Research Network as submerged structures deliberately or accidentally placed on the substratum to imitate some of the characteristics of natural reefs. These structures can be built from a wide variety of materials, and have been deployed in many 448 BRAZILIAN JOURNAL OF OCEANOGRAPHY, 60(4), 2012 coastal regions of the world for diverse reasons such as enhancing tourism, coastal protection and fisheries management (BAINE, 2001). The potential use of these artificial structures for the restoration and rehabilitation of fisheries seems to be one of the main reasons for their use (CLARK; EDWARDS, 1999; BAINE; SIDE, 2003) and some studies have started to look into comparisons between artificial and surrounding natural reefs (e.g. ASELTINE-NEILSON et al., 1999; BADALAMENTI et al., 2002; PERKOLFINKEL; BENAYAHU, 2004, 2007; ARENA et al., 2007). However, there is still only limited knowledge regarding the relations between these structures and the surrounding environments, and this lack of comparative knowledge has in some cases been given as the main reason for the poor understanding of the ecology of artificial reefs (SVANE; PETERSEN, 2001). Most of the studies undertaken on the ecology of artificial reefs have focused on relatively young communities, as many of these reefs have only been deployed in recent years. Current knowledge on the communities that have established themselves in artificial reefs on the long term is still limited, but there is some evidence that the time frame required to develop a diversified artificial reef community is well over a decade (CUMMINGS, 1994; PERKOLFINKEL; BENEYAHU, 2005; SANTOS; MONTEIRO, 2007). Because of this, accidentally sunken shipwrecks provide an excellent natural experimental arena, as some of these structures have lain submersed for many decades or, in some cases, centuries. However, and surprisingly, very few studies have been carried out comparing the ecology of these older shipwrecks with those of their surrounding environments (e.g. ZINGTEN et al., 2008), but even those have focused mainly on shipwreck sites with time spans inferior to 100-150 years. The shipwreck site currently known to marine archeologists as “Faro A” (Fig. 1) was presumably an English cargo vessel traveling from Northern Europe to the Mediterranean port of Izmir/Smyrna as part of a large British convoy (BLOT et al., 2005). In June 1693, while sailing off the southern Portuguese coast, the convoy was attacked by the French navy and the “Faro A” ship sunk a few miles from the city of Faro in southern Portugal (BLOT et al., 2005). The wreck remained undiscovered until a team of recreational scuba divers accidentally located it in 1996, and has since been studied by marine archeologists and biologists. One among several dozens of historical wreck sites currently known off the coast of Portugal (BLOT, 2002), the “Faro A” immediately appeared as “different” to marine archeologists, mainly due to two features: 1) the significant protuberances caused by a cargo of iron bars and iron artillery, all heavily covered with marine concretions and 2) the single presence of seven pewter plates as part of the minor artifacts commonly found on wreck sites from the same period (BLOT et al., 2005). Due to its historical importance, the “Faro A” wreck site has been declared of national importance by the Portuguese Government and restrictions have been imposed on fishing activities (both commercial and recreational) (...truncated)