Patterns of colonization and succession of benthic assemblages in two artificial substrates

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<ul><li><p>Journal of Sea Research 88 (2014) 7886</p><p>Contents lists available at ScienceDirect</p><p>Journal of Sea Research</p><p>j ourna l homepage: www.e lsev ie r .com/ locate /seares</p><p>Patterns of colonization and succession of benthic assemblages in twoartificial substrates</p><p>A. Spagnolo , C. Cuicchi, E. Punzo, A. Santelli, G. Scarcella, G. FabiNational Research Council-Institute of Marine Sciences (CNR-ISMAR), Largo Fiera della Pesca, 2-60125 Ancona, Italy</p><p> Corresponding author. Tel.: +39 071 207881.E-mail address: a.spagnolo@ismar.cnr.it (A. Spagnolo)</p><p>1385-1101/$ see front matter 2014 Elsevier B.V. All rihttp://dx.doi.org/10.1016/j.seares.2014.01.007</p><p>a b s t r a c t</p>a r t i c l e i n f o<p>Article history:Received 8 August 2013Received in revised form 13 January 2014Accepted 16 January 2014Available online 24 January 2014</p><p>Keywords:Artificial reefsArtificial substratesBenthic communitiesCommunity composition</p><p>Benthic communities colonizing two different typologies of artificial structures, Tecnoreef pyramids (PY), andplinthmodules (PL), differing formaterial and shape,were investigated for three years after their deployment ona soft bottom offshore Pedaso (Western Adriatic Sea). The aims were to describe the colonization patterns ofbenthic assemblages on the two artificial modules, to highlight possible differences between them and to detectthe effectiveness of the artificial reef on the ecosystem functioning.The composition of the benthic communities settled on the two types of artificial substrates was different espe-cially just after the reef deployment. Abundance and species richness were higher on PL in the first two years,while an explosion of individuals characterized PY in the third year. This suggested a delay of about one yearin the colonization processes on PY likely due to the material and shape. The community settled of the artificialstructures was dominated by hard-substrate species which are commonly absent in the natural environment.The occurrence of these organisms enriched the local soft-bottom communities and contributed to habitat diver-sification. This, togetherwith the importance of these species in the diet of a few reef-dwelling fish, confirms thetrophic role and the ecological importance of artificial reefs in areas characterized by soft seabed.</p><p> 2014 Elsevier B.V. All rights reserved.</p><p>1. Introduction</p><p>An artificial reef is a submerged structure placed on the seabed de-liberately, to mimic some characteristics of a natural reef (UNEP-MAP,2005). In Europe this modern concept of artificial reefs was adopted inthe second half of the 1900s and, since then, artificial structures havebeen deployed in many countries (Fabi et al., 2011).</p><p>Concrete is themost commonmaterial in Europe for construction ofartificial reefs (Fabi et al., 2011) because it ensures good stability andallows the realization of modules of various shapes and sizes. In 1980sresearch was carried out in Europe to test new materials and differentmodule shapes to reduce costs and obtain good ecological responseand structural stability. One of these materials is the cement-stabilizedcoal-ash coming from coal-fired power stations (Bombace et al.,1997; Jensen et al., 1994; Peter et al., 1982; Relini, 2000; Relini andPatrignani, 1992).</p><p>The choice of material should consider the compatibility with themarine environment, the resistance to the chemical and physical forcesin constant action in themarinewaters, the time-life, and the suitabilityfor colonization by benthic communities, to induce the lowest environ-mental impact and to improve the natural environment. The ecological</p><p>.</p><p>ghts reserved.</p><p>importance of fouling assemblages in artificial community developmentwas seldom the main focus of the studies carried out up to 1980s. Designof artificial reefs, as a matter of fact, has been typically driven by fisheriesecology whilst ignoring the role of epiflora and epifauna which wereinvestigated separately (Baine, 2001). Starting from '90s the potentialrole of macrobenthic communities in providing food for commercialfish faunawas recognized and studies concerningmacrobenthic coloniza-tion assumed increasing importance (Ardizzone et al., 1997; Badalamentiet al., 1993; Clynick et al., 2007; Collins and Jensen, 1996; Fabi et al., 2006;Farias-Franco et al., 2013; Johnson et al., 1994; Lindquist et al., 1994;Redman and Szedlmayer, 2009; Relini et al., 2002).</p><p>Besides environmental factors (e.g., temperature, salinity, light,depth), substratum and relative position to the seafloor also play an im-portant role in the settlement, recruitment and growth of benthic or-ganisms (Glasby, 1999; Kocak and Zamboni, 1998). The material usedin construction of artificial reefs can strongly affect fouling assemblagedevelopment. For instance, Woodhead and Jacobson (1985) reportedsome differences in species preferences and colonization rates betweenartificial reefsmade from concrete and from coal combustionwastes, al-though the overall fouling assemblages were similar. Anderson andUndewood (1994), studying the effects of four different substrates,highlighted greater abundance of benthic species on concrete andplywood than on fiberglass or aluminum. In the northern Adriatic Sea,Bombace et al. (1997) found higher species richness on concrete</p><p>http://crossmark.crossref.org/dialog/?doi=10.1016/j.seares.2014.01.007&amp;domain=pdfhttp://dx.doi.org/10.1016/j.seares.2014.01.007mailto:a.spagnolo@ismar.cnr.ithttp://dx.doi.org/10.1016/j.seares.2014.01.007http://www.sciencedirect.com/science/journal/13851101</p></li><li><p>79A. Spagnolo et al. / Journal of Sea Research 88 (2014) 7886</p><p>modules in respect to coal-ash ones and a selective settlement of theburrowing bivalve Pholas dactylus on the horizontal surfaces of coal-ash blocks.</p><p>Studies have also shown that rough surface texture enhancesbenthic settlement providing shelter and supporting greater diversity(Beserra Azevedo et al., 2006; Harlin and Lindbergh, 1977; Hixon andBrostoff, 1985). Other factors affecting the colonization processes of anartificial reef and the diversification of communities are shape, dimen-sion and extension along the water column as well as orientation ofsurfaces. Ardizzone and Chimenz (1982) found that a difference of2-m distance from the sea bottom was sufficient to modify the benthiccommunity at Fregene artificial reef (Tyrrhenian Sea). Very differenttypes of epibiotic assemblages have been shown to occur on surfacesof different orientation, upper vs lower surfaces, vertical vs horizontalones (Bombace et al., 1997; Connell, 1999; Hurlbut, 1991; Spagnoloet al., 2004; Todd and Turner, 1986; Wendt et al., 1989).</p><p>In the case of eutrophic waters, the orientation of surfaces is strictlylinked to light and sedimentation rates. Indeed, in areas of strong sedi-mentation such as in front of a river mouth, the horizontal surfaces canbe covered by a very fine mud; conversely, hydrodynamism produces acontinuous turn-over on the vertical walls reducing accumulation ofsuspended material. As a consequence, the horizontal surfaces will besettled by both hard-substrate species and soft-bottom organismswhilstthe vertical walls will bemainly colonized by hard-bottom, filter-feederssuch as bivalves (e.g. Mytilus galloprovincialis, Ostrea edulis, Crassostreagigas), hydroids, and barnacles (Spagnolo et al., 2004).</p><p>Therefore, it is likely that the combined effects ofmaterial and orien-tation may greatly influence the development of epibiotic assemblages.</p><p>The present study reports on the differences in benthic settlementand species composition between two types of artificial modules</p><p>Fig. 1. Location along the Adriatic coast of the Pedaso artificial reef and its pa</p><p>(Tecnoreef pyramids and plinth-pole concrete modules) used for theconstruction of an artificial reef in the central Adriatic Sea. The twomodules differ for material and shape. Tecnoreef pyramids representa new module widely used in the construction of artificial reefs(Italy, Oman, Dubai, and Abu Dhabi). Fish repopulation and habitatdiversification are two potential functions of these structures but,at present, their scientific references are very scarce. Instead, anti-trawling is the main role of plinth-pole modules. The aims of thispaperwere to describe the colonization patterns of benthic assemblageson the two artificial modules, to highlight and analyze possible differ-ences between them and to detect the effectiveness of the artificialreef on the ecosystem functioning.</p><p>2. Material and methods</p><p>2.1. Study area</p><p>Work was done at the Pedaso artificial reef (Western Adriatic Sea;Fig. 1), deployed in September 2005 and covering an area of 81 ha(225 m 3200 m). It is located at a distance of 3 nm from the coastand at 14.515.0 m depth, on a muddy bottom without natural rockyoutcrops or seagrasses. Benthic community inhabiting the natural softbottom is mainly represented by organisms belonging to the Biocoeno-sis of coastal terrigenousmud and offinewell-sorted sand (unpublisheddata). The sandy coast is protected by several breakwaters. The area isaffected by the inflow of five rivers (Chienti, Tenna, Aso, Tesino, andTronto); it is characterized by a horizontal thermohaline stratificationin summer, with a water temperature of 24.527.3 C at the surfaceand of 18.222.9 C close to the bottom (Campanelli et al., 2011).Salinity ranges from 35.0 to 36.0 psu near the surface and from 35.0 to</p><p>rtial scheme. A particular of the two types of substrates is also reported.</p></li><li><p>80 A. Spagnolo et al. / Journal of Sea Research 88 (2014) 7886</p><p>38.0 psu close to the seabed (Campanelli et al., 2011). Themain bottomcurrent is towards South and sporadically reaches a speed of 30 cm s1</p><p>(unpublished current meter data).Pedaso artificial reef was planned to respond to different require-</p><p>ments. One of the main aims was to contrast the illegal trawlingwhich is often carried out in the coastal area inside the 3 nm offshore,where this type of fishery is forbidden (EC Reg. 1967/2006). Hence,214 plinth-pole structures, sufficiently heavy to stop the trawling nets,were placed along the artificial reef perimeter at a distance from eachother less than the free space needed by the fishing vessels to passwith the towed gear between one module and the other (Fig. 1).These structures consist of a plinth (2.1 2.1 1.3 m; hereafterindicated as PL) and a pole 4 m high, both made of common concrete(pH 12). The two elements have together a total height of 4.2 m and aweight of 8900 kg.</p><p>The other structures constituting the Pedaso artificial reef wereTechnoreef pyramids (hereafter indicated as PY), deployed for finfishenhancement. Seventy-six PY were placed inside the reef to increaseshelter opportunities and to enhance the settlement of benthic organ-isms representing a source of food for finfish species, with subsequentdevelopment of a resident fish assemblage and increase, consequently,of biomass. PY are made of sea-friendly certified reinforced concrete,manufactured using only natural components without syntheticadditives (pH 9). The basic Tecnoreef module consists of an octagonalslab with circular holes within the structure itself. The slabs areconnected together to form a complex pyramidal structure, having aweight of 2700 kg, height of 2.4 m and occupying an area of 14 m2 onthe bottom.</p><p>2.2. Sampling strategy</p><p>The macrozoobenthic community was investigated for three yearsstarting upon reef deployment. Three surveys per year were carriedout in summer, after the main recruitment period of the benthic organ-isms occurring in late spring. In each survey three PY and three PL wererandomly chosen. Poles were excluded to minimize the environmentalvariability linked to a vertical gradient in terms of light, currents,temperature, and larvae availability. It is known, in fact, that in the cen-tral and northern Adriatic Sea the highest settlement density of mussels(M. galloprovincialis) takes place between 1 and 5 m below the seasurface (Fabi et al., 1985, 1989). PY and PL are characterized by differentshapes and materials but have similar height and therefore can becomparable.</p><p>At each structure a standard area (40x40 cm) was randomly sam-pled on the vertical walls by means of the scraping technique, whichis commonly used to monitor benthic communities settled on artificialreefs (Relini and Relini, 1997): organisms were gently removed bydivers minimizing the samples lost and placed in net bags (mesh size:0.5 mm). Each sample represented a single replicate. The collectedmaterial was sieved on board through a 0.5mmmesh and all organismsretained were preserved in 5% buffered formalin. In the laboratory,macrofauna was sorted through a stereomicroscope and a binocularmicroscope, identified to species level when possible using standardnomenclature, quantified, and weighted. The affinity towards hard orsoft substrates of the taxa identified at species level was evaluatedusing available literature (Amouroux, 1974; Augier, 1992; BellanSantini and Ledoyer, 1972; Bellan et al., 1980; Bianchi et al., 1993;Bourcier et al., 1979; Chimenz Gusso et al., 2001; Nodot et al., 1984;Pres and Picard, 1964; Poppe and Goto, 1991, 1993; Rinelli andSpan, 1997; Ruffo, 1998; Salen-Picard, 1985).</p><p>2.3. Data analysis</p><p>2.3.1. Univariate analysesUnivariate measures such as species abundance (N; number of indi-</p><p>viduals d m2), species richness, Shannon diversity (H; Pielou, 1974)</p><p>and Simpson index (; Simpson, 1949) were calculated on benthicabundance data for each replicate. Prior to analysis, the species abun-dance data were log transformed as log (x + 1) to respect the assump-tion regarding the homogeneity of variancewithin each group. Changesin these biological indices were examined using a 3-way mixed factorsanalysis considering type of substrate (two levels and fixed factor),years (three levels and fixed factor) and surveys (three levels andrandom factor nested in year and orthogonal to substrate). as the inter-actions of the random factor were not significant the terms substrateand years were treated as orthogonal. In the case of significant interac-tions a pair-wise test was conducted comparing the two modulesin each year.</p><p>Because the assumption of normality needed for ANOVA was notrespected for the four univariate measures, the analysis was conductedusing a permutation analysis of variance (PERMANOVA) based onEuclidean distances. Although PERMANOVA is designed formultivariateanalysis on dissimilarity matrices, it can be used to perform univariateanalyses if applied on a Euclidean distance matrix. In such case thesums of squares and F-ratios are exactly the same as Fisher's univariateF-statistic of traditional ANOVA. PERMANOVA calculates p-values usingpermutations, rather than relying on tabled p-values, which assumenormality. Therefore, in the case this assumption is not met, this ap-proach can be used to compare univariate measures (Anderson, 2005).</p><p>2.3.2. Multivariate analysesMultivariate analyses were performed to identify how the benthic</p><p>assemblage changed with time and type of module. Pri...</p></li></ul>

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