MARINE ECOLOGY PROGRESS SERIES Vol. 193: 241-249,2000 Published February 28 Mar Ecol Prog Ser Bio-mineralogy as a structuring factor for marine epibenthic communities 'Istitulo di Scienze del Mare, Universita di Ancona, Via Brecce Bianche, 60131 Ancona, Italy 2~arineEnvironment Research Centre, ENEA Santa Teresa, PO Box 316, 19100 La Spezia, Italy 3~ipartimentoper 10 studio del Territorio e delle sue Risorse, Universita di Genova, Viale Benedetto XV 5, 16132 Genova, Italy ABSTRACT The meralogical features of the substrate were generally cons~dereda rmnor factor m structunng manne benthic communities The alm of th~swork 1s to venfy whether the presence of quartz nunerals in rock may exphcate dlfferences, usually explamed m terms of substrate roughness or other factors In epibenthic cornrnun~hes Laboratory tests on the hydroid Eudendnum glomeratum showed that ~tsplanulae settle preferentially on carbonat~c,rather than quartzltic substrates To test the Influence of quartz on established communities, we analysed the specles composition and quanti- tat~vestructure of subhttoral sesslle assemblages on Wferent rocks In several locahhes of the L~gurian and Tyrrhenian seas The observed dlfferences appeared to be related to the presence of quartz in the substrate rock The ~nteractionsbetween organisms and minerals (bio-mmeralogy)mlght play a slgnlf- icant role on benthic communities affechng not only the inihal colonlsahon but also later assemblages This potential role has been largely neglected to date and further studies are needed to prove ~tsImpor tance KEY WORDS: Substrate colonisation . Mineral composition . Marine benthos distnbution . Hard substrates . Bio-mineralogy INTRODUCTION communities growing on rocks of different nature. A species assemblage, which may be slightly more The spatial distribution and structure of marine ben- attracted to a particular substrate, could affect succes- thic communities are due to numerous abiotic and sion by its subsequent interaction with later assem- biotic factors which, in turn, are influenced by the blages. A similar effect was evidenced in the colonisa- presence of the organisms, in a mutual exchange of tion of artificial substrates, with respect to both species inputs. Among the abiotic factors, the mineralogical composition and abundance (Anderson & Underwood features of the substrate were generally considered of 1994, Holm et al. 1997). Less information is available scarce importance, but recent studies by Cerrano et al. for natural substrates (McGuiness 1989), but it is com- (1998) have shown that the presence of quartz in the mon knowledge that the softness and asperity of a rock sand may affect the initial steps of infauna colonisa- can favour or hamper biotic colonisation through selec- tion. Cerrano et al. (1998) introduced the term bio-min- tive larval settling, retention of water (in the littoral) eralogy to explicate the interrelationships between and organic matter, and provision of refuges from pre- biological systems at different hierarchies (cell, organ- dation or grazing (Den Hartog 1972, Levinton 1982, ism, species, community) and minerals. Walters & Wethey 1996). Bio-mineralogy could influence hard-bottom assem- More is known about the influence of substrate min- blages and explain some 'anomalies' in the structure of eralogy on bioboring, which is prevented by high percentages of quartzitic or pelitic components in the rock. Sublittoral endolitic communities are charac- 0 Inter-Research 2000 Resale of full article not permitted 242 Mar Ecol Prog Ser 193: 241-249. 2000 during November 1998 at 20 to 25 m depth. The fertilised eggs develop in verticils of 5 to 10 fixed to a rudimentary polyp, the blas- tostyle, deprived of mouth and tentacles. Each egg is enveloped by a non-branched spadix. The verticils of eggs were mechani- cally detached from the mother colony and placed in 250 m1 cups filled with filtered natural sea water at a temperature of 15°C. Cerrano et al. (1997) demon- strated that light exposure is nec- essary to trigger egg hatching and therefore we reared the eggs in lit conditions for 3 d. New re- leased planulae were divided into 4 stocks of 60 specimens and each Fig. 1. Sublittoral rock showing differences in the distribution of borers due to the stock was placed for 12 d in an mineral composlt~onof the substrate. The white calcitic vein IS widely bored by the experimental Petri dish in com- sponge Cliona celata which is absent on marl limestone (grey). Herein only the date- plete darkness to avoid problems mussel Lithophaga lithophaga is able to penetrate (arrows) related to their very high pho- totrophy. Petri dishes were pre- pared by sticking a uniform layer terised mainly by clionid sponges and bivalves. Clionid of sand grains with Eukitt; half of the surface was cov- sponges use hatching cell pseudopodes and the pro- ered by quartz sand, and half by sand derived from duction of carbonic acid to penetrate limestone (Riit- Carrara marble. The 2 sand types have the same gran- zler & Rieger 1973, Pomponi 19?9), but Cliona celata ulometric (125 to 250 pm) and morphological features Grant preferentially bores, in the Mediterranean Sea, (roundness, 0.35 to 0.7; projection of sphericity, 0.8 to substrates richer than 60% in carbonates (unpubl. obs.). Bivalves, such as species of Lithophaga, bore with the help of sulphuric acid and/or neutral muco- proteins (Russo & Cicogna 1992), and are also able to penetrate marl limestone, which is impenetrable by clionids (unpubl. obs., Fig. 1). All this has important consequences on the rock texture and roughness and, ultimately, on the community structure. To check the influence of substrate mineralogy on the larval settling, a series of laboratory tests was conducted using planulae of the hydroid Eudendrjum glomeratum (Picard),a very colnmon species of the sublittoral Med- iterranean zoobenthos (Boero et al. 1986). In order to Rome - seek a relation between the mineralogy of natural sub- m strates and the structure of sessile epibenthic communi- ties, the species composition and percent cover of as- semblages living on different kinds of rock in the western Mediterranean Sea were compared. MATERIAL AND METHODS Laboratory. Planulae of the hydroid Eudendrium glomeratum were obtained from female colonies col- Fig. 2. Geographic layout of the fleld-study sites in the Lig- lected on the rocky cliff of the Portofino Promontory urian and Tyrrhenian seas (NW Mediterranean) Bavestrello et al.: Structuring of marine epibenthic communities 243 Table 1. Locahties for field studies on subllttoral rocky bottoms Locality Contrasted mineralogies Depth No. of No. of range (m) stations species Ligurian Sea Quartzite vs Puddingstone, mar1 5-7 14 60 (Gallinaria Island) limestone and sandstone (Portofino region) Giglio Island Granite (most of vs Limestone (western part 6-10 16 54 the island) of the island) Northeast Sardin~a Granite (most of the vs Limestone-dolom~te 18-34 20 4 4 coast and small islands) (Tavolara Island) 0.9). Both kinds of sand were previously stored at taken into account the epibenthic communities on the 100°C for 24 h, which enabled us to obtain an artificial rocky bottom (Bianchi et al. 1987, Cattaneo-Vietti et al. hard bottom on the entire Petri dish surface, with very 1988). One of the most studied sites is the region similar physical features but with 2 different mineralo- around Portofino (Tortonese 1958, 1962, Morri et al. gies. 1988), but recent research has also been done on the Field. The data matrices were produced using un- Island of Gallinaria (Balduzzi et al. 1994).These stud- published data sets on subtidal epibenthic communi- ies underlined that epibenthc communities on sublit- ties of the Ligurian Sea (Gallinaria Island and Portofino toral rocks at Portofino are dominated by flourishing region) and Tyrrhenian Sea (Giglio Island and north- gorgonian populations, whereas at Gallinaria, gor- east Sardinia) (Fig. 2). The data sets were chosen in gonians are scarce and sponges dominate. From a min- order to be able to contrast communities from an equal eralogical point of view, Gallinaria Island is exclusively number of stations on rocks rich in quartz, such as quartzitic (Orsino 1975), whereas the coast around quartzite and granites, or deprived of that mineral Portofino is characterised by puddingstone, mar1 lime- (Table 1).All data sets consist of percent cover data of stone and sandstone, none of which has a significant conspicuous species (Hiscock 1987), derived from quartz component (Boni et al. 1969). underwater visual inventories by SCUBA divers using The Giglio Island is included in the southern group quadrats (Bianchi et al. 1991). Cover data for a total of of the Tuscan Archipelago, at the border between Lig- 96 species (Table 2) were available, but each data set urian and Tyrrhenian seas. Its rocky coast is mostly was analysed separately according to depth zone and granite, but a small portion on the western side is corn- geographical location, so that communities only posed of limestone (Alvisi et al. 1994). The subtidal showed differences in the mineralogical nature of the epibenthic communities of Giglio Island were first substrate and possibly exposure. To avoid the influ- described by Balduzzi et al. (1996). ence of sedimentation, which may alter the effects The northeast corner of Sardinia is mostly composed of mineralogical composition at the rock surface of granite. A striking exception is the Tavolara Island (Bavestrello et al. 1995a), vertical stations (70 to 95" made by a gigantic limestone-dolomite slab (Lorenzoni slope) were selected. Matrices of species cover data & Chiesura-Lorenzoni 1973). Together with Molara, were compared by correspondence analysis (Legendre Molarotto and other minor islets and rocks (all granitic), & Legendre 1998), and species numbers and total Tavolara forms a small archipelago, the epibenthic cover by l-way ANOVA. Prior to analysis, percentage communities of which have been studied by Navone et cover values were arcsine transformed to meet the al. (1992). assumption of homogeneity of variances (Underwood 1997).