Biol. Mar. Mediterr. (2012), 19 (1): 49-52
E. Ricevuto, M. Lorenti, F.P. Patti, M.B. Scipione, M.C. Gambi Stazione Zoologica Anton Dohrn, Napoli, Italy.
[email protected]
TEMPORAL TRENDS OF benthic INVERTEBRATE SETTLEMENT ALONG A GRADIENT OF OCEAN ACIDIFICATION AT NATURAL CO2 VENTS (Tyrrhenian Sea) VARIABILITÁ TEMPORALE DELL’InSEDIAMENTO DI INVERTEBRATI bentonici LUNGO UN GRADIENTE DI ACIDIFICAZIONE DELLE ACQUE Abstract - We report data of a temporal analysis of benthic invertebrate settlement/colonization on artificial structures (scouring pads) along a gradient of ocean acidification at natural CO2 vents at Ischia Island (Tyrrhenian Sea, Italy) in different periods of the year. The main groups collected were polychaetes, amphipod, isopod and tanaid crustaceans and mollusks. The analysis shows high temporal variability in settlement although some common trends are detectable. While mollusks show a clear reduction both in species and abundances in the acidified stations (except for Mytilus galloprovincialis), the other groups showed a few species (es. the polychaete Platynereis dumerilii, Amphiglena mediterranea and Syllis prolifera; the amphipod Caprella acanthifera, the tanaid Leptochelia savignyi and the isopod Dynamene bifida) which thrive well and are sometimes more abundant in extremely low pH areas than in control ones. Key-words: CO2 vents, ocean acidification, benthic organisms, settlement, temporal trend.
Introduction - Recent studies forecast a dramatic increase of partial pressure of CO2 at the ocean surface within the current century, as a consequence of the increasing atmospheric CO2 concentrations, with a resulting occurrence of ocean acidification (OA). To date, relatively few experiments have been conducted in situ to detect possible consequences of anthropogenic CO2 on marine ecosystems (HallSpencer et al., 2008; Kroeker et al., 2011). Effects of OA on the early life-history and on the settlement/colonization of most benthic invertebrates and its temporal variability are still poorly known, but represent crucial aspects, since early stages seem to be more sensitive to OA than adults (Kroeker et al., 2010). Species selection occurring on early stages may have far reaching consequences for the make-up and structure of benthic communities, although colonization by adult mobile forms may be of importance. Initial data on benthic settlement/colonization along a gradient of OA (Cigliano et al., 2010) indicated species selection acting especially against strongly calcified organisms, mollusks and foraminifers in very acidic water, whereas other taxa, less or not calcified (peracarid crustaceans, polychaetes), result particularly abundant in such low pH areas. The aim of this study was to reproduce the original sampling by Cigliano et al. (2010) in different periods of the year, in order to assess temporal variations on invertebrate settlement/colonization pattern along a gradient of OA operating on a shallow area naturally acidified by volcanic carbon dioxide vent systems. Materials and methods - The study area is a volcanic gas vents system (9095% CO2) which occurs in shallow waters around Castello Aragonese, Ischia island (Tyrrhenian Sea, Italy). The gradient of water acidification occurs within approx. 300 m (Hall-Spencer et al., 2008). Six stations, 3 on the north and 3 on the south side of the Castello, were selected, based on previous observation of pH and venting activity. Two were located in control areas, at normal pH conditions (N1 and S1), two in intermediate areas, characterized by high pH fluctuations (N2 and S2)
E. Ricevuto, M. Lorenti, F.P. Patti, M.B. Scipione, M.C. Gambi
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(Kroeker et al., 2011) and two in areas of high venting activity characterized by low pH conditions (N3 and S3) (Cigliano et al., 2010). In each station, three artificial collectors, represented by 8 cm diameter rounded nylon scouring pads (Cigliano et al., 2010), were placed on buoyed moorings approximately 80 cm from the bottom at 2-3 m depth. Artificial collectors were deployed for one month in September 2009, March 2010 and May 2010. After removal, scouring pads were fixed in 4% formalin in sea water and were later transferred to 70% alcohol for sorting under stereomicroscope to the lowest possible taxon. For comparison purposes with Cigliano et al. (2010) (AprilMay 2008), abundance data of the main groups were included in the present analysis. Results and conclusions - A total of 10,927 individuals of benthic macrofauna were sampled. The most abundant groups were Crustacea (2918 Amphipoda, 1294 Tanaidacea, 950 Isopoda, 114 Decapoda, 107 Cumacea), Polychaeta (3527 individuals) and Mollusca (1625 Bivalvia, 219 Gasteropoda, 83 Nudibranchia). The total community assemblage showed lower abundances in March and higher in May 2010, likely depending on the life cycle and on the recruitment rate and period of most invertebrates. The main exception is Polynoidae polychaetes, occurring only in March. A general spatial trend showed that, although many taxa, especially the most calcified ones (mollusks, serpulid polychaetes), were di absent strongly reduced in the 43° Congresso della Società Italiana Biologiaor Marina Marina diwere Camerota (SA), 4-8 giugno 2012 along the pH gradient, acidified stations, total abundances relatively constant and on the south side sometimes even higher near the vent (e.g., in September). Most of the individuals were juveniles, although adult forms also occurred, especially among polychaetes and crustacean peracarids. Polychaeta dominated by Amphiglena mediterranea (45% of all polychaetes), Exogoninae spp. (19%), Syllis prolifera (18%), Platynereis dumerilii (6%), Polyophthalmus pictus (4.6%), showed a general decrease of 300
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Fig. 1 - Trends of abundance of some of the most abundant groups collected in the 6 stations on Fig. 1 - Trends of abundance of some of the in most abundant groups the from 6 stations on et substrates exposed for one month different periods of collected the year. in Data Cigliano substrates for included. one month in different periods of the year. Data from Cigliano et al. al. (2010) exposed (Apr) were (2010) (Apr)dell’abbondanza were included. dei principali gruppi raccolti nelle 6 stazioni di studio da substrati Andamento Andamento dei principali raccolti nelle 6(Apr) stazioni studio da esposti per undell’abbondanza mese in diversi periodi. I dati dagruppi Cigliano et al. (2010) sono di inclusi. substrati esposti per un mese in diversi periodi. I dati da Cigliano et al. (2010) (Apr) sono inclusi.
The nMDS ordination (Fig. 2), based on Bray-Curtis similarity, grouped samples
Temporal trends of benthic invertebrate settlement along a gradient of ocean acidification at natural CO2 vents
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abundance along the pH gradient, in the Northern side, from N1 to N3, especially in September and May; whereas on the south side there is an evident increase of the abundance from S1 to the acidified station S3, especially in September and May (Fig. 1). Amphiglena mediterranea, Syllis prolifera and Platynereis dumerilii, although occurring at all stations, showed a constant increase in abundance in the acidified sites. Mollusca (Fig. 1), mostly represented by juvenile stages of the bivalve Mytilus galloprovincialis (76.8%), occurred also in the acidified stations; gastropods were virtually absent in all acidified stations. Tanaidacea (Fig. 1), dominated by Leptochelia savignyi (96.6%), showed peak abundance at low pH, especially in southern station (S3). Isopoda, dominated by Dynamene bifida (83.4%), were particularly abundant in the intermediate and acidified southern stations (S2 and S3), while Amphipoda (Fig. 1), mainly represented by Caprella acanthifera (21.6%), showed a quite constant abundance. The nMDS ordination (Fig. 2), based on Bray-Curtis similarity, grouped 43° Congresso dellaperiod. Società The Italiana di Biologia Marina samples according to station and sampling differences in time were the Camerota (SA), 4-8 giugno most relevant to the observed Marina patterndi(ANOSIM for time factor: 2012 Global R=0.566, P
