Biol. Mar. Mediterr. (2007), 14 (2): 178-179 R. Cupido, S. Cocito, S. Sgorbini ENEA Centro Ricerche Ambiente Marino,P.O. Box 224 - 19100 La Spezia, Italia. roberta.cupido@santateresa.enea.it EPIBIOSIS IN PARAMURICEA CLAVATA AFTER MORTALITY EVENTS IN THE LIGURIAN SEA EPIBIOSI IN PARAMURICEA CLAVATA IN SEGUITO AD EVENTI DI MORTALITÀ NEL MAR LIGURE Abstract – A population of the gorgonian Paramuricea clavata (Cnidaria), heavily damaged by two mortality events, was studied in the Ligurian Sea for three years (2004-2006). Composition, diversity and position of epibionts on the gorgonian colonies were analysed. Encrusting and erect bryozoans were the best space competitors on apical, median and basal portions of damaged gorgonian colonies. Key-words: mortality, Paramuricea clavata, epibiosis, bryozoans, Ligurian Sea. Introduction – A population of the gorgonian Paramuricea clavata was heavily damaged by two mortality events recorded in 1999 and 2003 in the Gulf of La Spezia (Ligurian Sea) (Cupido et al., 2006). Denudate axes of damaged colonies are typically colonized by a great variety of sessile species with three dimensional arborescent growth or developing sheets (Harmelin and Marinopoulos, 1994). In this study we analyse composition, diversity and position of epibionts on different portions of damaged colonies of P. clavata in the three years after the morality events. Materials and methods – The study was carried out yearly in summer 2004, 2005 and 2006 in three locations in the Gulf of La Spezia. Within each location, 6 replicates of 1m2 were sampled. For each gorgonian colony, epibiont species present on apical, median and basal portion of the colony were recorded or sampled to check the taxonomic identity. Frequency of epibiont species was computed. Epibionts were divided in 7 groups: tunicates, serpulids, cnidarians, poriferans, encrusting bryozoans, erect bryozoans, algae. Shannon-Wiener Diversity Index (H’) and Pielou’s Evenness Index (J) were calculated for each year. Differences between the occurrence of the most represented groups of epibionts on the apical and basal portion of the colony were tested (t-test). Results – 24 taxa were found in 2004, 23 in 2005 and 26 in 2006. Throughout the monitoring period, the most represented group was that of bryozoans, with encrusting species, such as Beania magellanica (Busk), Rynchozoon sp., Schizobrachiella sanguinea (Norman), Schizomavella auriculata hirsuta (Calvet), Schizomavella cornuta (Heller), Turbicellepora incrassata (Lamouroux), and erect species, such as Chartella papyrea (Pallas), Chartella tenella (Hincks), Margaretta cereoides (Ellis & Solander), Pentapora fascialis (Pallas), Reteporella grimaldii (Jullien), Smittina cervicornis (Pallas), Cellaria salicornioides (Audouin), Frondipora verrucosa (Lamouroux). 8 taxa belonging to the poriferans, 3 to cnidarians, 4 to algae, 1 to serpulids and 1 to tunicates were recorded. Frequency of erect bryozoans was higher in 2004 and 2006 if compared with the encrusting ones, differently from 2005 when B. magellanica was notably abundant (Fig. 1). From 2004 to 2006, epibionts’ diversity decreased (H’2004=0.91, H’2005=0.69, H’2006=0.62), mainly because of the lower frequencies of encrusting bryozoans, cnidarians, and serpulids. Eveness index paralleled diversity index (Pielou’s Evenness Index: J2004=0.57, J2005=0.38, J2006=0.34). Few bryozoans species were always dominant, namely S. cornuta, C. papyrea, C. tenella, C. salicornioides. Encrusting bryozoans were more frequently located on the apical and median portions of P. clavata, together with cni- frequencies of encrusting bryozoans, cnidarians, and serpulids. Eveness index paralleled diversity index (Pielou's Evenness Index: J2004=0.57, J2005=0.38, J2006=0.34). Few bryozoans species were always dominant, namely S. cornuta, C. papyrea, C. tenella, C. salicornioides. Encrusting bryozoans were more frequently located on179the apical and median portions of P. clavata, together with cnidarians, when present (Fig. 1). Frequencies of encrusting portion were always higher when darians, when present (Fig. 1). bryozoans Frequenciesonofapical encrusting bryozoans on apical portion compared with the basal (t-test, < 0.05). In 2004(t-test, and 2005, were always higher whenportion compared withPthe basal portion P < erect 0.05). bryozoans In 2004 and by poriferans, massive species, were common themore basal and poriferans, 2005, erect represented bryozoans and represented by more massive species, on were commonthan on the basal portions thanPon apical In ones (t-test, P < 0.05). In 2006, while portions on apical ones (t-test, < 0.05). 2006, while differences in poriferans differences in distribution did not change, were on found indifdistribution didporiferans not change, erect bryozoans were erect foundbryozoans indifferently apical and ferently on apical and basal portions of the colony (t-test, P > 0.05). basal portions of the colony (t-test, P > 0.05). tunic ates basal 2005 2004 serpulids 2006 median apical c nidarians poriferans enc rusting bryozoans erec t bryozoans algae 0 0.5 1 1.5 0 0.5 1 frequencies 1.5 0 0.5 1 1.5 Fig. 1 - Frequenciesofof different groups of epibionts to theironposition on Paramuricea Fig. 1Frequencies thethe different groups of epibionts related related to their position Paramuricea clavata colony clavata median colonyand (apical, basal portion) in 2004, 2005 and 2006. (apical, basal median portion) and in 2004, 2005 and 2006. Frequenze dei posizione lungo la la colonia di P. Frequenze dei diversi diversi gruppi gruppididiepibionti epibiontiininrelazione relazionealla allaloro loro posizione lungo colonia di clavata P. clavata (zona apicale, apicale, mediana mediana e basale) nel 2004, 2004, 2005 (zona 2005 ee 2006. 2006. Conclusions – Damaged colonies of the P. clavata population in the Gulf of La Spezia were a suitable substratum for the establishment of different groups of epibionts, Conclusions – Damaged colonies of the P. clavata population in the Gulf of La particularly bryozoans. Prevalent colonisation of apical portions of P. clavata Spezia were for a suitable substratum for the establishment of different groups of epibicolonies by encrusting bryozoans can be interpreted as an adaptation to the heavy onts, particularly for bryozoans. Prevalent colonisation of apical portions of P. clavata sedimentation that characterise (Cocito etas al., 2002). Differently, erect colonies by encrusting bryozoansthe can area be interpreted an adaptation to the heavy sedimentation thatadvantage characterise the growth area (Cocito et al., 2002). Differently, erect bryobryozoans, taking of the form (Jackson, 1979), succeeded in starting zoans, takingofadvantage the growth (Jackson, 1979), starting colonisation the basalof portion of form the colony and, oversucceeded time, inin colonising colonisation of the basal portion of the colony and, over time, in colonising indifferindifferently all the axis. ently all the axis. References COCITO S., BEDULLI D., SGORBINI S. (2002) – Distribution of the sublittoral epibenthic References assemblages on a rocky shoal in the Ligurian Sea (NW Mediterranean). Sci. Mar., 66 (2): 175-181. COCITO R., S., BEDULLI D., BORDONE SGORBINI S.A., (2002) – Distribution of the–sublittoral assemCUPIDO COCITO S., SGORBINI S. 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