size evaluation of delectopecten vitreus

Biol. Mar. Mediterr. (2010), 17 (1): 308-309
P. Panetta, F. Mastrototaro, F. Capezzuto, G. Sassanelli, M. Taviani*
Department of Animal and Environmental Biology, University of Bari,
Via Orabona, 4 - 70125 Bari, Italia.
[email protected]
*ISMAR-CNR, Bologna, Via Gobetti, 101 - 40129 Bologna, Italia.
SIZE EVALUATION OF DELECTOPECTEN VITREUS
(MOLLUSCA, BIVALVIA) FROM SANTA MARIA DI LEUCA
DEEP-WATER CORAL SITE (IONIAN SEA)
OSSERVAZIONI SULLA TAGLIA DI UNA POPOLAZIONE
DI DELECTOPECTEN VITREUS (MOLLUSCA, BIVALVIA)
PROVENIENTE DAL SITO A CORALLI PROFONDI
DI SANTA MARIA DI LEUCA (MAR IONIO)
Abstract – The size of a Mediterranean population of the deep sea pectinid Delectopecten vitreus
(Mollusca, Bivalvia) is discussed with respect to Atlantic counterparts. The Mediterranean specimens
collected in the Ionian Sea at the Santa Maria di Leuca deep water coral site are characterized by a
size smaller than Atlantic stocks.
Key-words: Delectopecten vitreus, population, deep coral epifauna.
Introduction – Delectopecten vitreus (Gmelin, 1791) is a quasi-cosmopolitan
pectinid bivalve distributed in the Atlantic, Indian and Pacific Ocean, from
infralittoral down to abyssal depths (e.g., Schein, 1989). D. vitreus is characterized
by a planktotrophic development (Dijkstra and Gofas, 2004) and its long-lasting
meroplanktonic life ensures its wide geographic dispersion. The species is rather
frequent in the Mediterranean Sea and living specimens were found byssate on
a variety of substrates (e.g, Smriglio, 2005; Mastrototaro et al., 2010). D. vitreus
commonly occurs in the deep-water Pleistocene record of the Mediterranean
basin and this includes also submerged situations datable to the last glacial epoch
(Taviani and Colantoni, 1984; Di Geronimo et al., 2005). The biology and population
structure of Mediterranean D. vitreus stocks are poorly known. In this contest the
size distribution of D. vitreus specimens collected alive in the Santa Maria di Leuca
(SML) deep water coral site (Ionian Sea) is discussed.
Materials and methods – All live specimens considered in this study were
sampled during various missions of RV Urania and Universitatis, devoted to the
study of the SML coral site (Mastrototaro et al., 2010); they were measured with an
electronic calliper (Total length=TL and total height=TH in mm). The size-frequency
distribution was elaborated considering size classes of 2 mm. The relationship
between total length and total height was tested by means of linear regression.
Stereomicroscopic observations of the external shell morphology were aimed at
examining microsculpture features.
Results – A total of 181 specimens were living-collected, from 451 to 1100 m depth,
either on both artificial substrates (mostly entangled fishing lines or plastic litter) or dead
on scleractinian coral colonies off the Santa Maria di Leuca (SML) deep water coral
site. Such shells are equipped with fragile valves marked by concentric rows of small
scales and vesicles as reported by Schein (1989) as typical for the subspecies D. vitreus
vitreus. The TL ranged from 6 to 16 mm. The length and height were highly correlated
(Fig. 1a). The size distribution (TL) showed a bimodal trend with a modal component
of 9-10 mm (19% of the specimens collected) and another of 13-14 mm (16%) (Fig. 1b).
Size evaluation of D. vitreus from Santa Maria di Leuca deep-water coral site
309
Fig. 1 - a) Relationship between Total length and Total height of specimens of D. vitreus collected
in SML deep water coral site. b) Size-frequency distribution of D. vitreus collected in
SML deep water coral site.
a) Relazione tra la lunghezza totale e la larghezza totale degli esemplari di D. vitreus provenienti dal
sito a coralli profondi di S. Maria di Leuca. b) Distribuzione lunghezza-frequenza degli esemplari di
D. vitreus rinvenuti nel banco a coralli profondi di S. Maria di Leuca.
Conclusions – The SML population showed a size smaller than the Atlantic one
(mean size of 20 mm) (Shein, 1989). The observed smaller size could be possibly
result from a response of D. vitreus to the higher bottom temperatures of the bathyal
Mediterranean (ca 13-14 °C) or perhaps to differences in the trophic regimes.
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