Page 1 - gambi_lorenti_alii_1997

Biol. Mar. Medii. (1997). 4 (1): 384-387

M.C. GAMBI, M. LORENTI, S. BUSSOTTI*, P. GUIDETTI*
Stazionc Zoologica "A. Dohrn" Napoli, Laboratorio di Ecologia dcl Bcnthos,
Punta S.Pictro - 80077 Ischia (NA), Italia.
*Ist. di Anatomia Comparata, Università di Gcnova, Italia.

BORERS IN POSIDONIA OCEANICA SCALES:
TAXONOMICAL COMPOSITION AND OCCURRENCE

ORGANISMI PERFORATORI NELLE SCAGLIE DI POSIDONIA
OCEANICA: COMPOSIZIONE TASSONOMICA E DISTRIBUZIONE

Abstract
The occurrence of three species of polychnetes (Lysidice ninetia. L. collaris crnrl Nematonereis
unicornis) und one species of isopods (Limnoria tiiberculata) horittg inlo Posidonia oceanica scales
is recorderl. A srrrvey revealed the e.rtent of the phenomenon ulong tlie ilnlian c0o.st.v in hecls locu~ecl
JPom I m to 28 m depth. Polychnetes ivere eveiily disrribnted, n.hile isoporls occurrecl rrt Jkri~er si/e.s.
Microniche differentintion within the scales between the two tnxotiomic gro~rps of borers wus crlso
observecl.

Key-words: Posidonia oceanica, borers, Polychaeta, Isopoda.

Introduction
An important component of the stem habitat of Posidonia oceanica beds is
built up by scales, i.e. the remains of shed leaves bases persisting along the rhizome
and showing various degrees of tissue decaying. The occurrence of invertebrates
burrowing inside stems of Australian seagrasses has been recently pointed out by
Brearley and Walker (1993, 1996). As far as Mediterranean seagrasses are concerned,
no organic record was available. A survey carried out at severa1 sites along the
western coasts of Italy highlighted the widespread occurrence of the phenomenon
at the Posidonia stem level.

Materia1 and Methods
Investigated beds are located at various sites along the coasts of Liguria, Sardinia
and Campania, and in the islands of Ventotene, Ischia, Ustica, Favignana, Levanzo
and Linosa, at depths ranging from 1 m to 28 m (Table 1). At some sites various
beds were surveyed, also in different periods, during the years 1995-1996.
A number of Posidonia shoots varying between 5 and 100 was collected at
each site and then scales of each shoot examined for the presence of borers and/
or traces of their empty burrows.

Results and Discussion
Two groups of borers were singled out, belonging to polychaetes and crustacean
isopods, respectively. Burrowing of at least one of the two groups has been detected
at al1 sites investigated. The percentage of infested stems varied greatly between
beds, ranging from 6 to 58% and reaching 95-100% in some localities (e.g., off