a
Polychaete Borers of Posidonia oceanica Scales
401
group going from the second scale to that one
with the lowest thickness; group 2= the group
following the previous one up to the next scale
with the lowest thickness; group 3= the remaining scales up to the end of the rhizomes. These
groups may roughly represent different years,
according to the lepidochronology technique
(Pergent 1990). Borers found in the first scale and
in each group have been checked.
Results and Discussion
A total of 1503 living rhizomes and 201 dead rhizomes were analysed. In total 326 specimens of
boring polychaetes have been collected belonging to 5 species of Eunicidae: Lysidice collaris
(Grube) (59% of the specimens sampled);
Lysidice ninetta Audouin and Milne-Edwards
(32%), Nematonereis unicornis Schmarda (8%);
Paiola siciliensis (Grube) (2 specimens);
Marphysa fallax Marion and Bobretzky (2 specimens). While the two species of Lysidice and N.
unicornis have been previously reported to bore
on scales (Gambi et al. 1997; Guidetti et al. 1997),
P. siciliensis and M. fallax are newly recorded as
scale borers. Morphological description of these
species can be found in George and HartmannSchroeder (1985), and in Martin (1987), while
information on distribution and ecology can be
found in Cantone (1993), as regards the Italian
coasts.
Generally, in all the samples examined, in
each affected shoot only a single polychaete
borer was recorded. In a few cases two specimens
were record in the same shoot, while only on a
single occasion two specimens were observed
inside of the same scale (Fig. 1a).
The spatio-temporal analysis of the index of
borers (IB) showed the occurrence of polychaete
borers (mainly the two species of Lysidice) at all
stations and in all sampling months (Fig. 2a),
except at the shallowest site (1 m) at the Castello
meadow where polychaetes were occasional. The
mean values of the IB ranged from 19-21 % at the
shallow sites of both studied meadows (3-5 m) to
29% at the deep site (22 m) of the Lacco meadow.
Traces of previous colonisation of these organisms (index of traces, IT) were present in all stations and seasons, and contributed to the index
of colonisation (Ie) whose means ranged
between 42 and 58%, indicating that the phenomenon of boring is relatively frequent.
The temporal analysis did not show any particular pattern in borer colonisation, but relatively homogeneous abundances in all months
(Fig. 2b). The mean number of individuals/m 2
was 66±22 and 84±25 for the shallow sites
(Castello and Lacco, respectively), and 49±15 for
the deep site off Lacco. In the Castello meadow at
Fig. I. a Two Posidonia oceanica scales with polychaete borers (arrows) inside; note that the right scales contain two specimens.
b Living bases of Posidonia leaves with evident traces of grazing by polychaete borers (note the necrotic tissues around the
grazed margins)
b
Polychaete Borers of Posidonia oceanica Scales
401
group going from the second scale to that one
with the lowest thickness; group 2= the group
following the previous one up to the next scale
with the lowest thickness; group 3= the remaining scales up to the end of the rhizomes. These
groups may roughly represent different years,
according to the lepidochronology technique
(Pergent 1990). Borers found in the first scale and
in each group have been checked.
Results and Discussion
A total of 1503 living rhizomes and 201 dead rhizomes were analysed. In total 326 specimens of
boring polychaetes have been collected belonging to 5 species of Eunicidae: Lysidice collaris
(Grube) (59% of the specimens sampled);
Lysidice ninetta Audouin and Milne-Edwards
(32%), Nematonereis unicornis Schmarda (8%);
Paiola siciliensis (Grube) (2 specimens);
Marphysa fallax Marion and Bobretzky (2 specimens). While the two species of Lysidice and N.
unicornis have been previously reported to bore
on scales (Gambi et al. 1997; Guidetti et al. 1997),
P. siciliensis and M. fallax are newly recorded as
scale borers. Morphological description of these
species can be found in George and HartmannSchroeder (1985), and in Martin (1987), while
information on distribution and ecology can be
found in Cantone (1993), as regards the Italian
coasts.
Generally, in all the samples examined, in
each affected shoot only a single polychaete
borer was recorded. In a few cases two specimens
were record in the same shoot, while only on a
single occasion two specimens were observed
inside of the same scale (Fig. 1a).
The spatio-temporal analysis of the index of
borers (IB) showed the occurrence of polychaete
borers (mainly the two species of Lysidice) at all
stations and in all sampling months (Fig. 2a),
except at the shallowest site (1 m) at the Castello
meadow where polychaetes were occasional. The
mean values of the IB ranged from 19-21 % at the
shallow sites of both studied meadows (3-5 m) to
29% at the deep site (22 m) of the Lacco meadow.
Traces of previous colonisation of these organisms (index of traces, IT) were present in all stations and seasons, and contributed to the index
of colonisation (Ie) whose means ranged
between 42 and 58%, indicating that the phenomenon of boring is relatively frequent.
The temporal analysis did not show any particular pattern in borer colonisation, but relatively homogeneous abundances in all months
(Fig. 2b). The mean number of individuals/m 2
was 66±22 and 84±25 for the shallow sites
(Castello and Lacco, respectively), and 49±15 for
the deep site off Lacco. In the Castello meadow at
Fig. I. a Two Posidonia oceanica scales with polychaete borers (arrows) inside; note that the right scales contain two specimens.
b Living bases of Posidonia leaves with evident traces of grazing by polychaete borers (note the necrotic tissues around the
grazed margins)
b