CHAPTER 52
Functional Diversity in the Posidonia oceanica Ecosystem: an Example
with Polychaete Borers of the Scales
M.e. Gambi and G. Cafiero
ABSTRACT
Species composition and spatia-temporal distribution of polychaete borers in Posidonia oceanica (L.) Delile scales, were studied in 4 stations located in two meadows off the Island of Ischia
(Gulf of Naples) with different typology and at different depths: Castello at 1 m and 3-5 m depth,
Lacco Ameno at 3-5 m and 22 m depth. Five species, all belonging to the family Eunicidae, were
found as borers of scales: Lysidicecollaris (Grube) (59% ofthe specimens collected), Lysidice ninetta Audouin and Milne-Edwards (32%), Nematonereis unicornis Schmarda (8%), Palola siciliensis
(Grube) and Marphysa fallaxMarion and Bobretzkywith only 2 specimens each.The spatio-temporal analysis showed the occurrence of polychaete borers (mainly the two species of Lysidice)
at all stations and in all sampling months, except at the shallowest site (1 m) at the Castello
meadow. The mean values of rhizomes affected by borers 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 boring have been also frequently observed (37%) in the dead rhizomes, where specimens of 4 of the 5 recorded species were also found with a frequency of 23%. The mean number of individuals/m 2 was 66±22 and B4±25 for the shallow sites {Castello and Lacco, respectively},and 49±15 for the deep site at Lacco. The temporal analysis did not show any particular
pattern in borer colonisation, but relatively homogeneous abundances in all studied months.
Boring of living leaf bases (with detachment of the entire living shoot), and of the adjacent leaf
tissues were sometime observed. The phenomenon of consumption of living tissues was very
limited in the shallow meadows (Castello and Lacco 3-5 m, mean index of herbivory= 0.6% and
0.8% of the analysed rhizomes, respectively), while it was relatively more important in the deep
site (Lacco 22 m, mean index of herbivory= 2.6%). The scales of P. oceanica represent an unique
and preferential microhabitat for some boring polychaetes, whose colonisation resulted to be
frequent/ common to different meadows and depths and constant in time. The feeding and
mechanical action of polychaete borers have strong ecological implications in enhancing scale
fragmentation and decay by microbial activity, and in providing further microniches for other
organisms (e.g. small polychaetes, sipunculids) that colonise the empty burrows. Last but not
least the direct grazing on living plant tissues may have a direct impact on the system.
I ntrod uction
The high animal biodiversity recorded in the
Posidonia oceanica (L.) Delile ecosystem is related to the availability of microhabitats which are
provided by the high spatial complexity of the
plant and of the system (Mazzella et al. 1992). For
the fauna associated to P. oceanica meadows it
has been possible to recognize specific adaptations to microhabitats of the leaf and rhizome
layers and of the «matte". The knowledge on the
structural and functional diversity of each of
these layers and microhabitats is different. While
the vagile fauna of the leaf stratum is relatively
well known, also from a trophic point of view
(Gambi et al. 1992), the fauna inhabiting the rhizomes is far less studied (Somaschini et al. 1994),
except for echinoderms and other large detritivores (Mazzella et al. 1992).
Within the compartment of the rhizomes,
Stazione Zaalogica "A. Dahrn", Lahoratoria di Ecologia del Benthos, Punta S. Pietro, 80077 Ischia (Napoli), Italy
F.M. Faranda, L. Guglielmo, G. Sperle (eds)
Mediterranean Ecosystems: Structures and Processes
@ Springer-Verlag ltalia 2001
Functional Diversity in the Posidonia oceanica Ecosystem: an Example
with Polychaete Borers of the Scales
M.e. Gambi and G. Cafiero
ABSTRACT
Species composition and spatia-temporal distribution of polychaete borers in Posidonia oceanica (L.) Delile scales, were studied in 4 stations located in two meadows off the Island of Ischia
(Gulf of Naples) with different typology and at different depths: Castello at 1 m and 3-5 m depth,
Lacco Ameno at 3-5 m and 22 m depth. Five species, all belonging to the family Eunicidae, were
found as borers of scales: Lysidicecollaris (Grube) (59% ofthe specimens collected), Lysidice ninetta Audouin and Milne-Edwards (32%), Nematonereis unicornis Schmarda (8%), Palola siciliensis
(Grube) and Marphysa fallaxMarion and Bobretzkywith only 2 specimens each.The spatio-temporal analysis showed the occurrence of polychaete borers (mainly the two species of Lysidice)
at all stations and in all sampling months, except at the shallowest site (1 m) at the Castello
meadow. The mean values of rhizomes affected by borers 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 boring have been also frequently observed (37%) in the dead rhizomes, where specimens of 4 of the 5 recorded species were also found with a frequency of 23%. The mean number of individuals/m 2 was 66±22 and B4±25 for the shallow sites {Castello and Lacco, respectively},and 49±15 for the deep site at Lacco. The temporal analysis did not show any particular
pattern in borer colonisation, but relatively homogeneous abundances in all studied months.
Boring of living leaf bases (with detachment of the entire living shoot), and of the adjacent leaf
tissues were sometime observed. The phenomenon of consumption of living tissues was very
limited in the shallow meadows (Castello and Lacco 3-5 m, mean index of herbivory= 0.6% and
0.8% of the analysed rhizomes, respectively), while it was relatively more important in the deep
site (Lacco 22 m, mean index of herbivory= 2.6%). The scales of P. oceanica represent an unique
and preferential microhabitat for some boring polychaetes, whose colonisation resulted to be
frequent/ common to different meadows and depths and constant in time. The feeding and
mechanical action of polychaete borers have strong ecological implications in enhancing scale
fragmentation and decay by microbial activity, and in providing further microniches for other
organisms (e.g. small polychaetes, sipunculids) that colonise the empty burrows. Last but not
least the direct grazing on living plant tissues may have a direct impact on the system.
I ntrod uction
The high animal biodiversity recorded in the
Posidonia oceanica (L.) Delile ecosystem is related to the availability of microhabitats which are
provided by the high spatial complexity of the
plant and of the system (Mazzella et al. 1992). For
the fauna associated to P. oceanica meadows it
has been possible to recognize specific adaptations to microhabitats of the leaf and rhizome
layers and of the «matte". The knowledge on the
structural and functional diversity of each of
these layers and microhabitats is different. While
the vagile fauna of the leaf stratum is relatively
well known, also from a trophic point of view
(Gambi et al. 1992), the fauna inhabiting the rhizomes is far less studied (Somaschini et al. 1994),
except for echinoderms and other large detritivores (Mazzella et al. 1992).
Within the compartment of the rhizomes,
Stazione Zaalogica "A. Dahrn", Lahoratoria di Ecologia del Benthos, Punta S. Pietro, 80077 Ischia (Napoli), Italy
F.M. Faranda, L. Guglielmo, G. Sperle (eds)
Mediterranean Ecosystems: Structures and Processes
@ Springer-Verlag ltalia 2001