epibiosis in paramuricea clavata after mortality events in the

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.
[email protected]
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
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