358
M.A. Colangelo et al.
taxon and their diversity was high in areas with a
moderate gas seepage or sulphur deposit. The
primary influence of the sediment characteristic
on the composition of meiobenthic assemblages
cannot be disregarded (Wieser 1959). The total
copepod densities are in the range of values
recorded in sandy habitats (Hicks and Coull
1983) and seem to conform to the rule that copepods dominate or become numerically abundant
as the particle size of the sediment increases
(Coull 1985). The coarse to very coarse grain size
of the sandy patches in Panarea's caldera, with
their wide interstitial spaces, could explain the
copepod dominance at this site. Nematode densities increased their relevance at stations characterised by bubble streams (S12H and S12M)
(Table 2). Probably, in those areas, there is a sufficient production of sulphur bacteria (Acunto et
al 1995) to support populations of some specialised nematode species (Giere 1992).
Moreover, the drawdown of interstitial water to
replace water displaced by the rising gas, would
bring detrital material and phyoplankton into
the sediment (Dando et al. 1995) with benefit to
all meiobenthic organisms.
At site S 16. which is probably located in a
hydrothermal field with higher HzS content (max
6.5 val.%; Italiano and Nuccio 1991) in the gas
mixture, colloidal sulphur precipitation
occurred. The disturbance effects on the whole
meiobenthic community appeared clearly evident and were likely due to the direct clogging of
the interstitial spaces among the very coarse
sand grains due to sulphur deposition. Such a
kind of disturbance probably affected, to a minor
extent, also meiobenthos at the control station
(SI6C. Table 2). which could have been affected
by very fine colloidal sulphur particles, though
not macroscopically evident.
At S12, characterised by a less relevant
hydrothermal seepage (Le. simple bubble
stream) the three stations showed significantly
different copepod assemblages (Table 4, Figs. 2,
3). At the control station (S12C), there were less
species (10) and Cyclopina sp. and
Hemicyclopina sp. were dominant. At station
SI2M, where a moderate bubbling occurred. the
highest number of species was observed (27) but
evenness was reduced due to the dominance of a
few species (Amphiascus minutus, Ameira longicaudata, Tryphoema efr. bocqueti and Laophonte
cornuta). Finally at station S12H, with more
intense gas emissions, an intermediate value of
the number of species (17) with higher evenness
was reported (Fig. 3).
On the whole, the overall situation of the
species biodiversity. emerging by the present
investigation on meiobenthic communities
exposed to increasing hydrothermal seepage,
could be interpreted in the light of «the intermediate disturbance" theory of diversity maintenance (Huston 1979). Where disturbance is minimal (e.g. at SI2C) diversity is reduced because of
competitive exclusion between species; with a
slightly increased level or frequency of disturbance (e.g. at S12H and even more at 812M) competition decreases, resulting in an increased
diversity. At higher or more frequent levels of
disturbance (e.g. at site S16 and partly at SI2H)
species start to become eliminated by stress, so
that diversity falls again.
References
Acunto S, Maltagliati F, Benedetti-Cecchi L, Lardicci C, Cinelli P,
Cognetti G (1995) Osservazioni sui popolamenti bentonid
di un'area interessata da fenomeni di vulcanismo secondario nei pressi deIl'Isola di Panarea (Me). In: Faranda PM
(00) Caratterizzazione ambientale marina del sistema Eolie
e dei baemi limitrofi di Cefalu e Gioia (EOCUMM94). G.
Lang, Genova, pp 251-256
Buchanan JB (1984) Sediment analyses. In: Holme NA, McIntyre
AD (eds) Methods for the study of marine benthos. (IPB
Handbook, 16). Blackwell Scientific Publications, London,
pp 41-65
Clarke KR, Warwick RM (1994) Changes in marine communities:
an approach to statistical analysis and interpretation. Nat
Environ Res Counc, UK
Coull BC (1985) Long-term variability of estuarine meiobenthos:
an 11 year study. Mar Ecol Prog Ser 24: 205-218
Dando PR, Hughes JA, Thiermann F (1995) Preliminaryobservations on biological communities at shallow hydrothermal
vents in the Aegean Sea. In: Parson LM, Walker CL, Dixon DR
(eds) Hydrothermal vents and processes. Geol Soc. London,
Spec Publ 87. pp 303-317
Dixon PM (1993) The Bootstrap and the Jackknife: describing the
precision of ecological indices. In: Scheiner SM. Gurevitch J
(eds) Design and analysis of ecological experiments.
Chapman and Hall. New York, pp 290-318
Fricke H, Giere 0, Stetter K, Alfredsson GA) Kristjansson JK,
Stoffers P, Svavarsson J (1989) Hydrothermal vent communities at the shallow subpolar Mid-Atlantic ridge. Mar BioI 102:
425-429.
GabbianeI1i G, Cortecci G, Capra A) Giacomelli L, Pompilio M,
Rossi PML (1996) Lineamenti geo-vulcanologici ed ambientali de.ll'area craterica sottomarina di Dattilo-Lisca Bianca
(Isola di Panarea, Arcipelago Eoliano). In: Faranda FM,
Pavero P (OOs) Caratterizzazione ambientale marina del sistema Bolie e dei bacini limitrofi di Cefalu e Gioia
(EOCUMM95). G. Lang, Genova, pp 475-484
Giere 0 (1992) Benthic life in sulfidic zones of the sea - ecological and structural adaptations to a toxic environment. Verh
Dtsch Zool Ges 85: 77-93
M.A. Colangelo et al.
taxon and their diversity was high in areas with a
moderate gas seepage or sulphur deposit. The
primary influence of the sediment characteristic
on the composition of meiobenthic assemblages
cannot be disregarded (Wieser 1959). The total
copepod densities are in the range of values
recorded in sandy habitats (Hicks and Coull
1983) and seem to conform to the rule that copepods dominate or become numerically abundant
as the particle size of the sediment increases
(Coull 1985). The coarse to very coarse grain size
of the sandy patches in Panarea's caldera, with
their wide interstitial spaces, could explain the
copepod dominance at this site. Nematode densities increased their relevance at stations characterised by bubble streams (S12H and S12M)
(Table 2). Probably, in those areas, there is a sufficient production of sulphur bacteria (Acunto et
al 1995) to support populations of some specialised nematode species (Giere 1992).
Moreover, the drawdown of interstitial water to
replace water displaced by the rising gas, would
bring detrital material and phyoplankton into
the sediment (Dando et al. 1995) with benefit to
all meiobenthic organisms.
At site S 16. which is probably located in a
hydrothermal field with higher HzS content (max
6.5 val.%; Italiano and Nuccio 1991) in the gas
mixture, colloidal sulphur precipitation
occurred. The disturbance effects on the whole
meiobenthic community appeared clearly evident and were likely due to the direct clogging of
the interstitial spaces among the very coarse
sand grains due to sulphur deposition. Such a
kind of disturbance probably affected, to a minor
extent, also meiobenthos at the control station
(SI6C. Table 2). which could have been affected
by very fine colloidal sulphur particles, though
not macroscopically evident.
At S12, characterised by a less relevant
hydrothermal seepage (Le. simple bubble
stream) the three stations showed significantly
different copepod assemblages (Table 4, Figs. 2,
3). At the control station (S12C), there were less
species (10) and Cyclopina sp. and
Hemicyclopina sp. were dominant. At station
SI2M, where a moderate bubbling occurred. the
highest number of species was observed (27) but
evenness was reduced due to the dominance of a
few species (Amphiascus minutus, Ameira longicaudata, Tryphoema efr. bocqueti and Laophonte
cornuta). Finally at station S12H, with more
intense gas emissions, an intermediate value of
the number of species (17) with higher evenness
was reported (Fig. 3).
On the whole, the overall situation of the
species biodiversity. emerging by the present
investigation on meiobenthic communities
exposed to increasing hydrothermal seepage,
could be interpreted in the light of «the intermediate disturbance" theory of diversity maintenance (Huston 1979). Where disturbance is minimal (e.g. at SI2C) diversity is reduced because of
competitive exclusion between species; with a
slightly increased level or frequency of disturbance (e.g. at S12H and even more at 812M) competition decreases, resulting in an increased
diversity. At higher or more frequent levels of
disturbance (e.g. at site S16 and partly at SI2H)
species start to become eliminated by stress, so
that diversity falls again.
References
Acunto S, Maltagliati F, Benedetti-Cecchi L, Lardicci C, Cinelli P,
Cognetti G (1995) Osservazioni sui popolamenti bentonid
di un'area interessata da fenomeni di vulcanismo secondario nei pressi deIl'Isola di Panarea (Me). In: Faranda PM
(00) Caratterizzazione ambientale marina del sistema Eolie
e dei baemi limitrofi di Cefalu e Gioia (EOCUMM94). G.
Lang, Genova, pp 251-256
Buchanan JB (1984) Sediment analyses. In: Holme NA, McIntyre
AD (eds) Methods for the study of marine benthos. (IPB
Handbook, 16). Blackwell Scientific Publications, London,
pp 41-65
Clarke KR, Warwick RM (1994) Changes in marine communities:
an approach to statistical analysis and interpretation. Nat
Environ Res Counc, UK
Coull BC (1985) Long-term variability of estuarine meiobenthos:
an 11 year study. Mar Ecol Prog Ser 24: 205-218
Dando PR, Hughes JA, Thiermann F (1995) Preliminaryobservations on biological communities at shallow hydrothermal
vents in the Aegean Sea. In: Parson LM, Walker CL, Dixon DR
(eds) Hydrothermal vents and processes. Geol Soc. London,
Spec Publ 87. pp 303-317
Dixon PM (1993) The Bootstrap and the Jackknife: describing the
precision of ecological indices. In: Scheiner SM. Gurevitch J
(eds) Design and analysis of ecological experiments.
Chapman and Hall. New York, pp 290-318
Fricke H, Giere 0, Stetter K, Alfredsson GA) Kristjansson JK,
Stoffers P, Svavarsson J (1989) Hydrothermal vent communities at the shallow subpolar Mid-Atlantic ridge. Mar BioI 102:
425-429.
GabbianeI1i G, Cortecci G, Capra A) Giacomelli L, Pompilio M,
Rossi PML (1996) Lineamenti geo-vulcanologici ed ambientali de.ll'area craterica sottomarina di Dattilo-Lisca Bianca
(Isola di Panarea, Arcipelago Eoliano). In: Faranda FM,
Pavero P (OOs) Caratterizzazione ambientale marina del sistema Bolie e dei bacini limitrofi di Cefalu e Gioia
(EOCUMM95). G. Lang, Genova, pp 475-484
Giere 0 (1992) Benthic life in sulfidic zones of the sea - ecological and structural adaptations to a toxic environment. Verh
Dtsch Zool Ges 85: 77-93