CHAPTER 48
Effect of Submerged Structures on the Diversity of Macrozoobenthos
in the Northern Adriatic Sea
R. Crema 1, D. PrevedelUl, and A. Castellfl
ABSTRACT
Offshore exploitation of oil and other hydrocarbons requires the installation of platforms or similar structures fixed to the sea bottom. Generally, such structures remain in situ for long time after
the end of drilling and production activities. The macrozoobenthic communities of a sea area
located in the Northern Adriatic Sea surrounding one of these platforms were studied on two
occasions: the first prior to the installation of the platform (1985) and the second 8 years later
(1993),after production and other activities had terminated. On both occasions, samplings were
performed according to similar sampling grids extending about 3.5 km from the platform site.
Comparing the community composition of the two periods, a remarkable decrease of surface
deposit feeders was observed in the second period. Ordering techniques, applied to the entire
set of community samples of both periods/ pointed out not only the expected separation of the
sampling points of the two periods but also a different pattern of dispersion. In fact, the samples
of the first period were more dispersed in the model than those of the second period. The BrayCurtis similarity values between samples exhibit a significantly greater similarity between pairs
of samples of the second period. In spite of the fact that the diversity values of each individual
sample are not different in the two sets, the different patterns of the increase of diversity, when
plotted against the number of samples, further confirms the greater faunal uniformity among
the samples of the second period. The results are discussed in light of sedimentological studies,
performed in the same area, which highlight the role of the submerged structure in increasing
the hydrodynamic energy near the bottom. This is consistent with the more recent findings in
the literature on the dynamic variables that control the infauna distribution.
Introduction·
The impact of oil and gas search and exploitation
on the marine life derives mainly from the well
drilling phase. which involves the installation of
large platforms fIxed to the bottom and discharge into the sea of cuttings extracted from the
bottom and drilling muds. The fate and effect of
these discharges have been extensively studied
(Harper et al. 1981; Davies et al. 1984; Hartley
1984, 1996; Kingston 1987; Neff et al. 1989;
Reiersen et al. 1989; Gray et al. 1990; Kroncke et
al.1992; Daan et al.1994; Olsgard and Gray 1995)
and depend largely on the specifIc mud formulation. The water-based muds, consisting of a suspension of inert weighting materials (mainly
barite) in water, cause a non -selective reduction
in the benthic macrofauna, whereas the oil-based
muds, in which the inerts are suspended in oil or
in a synthetic pseudo-oil base fluid, cause the
occurrence of opportunistic species like in many
other observed cases of organic pollution.
Mter the end of the drilling phase, the environmental impact of platform activities becomes
less severe. During production, oil-field brines
are frequently discharged in addition to the
wastes of a small manned station that operates
the platform. When the oil or gas reserve is
exhausted, the platforms generally remain in situ
for a long time, before their fmal decommissioning. in the absence of any relevant activity and
any discharge to the sea.
In Italy search for and exploitation of offshore oil and gas reserves is particularly well
I Dipartimento di Biologia Animale, Universita di Modena, Via dell'Universita 4,41100 Modena, Italy
2 Dipartimento di Zoologia ed Antropologia Biologica, Viale Regina Margherita 15,01100 Sassari, Italy
F.M. Faranda. 1. Guglielmo, G. Spezie (eels)
Mediterranean Ecosystems; Structures and Processes
@ Springer-Verlag ltalia 2001
Effect of Submerged Structures on the Diversity of Macrozoobenthos
in the Northern Adriatic Sea
R. Crema 1, D. PrevedelUl, and A. Castellfl
ABSTRACT
Offshore exploitation of oil and other hydrocarbons requires the installation of platforms or similar structures fixed to the sea bottom. Generally, such structures remain in situ for long time after
the end of drilling and production activities. The macrozoobenthic communities of a sea area
located in the Northern Adriatic Sea surrounding one of these platforms were studied on two
occasions: the first prior to the installation of the platform (1985) and the second 8 years later
(1993),after production and other activities had terminated. On both occasions, samplings were
performed according to similar sampling grids extending about 3.5 km from the platform site.
Comparing the community composition of the two periods, a remarkable decrease of surface
deposit feeders was observed in the second period. Ordering techniques, applied to the entire
set of community samples of both periods/ pointed out not only the expected separation of the
sampling points of the two periods but also a different pattern of dispersion. In fact, the samples
of the first period were more dispersed in the model than those of the second period. The BrayCurtis similarity values between samples exhibit a significantly greater similarity between pairs
of samples of the second period. In spite of the fact that the diversity values of each individual
sample are not different in the two sets, the different patterns of the increase of diversity, when
plotted against the number of samples, further confirms the greater faunal uniformity among
the samples of the second period. The results are discussed in light of sedimentological studies,
performed in the same area, which highlight the role of the submerged structure in increasing
the hydrodynamic energy near the bottom. This is consistent with the more recent findings in
the literature on the dynamic variables that control the infauna distribution.
Introduction·
The impact of oil and gas search and exploitation
on the marine life derives mainly from the well
drilling phase. which involves the installation of
large platforms fIxed to the bottom and discharge into the sea of cuttings extracted from the
bottom and drilling muds. The fate and effect of
these discharges have been extensively studied
(Harper et al. 1981; Davies et al. 1984; Hartley
1984, 1996; Kingston 1987; Neff et al. 1989;
Reiersen et al. 1989; Gray et al. 1990; Kroncke et
al.1992; Daan et al.1994; Olsgard and Gray 1995)
and depend largely on the specifIc mud formulation. The water-based muds, consisting of a suspension of inert weighting materials (mainly
barite) in water, cause a non -selective reduction
in the benthic macrofauna, whereas the oil-based
muds, in which the inerts are suspended in oil or
in a synthetic pseudo-oil base fluid, cause the
occurrence of opportunistic species like in many
other observed cases of organic pollution.
Mter the end of the drilling phase, the environmental impact of platform activities becomes
less severe. During production, oil-field brines
are frequently discharged in addition to the
wastes of a small manned station that operates
the platform. When the oil or gas reserve is
exhausted, the platforms generally remain in situ
for a long time, before their fmal decommissioning. in the absence of any relevant activity and
any discharge to the sea.
In Italy search for and exploitation of offshore oil and gas reserves is particularly well
I Dipartimento di Biologia Animale, Universita di Modena, Via dell'Universita 4,41100 Modena, Italy
2 Dipartimento di Zoologia ed Antropologia Biologica, Viale Regina Margherita 15,01100 Sassari, Italy
F.M. Faranda. 1. Guglielmo, G. Spezie (eels)
Mediterranean Ecosystems; Structures and Processes
@ Springer-Verlag ltalia 2001