A LONG-TERM MONITORING ACTIVITY ON A

Archo Oceanogr. Limnol. 22 (2001), 145-148
Istituto di Biologia del Mare, Venezia, Italia
A LONG-TERM MONITORING ACTIVITY ON A POSIDONIA OCEANICA
MEADOW AT MONTEROSSO AL MARE (LIGURIAN SEA)
A. PEIRANO, C. NIKE BIANCHI, D. SAVINI AND G. FARINA
ENEA, Marine Environment Research Centre, Santa Teresa, P O Box 316, I-19100 La Spezia (Italy)
INTRODUCTION
Posidonia oceanica (L.) Delile is a sea-grass species endemic to the Mediterranean
Sea. Its meadows show at present alarming signs of degradation, especially in the
northern parts of the Mediterranean. This degradation may be explained either by
pollution, resulting in greater water turbidity and hence diminished plant vitality; or,
by the natural decline of the plant which is believed to have had its climatic optimum
around 6000-2750 B P (Pérès, 1984). Regression of Posidonia meadows has been
surely accelerating in recent decades: in the Ligurian Sea, for example, it can be
reckoned that nearly 30 % of their original surface area has been lost in the 1960s,
during the period of rapid urban and industrial development along the Ligurian coast
(Bianchi & Peirano, 1995; Peirano & Bianchi, 1997). These years, however, also
corresponded to a cold phase in the secular temperature trend (Bianchi, 1997).
Clearly, long-term data are necessary to distinguish between the effects of climate
change and those of human pressure.
However, the long-term monitoring of sea-grass meadows is not a common
practice among marine biologists. Data on meadow evolution are usually inferred
from lepidochronological analyses (Pergent, 1990) or plastochrone interval index
(Duarte et al., 1994), two methods that allow estimating decadal rhizome elongation
and number of leaves produced per year with limited sampling efforts. However, also
these two techniques depend on annual series of measures when is necessary to
estimate parameters such as, for instance, mean leaf length or mean leaf production.
Therefore, they cannot detect changes in epiphytes or in herbivory that may influence
the length of leaves and their number per shoots (Montfrans et al., 1984).
This paper presents the first results of a long-term monitoring programme, started
in 1991, of the Posidonia oceanica meadow of Monterosso al Mare (SP), included in
the ‘Cinque Terre’ National Marine Park. The programme aims at following meadow
and plant evolution at decadal scale, correlating observed changes with climate.
146
A. PEIRANO, C. NIKE BIANCHI, D. SAVINI AND G. FARINA
MATERIAL AND METHODS
Twenty orthotropic shoots were sampled in March, June, September and December
by SCUBA diving in three stations located near the upper and the lower limits of the
seabed and at intermediate depth (5, 10 and 17 m). Density was evaluated by
counting shoots within 1 m2 quadrats in three replicates, percent cover was estimated
visually (Peirano et al., 1995).
Mean annual values of phenological and sinecological parameter (as mean of
seasonal values), as well as the study of annual leaf production and associate
communities, were accomplished using the methods proposed by Drew (1971) and
Giraud (1977), lepidochronological analysis and the index of epiphytism (Morri,
1991).
RESULTS AND DISCUSSION
Despite the limited period, first analysis of annual records evidenced that the deeper
station showed a constant, lower value of shoots' density, whereas the shallower
station (5 m) showed shoots with shorter leaves (Fig. 1). The first situation may be
explained with the regressed status of the meadow and the lower amount of light that
reaches the deeper site (Torricelli & Peirano, 1997), the second with the greater
exposure to water movement.
Notwithstanding these differences, the three stations showed a similar pluriannual
trend, consisting of a decrease in density and an increase in mean leaf length (Fig. 1).
This may viewed as a clue of a general response of the meadow to something that is
changing. Whether there is a link with climate or not is unclear (Bianchi, 1997;
Peirano et al., 1998). Flowering and fruiting occurred for three years consecutively,
1992 to 1994 (Stoppelli & Peirano, 1996). Sexual reproduction episodes were limited
to particular zones of the meadows and their occurrence in samples were rare. The
only two or three shoots that were sampled were not included in calculations). This
increased plant vitality might optimistically be considered as a sign of recovery from
heavier human aggression in previous years (Góngora Gonzáles et al., 1994), but a
longer period of observation is needed to understand what is really going on.
REFERENCES
BIANCHI C. N. & PEIRANO A., 1995. Atlante delle fanerogame marine della Liguria:
Posidonia oceanica e Cymodocea nodosa. ENEA, Centro Ricerche Ambiente
Marino, La Spezia: 1-146.
BIANCHI C. N., 1997. Climate change and biological response in the marine benthos.
In: M. Piccazzo (Ed.), Atti del 12° congresso dell'associazione italiana di oceanologia e limnologia. AIOL, Genova, 1: 3-20.
A LONG-TERM MONITORING ACTIVITY ON A POSIDONIA OCEANICA MEADOW
147
FIG. 1 Density and leaf length trends (mean ± standard deviation) at three depths in the Posidonia
oceanica meadow of Monterosso al Mare, 1992-1997. The dotted line indicates the overall mean.
DREW E. A., 1971. Botany. In: J. D. Woods & J. N. Lithgoe (Eds), Underwater Science. An introduction to experiments by divers. Academic Press, London: 175233.
DUARTE C. M., MARBÁ N., AGAWIN N., CEBRIÁN J., ENRÍQUEZ S., FORTES M. D.,
GALLEGOS M. E., MERINO M., OLESEN B., SAND-JENSEN K., URI J. & VERMAAT
J., 1994. Reconstruction of seagrass dynamics: age determinations and associated
tools for the seagrass ecologist. Mar. Ecol. Prog. Ser., 107: 195-209.
GIRAUD G., 1977. Essai de classement des herbiers de Posidonia oceanica (Linné)
Delile. Bot. mar., 20 (8): 487-491.
GÓNGORA GONZÁLES E., IMMORDINO F., PEIRANO A. & STOPPELLI N., 1996. Granulometric and geomorphologic features of the Bay of Monterosso al Mare (SP) and
their relationship with the evolution of Posidonia oceanica meadow. In:
G. Albertelli, A. De Maio & M. Piccazzo (Eds), Atti dell'11° congresso della
associazione italiana di oceanologia e limnologia. AIOL, Genova: 395-404.
MONTFRANS J., WETZEL R. L. & ORTH R. J., 1984. Epiphyte-grazer relationships in
seagrass meadows: consequences for seagrass growth and production. Estuaries,
7 (4A): 289-309.
MORRI C., 1991. Présentation d'un indice synthétique pour l'évaluation de l'épiphytisme foliaire chez Posidonia oceanica. Posidonia Newsletter, 4 (1): 33-37.
148
A. PEIRANO, C. NIKE BIANCHI, D. SAVINI AND G. FARINA
PEIRANO A. & BIANCHI C. N., 1997. Decline of the sea grass Posidonia oceanica in
response to environmental disturbance: a simulation-like approach off Liguria
(N W Mediterranean Sea). In: L. E. Hawkins, S. Hutchinson, S. Jensen,
A. C. Williams & M. Sheader (Eds), Responses of marine organisms to their
environment. University of Southampton, U K: 87-95.
PEIRANO A., SAVINI D., BIANCHI C. N. & FARINA G., 1998. Studio pluriannuale
della prateria di Posidonia oceanica (L.) Delile di Monterosso al Mare (SP):
primi risultati. (in prep.)
PEIRANO A., STOPPELLI N. & BIANCHI C. N., 1995. Monitoring and study techniques
of sea grasses in Liguria. Riv. marit., suppl., 12: 88-91.
PÉRÈS J. M., 1984. La régression des herbiers à Posidonia oceanica. In:
C. F. Boudouresque, A. Jeudy de Grissac & J. Olivier (Eds), International workshop on Posidonia oceanica beds. GIS Posidonie, Marseille, 1: 445-454.
PERGENT G., 1990. Lepidochronological analysis of the seagrass Posidonia oceanica
(L.) Delile: a standardized approach. Aquat. Bot., 37: 51-64.
STOPPELLI N. & PEIRANO A., 1996. Continuous flowering of Posidonia oceanica
(L.) Delile in the Bay of Monterosso al Mare (SP) (north-western Mediterranean
Sea). Boll. Mus. Ist. biol. Univ. Genova, 60-61: 31-40.
TORRICELLI L. & PEIRANO A., 1997. Produzione primaria fogliare di Posidonia oceanica (L.) Delile di Monterosso al Mare (SP): variazioni lungo un gradiente batimetrico. Biol. mar. medit., 4 (1): 81-85.