THE USE OF RECONSTRUCTIVE METHODS IN COMBINATION WITH “BEYOND BACI” DESIGNS:
THE CASE STUDY OF CAPO FETO (SW SICILY, ITALY)
Giuseppe Di Carlo* , Fabio Badalamenti, Claudia Passalacqua
IRMA-CNR, sez. di IAMC, Laboratorio di Biologia Marina, Castellammare del Golfo (TP), Italy
Abstract
Changes in leaf production and rhizome elongation rates of Posidonia oceanica have been evaluated by means of reconstructive methods
to evaluate the response to a dredging carried out in 1993. Asymmetrical sampling design “beyond BACI” was used to detect the impact
with a single sampling as dating methods obviated lack of pre-impact data. Leaf production and rhizome elongation rates were
reconstructed for 4 years before 4 years after the impact. Rhizome elongation almost doubled after the impact. Control sites did not present
any significant variations from before to after the impact. Results suggest a pulse disturbance, since leaf production did not change and
internodal length increased in a short-time scale.
Keywords: Posidonia oceanica; reconstruction methods; impact
Rapp. Comm. int. Mer Médit., 37,2004
514
Introduction
P. oceanicameadows are recognized to be key ecosystems in the
marine environment. In the last decade a regression of P. oceanicabeds
has been reported due to anthropogenic causes (1,2). A submerged
pipeline was deployed at Capo Feto (SW Sicily, Italy) in 1993. This
caused an increase of water turbidity and sedimentation rate. Vertical
rhizomes overcome burial process by increasing internodal length, but
when the balance between sedimentation and plant growth is lost, the
plant suffocates (3). This study utilises a “beyond BACI” sampling
design (4) in combination with reconstruction methods (5) to assess the
response of the seagrass P. oceanica to the impact caused by a coastal
dredging.
Material and Methods
144 vertical shoots shoots of P. oceanica were randomly sampled in
October 2000 at depths of maximum shoot density both at impact
(Capo Feto) and control sites (Tonnarella). The length of all internodes
was measured using a stereomicroscope (5). The 1:1 relationship
between leaf and vertical internode allows the number of vertical
internodes between two consecutive minima in length to be used as a
surrogate for the number of leaves produced during a time period.
Asymmetrical analyses of variance were used to examine temporal
differences between the potentially impacted meadow and the average
of control meadows (6). Data were examined by Cochran’s C test for
homogeneity of variances. Appropriate transformations, whenever
necessary (7). ANOVA was performed using GMAV5 (University of
Sydney).
Results
The results show that there is no evident variation in leaf production
rate from before to after pipeline deployment both at Capo Feto and
Tonnarella (impact/controls). However, annual rhizome elongation
rates were found to be significantly different from before to after the
impact at Capo Feto (impact), while no difference was recorded at both
control sites (Tonnarella) (Fig. 2). Indeed, an increase of internodal
length was recorded at the impacted site starting from 1994. Such
increase in rhizome elongation seen after the disturbance could re?ect
an integrated response of the plant at a different magnitude of response
to the impact (6).
Discussion
In Posidonia oceanicavertical growth has been demonstrated to be
sensitive to sediment dynamics (8,9,10). Internodal length is strictly
related to burial and erosion processes (10). In this study, an excess in
sedimentation rate lead to an increase vertical growth to overcome
burial. Reconstructive methods represent a useful procedure to assess
seagrass dynamics, proving a tool for the assessment and management
of coastal ecosystems (11). The combination of dating methods with
“beyond BACI” designs can be considered an excellent approach to
evaluate environmental impacts, especially when pre-impact data are
lacking.
Fig. 2. Rhizome elongation rate variation before and after the putative
impact at Capo Feto.
References
1 - Pérès, J.M. 1984. La régression des herbiers à Posidonia oceanica. Pp.
39-44. In: Boudouresque C.F., Jeudy de Grissac A., Oliver J. (Eds.) Inter-
national Workshop on Posidonia oceanicabeds. GIS Posidonie Publ.,
Marseille.
2 - Short, F.T., Wyllie-Echeverria, S. 1996. Natural and human-induced
disturbance of seagrasses. Environ. Conserv. 23(1): 17-27.
3- Hemminga, M., Duarte C. 2000. Seagrass Ecology. Cambridge
University Press, Cambridge.
4 - Underwood, A.J., 1992. Beyond BACI: the detection of environmental
impacts on populations in the real, but variable, world. J. Exp. Mar. Biol.
Ecol. 161: 145–178.
5 - Duarte, C.M., Marbà, N., Agawin, N., Cebrian, J., Enriquez, S., Fortes,
MD., Gallegos, M.E., Merino, M., Olesen, B., Sand-Jensen, K., Uri, J.,
VERMAAT J. 1994. Reconstruction of seagrass dynamics: age determina-
tion and associated tools for the seagrass ecologist. Mar. Ecol. Prog. Ser.
107: 195-209.
6 - Guidetti, P. 2001. Detecting environmetal impacts on the Mediter-
ranean seagrass Posidonia oceanica(L.) Delile: the use of reconstructive
methods in combination with “beyond BACI” design. J. Exp. Mar. Biol.
Ecol.260: 27-39.
7 - Underwood, A.J., 1997. Experiments in Ecology: Their Logical Design
and Interpretation Using Analysis of Variance. Cambridge Univ. Press.
8 - Marbà, N., Duarte, C. 1994. Growth Response of the seagrass Cymo-
docea nodosato experimental burial and erosion. Mar. Ecol. Prog. Ser.
107: 307-311.
9 - Marba, N., Duarte, C.M., Cebrian, J., Gallegos, M.E., Olesen, B.,
Sand-Jensen, K. 1996. Growth and population dynamics of Posidonia
oceanicaon the Spanish Mediterranean coast: elucidating seagrass
decline. Mar. Ecol. Prog. Ser.137: 203-213.
10 - Duarte, C.M., Terrados, J., Agawin, N., Fortes, M.D., Bach, S.,
Kenworthy, W.J., 1997. Response to a mixed Philippine seagrass meadow
to experimental burial. Mar. Ecol. Prog. Ser. 147: 285–294.
11 - Durako, M.J., Duarte, C.M., 1997. On the use of reconstructive aging
techniques for assessing seagrass demography: a critique of the model test
of Jensen et al,.1996. Mar. Ecol. Prog. Ser. 146: 297–303.
Fig. 1. Study area.
