Irene,
  Regarding the use of multivariate statistics, this reference is one of
the best:

Field, J.G., K.R. Clarke, and R.M. Warwick (1982) A practical strategy for
analysing multispecies distribution patterns. Mar. Ecol. Prog. ser. 8:
37-52.

Cheers,
Tracey
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Tracey Sutton                                 [log in to unmask]
Oceanic Biology Laboratory                    (813) 893-9187
Department of Marine Sciences                 FAX     X-9189
University of South Florida
140 7th Avenue South
St. Petersburg, FL 33701 USA
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