Superficial sediments and their relation to polychaete families in a subtropical embayment, Mexico

The soft bottoms in front of Mazatlan Bay and "Isla de la Piedra" Peninsula were studied to produce maps (depth, grain size and organic matter content in sediments). Sixty samples were obtained with a 30 x 30 van Veen grab (4 -21 m depth) and polychaetes were extracted from 21 subsamples. Grain size ranged from -1.05 phi (gravel) to 3.81 phi (very fine sand), with fine sand predominating. Organic matter content in sediment was 0.91-3.06 % (most va lues = 1-2 %). Thirty polychaete families (905 individuals/m(2) in mean) we re found, and Cirratulidae, Spionidae, Onuphidae, and Pilargiidae were domi nant. Pearson's correlation of grain size, organic matter and depth proved significant (p<0.01; p<0.02), confirming the observed relationships of dist ribution patterns in the area. A Principal Component Analysis showed the as sociation of several families to depth (Factor 1), to grain size (Factor 2) , and to organic matter (Factor 3). Nevertheless, the distribution of polyc haete families in the area may be governed by the combination of the three abiotic variables. Results indicated that abiotic and biotic variables have not changed considerably since 1980.