The analysis of small-and mesoscale dispersion patterns ofMarenzelleria viridis (Polychaeta: Spionidae) in a coastal water area of the southern Baltic
© Biologische Anstalt Helgoland 1996
The horizontal mesoscale distribution ofMarenzelleria viridis (Verrill, 1873), a spionid polychaete introduced from North American coastal waters during the 1980s, was studied in shallow water in the southern Baltic (German coast). The polychaete achieved an individual dominance of 80% and abundances up to around 8500 ind./m2. Samples taken from a small (1.2 m×1.2 m, 6×6 samples, depth 0–35 cm) and a large station grid (5.5 m×5.5 m, 11×11 samples, depth 0–35 cm) were used to calculate dispersion indices for subpopulations of adult and juvenileM. viridis and subdominant chironimids (theChironomus plumosus andCh. halophilus complexes). The distribution patterns were significantly patchy. The patch sizes were estimated with the help of the dispersion indices and by analysing the correlograms in which spatial autocorrelations such as Moran's I and Geary's c values were plotted versus the field distance k. The patch sizes were heterogenous. The smallest patches found were 0.04 m2. The largest sizes observed were 9 m2. It is conceivable that smaller patches merge to form larger aggregations. Calculation of the abundance and rank correlations between subpopulations revealed significant positive relationships. These indicate principal suspension feeding. Sediment structure, substrate preference, feeding mode and biotic or abiotic attraction centres are considered to be the main causes of aggregation and the positive correlations.