The analysis of pattern in communities of bryozoa. I. Discrete sampling methods

Hitherto, discrete sampling methods for the analysis of spatial dispersion patterns have always been based on a unit ( e.g. a quadrat) of standardized dimensions. A new technique is described, of use when the sampling units (as with Fucus fronds) cannot have a constant area. Based on computer simulation, the method permits the comparison of an observed frequency distribution with a Poisson series. By its use, it is shown that the colonies of Electra pilosa (L.) (larvae planktotrophic), on a randomly collected sample of Fucus serratus L., occur in aggregations - though they are not necessarily ‘gregarious’. Aggregation perhaps facilitates cross ( i.e. inter-colony) fertilization. Bryozoa having short-lived larvae are well known to occur in dense aggregations. Thus, in ‘rapids’ systems, several species are found in great abundance on the fronds of Laminaria digitata (Huds.) Lamour and intermingled with Spirorbis spp. Such a community, dominated by Spirorbis corallinae de Silva & Knight-Jones, Hippothoa hyalina (L.) and Scrupocellaria reptans (L.), has been sampled using random quadrats. Local clumping was generally apparent and, under such conditions, it is concluded that analysis based on quadrat sampling is unlikely to detect any spacing out which may be present. The abundance of Spirorbis and bryozoa are positively correlated, except at very high densities of the former.