Faunistisch overzicht van de mariene mosdiertjes van Nederland (Bryozoa: Stenolaemata, Gymnolaemata)

Faunistic survey of the marine bryozoans of the Netherlands (Bryozoa: Stenolaemata, Gymnolaemata) Older literature on marine bryozoans of the Netherlands often doesn’t distinguish between records of colonies washed ashore and autochthonous records. The first reliable review of autochthonous records was published by Heerebout (1970), the second and last by Mulder (1983). The present review is mainly based on data from a short regional survey. Forty-three brackish water and marine bryozoan species are now definitely known to occur in the Netherlands. Most of them are characteristic of sheltered, estuarine and brackish waters. The virtual absence of rocky and coarse grounds offshore is reflected in the fauna. Cyclostomatida and Cheilostomatida are scarce, whereas Ctenostomatida are relatively well represented. This has been pointed out already by Lacourt (1949), whose data included species washed ashore as well. Hard substrates in the Netherlands are almost completely anthropogenic in origin and on the open coast extend into the very shallow sublittoral only. Another reason for the scarcity of pure marine species may be the extremes in watertemperature in Dutch waters. Evidently both reasons are interconnected.