CALCIFICATION RATES OF RAPIDLY COLONIZING BRYOZOANS IN HAURAKI GULF, NORTHERN NEW-ZEALAND

Very little is known about calcification rates of bryozoans, despite their importance in modern temperate-latitude shelf. carbonate sediments and in temperate limestones. Here we report the carbonate production rates for 19 species of bryozoans over 3, 9, and 12-month periods from a settling experiment in 14 m water depth at Cape Rodney, Hauraki Gulf. Based on the larger bryozoan colonies, estimates of calcification rate range from 25 to 740 mg CaCO3 y-1. Extrapolation of calcification rate to overall bryozoan sediment production is not straightforward, but a value of 24-240 g CaCO3 m-2 y-1 for the sample site has been determined, equivalent to a sediment accumulation rate of 4-40 cm per 1000 years (ky). In reality, over a large shelf region both dilution by other organisms and a patchy areal distribution of living bryozoans would reduce these values to only a few cm ky-1. The relatively low rates of accumulation deduced here are mainly consistent with the few other studies of bryozoan sedimentation in temperate waters, and also with those typically reported (1-3 cm ky-1) for many occurrences of temperate bryozoan-rich limestones from the rock record.