Calcification rates of rapidly colonising bryozoans in Hauraki Gulf, northern New Zealand

Abstract

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.

Keywords:

• Bryozoa
• calcification rate
• carbonate sediments
• sedimentation rate
• Hauraki Gulf
• New Zealand