Age, growth and carbonate production by erect rigid bryozoans in Antarctica

Abstract

Well-calcified marine bryozoans are often important producers of temperate and polar shelf carbonate sediments. In cold waters, bryozoans can be long-lived, and their skeletons therefore reflect many years of growth and carbonate production. This study examines growth, age, and calcification in 12 specimens of three species of cheilostomate Antarctic bryozoans from the Ross Sea (77° 53.394′ S and 166° 40.286′ E, 500 m water depth). Cellarinella nutti and C. nodulata, erect branching bryozoans in the family Sclerodomidae, reached a maximum age of 18 years, grew 1 to 8 mm/year and added new carbonate at a rate of 3 to 57 mg/year. Swanomia belgica, family Cellariidae, reached a maximum age of 23 years, added to branch length at 1 to 4.4 mm/year and calcified at 1 to 23 mg/year. Antarctic bryozoans can be quite long-lived (up to 50 years), but they exhibit slower growth rates than their temperate counterparts, perhaps due to the shortness of the growing season. Seasonal growth checks in many erect Antarctic bryozoans may result from low food availability in winter. There is a clear relationship between growth rate and age, where the polar cellariid bryozoans that live the longest are the slowest-growing. The combination of slow growth, long life-spans, and seasonal growth checks make Antarctic erect bryozoans excellent recorders of environmental conditions and benthic calcification. Calcification rates in Antarctic cellarinellids are generally low: 10–20 g CaCO 3/year, with sedimentation rates of about 0.3 to 1.0 g CaCO 3/m 2/year. Carbonate sediments in which bryozoans are a significant component must accumulate at slow rates in the Antarctic.