Life-history strategies of a species of Catenipora (Tabulata; Upper Ordovician; southern Manitoba, Canada)



Detailed study of coralla by transverse serial sections permits the determination and evaluation of life-history strategies (survival and growth characteristics) in response to different physical environments, for Catenipora foerstei Nelson, 1963 from the Selkirk Member, Red River Formation, in Manitoba. We recognize various modes of corallite increase: one type of axial increase, four types of lateral increase, and agglutinated patches of corallites in association with normal, undamaged corallites; and one type of axial increase, one type of lateral increase, and temporary agglutinated patches from the recovery processes of corallites damaged by sediment or bioclast influx. In addition, the formation of new ranks by lateral increase is the most effective method for rapid growth of a corallum or for reconstructing part of a corallum damaged by physical disturbances. Fluctuations in the tabularial area of corallites occur in cycles over vertical intervals ranging from 3.20–7.90 mm. We consider each cycle to represent annual growth. Average annual growth of the three coralla ranges from 4.20–6.27 mm. According to correlations between annual growth cycles and other growth characteristics, a high frequency of offsetting is associated with rapid vertical growth. Specifically, annual growth is relatively high in association with episodes of sediment or bioclast influx, probably generated by storms. In some coralla, however, annual growth is highest in the cycle characterized by few new corallites or by extraordinarily high rates of offsetting by normal, undamaged corallites as well as damaged corallites. This suggests that vertical growth could also be affected by factors other than storm-related disturbance.