Proof of concept for measuring growth of shelf marine calcifiers: 'A Bryozoan odyssey'

Abstract

Context: The variation observed in growth rate estimates of bryozoans raise questions regarding the validity of the methods used to measure growth in these animals. Naturally, the best way for measuring growth rate is to understand the growth in situ, but access is not always straightforward. Aims: This study assesses a field experiment for measuring in situ growth of heavily calcified bryozoans in the open ocean at 56 m, the deepest such deployment attempted for bryozoans. Methods: Cellaria immersa colonies were collected by dredge from the continental shelf off Otago, marked using calcein, mounted on a purpose-built frame, called 'Odyssey', and returned to the shelf for 3 months in the Austral summer (November-February). Key results: Data from 10 internodes indicated that growth was, on average, 0.97 ± 0.84 mm year-1 and showed some interesting intracolonial growth patterns. Conclusions and implications: The data obtained from this study are only indicative at this stage, but we have succeeded in developing a reproducible experimental set-up for in situ growth experiments of shelf bryozoans, enabling us to record growth, lifespan, and calcification rates of heavily calcified and ecologically important species. Understanding such key species is critical to identifying their role in the ecosystem and providing valuable information for future conservation initiatives.