Abstract
Understanding growth rates and the factors that influence growth is important for any organism, and is especially complicated in colonial organisms such as bryozoans. The aim for this is study was to investigate the factors that influence colony growth in bryozoans, with a focus on the Otago Harbour. Ideally one could do so by developing culture techniques and baseline data for suitable model species and then assessing how their growth rates are influenced by environmental factors (e.g., season, temperature, food). I started out by conducting surveys of Otago Harbour to find out what bryozoans live there (Chapter 2). Of the twelve bryozoan taxa found in Otago Harbour, eight of these taxa had not been recorded in a prior survey. Conversely, nineteen species previously noted as present were not found in our surveys. A long-term dataset for an abundant local bryozoan (Watersipora subatra) was then developed to obtain baseline growth and development data (Chapter 3). Wild colony growth of W. subatra populations was recorded as high as 111 mm/y during summer 2022, and as low as 27 mm/y during winter 2021, with a realistic annual growth rate lying somewhere between the two values. Then, manipulative experiments were conducted to investigate the effect of raised temperature on growth (Chapter 4). Wild Bryozoa found in Otago Harbour exhibited both a susceptibility and tolerances to increases in heat; significance was found between increases of +1 or +2 degrees and the colony and zooid characteristics of Beania sp., and in the composition of Caberea zelandica, no significance was found in any parameter of Bugulina flabellata. Then the effect of food availability on growth rate was investigated, using Watersipora subatra (Chapter 5). The highest growth rate was recorded when feeding the colonies a mixed diet, and there was a clear preference when comparing the results of single plankton feeds (mixed treatments yielded a growth rate nearly four times that of ambient wild growth). Finally, I collated the results of these experiments within the context of the wider bryozoan growth literature (Chapter 6), allowing for the foundation of a framework to understand the factors that influence growth in Bryozoa within and indeed outside of Otago Harbour.