A preliminary investigation of change in Bryozoa zooid size along a thermal gradient of the North Atlantic Sea region

This study assessed trends in bryozoan zooid size along coastal sea-temperature gradients observed in the North Atlantic from the Shetland Islands, through several locations along the Norwegian coast to the Svalbard Archipelago in the Arctic. Three species, Microporealla arctica Norman 1903, M. ciliata sensu Hayward & Ryland 1998 and Escharella immersa (Fleming, 1828), were chosen as study organisms for the investigation. Results indicated that bryozoan zooid size tended to increase towards higher latitudes. In general, differences in zooid length, width and area were statistically significant between colonies collected in the vicinity of Shetlands Island, the Norwegian coast and Svalbard Fjord. However, when considering the mean value of zooid characteristics calculated for each particular species, it can be seen that each of tehm showed different levels of sensitivity to the environmental conditions. Microporella ciliata was the most susceptible to changing conditions, E. immersa showed a high variability of response and M. arctica presented the lowest level of plasticity.