The larval morphology and the effects of sound frequencies on the settlement behaviour of the biofouling Bryozoan: Watersipora subatra
Authors:   , McLachlan Renae 
Published: November 2021

<p>Biofouling is a global issue, it is an ongoing expense for the maritime industry, billions of dollars are spent annually due to increased fuel consumption, research, maintenance and upkeep. The toxicity of anti-fouling paints is also a serious issue for the marine environment, because of the non-selective nature of the toxins they contain, they also affect non-target species, potentially harming local ecosystems. Biofouling acts as a vector for invasive species, allowing these species to spread world-wide, establish themselves in new ecosystems and potentially alter the biodiversity of the native flora and fauna. These issues with biofouling have seen an increase in research into the prevention of settlement of unwanted organisms on ship hulls; especially biofriendly, alternative options to toxic anti-fouling paints. A holistic approach to researching fouling species is vital in reducing and preventing biofouling, and with the increase in human activity in the marine environment, the effects of anthropogenic sounds on marine organisms is of growing interest. The potential effect of vessel noise on the larvae of bryozoan species has yet to be explored even though the Phylum Bryozoa is notorious for biofouling species. The morphology of larvae is also important in understanding the ecology of marine species, as various factors that influence the larval stage of a species can have latent effects in other life stages. Insight into the morphology of fouling larvae is important in understanding their life histories to develop more robust antifouling methods. Bryozoan larvae have a diverse range of morphological features to increase their survivability; a number of structures have been identified in aiding locomotion, phototaxis behaviour, suitable habitat exploration and metamorphosis. There is still a lot of speculation over the purpose of different structures and whether they have the potential to be used in other behaviours (such as auditory capabilities). This thesis focuses on the biofouling bryozoan species, Watersipora subatra, and examines their larval morphology and behaviour to better understand their early ecology and identify potential structures with auditory capabilities. SEM images of the larvae were used to identify a number of sensory organs that could potentially detect sound. A sound experiment was also conducted to test whether their larvae respond to different frequency levels (100Hz, 500Hz and 1000Hz). There was no significant difference in the settlement rate at the end of a 24-hour period between the different treatments. However, the larvae exposed to the lower frequency (100Hz) tended to be slower at settling in the initial 8 hours of the experiment, which is the optimal time to settle to increase post-settlement survivability. There is the potential for the larvae of bryozoan species to respond to sound frequencies, although more research is needed to fully elucidate their potential to sense sound and to potentially aid in developing a biofriendly, preventative solution to biofouling.</p>