Our investigation of food web structure on Volcano 1, South Tonga Arc is well underway, with stable isotope samples prepared and ready for analysis. We are interested in seeing if two of the sampled hydrothermal sites which are found in the photic zone have different food web structure than a third sample site which is in the aphotic zone. The results of the stable isotope analysis will help to elucidate the number of carbon end sources found at these three sites as well as the number of trophic levels found within these communities.
There are three primary anecdotal findings of this study that occurred during the preparation of the stable isotope samples. The first of these was observed during the dissection of the limpets that were collected from the three sites. On two occasions the digestive tracts of the limpets found at ‘Barracuda’ (one of
the photic zone sites) were observed to contain green algae. It will be interesting to see if the stable isotope signatures of these limpets reflect this observation, as we also have a sample of green algae which we can use to compare stable isotope signatures. The second observation was of white surface fouling on the external shell surface of the limpets found at ‘Bubbles’ (the aphotic site). Closer examination of preserved specimens and some expert consultation revealed that these markings were actually a by-product of limpet egg cases secreted onto the shell surface. The final observation was made while dissecting crabs that were collected from a fourth photic zone site named ‘Fishy’. The crabs from this site were found to have what appeared to be bacterial filaments growing on their maxillipeds and the tips of their chilipeds. As with the limpets, the stable isotope signatures of these crabs will further elucidate their position in the food web at this site.
Next up we will be looking at video footage taken during transects up to and around our study sites. Our goal will be to describe the stratification of both the physical habitat structure and species compositions at varying depths on Volcano 1. Stay tuned for more information on this study as the isotope results are acquired and video footage is analyzed.
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