Gut content of Tripneustes gratilla in Changuu Island (Unguja Island, Zanzibar Archipelago, Tanzania)

To determine the gut content of T. gratilla, we sampled 10 sea urchins along a transect parallel to the coastline and transported them to the Institute of Marine Sciences (Stone Town, Zanzibar). The urchins were collected upon encounter along the transect with the rule of not collecting urchins from the same seagrass patch. This rule was applied to avoid bias towards specific seagrass species. For this analysis, we weighed the sea urchins, measured their diameter to the nearest millimeter with a ruler, and stored them in a 90% ethanol solution. For the gut content analysis, the sea urchins were opened and the content from the whole digestive tract was extracted. The gut content was placed in a Petri dish, and then transferred to a 250 µm mesh to remove the sediment. After the sediment removal, we weighed the gut content fresh weight. Approximately 1 gram (fresh weight) was taken as a sub-sample from the gut content and placed in a new Petri dish to observe under the magnifying glass. Each sample was compared to an example of seagrass material that was prepared specifically for identification after the grazing and digestion process of each species. We imitated this effect by grinding the seagrass species to a similar size and storing them in 90% ethanol solution. Using this method, we could separate the gut contents into the different seagrass species. Contents were then dried in the oven at 60 degrees for 24 hours to obtain their dry weight, and percentage of each seagrass species in the gut was calculated.