Feeding biology, digestive physiology, and metabolic rate of the Florida lancelet, Branchiostoma floridae

The present study investigates some aspects of the feeding and digestive biology and physiological energetics of the Florida lancelet, Branchiostoma floridae. Lancelets, like urochordates, are demonstrated to use a pharyngeal mucous net to capture suspended food particles. Florida lancelets are able to process 115 ml sea water·h-1 and retain particles ranging in size from 0.062--100 mum. This indicates that the lancelet diet could encompass a wide range of food sources, including diatoms, algae, bacteria, and colloidal organic matter.; Captured food particles are transported in the mucous net to posterior regions of the gut, where digestive and absorptive processes occur. The bulk of digestion most likely occurs in the iliocolon, while absorption of the products of digestion occurs mostly in the hepatic caecum and stomach. On average, B. floridae is able to remove 47--57% of ingested energy from a diet of mixed algae, while the remaining energy is egested. The average gut passage time for ingested particles is 80 min.; The average rate of oxygen consumption is 0.0995 mlO2 (STPD)·g -1 (wet)·h-1, which corresponds to an estimated metabolic rate of 0.056--0.062 cal·h-1 , at an average body weight of 0.125 g. Based on this estimate, each animal would need to ingest 31.8--35.21mug of algae per hour to meet its metabolic demand. Published values of the chlorophyll A concentration in its natural habitat indicate that a 125 mg lancelet would need to filter 2--3 l·h-1 to remove sufficient food to support its metabolism. The measured filtration rate of 115 ml·h-1 suggests that B. floridae obtains additional energy from non-chlorophyll containing foods within the measured range of particles lancelets are able to retain.; Because lancelets are common and abundant in shallow coastal waters and a source of food to some carnivorous animals, lancelets may play a unique role in coastal marine food webs by directly transferring microbial production to higher trophic levels. It also appears that lancelets have the potential to be raised in aquaculture, because their filtration rate, digestive efficiency, and oxygen consumption rate are comparable to suspension feeding invertebrates that have been successfully aquacultured.