Presenter: Ching-Tsun Chang (University of Hawaii at Manoa)

Description:
The gelatinous zooplankton blooms and interactions between gelativores and prey contribute to carbon cycling. Sharptail mola, Masturus lanceolatus (family Molidae), inhabits tropical and subtropical ocean regions, and it is generally regarded as gelativores, playing an important role in transferring energy from gelatinous zooplankton to high trophic level predators. Their food habits may be influenced by the environment and/or body size particularly given their migrations and the potential seasonal variation of resource distribution. Little is known about the feeding ecology of sharptail mola. Carbon and nitrogen stable isotope compositions were coupled with stomach content analysis to explore the seasonal feeding behavior and ontogenetic diet shifts of sharptail mola in the waters off Taiwan. Our results showed that sharptail mola fed on a wide variety of prey items from coastal, epipelagic to mesopelagic zones, dominated by gelatinous plankton and hyperiid amphipods. Small (< 80 cm SL) sharptail mola consumed small prey such as salps, pyrosomes, amphipods (Phronima sp.), and pteropods. Large (> 80 cm) individuals increased their trophic level by 0.5 and consumed more large-size and high trophic level prey, such as cephalopods and fishes. Large sharptail mola mainly occurred in summer, and they fed on more cephalopods and pyrosomes than those found in other seasons. In spring, the body sizes of sharptail mola were the smallest and had the highest δ¹³C values. They consumed more benthic and coastal prey compared to other seasons. It suggested that sharptail mola had different resource utilizations during their ontogeny and seasonal migrations. Sharptail mola displayed a change of trophic roles between coastal and pelagic-derived predators, linking the energy flow between two ecosystems. The study provides further insights into the trophic ecology of sharptail mola related to ontogenetic shifts and seasonal variations in marine ecosystems.