Apparent diel feeding by the ctenophore Mnemiopsis leidyi A. Agassiz 1865 (Ctenophora, Lobata)

Abstract

The ctenophore Mnemiopsis leidyi A. Agassiz (1865) is not generally believed to exhibit diel feeding. As a result, the majority of studies documenting feeding of M. leidyi have been performed during the day, which may underestimate or overestimate daily clearance and ingestion rates if feeding changes over the diel cycle. Here, diel feeding by M. leidyi was examined during seven separate 24-h periods using gut content analysis. The total prey abundance and number of prey consumed per ctenophore did not differ between day and night; however, the percent of ctenophores with empty guts was higher during the day. These data show that, although fewer ctenophores consumed prey during the day, those that did consumed a larger number than at night. Additionally, the composition of the prey assemblage and the diet of M. leidyi did not differ between day and night; however, the composition of the prey assemblage differed from that observed in ctenophore guts, indicating selective feeding. Despite the lack of an overall difference in prey abundance and diet composition, isopods, cumaceans, decapod shrimp larvae and mantis shrimp larvae were observed in ctenophore guts only at night. These observations emphasize the importance of both day and night sampling, especially in ecosystems where prey availability changes significantly over the diel cycle.