Locomotory behavior of competent cyphonautes larvae in response to positive and negative cues in flow

Abstract

Previous research has shown evidence of chemosensory behavioral responses in invertebrate larvae across species and using varying stimuli. Diverse exploratory behaviors in larval Membranipora spp. Cyphonautes on suitable settlement substrates (macroalgae) have been defined (Matson et al. 2010), but little is known about the behavioral mechanisms used to find settling habitats in the first place. We investigated the behavioral swimming response to hypothesized positive and negative chemical cues in late-stage cyphonautes larvae (Membranipora spp.) to determine whether cyphonautes have noticeably different behavioral responses to chemical cue plumes. We compared the response of larvae to a control (filtered seawater) cue, a positive cue (the red alga, Mazzaella splendens), and a negative cue (predator, Corambe spp.). Larvae were collected from plankton tows and exposed to plumes of cue water for five minutes under a unidirectional, laminar flow regime. Locomotory behaviors (swimming direction relative to flow, circling behavior, crawling behavior, tank wall interactions) were recorded. The results suggest that cyphonautes larvae swim more frequently toward the source of the cue when it is a positive cue, but do not respond negatively to predator cues (from a predator of their adult form). These results are consistent with the hypothesis that competent cyphonautes larvae actively use chemosensation to locate algal blades for settlement. Additionally, the results suggest that circular swimming and swimming perpendicular to flow, in addition to swimming towards a stimulus source, might aid cyphonautes larvae in finding substrate for settlement