Swimming behavior and prey retention of the polychaete larvaePolydora ciliata(Johnston)

Abstract

SUMMARYThe behavior of the ubiquitous estuarine planktotrophic spionid polychaete larvae Polydora ciliata was studied. We describe ontogenetic changes in morphology, swimming speed and feeding rates and have developed a simple swimming model using low Reynolds number hydrodynamics. In the model we assumed that the ciliary swimming apparatus is primarily composed of the prototroch and secondarily by the telotroch. The model predicted swimming speeds and feeding rates that corresponded well with the measured speeds and rates. Applying empirical data to the model, we were able to explain the profound decrease in specific feeding rates and the observed increase in the difference between upward and downward swimming speeds with larval size. We estimated a critical larval length above which the buoyancy-corrected weight of the larva exceeds the propulsion force generated by the ciliary swimming apparatus and thus forces the larva to the bottom. This modeled critical larval length corresponded to approximately 1mm, at which, according to the literature, competence for metamorphosis and no more length increase is observed. These findings may have general implications for all planktivorous polychaete larvae that feed without trailing threads. We observed bell shaped particle retention spectra with a minimum prey size of approximately 4m equivalent spherical diameter, and we found that an ontogenetic increase in maximum prey size add to a reduction in intra-specific food competition in the various larval stages. In a grazing experiment using natural seawater, ciliates were cleared approximately 50% more efficiently than similar sized dinoflagellates. The prey sizes retainable for P. ciliata larvae covers the microplankton fraction and includes non-motile as well as motile prey items, which is why the larvae are trophically positioned among the copepods and dinoflagellates. Not only do larval morphology and behavior govern larval feeding, prey behavior also influences the feeding efficiency of Polydora ciliata.

Active downward propulsion by oyster larvae in turbulence

“…Even in still water the propulsive force used for swimming exceeded estimates for other ciliated larvae (||F V ||=0.5×10 -9 to 5.8×10 -9 N) (Jonsson et al, 1991;Emlet, 1994;Hansen et al, 2010) because oyster veligers are larger or more dense than larvae studied previously. In turbulence, the propulsive force and behavioral velocity magnitudes of both swimming and diving larvae grew steadily with dissipation rate.…”

Feeding rates and abundance of marine invertebrate planktonic larvae under harmful algal bloom conditions off Vancouver Island

“…Passive selection is frequently a size-based selection that could be explained partly by the morphology of the predator's filtering structures (Boyd, 1976). The size of H. akashiwo is within or at the upper limit (depending on larvae type) of the spectrum of particle sizes commonly ingested by meroplanktonic larvae (Rassoulzadegan and Fenaux, 1979;Hansen, 1991a;Raby et al, 1997;Jeong et al, 2004;Vargas et al, 2006;Hansen et al, 2010). However, P. triestinum seems to be too large to be captured by veliger and trochophore larvae, whereas the available diatom species may be too thin to be efficiently captured by cirripede nauplii and too long to be ingested by veliger and trochophore larvae.…”

Feeding, growth and metabolism of the marine heterotrophic dinoflagellate Gyrodinium dominans

“…Due to their significant grazing pressure, heterotrophic dinoflagellates are important regulators of phytoplankton production (Putland 2000), as well as significant conveyors of remineralization in the euphotic zone (Sherr & Sherr 2000). Additionally, microscopic examination of the gut contents, feeding structures, and faecal material of invertebrates and fish larvae reveal that they consume microzooplankton, including heterotrophic dinoflagellates (Stoecker & Capuzzo 1990, Hansen et al 2010. Thus, these organisms act as an important trophic link between nanoplankton and the larger mesozooplankton and macrozooplankton (Gifford 1988).…”