Locomotion of marine invertebrate larvae: a review

Abstract

Marine invertebrate larvae swim by using cilia or muscles, or a combination of these. The effectiveness of cilia as locomotory organelles diminishes with increasing body size above 1 mm. Thus, larvae propelled by cilia are small and, owing to the small Reynold's numbers that operate in this size range, their movements are governed by viscous forces rather than inertial ones. Cilia may be distributed uniformly over the surface of the larva and (or) localized on rings, bands, arms, or lobes. During development the pattern of ciliation may change; this often increases the swimming ability of the larva, particularly its manoeuverability. In many cases, redistribution of cilia coincides with the onset of feeding behavior. The locomotory currents produced by ciliary beating or the action of swimming appendages may simultaneously convey food particles to the mouth. Muscles may have enabled some larvae to exceed the size limit imposed by ciliary propulsion and also have enabled greater swimming speeds. Invertebrate larvae that use muscular locomotion possess some form of skeleton (hydrostatic, exoskeleton. or notochord) to provide the necessary resistance for muscular contraction. The density of most marine invertebrate larvae exceeds that of seawater, therefore, they must swim to stay suspended. A wide variety of parachute structures, density-reducing devices, and passive hydrodynamic mechanisms counteract the sedimenting effects of gravity. The timing of development in some larvae is such that when the tendency to sink exceeds the ability to swim, the larva is preparing for settlement and metamorphosis.

Vertical positioning and swimming performance of lobster larvae (Homarus gammarus) in an artificial water column at Helgoland, North Sea

“…other decapod crustacean larvae which show swimming speeds ranging from 0.1 to 3.3 cm s (1 . Equally, the locomotion varies with the age of the larva (see Chia et al 1984). In our experiment the percentage of larvae swimming near the bottom increased with stage during the drift through the current channel.…”

Neural control of the velum in larvae of the gastropod,Ilyanassa obsoleta

“…Shorter, post-oral cilia, when present, are located on a nearby parallel ridge and collect food particles downstream from the pre-oral band. Separating the two bands is a food groove, in which the combined currents of ciliary activity entrap and transport food particles to the mouth (Chia and Buckland-Nicks, 1984;Strathmann and Leise, 1979).…”

Predicting suitability of cockleAustrovenus stutchburyirestoration sites using hydrodynamic models of larval dispersal

“…instead, we simulated potential differences in transport by varying sinking rates of larvae. Particles were assigned one of four fall velocities (0.0000, 0.0001, 0.0010, and 0.0025 m s -1 ) as proxies for variability in larval sinking rate (Chia et al 1984;Lundquist et al 2004a). The neutral fall velocity (0.0000 m s -1 ) was used to representative passive particles; 0.0001 m s -1 is lower than reported settling velocities of most invertebrate larvae; 0.0010 m s -1 is within the range of reported settling velocities for small, earlystage larvae of bivalves; and 0.0025 m s -1 is at the lower range of settling velocities of larger larvae such as latestage bivalve veligers (Chia et al 1984).…”

“…although dispersal of most estuarine organisms is poorly known, coastal and estuarine circulations are increasingly modelled hydrodynamically, estimating larval dispersal trajectories based on duration of larval periods and larval sinking velocity (Chia et al 1984;Palumbi et al 2003). modelling larval transport of estuarine organisms with hydrodynamic forcing is valuable for predicting spatial and temporal variability in larval settlement (Blanton et al 1999;Lundquist et al 2004a), and in this context, whether restoration sites are likely to receive larval recruits and/or serve as source populations that contribute recruits to other locations within an estuary.…”