Can waterborne settlement cues trigger the larval transition from the plankton to the seafloor?
In coastal marine benthic species, populations are connected via transport of
their swimming larvae. To thoroughly understand how larvae move between
populations, we need to understand larval swimming behavior in the water column. In
particular, the larval behaviors that trigger the transition from the plankton to the
seafloor have remained a black box. One possibility is that waterborne cues
originating from a settlement surface may mix up into the water column where
swimming larvae can respond to them. Waterborne chemical settlement cues have
been characterized well for barnacle cyprids (settlement stage larvae). Additionally,
flow is known to affect both swimming behavior and settlement in barnacle cyprids.
But the interactive effect of flow and chemical cues on larval swimming is not well
described. In this study, we will use barnacle cyprids as a model to investigate their
behavioral responses to discrete filaments of dissolved settlement cues in a realistic
flow environment generated in WHOI’s racetrack flume. Preliminary experiments in
still water containers are underway to characterize vertical swimming behavior (e.g.,
speed, tortuosity, sinking rate) and establish a threshold concentration of settlement
cue at which a significant change in swimming behavior is distinguishable. In the
flume, we will use sensitive digital video to observe the behavior of swimming
barnacle cyprids in ecologically relevant turbulent flows as they come into contact
with streams of settlement cues. This study will improve our understanding of
environmental influences on settlement of invertebrate larvae and provide critical to
models of larval exchange and population connectivity.