Subsurface Eddy Facilitates Retention of Diel Vertical Migrators in a
Biological Hotspot
Abstract
Diel vertical migration (DVM) is a common behavior in zooplankton
populations world-wide. Every day, zooplankton leave the productive
surface ocean and migrate to deep, dark waters to avoid visual predators
and return to the surface at night to feed. This behavior may also help
retain migrating zooplankton in biological hotspots. Compared to fast
and variable surface currents, deep ocean currents are sluggish, and can
be more consistent. The time spent in the subsurface layer are driven by
day length and the depth of surface mixed layer. A subsurface,
recirculating eddy has recently been described in Palmer Deep Canyon, a
submarine canyon adjacent to a biological hotspot. Previous circulation
model simulations have shown that residence times of particles increase
with depth within this feature. We hypothesize that DVM into the
subsurface eddy increases local retention of migrating zooplankton in
this biological hotspot and that shallower mixed layers and longer day
length would increase the time in the subsurface layer. We demonstrate
that vertically migrating particles have residence times on the order of
30 days, which is significantly greater than residence times of
near-surface, non-migrating particles. The interaction of DVM with this
subsurface feature may be important to the establishment of the
biological hotspot within Palmer Deep Canyon by retaining critical food
resources in the region. Similar interactions between DVM behavior and
subsurface circulation features, modulated by mixed layer depth and day
length, may also increase residence times of local zooplankton
populations elsewhere.