Oxygen-mediated plasticity confers hypoxia tolerance in a corallivorous polychaete

There is mounting evidence that the deoxygenation of coastal marine
ecosystems has been underestimated, particularly in the tropics. These
physical conditions appear to have far-reaching consequences for marine
communities, and have been associated with mass mortalities. Yet little is
known about hypoxia in tropical habitats or about the effects it has on
reef-associated benthic organisms. We explored patterns of dissolved
oxygen (DO) throughout Almirante Bay, Panama and found a hypoxic gradient,
with areas closest to the mainland having the largest diel variation in
DO, as well as more frequent persistent hypoxia. We then designed a
laboratory experiment replicating the most extreme in situ DO regime found
on shallow patch reefs (3 m) to assess the response of the corallivorous
fireworm, Hermodice carnaculata to hypoxia. Worms were exposed to hypoxic
conditions (8 h ~ 1 mg l-1 or 3.2 kPa) 16 times over an 8-week period, and
at 4 and 8 weeks their oxygen consumption (respiration rates) were
measured upon reoxygenation, along with regrowth of severed gills.
Exposure to low DO resulted in worms regenerating significantly larger
gills compared to worms under normoxia. This response to low DO was
coupled with an ability to maintain elevated oxygen
consumption/respiration rates after low DO exposure. In contrast, worms
from the normoxic treatment had significantly depressed respiration rates
after being exposed to low DO (week 8). This indicates that
oxygen-mediated plasticity in both gill morphology and physiology may
confer tolerance to increasingly frequent and severe hypoxia in one
important coral predator associated with reef decline.