Dangers for Unprotected Embryos on the Benthos
Abstract
One of the arguments for the persistence of planktonic larval stages in the life
cycles of benthic marine invertebrates is that pelagic larvae experience a release from
predation when they move off the benthos and into the water column. However, it is
difficult to substantiate this hypothesis because we lack comparative data on mortality
rates of unprotected (e.g., not in egg capsules or gelatinous masses) embryos and larvae
on the benthos and in the water column. The aim of this study was to provide some of
this missing information, by comparing development success in benthic and pelagic
environments. Dendraster excentricus embryos were placed in enclosed development
chambers under three treatment conditions: 1) directly on the substratum (unscreened
benthic), 2) on a screen on the substratum (screened benthic), and 3) on a screen raised 3
cm above the substratum (screened pelagic). Development success for pelagic embryos
was consistently higher than those on the benthos, substantiating the hypothesis that
embryos experience a release from predation as they move off the benthos. In addition,
the screened benthic treatment had significantly higher development success than the
unscreened benthic treatment, indicating that macro-predators (>55 μm) may
significantly reduce development success for unprotected larvae. Higher development
success of protected pelagic treatments may have been due to lower abundances of
pelagic micro-predators or anoxic conditions on the benthos.