Virgin Islands National Park: Coral Reef: Population Dynamics: Diadema antillarum

A potential consequence of individuals compensating for density-dependent
processes is that rare or infrequent events can produce profound and long-term
shifts in species abundance. In 1983–1984 a mass mortality event reduced the numbers
of the abundant sea urchin Diadema antillarum by 95–99% throughout the caribbean and
western atlantic. Following this event, the abundance of macroalgae increased and
the few surviving D. antillarum responded by increasing in body size and fecundity.
these initial observations suggested that populations of D. antillarum could recover
rapidly following release from food limitation. In contrast, published studies of
field manipulations indicate that this species had traits making it resistant to
density-dependent effects on offspring production and adult mortality; this evidence
raises the possibility that density-independent processes might keep populations at
a diminished level. Decadal scale (1983–2011) monitoring of recruitment, mortality,
population density and size structure of D. antillarum from st John, us Virgin
Islands, indicates that population density has remained relatively stable and more
than an order of magnitude lower than that before the mortality event of 1983–1984.
We detected no evidence of density-dependent mortality or recruitment since this
mortality event. In this location, model estimates of equilibrium population
density, assuming density-independent processes and based on parameters generated
over the first decade following the mortality event, accurately predict the low
population density 20 years later (2011). We find no evidence to support the notion
that this historically dominant species will rebound from this temporally brief, but
spatially widespread, perturbation.