Abstract
During a cold La Niña period (August 2007-January 2008) in the central
Galápagos archipelago, 70% of Pocillopora finger corals were
bleached across three long-term monitoring sites, affording an
opportunity to examine the impact of El Niño Southern
Oscillation-related temperature anomalies on the persistence of these
corals and their associated community of fish and mobile
macroinvertebrates. Using a time series empirical approach, we tagged
and tracked the fate of 96 coral heads and their associates. When
surveyed in July 2008, live (recovered) and dead corals supported
similar levels of randomized observed species richness and Chao 1
estimated species richness. Whereas richness on the surviving live
corals remained fairly stable, Chao 1 estimated richness on dead corals
underwent a nearly 50% increase between July and January 2009,
thereafter declining to 50% of originally surveyed richness by February
2010. This nonlinear change in species richness was largely due to
influx and decline in opportunistic generalists including pencil urchin
bioeroders, gastropod snails, and hermit crabs that colonized dead
corals and fed on sessile invertebrates and algae that had initially
recruited to dead and undefended coral substrate. Thus, dead corals
retained high overall species richness until live corals had recovered;
after which richness declined as dead corals eroded and disappeared
(July 2011). Live corals attracted a less speciose but stable assemblage
of mutualistic xanthid crabs and fishes that increased in abundance over
time with the recovery and growth of live coral tissue. Overall, three
physical features of the finger coral habitats (coral vital status,
total surface area, and maximum branch length) predicted the number of
species associated with each colony. The delayed diversity loss of
associated species following La Niña disturbance to a foundation species
represents a local extinction debt of 32-49-month duration. A better
understanding of the scale of extinction debt in foundational marine
ecosystems is needed to quantify the breadth of impacts of climate
oscillations on biodiversity and ecosystem functioning.
Keywords : species richness, foundation species, climate
oscillations, temperature anomalies, coral bleaching, generalists,
specialists