Can Sea Urchins Beat the Heat? Sea Urchins, Thermal Tolerance and Climate Change
Date
2015-06-09
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Abstract
The massive die-off of the long-spined sea urchin, Diadema antillarum, a significant
reef grazer, in the mid 1980s was followed by phase shifts from coral dominated to
macroalgae dominated reefs in the Caribbean.While Diadema populations have recovered
in some reefs with concomitant increases in coral cover, the additional threat
of increasing temperatures due to global climate change has not been investigated in
adult sea urchins. In this study, I measured acute thermal tolerance of D. antillarum
and that of a sympatric sea urchin not associated with coral cover, Echinometra
lucunter, over winter, spring, and summer, thus exposing them to substantial natural
thermal variation. Animals were taken from the wild and placed in laboratory tanks
in room temperature water (∼22 ◦C) that was then heated at 0.16–0.3 ◦C min−1 and
the righting behavior of individual sea urchins was recorded. I measured both the
temperature at which the animal could no longer right itself (TLoR) and the righting
time at temperatures below the TLoR. In all seasons, D. antillarum exhibited a higher
mean TLoR than E. lucunter. The mean TLoR of each species increased with increasing
environmental temperature revealing that both species acclimatize to seasonal
changes in temperatures. The righting times of D. antillarum weremuch shorter than
those of E. lucunter. The longer relative spine length of Diadema compared to that of
Echinometra may contribute to their shorter righting times, but does not explain their
higher TLoR. The thermal safety margin (the difference between the mean collection
temperature and the mean TLoR) was between 3.07–3.66 ◦C for Echinometra and
3.79–5.67 ◦C for Diadema. While these thermal safety margins exceed present day
temperatures, they are modest compared to those of temperate marine invertebrates.
If sea temperatures increase more rapidly than can be accommodated by the sea
urchins (either by genetic adaptation, phenotypic plasticity, or both), this will have
important consequences for the structure of coral reefs.
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Keywords
Research Subject Categories::NATURAL SCIENCES::Biology::Terrestrial, freshwater and marine ecology::Marine ecology, Sea urchins, Thermal tolerance, Coral reefs, Global climate change, Animal Behavior, Conservation Biology, Environmental Sciences, Evolutionary Studies, Marine Biology
Citation
PeerJ 3:e1006 https://dx.doi.org/10.7717/peerj.1006