[Coral-List] Corals Persist But Bioerosion Rises in Low-pH waters

Nyssa Silbiger Silbiger at Hawaii.edu
Fri Jun 19 19:55:25 EDT 2015

Dear Coral Listers,
  I wanted to contribute to this growing conversation on bioerosion and
ocean acidity. My colleagues and I have 3 recent papers using experimental
set-ups and natural pH gradients that all indicate that bioerosion
increases with increasing ocean acidity. In our experimental paper
(Silbiger and Donahue 2015), we manipulated pH and temperature conditions
in mesocosms containing dead coral rubble (representative natural
communities of macrobioeroders and secondary calcifiers). We found that
dissolution increased substantially with increasing pH and temperature
while calcification had a non-linear relationship (increasing and then
decreasing after a threshold was reached). In our 2nd and 3rd paper, we
measured net erosion (Silbiger et al. 2014), erosion  (Silbiger et al.
2015), and secondary accretion (Silbiger et al. 2015) along a natural
environmental gradient. We measured and compared different known
environmental drivers of accretion and erosion including pH, nutrients,
chlorophyll, depth, and hydrodynamics as a function of distance from shore.
Again, in these studies, we saw that pH was the dominant driver of
bioerosion and net erosion. For secondary accretion, distance from shore
and depth ranked highest indicating that hydrodynamic processes were
driving the patterns in secondary accretion across the transect. Here, we
also introduced a novel microCT method for separating out secondary
accretion and erosion from experimental substrates with a known deployment
time. We were able to obtain highly accurate erosion rates without
confounding erosion with the settlement of encrusters. Each of these
studies suggest that bioerosion is highly sensitive to ocean acidity and
that erosion is more sensitive to pH than secondary accretion.

The recent paper by Barkley and colleagues also found an increase in
bioerosion across a natural pH gradient in Palau further suggesting that
this phenomenon is not location specific, but rather is occurring at reefs
throughout the world.

Silbiger, NJ,  Guadayol, Ò., Thomas, FIM , Donahue, MJ. (2014) Reefs shift
from net accretion to net erosion along a natural environmental gradient.
MEPS. 515:33-44

Silbiger, NJ, and Donahue, MJ (2015) Secondary calcification and
dissolution respond differently to future ocean conditions. Biogeosciences
12: 567-578 <http://www.biogeosciences.net/12/567/2015/bg-12-567-2015.pdf>

Silbiger, NJ,  Guadayol, Ò., Thomas, FIM , Donahue, MJ (2015) Impacts of
multiple environmental stressors on coral reef erosion and secondary
accretion. PeerJ Preprint, 3:e1451 <https://peerj.com/preprints/1190/>


*Nyssa Silbiger, PhD*
NOAA Dr. Nancy Foster Scholar
Hawaii Institute of Marine Biology
Ph: 808 236 7424
email: silbiger at hawaii.edu

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