[Coral-List] New paper on the dispersal (or lack of) of coral larvae across the East Pacific Barrier

[Sally Wood]

A bit late but some of you might be interested in a new paper published in
Nature Communications in August, which revisits the theory that El Niño
events may promote long distance dispersal across the East Pacific Barrier:

El Niño and coral larval dispersal across the Eastern Pacific marine Barrier
<http://www.nature.com/articles/ncomms12571>, Wood, S., Baums, I.B., Paris,
C.B., Ridgwell, A., Kessler, W.S., Hendy, E.J., Nature Communications
7:12571 (2016).

The study, which compares a modelling approach with genetic data across the
Pacific, is a collaboration between the University of Bristol's Coral Reef
research group, the Paris laboratory at RSMAS and the Baums laboratory at
Penn State, with input from oceanographer Billy Kessler at NOAA's Pacific
Marine Environmental Laboratory and climatologist Andy Ridgwell at the
University of California at Riverside.

The press release (printed below) can be viewed here
<http://www.bris.ac.uk/news/2016/august/reef-castaways.html>, and the full
paper obtained here <http://www.nature.com/articles/ncomms12571>. An
animation of example modelled dispersal paths by month of release can be
viewed here <https://www.youtube.com/watch?v=mMzuPcBTq5c>.


*---------- U. Bristol press release 23rd Aug 2016 -----------*

*Reef castaways: Can coral make it across Darwin’s ‘impassable’ barrier?*



An international team of researchers have shown that vulnerable coral
populations in the eastern tropical Pacific have been completely isolated
from the rest of the Pacific Ocean for at least the past two decades.



Ocean currents can change speed and even direction depending on the season
or climatic events like El Niño.



The new study led by University of Bristol researchers has used a
state-of-the-art computer model to trace the journeys of coral larvae
transported at the whim of these currents.



The international team discovered that even during the record-breaking El
Niño of 1998, coral larvae could not survive long enough to make the 5,000
km trip from reefs in the central Pacific to those in the east.



These findings support the opinion of Charles Darwin, who considered this
intimidating expanse of open ocean ‘impassable’ - countering recent
arguments that the ‘East Pacific Barrier’ must be breachable since the same
coral species are found on both sides. If so, the study argues, such
breaches have not occurred recently.



Dr Sally Wood
<http://www.bristol.ac.uk/earthsciences/people/person/sally-wood/overview.html>,
from the Coral Reef Research at Bristol
<http://www.bristol.ac.uk/biology/research/ecological/coral/> (CRAB) group
in the School of Earth Sciences <http://www.bristol.ac.uk/earthsciences/>
and lead author of the paper, explains: “Coral build the framework of
tropical coral reefs, creating habitats which support one of the most
diverse ecosystems on Earth.



“Whether coral reefs can survive the pressure of climate change as well as
local stresses will depend to a large extent on the ability of coral to
reproduce and disperse; to replenish damaged populations, migrate from
deteriorating conditions and colonise new frontiers. So it’s important to
map where coral are able to get to.”



Dr Erica Hendy
<http://www.bristol.ac.uk/earthsciences/people/person/erica-hendy/overview.html>,
Lecturer in Biogeochemical Cycles in the School of Earth Sciences, added:
“However, you simply can’t tag a coral larvae to follow where it ends up as
you would a large marine animal like a turtle or shark. Coral larvae are
smaller than a poppy seed, soft-bodied and released in overwhelming
numbers.



“When swept off their home reef, they have an infinitesimally small chance
of ever reaching a suitable place to settle and become a coral colony. We
therefore use computer simulations to answer these critical questions about
coral biology and conservation.”



The study tracked the journeys of over five billion model ‘larvae’ from 636
remote reefs scattered across the central and eastern Pacific Ocean over a
14 and a half year period. Using the state-of-the-art Connectivity Modeling
System <https://github.com/beatrixparis/connectivity-modeling-system>,
developed by Claire Paris
<https://www.rsmas.miami.edu/people/faculty-index/?p=claire-paris-limouzy>,
associate professor of ocean sciences at the University of Miami’s Rosenstiel
School of Marine and Atmospheric Science
<https://www.rsmas.miami.edu/people/faculty-index/?p=claire-paris-limouzy>
and run on the University of Bristol’s BlueCrystal supercomputer
<https://www.acrc.bris.ac.uk/>, the researchers could manage the massive
computational demands of modelling such large numbers.



This allowed the team to test, for the first time, a long-standing theory
that countered Darwin - that El Niño events promote long-distance dispersal
of coral larvae across the Pacific Ocean.



The results showed that the eastern Pacific corals (from Baja California in
the north to the coastline of Ecuador and the Galapagos Islands in the
south) have been completely cut off from the rest of the Pacific since at
least the 1998 El Niño.



As is happening worldwide at the moment, this extreme El Niño wiped out
many of the corals in the eastern Pacific.



Coral populations recover from such stress events through the proliferation
of survivors and colonisation by new recruits from neighbouring
less-impacted reefs. However, the more isolated a reef, the more
self-reliant, and the higher the likelihood of local extinctions.



The study’s findings provide evidence that local conservation is essential
for the sparse and poorly-protected, but economically and
environmentally-important coral reefs of the eastern Pacific Ocean.



Dr Wood concluded: “Our results demonstrate that it is even more important
to conserve the genetic diversity of the remote reefs in this
environmentally hostile part of the Pacific.



“They’re on their own out there, so whatever we can do to protect them
locally really will have an impact.”

*Dr Sally Wood  *

School of Earth Sciences, University of Bristol
Wills Memorial Building, Queens Road, BRISTOL BS8 1RJ
+44 (0)117 954 5429 | w: salwood.weebly.com | t: @SalWood82
<https://twitter.com/SalWood82>