Jarrold, M.D.,
and Munday, P.L.
2019
"Do CO2 cycles
and parental effects
have similar benefits
to growth of a
coral reef fish under
ocean acidification."
Biology Letters 15:
20180724,
NOTE:
Almost all lab
ocean acidification (OA)
studies use static pCO2
seawater values.
A marine organism will
typically be subjected to a
fixed (non-oscillating)
control or elevated pCO2
seawater value.
In a natural habitat
there would be substantial
pCO2 fluctuations.
Results obtained in static
OA experiments have been
overturned or reversed
when seawater pCO2
fluctuations are included
on daily, weekly or
even longer seasonal
scales (see, for example,
Comeau et al., 2014;
Jarrold et al., 2017).
So the results obtained
from static or stable pCO2
experiments are less relevant
than OA experiments with
fluctuating seawater pCO2.
SUMMARY:
Treatment conditions more like
real nature (cycling-cycling)
had survivor rates increase
(relative to the control-control treatment).
Treatment conditions
used for most
Ocean Acidification
studies
(control-stable)
experienced a
relative decrease
in juvenile survival.
A more realistic experiment
methodology completely changed
the future outlook for the survival
of this species, from negative
to positive!
The two researchers conclude
that "parental exposure to stable
elevated CO2 and within-generation
exposure to diel-cycling elevated
CO2 both alleviate the negative
effect of elevated CO2 on
juvenile growth of
[Amphiprion melanopus]."
And they say that their study
"adds to a growing body
of literature that highlights
the importance of
incorporating natural CO2
variability in OA experiments
to accurately predict the
responses of shallow water
coastal marine species
to rising CO2 levels."
DETAILS:
Jarrold and Munday (2019)
examined the growth and
survival of juvenile
cinnamon anemone fish
(Amphiprion melanopus)
reared in one of three
pCO2 treatments:
(1)
A control treatment where
pCO2 was kept constant
at 500 µatm,
(2)
A stable elevated treatment
where pCO2 was kept constant
at 1,000 µatm, or
(3)
A fluctuating elevated treatment
with a mean daily pCO2 value
of 1,000 µatm that oscillated
±300 µatm about the mean
in a 24 hour period.
Jarrold and Munday's
experiment began by
collecting adult breeding
pairs of anemone fish
from the Great Barrier Reef,
which were then acclimated
in one of the three
pCO2 treatments
in the three months
prior to the breeding
season.
Following egg hatching,
juveniles from parents
in the control treatment
were divided and reared
among all three of the
pCO2 treatments.
Juveniles from parents
in the stable elevated
and fluctuating elevated
treatments were kept
in their respective
pCO2 environments.
Altogether, this led to
five separate treatments:
(1)
Control-control, where parents
and juveniles were both exposed
to a constant 500 µatm pCO2
seawater environment,
(2)
Control-stable, where juveniles
from parents in the constant
500 µatm treatment were reared i
n a constant 1,000 µatm pCO2
environment,
(3)
Control-cycling, where juveniles
rom parents in the constant
500 µatm treatment
were reared in a fluctuating
1,000 ± 300 µatm pCO2 environment,
(4)
Stable-stable, where parents
and juveniles were both exposed
to a constant 1,000 µatm pCO2
seawater environment and
(5)
Cycling-cycling, where parents
and juveniles were both exposed
to a fluctuating 1,000 ± 300 µatm
pCO2 seawater environment.
After 28 days the authors
ended the experiment and
evaluated juvenile survival,
wet weight and standard length.
Juvenile survivorship was
highest (96.7%) in the
cycling-cycling treatment
and lowest (82.2%) in the
control-stable treatment.
The control-control treatment
had a survival percent of 88.7%.
The treatment closest to
a natural environment
(the cycling-cycling treatment,
where both parents
and offspring experience
fluctuating pCO2 values)
produced a result
that's opposite the result
observed in the treatment
most commonly utilized
in OA studies
(i.e., the control-stable treatment,
where the species is subjected
to non-fluctuating elevated
pCO2 seawater).
Jarrold and Munday write that
"juvenile exposure to stable
elevated CO2 (control-stable)
caused an 18.5% and 10.7%
reduction in wet weight
and standard length,
respectively, compared to
the control-control treatment."
However, they note that
"there were no significant
differences between the
control-control and other
treatment groups,
indicating that both diel CO2
cycles and parental exposure
to elevated CO2 restored growth
to the same level as control."
