N OV E M B E R 2015
I S S U E N O. 2
OCEAN ACIDIFICATION
AND FISH BEHAVIOR
Excess carbon dioxide from land-use changes, the combustion
of fossil fuels, etc. has increased the amount of CO2 in the
atmosphere. The ocean absorbs a portion of the excess CO2.
This process was once believed to be beneficial as it slowed
global warming but caused a drop in the pH of the seawater,
commonly known as ocean acidification (OA). Initial OA studies
focused on the impact this would have on marine calcifiers
(ex: corals, shelled organisms). The lowered pH impacts
shell formation and development, and causes deformities in
calcifying organisms. Only recently have researchers begun
to investigate OA effects on marine fishes.
Research conducted by the
Dixson lab focuses on four
interconnected research areas:
CO2
CO32- (μmol kg -3)
CO2 + H2O => HCO3- + H+
800
H++ CO32- => HCO3-
600
400
200
0
0 200 400 600 800
CO2 atm (ppm)
Assistant Professor
School of Marine Science and Policy
[email protected] |
@fish_scientist
www.dixsonlab.com
Bio and research interests
Atmospheric cycle of CO2
Levels of bicarbonate [CO32-]
and carbon dioxide [CO2]
Danielle L. Dixson, Ph.D.
CaCO3 => Ca2+ + CO32(coral)
(Hough-Guldburg et al. 2007
se of sensory cues in
u
behavioral processes
connectivity of the marine
environment
behavioral interactions
between species
effects anthropogenic changes,
such as ocean acidification,
terrestrial runoff, habitat
degradation etc., have on marine
organism behavior
These efforts are linked by a common
theme: understanding how marine
animals sense their environment, how
they use this information to make
decisions and the consequences these
behavioral choices have on marine
conservation and management in a
changing world.
Juvenile fish in conch shell.
Carrie Bow Cay, Belize
OA effects on marine fishes
Early research has shown sub-lethal effects of increased CO2, with very high
levels affecting survival, growth, development and metabolism in fish species.
However the levels used were extreme and not relevant to future climate change
predictions. Fish have the ability to buffer their internal pH by increasing the
amount of bicarbonate (HCO3-) and expelling chlorine (Cl-) through their surface
tissue. Researchers believed this ability would enable fish to remain unaffected
by reduced pH levels expected with OA. However, data collected focused on
adult fish, when early life history stages likely are more susceptible. Additionally,
important aspects such as behavior were ignored.
Abby Wood
Behavioral impacts of ocean acidification
Naturally occuring CO2 seeps
Milne Bay, Papua New Guinea
Impacts of OA levels expected by the end of the century on behavior and
cognition in coral reef fishes are severe. While no impacts have been found
in egg duration, egg survival, hatching size, growth rate or swimming ability,
the consequences of behavioral impairments are cause for concern. Fish are
unable to distinguish between chemical cues, causing inappropriate responses
to important information. For example, CO2 treated (1000ppm) fish become
attracted to the smell of a predator while present day control fish (380ppm)
avoid this cue 100% of the time. Auditory and visual cues are similarly affected.
Fish also are unable to learn from one other and become bold and aggressive,
spending less time in their habitat and developing increased activity levels. These
cognitive and behavioral changes equate to a 5-9 times increase in mortality.
Fish behavioral impacts due to ocean acidification
Consequences for prey
vulnerability to predators
ability to locate coral reef habitat
Sensory recognition
Behavioral
impairments
• olfactory
• visual
• auditory
activity
boldness
Consequences
for prey
distance from
What’s next?
shelter
Consequences for predators
• Olfactory
• Visual
aggression towards food• Auditory
tracking behavior
Lower pH impacts
To cope with the lower pH
in the ocean, fish naturally
increase their internal
bicarbonate levels. This
physiological response
disrupts the brain’s
GABAA receptor, which is
responsible for cognitive
function, causing the
behavioral abnormalities
described above.
Limited studies have been conducted
learning from
on predators, although negative
other
individuals
(damage to
Toreef)
cope with the lower pH in
the ocean,
fish naturally increase their internal bicarbonate levels. This
impacts of OA on some predators
physiological response disrupts the brain’s GABAA receptor, which is responsible for cognitive
function, causing the behavioral abnormalities describedhave
above. been shown (see graphic at
Habitat loss
GABA studies are needed to
left). Additional
understand the shared impacts of OA
with rising temperatures, pollutants, etc.
Experiments done at naturally occurring
CO2 seeps allow researchers to conduct
community level experiments, but this is
expensive and funding is limited.
CI HCO3GABA
GABA binding can be antagonized
experimentally with gabazine
GABA
Future seawater:
Elevated ƿCO3
Elevated H+
Regulatory
changes in fish:
Elevated HCO3Reduced CI Maintained H+
Hyperpolarizing current when binding of
GABA to the GABA-A receptor leads to inflow
of CI - and/or HCO3- into neurons
Altered
gradients of CI and/or HCO3over neuronal
membranes
Depolarizing current when binding of GABA
to the GABA-A receptor leads to outflow of CI and/or HCO3- from neurons
(Nilsson et al. 2012)
School of Marine Science and Policy
700 Pilottown Road | Lewes, DE 19958
Phone: 302-645-4226
Email: [email protected]
www.ceoe.udel.edu
CI HCO3-