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The Effects of Ocean Acidification in the California sea hare ( Aplysia californica )
Author(s) -
Zlatkin Rebecca L.,
Grosell Martin,
Heuer Rachael M.
Publication year - 2020
Publication title -
the faseb journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.709
H-Index - 277
eISSN - 1530-6860
pISSN - 0892-6638
DOI - 10.1096/fasebj.2020.34.s1.07006
Subject(s) - aplysia , ocean acidification , extracellular , bicarbonate , reflex , biophysics , chemistry , invertebrate , intracellular ph , membrane potential , chemoreceptor , receptor , biology , biochemistry , ecology , neuroscience , seawater , endocrinology
Fish and some invertebrates have demonstrated to be strong acid‐base regulators following exposure to ocean acidification‐relevant carbon dioxide (CO 2 ) levels through the accumulation of bicarbonate (HCO 3 − ) in extracellular and intracellular fluids. This allows for pH compensation, however, internal p CO 2 and HCO 3 − remain elevated. This compensation has been hypothesized to cause negative behavioral impairments, by altering ion gradients (HCO 3 − /Cl − ) along neuronal cell membranes that affect the function of the GABA A receptor, an important inhibitory receptor in the central nervous system of vertebrates and invertebrates. Aplysia californica , known for their simple and well‐mapped nervous system, have the potential to be strong model organisms to examine the relationship between CO 2 compensation and impaired behavior in invertebrates. We hypothesized that CO 2 ‐exposed animals would compensate for an acidosis by accumulating HCO 3 − . In the second portion of the study, we hypothesized that two important behaviors, the righting reflex and tail‐withdrawal reflex, would be impaired following CO 2 exposure, since this has been noted in many other species. Aplysia were exposed for 4–11 days to either control (400 μatm), 1,200 μatm (close to end of century predictions), or 3,000 μatm CO 2 . Hemolymph pH was measured using a custom gas‐tight chamber with a fiber‐optic pH microsensor, and HCO 3 − and p CO 2 were calculated using pH and measurements of total CO 2 using the Henderson‐Hasselbach equation. The amount of time it took the animal to right following release from the water column (righting reflex), and the amount of time it took the animal to relax its tail to 50% of the original length (tail‐withdrawal reflex) following a mild tail depression were recorded. We observed that animals were able to fully compensate pH at 1,200 μatm CO 2 , but experienced a significant but mild acidosis at the 3,000 μatm level. Hemolymph HCO 3 − and p CO 2 increased at both CO 2 levels, and were statistically significant when compared to controls. Increased CO 2 exposure did not significantly affect the righting reflex, but tail‐withdrawal reflex demonstrated a significant 36–37% decrease in relaxation time at both CO 2 levels, suggesting increased boldness and altered behavior at projected future CO 2 levels. Given these findings, Aplysia are promising models to study CO 2 ‐induced behavioral impairments since they are capable of regulating HCO 3 − and have a CO 2 ‐impaired behavior linked to simple neural networks amenable to electrophysiological testing. Further research using this model may help illuminate physiological mechanisms underlying CO 2 ‐induced behavioral impairments noted in many marine species that could threaten ecosystems in future oceans. Support or Funding Information This research was supported by the National Institute of Health Bridge to Baccalaureate Program (Award R25GM050083).