ICES CM 2015/ H:12
CO2-induced ocean acidification increases risk of predation in a coastal temperate
fish larvae
Ana M Faria (1), Ana F Lopes (1), Ana P Oliveira (2), Phil Munday (3), Emanuel J Gonçalves (1)
(1) MARE – Marine and Environmental Science Centre, ISPA−IU, Rua Jardim do Tabaco, 1149-041 Lisboa,
Portugal; (2) IPMA – Instituto Português do Mar e da Atmosfera, Algés, Portugal; (3) School of Marine and
Tropical Biology, James Cook University, Australia. Presenter contact details: [email protected], phone +351
218 811 700
Summary
The larval period of most marine organisms is highly vulnerable to predation. The ability to recognize
and avoid predators during this life stage should increase both the immediate and future prospects of
survival. A growing number of studies suggest that behaviour of early life stages of fishes may be
highly affected by ocean acidification. Fish reared under high CO2 levels fail to recognize predator
cues and adopt bolder and riskier behaviours, therefore increasing vulnerability to predators. Here we
tested if larvae of a temperate fish species, Atherina presbyter, have the capacity to recognize the
olfactory cues produced by predators, and whether this ability is disrupted by exposure to high levels
of CO2 (pH ~7.8 and 7.6). Additionally, we’ve investigated the preference for a light-dark
environment (scototaxis), which can represent “anxiety” or “fear”-like behavior. Results suggest that
larvae exposed to increasing CO2 conditions might be in a greater risk of predation compared to
larvae reared in control conditions.
Introduction
The ability to recognize a potential predator is an important component of antipredator behavior
because a failure increases the probability that the predator captures or injures the prey (Lima and Dill
1990). Although a suite of sensory mechanisms is available for predator detection, olfaction plays a
significant role in the initial detection of predators (Chivers et al. 2001). Recent research has
demonstrated that the ability of larval fish to detect predator odours and conspecific alarm cues is
hindered by ocean acidification (Dixson et al. 2010). Impairment of behaviour by elevated CO2 levels
could have far-reaching implications for survival and ultimately sustainability of adult populations.
Here we tested the hypothesis that exposure to high levels of CO2 increases risk of predation of sand
smelt Atherina presbyter larvae by disrupting the ability to recognize olfactory cues produced by
predators, and becoming more anxious and active.
Materials and methods
Wild-caught sand-smelt larvae were randomly assigned to one of three pCO2 treatments - control
(~600 µatm), medium (~950 µatm) and high (~1500 µatm) - and reared for 20 days. The response of
larvae to olfactory cues of a predator, Diplodus sargus, was tested in a two-channel flume chamber
(adapted from Gerlach et al. 2007), where larvae were given the choice of two streams of water
containing different olfactory cues. Experimental scototaxic (light/dark preference) testing was
performed as described by Hamilton et al. (2013). Proportion of time spent in the black and white
compartments (%) and number of times the individuals entered each compartment was recorded.
Results and Discussion
Results show that larvae reared in the high pCO2
treatment spent, on average, 76% of time in the
predator cue, which was significantly higher when
compared to larvae from control (51 %) and mid (65
%) pCO2 treatments (Fig 1A). This disruption of
olfactory behavior has also reported for other
tropical fish larvae (Dixson et al. 2010), and may be
attributed to an alteration of neuro-sensory
functioning following exposure to elevated CO2
(Nilsson et al. 2012).
We also show that control larvae have a significant
preference for the light compartment of the
experimental arena (Fig 1B), which might be related
to the fact that larva are transparent and in a light
environment they would be less visible to the
predators. However, larvae from mid and high CO2
treatments show no preference for any of the
compartments in the chamber. Despite the tendency
for control larvae to spend more time in light area
and be more active (Fig 1C) than larvae from mid
and high treatments, it wasn’t statistically significant
and we cannot conclude that high CO2 levels result
in increased anxiety, but we can conclude that the
lack of preference for the light comparment make
these larvae more easily detected by a predator.
These results contrasts with the results obtained by
Hamilton et al. (2013), who reported that control
rockfish had no preference for any of the
compartments, but fish exposed to high CO2 levels
had a strong preference for the dark zone.
Overall, our results suggest that impairment of
critical behaviours for predator detection and
avoidance might make these larvae more vulnerable
to the risk of predation in a high CO2 world.
Figure 1. Average time (s) spent in the predator cue
(A); average time (s) spent in the light compartment
(B); average entries in light and dark compartments
(C), by larvae reared in control, mid and high pCO2
conditions. Mean ± SE
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