Page 17 - Special Issue

bioacoustic Monitoring Contributes
to an Understanding of Climate Change
ocean because logistics have prevented scientists from acidi- fying the large volumes of seawater necessary to observe de- creases in absorption.
In addition to the decrease in sound absorption, the reduc- tion in ocean pH may affect oceanic animals in other ways. Larval fish are thought to rely on sensory cues such as ol- faction and hearing for predator avoidance and for localiz- ing reef settlement sites. Noisy reefs indicate the presence of predators, so most larval fish will avoid these noisy sites. Larval clownfish reared in waters with elevated CO2 levels did not avoid noisy sites; instead, they demonstrated no pref- erence for sites depending on noise level (Figure 3; Simpson et al., 2011). This suggests that ocean acidification may result in a breakdown of predator avoidance among fish species by disrupting their ability to detect and localize sound sources.
freshwater species
Predicting the impact of climate change on freshwater spe- cies is more difficult. The size of many freshwater systems is below the resolution of Global Climate Models (GCMs), which constrains the accuracy of climate projections for these environments (Hobday and Lough, 2011). Addition- ally, unlike the relatively homogenous oceans, freshwater systems are enclosed and habitat specific. Because climate models predict droughts in some regions and heavier rainfall in others, we cannot create a unifying prediction as to how climate change will impact freshwater species (Hobday and Lough, 2011). For example, streams associated with melt- ing glaciers may increase in flow and volume as the planet warms, whereas lakes and ponds in other regions may desic- cate as those environments experience droughts. Increased temperatures can result in a decrease in aquatic mixing and turnover, resulting in stratified regions with hypoxic condi- tions and low pH. Acidification of freshwater systems is pre- dicted, but it is not known if significant changes in sound ab- sorption will occur due to the small size of most freshwater systems. Clearly more data are needed.
An additional factor to consider in predicting the impact on climate change in freshwater environments is the effect of ambient temperature on the auditory system. Fishes are ectotherms that regulate their body temperature by refer- ence to external temperature, rather than by internal physi- ological setpoints. The water temperature at which animals were housed affects the hearing sensitivities of two species of catfish, the channel catfish (Ictalurus punctatus) and the tropical catfish (Pimelodus pictus). Thresholds of neural re-
10 | Acoustics Today | Summer 2014
Figure 3: Effect of carbon dioxide concentration on auditory be- havior of juvenile clownfish. Fish reared in ambient CO2 conditions avoided simulated predator noise, whereas fish reared in elevated carbon dioxide environments did not avoid the noise. Figure adapted from Simpson et al. (2011).
sponses from auditory nuclei in the brain varied with hous- ing temperature (Wysocki et al., 2009); at high temperatures, thresholds increased and hearing sensitivity decreased. The magnitude of these changes varied between the two species, and was further affected by how long the fishes were kept at a particular temperature. These results have particular impli- cations for how fishes may respond to climate change. First, temperature will not affect the hearing sensitivity of all spe- cies to the same degree, and second, if animals can acclimate to temperature variations, then the negative consequences of increased temperature on hearing sensitivity may be less- ened (Wysocki et al., 2009).
effect on Aerially
Communicating Animals
Climate change impacts terrestrial species as well as aquatic species. Changes in temperature (Figure 1- see page 9), pre- cipitation, and CO2 levels, combined with the increased climatic variability caused by global warming, can initi- ate or exacerbate habitat loss and thus affect biodiversity by altering species distribution, behaviors, and viability. As discussed above for aquatic species, studying these im- pacts in terrestrial species is also not trivial, because these impacts vary between different habitats (tropical and tem- perate zones, high and low elevations; Navas, 1996; Deutsch et al., 2008), and between different species (longer-lived species such as birds may be affected in a different manner than shorter-lived species such as insects; Şekercioğlu et al., 2012). Because of the complexity and variability of different habitats and the different life histories of species living in these habitats, we still do not know which species will ac- climate and adapt to a changed habitat, which will disperse to other habitats, and which may go extinct. This is where animal bioacoustics can play a major role, both by providing
Spring 2020, Special Issue | Acoustics Today | 17 Reprinted from volume 10, issue 3