Climate change caused by humans is not only affecting the growth and survival of marine animals, but it is also adversely impacting their senses and disrupting their behavior. A study led by the Virginia Institute of Marine Science shows that climate change is significantly affecting marine organisms by changing their sensory pathways — responsible for the perception of sensations.
The reason, according to Dr. Emily Rivest from Virginia Institute of Marine Science, is that changes in temperature, salinity, or ocean acidification causes stress to the organism and could impair its ability to produce a cue or signal. This, according to the study published in Frontiers in Marine Science, will have “broader consequences for marine life” and impact ecological and evolutionary interactions, including mating, predator-prey interaction, and habitat selection. For example, says the study, conditions of ocean acidification significantly impair sensory behavior of reef fish larvae and causes the larvae to settle in poor-quality habitats.
“Larvae of many marine taxa, such as corals, crabs, and mussels, use conspecific chemical cues to locate optimal settlement habitat. Changes in environmental conditions can influence sensory pathways used by larvae during dispersal and selection of suitable settlement sites, which could result in maladaptive habitat selection,” states the study.
Most studies regarding the impact of global change on marine organisms have focused on physiological effects, such as an oyster’s decreased ability to build or maintain a strong shell in an ocean that is becoming more acidic due to excess levels of carbon dioxide. It is only recently that researchers started investigating how multiple facets of global change can disrupt animal behavior. The current study is based on a review of 120 relevant journal articles that examined how human pressures on the environment is impacting each step in the sensory pathways between marine organisms.
The researchers explain, “Organisms disseminate and gather information from their environment using sensory pathways composed of four steps: production, transmission, reception/processing, and response, and these steps serve as the framework for our literature review and discussion.” The review distinguishes between information produced incidentally, what is known as a “cue” and information that an organism produces intentionally, termed as a “signal”.
“Our review emphasizes that behavior is the outcome of a sensory pathway that includes the production of information, transmission of that information through the environment, reception of the information by an organism, and then a response, that is, what the organism decides to do with the information,” says Rivest, who led the research team.
The team focused on environmental factors that are at the forefront of global attention — for example, those listed by the Intergovernmental Panel on Climate Change (IPCC) — covering rising temperature, ocean acidification, enhanced low-oxygen zones, salinity changes, increased turbidity, UVB radiation, hydrodynamics, stratification, and excess nutrients. They then examined literature to identify studies that reported the effects of these abiotic conditions on sensory pathways. They recommend looking at both global and local factors.
“Many marine organisms live in highly dynamic environments characterized by rapid fluctuations in abiotic conditions. To our knowledge, this is the first quantitative literature review on impacts of global change on marine sensory pathways, and the emergent patterns we identify provide unique insight and research directions for anticipating future impacts on ecological processes,” state the findings.
According to the research team, if a factor responsible for climate change affects the production of a visual cue or signal, it is “likely to affect the production of acoustic and chemical cues and signals as well,” and vice versa. They found that of the five environmental factors that affected production — rising temperatures, ocean acidification, low oxygen, salinity changes, and increased turbidity — four did so for multiple senses. “Ocean acidification, for example, was found to affect the production of visual, olfactory, and auditory cues and signals,” they reveal.
They found that studies on weakfish and croaker — popular recreational fish species in the Chesapeake Bay — have stated that warmer waters and increased turbidity change production of sounds that males of both species use to attract females, thus potentially affecting breeding success. “Most marine fish produce sounds for communication during mating. In the Atlantic croaker (Micropogonias undulatus) and Weakfish (Cynoscion regalis), a range of environmental factors, such as temperature, turbidity, and salinity, directly influence sound production. Global ocean change may shift these environmental conditions. Consequently, timing and success of reproduction could be affected by changing environmental conditions, such as ocean temperature,” says the study.
According to other reports reviewed by the team, increased turbidity due to nutrient pollution and frequent cloudbursts can degrade light transmission, possibly lowering feeding success among “highly visual avian predators” such as Cormorants. Furthermore, a 2016 study shows that ocean acidification makes tidepool snails more prone to sea-star predation by interfering with their ability to process and respond to chemical cues that starfish leave in the water.
Yet another report, examined by the researchers, shows that “raising cobia larvae in waters with elevated carbon dioxide levels affects their otoliths,” which likely alters their ability to detect sound. Otoliths are calcified bodies in the inner ear that vertebrates use to sense gravity and movement.
“Clearly, global ocean change will disrupt marine sensory pathways. The production and reception/processing of multiple modalities of cues/signals are vulnerable to global change stressors, indicating that there are generalizable mechanisms by which environmental change impairs these pathways steps, leading to altered sensory pathway outcomes. Factors that enhance organismal stress as a whole may amplify impacts to these sensory pathways. Further, global change factors tend to affect specific modalities of cue/signal transmission,” states the paper.
Unlike production, when it comes to transmission, the review found that factors impacting climate change tend to affect just one mode — this could be acoustic, visual, or olfactory. For instance, a study determined that the decline of a Florida coral reef was substantially affected by increased nitrogen from land-based runoff. The findings state that if there is a better understanding of the relationship between pathways and more local stressors such as nutrient pollution, then there could be a “more tractable way” to make a difference.
“Local environmental conditions will have a strong effect on the production, transmission, and reception/processing of cues/signals. Efforts to characterize and monitor local environmental conditions will improve predictions of impacts on local populations and communities,” the findings suggest.
The research team recommends further research in this emerging area. They explain knowing where and in how many places climate change breaks that sensory pathway would help anticipate how it might affect broader ecological processes, like food-web and population dynamics. “If we can show where climate change stressors impact the sensory pathway, then we can develop more targeted, effective management and conservation efforts,” says the team.
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