This article has been reviewed according to Science X's editorial process and policies. Editors have highlighted the following attributes while ensuring the content's credibility: Blue damselfish, with their striking blue hue, are easy to spot, even along Okinawa's heavily urbanized coastlines. But while abundant, their gene activity reveals a hidden cost to living in human-impacted environments.
A new Nature Communications study shows that fish living close to human activity can be well fed while simultaneously displaying molecular signs of chronic physiological stress, suggesting a possible "junk food effect." The research, conducted by scientists at the Okinawa Institute of Science and Technology (OIST), the French National Centre for Scientific Research (CNRS) and the Indiana University School of Medicine, also opens the possibility of using organisms themselves as recorders of environmental conditions, with genome-wide gene activity revealing ecological impacts invisible to conventional environmental monitoring. Coastal environments worldwide are increasingly under pressure from urbanization, including agricultural, industrial and residential activity. In Okinawa, less than 40% of the coastline remains natural and unaltered.
This is particularly relevant for young coral reef fish, which spend their early lives in calm, shallow waters close to shore. These nursery areas provide relatively safe conditions and abundant food, but their proximity to land also exposes young fish to the impacts of human activity. However, how these conditions affect fish during this important stage of their lives and into adulthood remains poorly understood—until now.
"Classic methods of ecological and environmental monitoring involve water sampling or counting the number of fish species, but this doesn't really tell us about the health of the fish," explains first author Emma Gairin, a research fellow and former Ph.D. student in the Marine Eco-Evo-Devo Unit at OIST. "To know what the fish is experiencing, looking at gene activity is key." But this is easier said than done. For wild animals in the field, scientists have typically focused on the activity of just a few genes at a time.
Yet many different factors can affect gene activity, such as temperature and salinity, making it difficult to tell whether differences in gene activity between fish from different environments are really associated with human activity. Gairin continues, "Our approach was to look at the activity of all genes, not just a few, from fish across multiple different sites to see if we can distinguish any clear environmental signatures." The researchers collected blue damselfish (Chrysiptera cyanea) from 18 different sites across Okinawa's main island with varying levels of urbanization, ranging from almost pristine reefs in northern Okinawa to heavily urbanized coastlines in the island's south. "Some of the sites we were sampling were really dirty and polluted, but still, there they were," says Gairin.
"But just because they are present, it doesn't mean that they're not under stress." When they analyzed the gene activity of these fish, they found, surprisingly, that many of the genes traditionally used as markers of pollution failed to track urbanization. Their activity was often better explained by factors such as temperature or nutritional status. Only when the researchers looked at gene activity across the genome as a whole did the signature of human activity clearly emerge.
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