Sydney, Sep 23 (The Conversation) - Species worldwide are actively relocating, with climate change prompting over 12,000 species to shift across land, freshwater, and ocean environments. They are moving to evade adverse conditions or to colonize previously inaccessible ecosystems.
In marine habitats, some tropical fish are relocating to temperate reefs to find cooler waters. This phenomenon is evident along Australia’s east coast, recognized as one of the most rapidly warming marine regions globally. New coral and fish species are frequently appearing in Sydney's waters, a trend expected to intensify with ongoing climate shifts.
Traditionally, these newcomers are monitored through visual surveys conducted by researchers or citizen scientists. However, many early arrivals are small, rare, nocturnal, or cave dwellers, making them easily overlooked. Consequently, the actual pace of species relocation might be underestimated.
This is where our new study, published in "Diversity and Distributions," becomes relevant. We transitioned from marine ecologists to forensic scientists, searching water for evidence of species on the move. By examining fragments of DNA floating in the ocean, we aimed to uncover the hidden changes in fish communities that conventional visual surveys might miss.
Every organism leaves traces in its environment. Fish shed mucus, scales, and waste, all containing DNA. By gathering and filtering seawater samples, we can extract environmental DNA (eDNA) and identify present species.
This technique operates comparably to forensic science. Just as detectives solve crimes by analyzing fingerprints or hair left at a scene, ecologists can map marine life from genetic fingerprints invisibly suspended in the ocean.
The concept of eDNA originated in the 1980s when scientists recognized they could extract DNA directly from soil or water samples. Initially used to study microbes, by the early 2000s, researchers realized it could also identify larger animals and plants.
Today, eDNA is employed globally, from soil to water bodies, to discover hidden or threatened species, track biodiversity, and even examine ancient ecosystems preserved in sediments.
In our study, we surveyed fish communities over 2,000 kilometers along Australia’s east coast. Sites spanned from the tropical Great Barrier Reef to subtropical waters, extending to New South Wales’ temperate kelp forests.
At each location, we conducted standard visual surveys, swimming along defined transect belts and documenting every fish observed. These surveys are foundational for monitoring marine biodiversity, building decades of invaluable data.
Concurrently, we collected seawater for DNA analysis. Though a few liters of water might seem insignificant, it contains the genetic fingerprints of countless species.
Back in the laboratory, we filtered these samples to capture DNA and sequenced them to get an overview of the species present.
Our comparison of traditional visual surveys with eDNA sampling yielded intriguing results. Each method uncovered different fish communities, but together, they provided a more complete picture than either alone could.
eDNA detected tropical species in temperate ecosystems previously unrecorded there, such as herbivores like the lined surgeonfish, the striated surgeonfish, and the common parrotfish, along with cryptic species like the black-blotched porcupinefish that evade divers.
For temperate species, traditional surveys surpassed eDNA in detection capability. This indicates that eDNA is an invaluable complement to, rather than a replacement for, visual surveys. Combining both methods allows for a clearer understanding of species relocations, enhancing our insight into climate change's impact on reefs.
These migrations are not Australia-exclusive. Globally, species are shifting their ranges as climate change modifies temperatures, ocean currents, and habitats. Some species may thrive in their new environments, while others struggle or get displaced.
Monitoring these transitions is essential for understanding how climate change is transforming oceans, necessitating improved methods to identify migrating species. (The Conversation)
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