#WildWednesday 🐟❄️ Meet the marbled rockcod (Notothenia rossii). Not the prettiest species in the ocean, perhaps, but one of the most resilient.

This is a fish built for extremes. It can grow up to nearly a meter long, live more than a decade, and survive in waters ranging from about -1°C to 5°C. It relies on biological antifreeze proteins in its body fluids to keep functioning where most fish simply could not.

As a juvenile, the marbled rockcod hugs shallow, sheltered bays, feeding on tiny drifting zooplankton. As it matures, it heads offshore to the deep continental shelf and transforms into a benthic predator, feeding on krill, small fish, and other seafloor life.

Same species, completely different lifestyle. But its story is not only about adaptation. It is also about pressure.

The marbled rockcod was one of the first fish species in the Southern Ocean to be heavily commercially targeted. Intense fishing in the 1960s and 70s drove populations into collapse. When targeted fishing was prohibited by CCAMLR in 1985, recovery became a long, slow process.

Decades later, there are signs of rebound, but the system it returns to is not the same one it left. Warming waters, shifting food webs, and changing krill dynamics are reshaping the Southern Ocean ecosystem faster than many Antarctic species evolved to handle. As a cold-specialist fish of the Southern Ocean, even small temperature changes can ripple through its growth, metabolism, and survival.

A fish that has already come back from collapse, now facing a changing ocean once again.

Image via iNaturalist CC-BY-NC by Gail Ashton PhD ...

What if one of Antarctica’s most recognisable penguins has actually been four different species all along? 🐧

That’s what new research led by Dr Jane Younger suggests after a decade of detective work across Antarctica and the Southern Ocean.

It started with something unusual in the DNA. 🧬 Gentoo penguins from different islands were far more genetically different from each other than scientists expected, even compared to entirely different penguin species.

So researchers went further, travelling to museums around the world to measure penguin specimens, before heading into the field to collect samples from the sub-Antarctic islands and the Antarctic Peninsula.

The result? A new study combining genome sequencing, physical measurements, ecological modelling, and evolutionary analysis suggests there may actually be four distinct gentoo penguin species hiding in plain sight.

Read more: https://www.abc.net.au/news/2026-05-21/research-finds-gentoo-penguins-four-species/106701568

Image Credit: Lars von Ritter Zahony / Ocean Image Bank ...

What was once thought to be a single Antarctic sea slug species is now believed to be at least 75 distinct species, all shaped by millions of years of Antarctic glacial cycles.

In a new study published in Molecular Phylogenetics and Evolution, researchers Dr Paige Maroni and Dr Nerida Wilson from The University of Western Australia uncovered hidden biodiversity using advanced genomic analysis across 130 specimens.

The study highlights:
🔬 The power of genomic science in uncovering cryptic species
🧊 How repeated glacial advances and retreats acted as an “evolutionary engine”
🌍 Why understanding past climate impacts is critical for predicting future ecosystem responses

Read more: https://www.uwa.edu.au/news/article/2026/may/glacial-cycles-shape-evolution-of-many-species-of-antarctic-sea-slug

Image via iNaturalist CC-BY-NC by Kim Nesbitt @nesbittphotography ...