Bacteria and excessive fertilization turn the starfish into a sticky substance

It began off the western coast of North America in 2013. Sunflower sea star and other types of sea stars have died a million times – or rather, some of them simply melt in mud. A severe loss to the ecosystem. Since then, scientists in other parts of the world have observed such stock collapses, the cause of which has long been unknown. Viruses in particular have been suspected, but a study by Citlalli Aquino of San Francisco State University and her team points to a different direction. In Frontiers in Microbiology, Aquino and Co. describes how a combination of environmental pollution and bacteria destroys starfish..

Scientists compared the bacterial communities in living quarters with species afflicted with “astral wasting disease” and identified important differences. The animals affected by the epidemic contained a particularly large number of bacteria that were well adapted to low oxygen and especially nutrient-rich conditions. Laboratory experiments confirmed this association: In an oxygen-poor environment, 75 percent of the starfish found ultimately suffered tissue damage that caused mucus and even death. If ponds are excessively fertilized or fertilized with more algae, this results in the rest. Tissue samples from starfish that died in 2013 also showed excessive concentrations of nitrogen: a sign of excessive fertilization.

The starfish takes in oxygen through its papules (gills of the skin). If its concentration in water is too low, animals can difficulty breathing, get stressed, and become more susceptible to disease or suffocation. Hypoxia can occur, for example, with algal blooms, which in turn are stimulated by a strong supply of nutrients, for example through ingress from air or wastewater. The dead sea star then feeds more bacterial flowering, which in turn consumes oxygen. The researchers write that this creates a starfish death vortex.

Ecosystem collapse

Fittingly, most of the mass extinctions occurred in summer and autumn when the water was heated: oxygen poorly dissolved in warmer water; Additionally, exposure to sunlight also promotes algal blooms. In Australia, the high death rate came on the heels of one of the longest and strongest heat waves at sea, after which the starfish may already be stressed and more susceptible to disease from external conditions.

That’s why viruses are still not completely ruled out as a reason: they can infect polluted starfish more easily. In any case, the disease has dire consequences for the ecosystem. Starfish is considered a predator and eats sea urchins, snails and other invertebrates, which can reproduce more vigorously without their opponents. On the Pacific coast of North America, axolotls were able to forage on kelp forests unhindered after the failure of the sunflower sea star. In many areas, the population of large brown algae has perished by as much as 80 percent: a colossal loss for this important and species-rich marine ecosystem, the future consequences of which remain unclear.