A soft and inconspicuous animal conceals an unexpected longevity, with aging that does not even follow the usual rules of growth.
The sea cucumber studied is Holothuria whitmaei, called black teatfish in English. This animal lives on tropical seafloors and contributes to nutrient recycling in sediments. It is also heavily harvested for food and is listed among internationally threatened species.
Holothuria whitmaei in its benthic habitat, among rocks and algae.
Credit: Theo Summer, CC0 1.0.
Image Wikimedia
In 2000, researchers collected a tiny piece of tissue from individuals living near Lizard Island, in the Great Barrier Reef. Each animal was then released. Twenty-four years later, the team returned to the same location and compared the DNA from the new samples with the old ones.
The result surprised the researchers: about 60% of the adults found were genetically matched to animals already sampled in 2000. In other words, a large proportion of these sea cucumbers had survived for at least another 24 years.
The calculations indicate that some individuals can live beyond 100 years. This figure comes from the very low mortality observed among adults, estimated at about 0.04 per year, then statistically projected over a long period.
Another surprise was that the animals found had barely grown. Many had even lost length and mass. This phenomenon of negative growth had already been observed in sea cucumbers. Its exact cause remains unknown.
This longevity directly changes how fishing should be assessed. A long-lived species that replaces its adults slowly can withstand far fewer catches than a model based on rapid growth. The authors therefore estimate that several current calculations of sustainable harvests may overestimate what these populations can actually withstand.
Other recent studies point in the same direction: another sea cucumber species has already been monitored over several decades, with individuals reaching at least 33 years of age. Future monitoring will need to clarify at what age Holothuria whitmaei becomes an adult and how long its populations actually take to recover after heavy fishing.