We have already reported on our website that this originally abundant shrimp is disappearing from Lake Matano due to the rapidly growing population of invasive cichlids, flowerhorns. Despite intensive searches in 2017 and 2018, not a single specimen was found! The IUCN Red List category for this species has therefore been changed to "Critically Endangered (Probably Extinct in the Wild)", see link.
In 2019, researchers with the help of local shrimp collectors managed to find these iconic shrimp again. In two places of Lake Matano they hid under a thick layer of stones. Shrimps are no longer found in places where they used to be abundant; they hide from predators deep (at least 30 cm) under stones. But they are not safe there. The bottom is now covered with a thick layer of mud and algae, which is not a normal condition, and threatens to run out of oxygen under the rocks.
On our expedition in 2022, we documented (see video) what such a search for the previously abundant shrimp looks like. It is necessary to pick up stones and search thoroughly. At the same time, you are often accompanied by flowerhorns, who wait for any movement and immediately eat the shrimp or a small crab. Observing shrimps in Lake Matano is no longer a joy…
During subsequent expeditions, we visited many more locations and looked for an environment that would be less suitable for flowerhorns and, on the contrary, provide suitable conditions for shrimps, but also for smaller species of snails that are on the verge of extinction due to invasive fish. In 2024 we were rewarded with the discovery of a small locality where Caridina dennerli does not hide under rocks! This is like a window into the past – this is how it used to look everywhere on the rocky shores of Lake Matano, before the voracious invasive flowerhorns took over. In this way, we can still observe other species of shrimps in Lake Towuti, although the flowerhorn has already spread there as well.
It doesn't mean that the situation of Caridina dennerli isn't so bad. Unfortunately, it's pretty damn bad. But it still makes sense to try to protect at least parts of the lake. Species that were originally abundant – and today only a step away from definitive extinction – still survive somewhere there.
It's also proof that time spent in the water observing and documenting is irreplaceable. It helps us to understand what is happening in the lakes, what are the relationships between the species and their environment. We are looking for factors that will help us protect endangered species – whether in lakes or in aquariums. We will not reveal more details about this unique location now, because Caridina dennerli is still sought after by collectors even in its sad situation…
Please do not buy wild Caridina dennerli and consider helping our initiative to save Sulawesi lakes yourself in one of the many ways – see here.
We thank EUAC, AKWB and Megazoo & Friends for the direct financial support of our trips to Lake Matano.
Markéta Rejlková
