Sulawesi Lake Ecosystems and What They Mean for Your Tank

Your Sulawesi shrimp spend the whole day picking at bare rock, even with food in the tank. That’s what their lakes built them for. A handful of very old Indonesian lakes hold almost nothing a shrimp can eat, so these shrimp evolved to graze a thin film for a small return. They share that poverty with endemic snails, crabs and fish, and lately with a growing list of fish that were never meant to be there. It’s also where Sulawesi shrimp and cherry shrimp part ways, whatever the paintwork suggests. The food web explains why your shrimp graze all day, and why it matters where they were bred.

Why the Sulawesi lakes are so poor in nutrients, and what that built into the shrimp

The Malili lakes are ultra oligotrophic,¹ so there’s very little in the water to eat, and their shrimp are built to graze for a small return. That’s a big part of why Sulawesi lakes are unique. The other part is that they’re the only hydrologically connected ancient lakes in the world, with unusual physicochemical conditions.¹

Think about what that does to an animal over the long life of these lakes. Nothing rains down from above. Everything edible is a thin film on a hard surface, and something else is already working on it. So a Sulawesi shrimp grazes all day for very little. That’s why a busy colony is usually a healthy one, and why the jar of food on your shelf matters less than you’d expect. Build the grazing film first and feed second, because what Sulawesi shrimp eat off mature rock is most of their diet.

The practical version is blunt. In water this warm, uneaten food is a liability, not insurance. The usual rule is to offer less than you think, then lift out whatever’s still sitting there a few minutes later. Feels stingy? Take it up with the lake, which has been serving smaller portions than you for a very long time.

Poverty is only half of what shaped these shrimp. The other half is water that’s warm, mildly alkaline, very low in minerals and slow to change. That side of the Sulawesi shrimp natural environment is what your tank copies, not any one lake reading.

Clean rock is the pasture in a Sulawesi lake, and silt is what takes it away

In a Sulawesi lake, the pasture is the living film on hard surfaces. The shrimp don’t all graze it from the same place, either. Collection records put them on gravel and boulders, on wood and under leaf litter.² That spread is the layout of the Sulawesi shrimp natural habitat a tank should copy. A planted Sulawesi tank that looks like an aquascape is usually a Sulawesi tank feeding nobody.

That film is also the first thing a lake loses when the land above it is disturbed. Nickel mining has developed inside the Malili watershed, and sedimentation sits alongside it among the pressures recorded on these lakes.³

Your tank runs a small version of the same problem. Detritus drifts into the low spots and settles over the texture the shrimp were grazing. The colony quietly loses pasture while the test kit still reads fine. So when you pick the best rocks for Sulawesi shrimp, texture matters more than shape. A bed you can siphon under beats a bed that looks like the lake.

Which other animals share the Sulawesi lake food web?

Snails, crabs and fish, many of them found nowhere else. The ancient lakes of Sulawesi stand out for high endemism in all four groups: fish, snails, shrimps and crabs.⁴ Both lake systems have been isolated long enough to grow their own animals from scratch.⁵

Among the invertebrates, the snails have diversified furthest. The rabbit snails, Tylomelania, count 28 lake species in the Malili system alone, and they work the lake bottom too.⁶ The crabs are fewer and in worse shape. All five crab species of the Malili lakes are listed as Endangered.⁴

For all that endemism, the communities themselves are simple. The Malili lakes hold few kinds of animal, arranged in simple community structures.¹ A food web that thin has little room for a newcomer. The lakes have had several.

What mining, invasive fish and collecting have changed about buying Sulawesi shrimp

Mining, invasive fish and collecting have made it matter where your shrimp were bred. Every Malili atyid shrimp species assessed on the IUCN Red List is now listed as Endangered or Critically Endangered.³ The shrimps and snails of these lakes, with their color, have proven very popular in the aquarium trade.³ That popularity landed on animals with nowhere else to go.

Then there’s what got put in. The flowerhorn cichlid, a hybrid bred for the ornamental trade, was introduced into Lake Matano and has since spread to all of the lake’s coastal areas.³ It eats the lake’s own animals, with shrimps, a crab and small snails all turning up in its stomach.⁷

Lake Poso has had it worse. Introduced fish species there now outnumber the native ones, and an invading Malawi cichlid eats juvenile Caridina among much else.⁸

Lake Poso is changing from the land as well, more slowly. Land use covers about a third of its catchment and already shows up as a minor to moderate load of metal pollutants. The authors still describe the lake as relatively resilient. They warn, though, that changes to its water balance could push it toward a richer, more productive state.⁹

None of that is a reason to feel bad about keeping these animals. It’s a reason to be fussy about where yours came from. Comparing two listings? The first question worth asking is whether the shrimp were bred in a tank, and every one of our Sulawesi shrimp lines is tank-bred by Shrimp Aquatics.

So treat the lakes as an explanation more than a design brief. They’re why this animal is fussy, why it grazes instead of waiting for dinner, and why the tank has to be finished before the shrimp arrive.

What the research says about Sulawesi lake ecosystems

Much of the work on these lakes is about their other animals, the snails, crabs and fish, more than the shrimp. Here’s the detail behind the short versions above.

On the snails: several of the Tylomelania lake species carry radula forms matched to the substrate they feed on.⁶

On the flowerhorn: stomach contents from 15 flowerhorns caught in Lake Matano included atyid shrimps, a crab and small hydrobioid snails, with the snails the most frequent item.⁷ Monitoring in 2022 and 2023 caught flowerhorns attacking the lake’s endemic crabs, several fish at a time.⁴

On Lake Poso: the 17 fish species introduced there now outnumber the 13 native ones. The Malawi golden cichlid Melanochromis auratus went from a single record at the outlet in 2012 to abundant across the whole lake by 2019. Its stomach contents cover a broad range of food, juvenile Caridina among them. Remains of adult shrimp turned up surprisingly rarely, though attacks on living shrimp were seen directly.⁸

References

9 Sources

1. The Ancient Lakes of Indonesia: Towards Integrated Research on Speciation (abstract), Integrative and Comparative Biology 51(4): 634-643, Oxford University Press, 2011.
2. Radiation of endemic species flocks in ancient lakes: systematic revision of the freshwater shrimp Caridina from the ancient lakes of Sulawesi, Indonesia, with the description of eight new species, The Raffles Bulletin of Zoology 57(2): 343-452, Lee Kong Chian Natural History Museum, 2009.
3. Wallace’s Dreamponds: Conserving Sulawesi’s Ancient Lakes, Shoal, a programme of Synchronicity Earth.
4. Endemic crabs from ancient Sulawesi lakes under double threat, Rejlkova M. and Iqram M., Oryx 58(1), Cambridge University Press, 2024.
5. The species flocks of lacustrine gastropods: Tylomelania on Sulawesi as models in speciation and adaptive radiation (abstract), Hydrobiologia 615: 181-199, Springer, 2008.
6. Mitogenomes do not substantially improve phylogenetic resolution in a young non-model adaptive radiation of freshwater gastropods, BMC Ecology and Evolution, 2024.
7. Alien invasion in Wallace’s Dreamponds: records of the hybridogenic “flowerhorn” cichlid in Lake Matano, with an annotated checklist of fish species introduced to the Malili Lakes system in Sulawesi, Aquatic Invasions 7(4): 521-535, 2012.
8. More non-native fish species than natives, and an invasion of Malawi cichlids, in ancient Lake Poso, Sulawesi, Indonesia, Aquatic Invasions 17(1), 2022.
9. Perspectives from modern hydrology and hydrochemistry on a lacustrine biodiversity hotspot: Ancient Lake Poso, Central Sulawesi, Indonesia (abstract), Journal of Great Lakes Research, 2023.