Sulawesi Shrimp Natural Habitat: Inside the Ancient Lakes

Where do Sulawesi shrimp actually live in the wild, and how much of that can your tank copy? Sulawesi shrimp come from two ancient lake systems on one Indonesian island, where they live in a thin strip near shore, in the top few meters on rock, gravel, sunken wood and leaf litter. Those systems are Lake Poso and the Malili lakes. Each species keeps to its own kind of surface, and what they all eat is the film of algae and bacteria growing on it. Copy that layout in your hardscape, not the lake as a whole, and the tank does the job the shoreline does.

The Sulawesi shoreline is rock, wood and sand, not a planted tank

The shoreline these shrimp live on is a hard bottom of rock, gravel, wood and leaf litter, and plants barely feature in the records. The systematic revision that described most of these species notes where each one was collected. Shrimp were taken on gravel in shallow water, on boulders in deeper water, on rocks, between large boulders below 3 m, on wood and under leaf litter. That same work treats shallow as above about 3 m and deeper as below it.¹

So picture a hard bottom with structure in it: angular rock, piles of it, sunken timber, and patches of sand and leaf litter in between. Different species sit in different parts of that, which is how a dozen close relatives share one shoreline. It’s worth knowing before you lay out a tank. A bare glass bottom with one ornament on it isn’t a small version of this.

The water over that shoreline is warm, mildly alkaline and very low in dissolved minerals. You copy that side of the Sulawesi shrimp natural environment with the water you mix, and the rock, wood and sand with your hardscape.

A Sulawesi shrimp can only use the top few meters of the lake

Most of a Sulawesi lake is off limits to a shrimp, because the deep water carries no oxygen.² The habitat you care about is a narrow rim around the edge.

And the shrimp sit far shallower than the oxygen alone would allow. The Sulawesi White Sock, or cardinal shrimp (Caridina dennerli), was recorded from shallow water down to about 10 m, on and under small rocks and between boulders. Another lake species was usually found between large boulders below 3 m.¹ That’s a well lit, wave washed strip of stone, not a deep, still basin.

Choosing a tank for these shrimp? We’d take floor area over height every time. Depth buys you nothing the animal uses, and it makes the warm layer near the bottom harder to keep moving.

Which surfaces Sulawesi shrimp graze on in the wild

In the wild, Sulawesi shrimp graze on rock, from small stones in the shallows to boulders deeper down, and some species work through dead leaves instead. Species in these lakes divide up the bottom, and each one keeps to its own surface. The cardinal shrimp and the Sulawesi Red Orchid (Caridina glaubrechti) are hard substrate dwellers on rocks. The Red Orchid sits mainly on smaller rocks in the shallows, and also on boulders in deeper water. A third Malili species is a soft substrate dweller, found mainly under dead leaves and only sporadically on macrophytes.¹ Ask which lake a species comes from and you have half the answer. Ask what it sits on and you have the rest.

Lake Poso carries its own endemic flock, shared with none of the Malili lakes,³ and that isolation is a large part of why Sulawesi lakes are unique. It has a surface specialist of its own too. Among the species on the full list of Lake Poso shrimp species described so far, one is adapted to living in freshwater snail shells.³

The sponge dwellers of the Towuti outlet bay

Caridina spongicola takes the idea further than any of them. It lives on and in an undescribed freshwater sponge, restricted to part of the outlet bay of Lake Towuti at a depth of 3 to 5 m. One dissected sponge held 137 shrimp, and the mean across the fifteen examined was 28.73. That’s a lot of tenants for one sponge. The shrimp appear to use its cavities as shelter and the diatoms collecting in it as food, while every other species in that Towuti group lives on rock.⁴

What you can copy from all this is the surface, not the species. Rock that does nothing to your water is the floor these animals evolved on. That’s why inert substrate for a Sulawesi tank is the one part of the setup we wouldn’t improvise.

How to turn the Sulawesi shoreline into tank hardscape

Read the collection records as a floor plan. Small rock and gravel stand in for the shallow shelf. Larger stones, stacked so they leave gaps and overhangs, stand in for the boulder fields a few meters down. The gaps are as much a part of the habitat as the stone. A piece of sunken wood and an open patch of sand cover the rest. Every one of those surfaces grows film, so more texture means more to graze.

Why does the texture matter so much? Because these aren’t rich lakes. What does grow in them grows slowly, and almost all of it grows on a surface.

The food is the film. Rock dwellers scrape it off stone and leaf litter dwellers work through the debris, while the sponge shrimp lives on diatoms that collect in its host.⁴ None of that arrives in a tank on stocking day. You have to grow the grazing surface first, and once a colony has settled it needs far less prepared food than most keepers offer. There’s more on that in how Sulawesi shrimp eat algae and biofilm in an aquarium.

The habitat is disappearing, and that decides where your shrimp comes from

The cardinal shrimp was assessed for the IUCN Red List on 20 August 2018 as Critically Endangered. The threats listed against it include fishing and harvesting, dams and water management, invasive species and effluent.⁵ Every one of those lands on the same shallow rim the animal can’t leave. The same pressures run through Sulawesi lake ecosystems as a whole. Several other lake species carry listings of their own, and endangered Sulawesi shrimp sets out where each one stands.

For a buyer the conclusion is short. At Shrimp Aquatics every line is tank-bred, so the animals in our Sulawesi shrimp tanks were not collected from Lake Matano. Ask any seller which lake a species comes from, and whether the stock was bred in captivity. If the answer’s vague, buy somewhere else.

References

5 Sources

1. Radiation of endemic species flocks in ancient lakes: systematic revision of the freshwater shrimp Caridina from the ancient lakes of Sulawesi, Indonesia, von Rintelen T. and Cai Y., Raffles Bulletin of Zoology 57(2): 343-452, 2009.
2. Geomicrobiological Features of Ferruginous Sediments from Lake Towuti, Indonesia, Vuillemin A. and colleagues, Frontiers in Microbiology 7: 1007, 2016.
3. Lake Poso’s shrimp fauna revisited: the description of five new species of the genus Caridina more than doubles the number of endemic lacustrine species (abstract), Klotz W., von Rintelen T., Wowor D., Lukhaup C. and von Rintelen K., ZooKeys 1009: 81-122, 2021.
4. Freshwater shrimp-sponge association from an ancient lake, von Rintelen K., von Rintelen T., Meixner M., Luter C., Cai Y. and Glaubrecht M., Biology Letters 3(3): 262-264, 2007.
5. Caridina dennerli, The IUCN Red List of Threatened Species 2018: e.T198055A109683594, von Rintelen K., IUCN, assessed 20 August 2018.