The diversity of snails in Sulawesi lakes is incredible. But don't imagine that you can find anywhere in Lake Towuti all 11 species of the genus Tylomelania that live here. In some places, only one species occurs, while two completely different ones live right next to it. Their occurrence is not limited by distance, but by changing conditions. The so-called microhabitats within the lake have the same water chemistry, but different physical conditions and food supply. This is related, among other things, to water movement and water currents, light availability (depth), the amount of organic matter, and above all, the type of substrate.
Because substrate preference is the primary factor determining the occurrence of individual Tylomelania species in lakes and the demands on keeping these snails in an aquarium, we include substrate preference in the list of all endemic snail species from Sulawesi. In this article, we will focus on Tylomelania, but similar substrate preference can be found in other snail species (not only from Sulawesi).
It's simple – if you were a tylomelania, you would eat what you crawl on. You have no other choice – the water is so clean that filtering food from it is pointless. Fine silt, sand or rocks represent completely different resources and require a different approach; and it is this diversity of environment and the resulting specialization that has contributed to the species diversity of Sulawesi snails. The radula, a structure in the snail's oral cavity that serves to scrape food and push it into the esophagus,is adapted to obtaining food from these different substrates. We don't normally see the radula; but it is obvious that different species of snails are found in different places.
Tylomelania spp. are divided into two main groups: one prefers hard substrates, the other soft. Only a relatively small number of species escape this division.
Hard substrate species
Snails that live on rocks. They feed on biofilm that they scrape off the rocks – this is not a visible growth of algae, which is very rare in the natural conditions of Sulawesi rivers and lakes. These snails live more abundantly in shallow water, often in turbulent conditions (there are surprisingly large waves on the lakes) or in strong river currents. The number of snails on the “bare” rocks is breathtaking!
A special subgroup are the species that are typically found on hardwood.
Soft substrate species
These are snails that move on sand or mud. As they search for food partially below the surface of the substrate and slide their heavy shells, they leave grooves behind them. They feed mainly on fine detritus, which is why they can be found at greater depths or anywhere where the bottom is flat and the water is calmer.
Exceptions
There are exceptions, of course. These are, for example, species that are found on plants, most often on the leaves and flower stalks of Ottelia mesenterium. This majestic plant can easily carry tylomelanias, even large species. However, most of the time these are not snail species that are specifically specialized for plants – after all, there are not many plants in lakes and they are scattered.
A significant group is the so-called generalists, which do not specialize in any substrate. However, they are closer to the species from soft substrates. They are found in the transitional zone, often where organic matter accumulates on the hard substrate – detritus, pieces of plants, fallen leaves from trees. Species from this group are most often kept in aquariums – and also thrive best in aquariums, which is why they are so popular.
We will discuss the husbandry requirements of Tylomelania snails – especially in relation to their preferred substrate – in a separate post.
