蘑菇直播

Freshwater pearl mussel (FPM) lives its whole life more or less burrowed into the riverbed. Juvenile FPM spend their first years totally burrowed to bottom gravel, and only after having become stronger and being able to resist the water current, they raise to feed on the riverbed. They also regulate their burrowing depth when necessary. During the warm water period, when the river water also contains more food particles, such as some algae and degrading organic matter, detritus, these fellows may 鈥渟it鈥� on the gravel鈥檚 surface. In wintertime, however, FPMs burrow deeper into gravel to be protected from freezing. So, the depth to which these creatures 鈥渄rag鈥� themselves depends on temperature as well as several other factors affecting their habitats. The speed at which the FPM moves is still extremely slow compared to most animals 鈥� only some centimetres per day.

How does the burrowing happen in laboratory conditions?

At the Konnevesi Research Station of 蘑菇直播, adult FPMs representing the populations of different Finnish rivers are maintained to help them to reproduce. The FPMs are kept in large, gravel-bottom flow-through tanks (Fig. 1). Couple of times a year, the gravel is changed, and the tanks are cleaned. Also, the FPMs themselves get a nice bath. After this 鈥渓inen chance鈥� operation, at the end of last year, we observed bustling around FPMs from five different rivers and photographed and filmed their burrowing behaviour.

Differences between populations could be seen. River Suomujoki FPMs started to find their place in the tank and burrow into the new 鈥渓inen鈥� during the first day after cleaning (Figure 3). In a month, most of the mussels were found burrowed in the gravel. Similar behaviour was observed among the representatives of the River Livojoki FPM population (Figure 4).

Compared to these two, River Simojoki FPMs seemed to choose a place which was a bit closer to the gravel bed surface (Figure 5a). On the other hand, when it comes to FPMs representing populations of South Ostrobothnia rivers, they hardly bothered to burrow at all. Their 鈥渟eated position鈥� was, however, somewhat different from their northern fellows: FPMs of the River Lapv盲盲rtin-Isojoki and River Karvianjoki settled horizontally in direction of the current on the gravel bed (Figures 5b and c).

Burrowing activity depends, of course, on the FPM individual itself as well. We put in a video camera for a couple of hours to record movements of River Livojoki FPMs after getting into a clean tank (Figure 6). mussels are ready to rumble!

Based on these one-time laboratory observations, no wider conclusions on burrowing behaviour of a certain FPM population can be made. However, they tell us how each FPM individual crawls to a pleasant place to spend its over 200-year life.