Tracking Fish Introduction in a Mountain Lake over the Last 200 Years Using Chironomids, Diatoms, and Cladoceran Remains

We analysed a 24 cm long sediment sequence (past similar to 200 years) from an alpine lake (Tatra Mts., Slovakia) for chironomids, cladocerans, and diatoms to reconstruct the effects of a historically documented fish introduction. Our results indicate that fish introduction predated the age of the sequence, and thus, we did not cover the lake's fishless period. The individual proxies coincide in showing two main lake development stages. The first stage lasted until similar to 1950 CE and was interpreted as the stage when brown trout and alpine bullhead co-occurred. The extremely low concentration of cladocerans, the dominance of small-bodied chydorids, and the low share of daphnids, together with the low proportion/absence of large-bodied tanypod chironomids, suggest a strong effect of both species. The beginning of the next stage is probably related to the ban on fish manipulations and grazing in the catchment. A significant increase in the total abundance of cladocerans and of daphnids may indicate the extirpation of trout. The steep increase in thermally plastic chironomid taxa since the end of the 20th century indicates climate warming. Generally, while cladocerans primarily indicate fish manipulations, chironomids and diatoms mainly reflect other local and global environmental stressors.

Automated summary

We analysed a sediment sequence to study the effects of fish introduction in an alpine lake. The results showed two main lake development stages, with the first stage coinciding with the co-occurrence of brown trout and alpine bullhead. The second stage was likely related to the ban on fish manipulations and grazing, with an increase in cladocerans indicating the possible extirpation of trout and a steep rise in thermally plastic chironomid taxa reflecting climate warming.