Environmental effects of fish introductions in small, high-latitude lakes

Abstract

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Fish introductions have been a common practice for thousands of years but only relatively the attention has focused on their ecosystem effects. Using a combination of paleo- and neo-limnological methods, we tried to unravel the trophic effects of such introductions in small, high-latitude and originally fishless lakes of northern Finland. These kinds of lakes constitute the numeric majority of world lakes and play a key role in global carbon and nutrient cycling. We focused on terrestrial energy utilization, seasonality of resources, trophic cascade effects and nutrient carbon cycle alterations. Present trophic interactions were investigated mainly with stable isotopes but also with fatty acids. Past trophic interactions were investigated with palaeo-proxies such as diatoms, pigments and Cladocera. We found that introduced fish relied heavily on terrestrial sources and exhibited seasonal patterns. Fish introduction cascaded through the food web and its effect could be tracked with the primary consumers. However, albeit our models predicted a significant eutrophication effect the lake trophic state did not change but rather primary production shifted from benthic to pelagic.

Keywords

• Introduced Species
• Limnology
• Stable isotopes
• palaeolimnology
• fish ecology