Carolina Trochine

Biomanipulation as a Restoration Tool to Combat Eutrophication: Recent Advances and Future Challenges

Eutrophication resulting from high nutrient loading has been the paramount environmental problem for lakes world-wide for the past four decades. Efforts are being made in many parts of the world to reduce external nutrient loading via improved wastewater treatment or diversion of nutrient-rich inflows. However, even after a reduction of the external phosphorus loading, the effects obtained may be unsatisfactory. This may reflect an insufficient reduction in the external nutrient loading to effectively limit phytoplankton growth. However, the lack of success may also be due to chemical or biological within-lake inertia preventing or delaying improvements. To overcome the resilience and thereby reinforce recovery, a number of physico-chemical and biological restoration methods have been developed. In this chapter, we describe recent developments of biological restoration methods related to eutrophication, their short-term and long-term effects, and discuss the possibility of using combined physico-chemical and biological methods to improve the long-term stability of restoration and to reduce restoration costs. As comprehensive reviews of the effect of fish manipulation in cold temperate lakes are numerous, for these waterbodies, we highlight recent results, including effects on biodiversity and metabolism, and present new approaches of biomanipulation. Our particular focus is, however, directed at biomanipulation in warm lakes and on combined treatments which are far less well described in the literature.

THE ROLE OF MICROORGANISMS IN THE DIET OF VERGER CF. LIMNOPHILUS (TRICHOPTERA: LIMNEPHILIDAE) LARVAE IN A PATAGONIAN ANDEAN TEMPORARY POND

The importance of fungi and bacteria attached to leaf litter in the diet and growth of shredders in flowing waters is well-documented. This study focuses on the role of microorganisms colonizing submerged leaf litter in the diet and growth ofVerger cf.limnophilus (Trichoptera: Limnephilidae) larvae in a Patagonian Andean temporary pond (Fantasma pond, 41°07′S, 71°27′W). First, the feeding habits were analyzed through an experiment that compared consumption of CPOM and FPOM. Once we determined thatV. cf.limnophilus consumed CPOM, we performed an experiment to compare consumption and growth rates of larvae fed on non-autoclaved and autoclaved decaying leaves. Algae was the most abundant group to colonize leaf surface, comprising 74% of total biovolume. Consumption of non-autoclaved leaves was fourfold that of autoclaved treatments, which produced negative insect growth rates. AlthoughV. cf.limnophilus processed leaves by shredding, microorganisms living on the leaf litter were found to be an important food resource. As microbial biomass represents a small percentage of the ingested food (0.22%),V. cflimnophilus appears to process relatively large quantities of detritus to obtain sufficient resources for growth (100 mg leaves to grow 3 mg).

Non-native Fish Occurrence and Biomass in 1943 Western Palearctic Lakes and Reservoirs and their Abiotic and Biotic Correlates

Invasion of non-native species is considered a major threat to global biodiversity. Here we present a comprehensive overview of the occurrence, richness and biomass contribution of non-native fish species in 1943 standing water bodies from 14 countries of the Western Palearctic, based on standardised fish catches by multi-mesh gillnetting. We expected strong geographical gradients to emerge in the occurrence of non-natives. We further hypothesised that the contribution by non-natives to the local fish community biomass was correlated with local richness and the trophic level of native and non-native species. Non-native fish species occurred in 304 of 1943 water bodies (16%). If the average number of occupied water bodies per country was weighted by number of water bodies per country, the grand mean occurrence of non-natives in Western Palearctic water bodies was 10%. Exotic (non-native to the Palearctic) and translocated (non-native only to parts of the Palearctic) species were found in 164 (8.4%) or 235 (12.1%) of the water bodies, respectively. The occurrence and local richness of non-native fish species increased with temperature, precipitation and lake area and were substantially higher in reservoirs than in natural lakes. High local biomass contributions of non-native species were strongly correlated with low richness of native species and high richness of non-native species, whereas the trophic level of the fish species had only a weak effect. Single non-native species rarely dominated community biomass, but high biomass contributions and thus strong community and ecosystem impacts can be expected if several non-native species accumulate in a water body.