Percorrer por autor "Amsinck, Susanne L."
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- Rapid ecological shift following piscivorous fish introduction to increasingly eutrophic and warmer Lake Furnas (Azores Archipelago, Portugal): a paleoecological approachPublication . Buchaca, Teresa; Skov, Tue; Amsinck, Susanne L.; Gonçalves, Vitor; Azevedo, José M. N.; Andersen, Thorbjørn J.; Jeppesen, ErikLake ecosystems are nowadays often subjected to multi-stressors, such as eutrophication, climate change, and fish manipulations, the effects of which can be difficult to disentangle, not least from the usual short-term limnological time-series that are available. However, multi-proxy paleoecological approaches may offer such opportunities, especially in the study of remote island lakes characterized by being species poor and buffered somewhat against the recent climate change. We used a paleoecological multi-proxy approach to determine the relative importance of nutrient loading, meteorological forcing, and fish species introduction for recent lake ecosystem development in Lake Furnas on the island of São Miguel, the Azores. The lake was stocked with cyprinids in the late nineteenth century and recently also with piscivorous fish, and has been affected by increasing agricultural activities in its catchment. We analyzed marker pigments, cladoceran remains, and subfossil diatoms in a 46-cm core representing the last 40 years. Remains of large-bodied cladocerans were virtually absent until the introductions of piscivorous pike and pikeperch in 1980 and 1982, respectively, after which the zooplankton community composition changed abruptly. First Ceriodaphnia sp. appeared (ca. 1980), followed by Daphnia a few years later. Carotenoids from cyanobacteria (myxoxanthophyll, aphanizophyll) were regularly present in the lake sediment with a major shift occurring around 1994, from N2-fixing to non-fixing groups. This shift coincided with the onset of anoxia in the lake water, evidenced by the presence of pigments from Chlorobiaceae (BChl-e homologues and isorenieratene), and with a rapid decrease in benthic-tychoplanktonic diatoms and an increase in cyanobacteria, chlorophytes, dinoflagellates, and cryptophytes. The composition of microbial and algal assemblages changed rapidly after Daphnia appearance, and the covariance between fish stocking, nutrient loading, and enhanced temperatures captured most of the variability in algae accumulation, and thus likely in lake primary production as well. Thus, lake production apparently did not respond strongly to specific changes in temperature, food-web structure, or nutrient input, but rather to the combined effects of all the three forcing mechanisms, emphasizing the role of multi-stressors in lake ecosystem functioning. Our study demonstrates the sensitivity of these remote species-poor lakes to increased nutrient loading, introduction of non-native species, such as fish and climate change.
- Using invertebrate remains and pigments in the sediment to infer changes in trophic structure after fish introduction in Lake Fogo: a crater lake in the AzoresPublication . Skov, Tue; Buchaca, Teresa; Amsinck, Susanne L.; Landkildehus, Frank; Odgaard, Bent Vad; Azevedo, José M. N.; Gonçalves, Vitor; Raposeiro, Pedro M.; Andersen, Thorbjørn J.; Jeppesen, ErikFish introduction may have marked effects on the trophic dynamics and ecological state of former fishless lakes, but due to scarcity of historical data this can seldom be documented. We used remains of cladoceran, chironomid and pigment assemblages in the sediment archive to unravel the effect of introduction of carp (Cyprinus carpio), rainbow trout (Oncorhynchus mykiss) and a cyprinid (Chondrostoma oligolepis) in Lake Fogo, the Azores (Portugal). The stratigraphical record showed two major shifts in community assemblage coinciding with the time of introduction of carp (AD ca. 1890) and trout (AD 1941), respectively. Carp introduction was followed by an abrupt and major decline in the abundance of chironomids, a shift in the cladoceran community from a benthic to a more pelagic dominated community, and Daphnia size was significantly reduced. Pigment assemblages also indicated a shift from a benthic to a pelagic dominated ecosystem, as cryptophytes became markedly more abundant at the expense of benthic diatoms. Trout introduction was followed by a return to a more benthic cladoceran and benthic algae (pigments) dominated state, which we attribute to trout predation on carp leading to improved water clarity. A steady increase in the abundance of pigments and cladoceran remains followed, suggesting enhanced productivity, which may be attributed to enhanced atmospheric nitrogen deposition and introduction of C. oligolepis. We conclude that fish introduction has profoundly altered the trophic dynamics and the relative importance of benthic and pelagic production in this species poor and natural fishless lake in the Azores, and likely in most others lakes at the archipelago islands as fish stocking has been a widespread practice.