Anne-Mette Hansen's research while affiliated with University of Southern Denmark and other places

Publications (12)

Article
1. The seasonal cycle of cyclopoid copepods during and following an approximately 50% reduction in planktivorous fish biomass was studied in shallow, eutrophic Lake Vaeng, Denmark, from 1986 to 1990. 2. The dominant cyclopoid copepods changed from Cyclops vicinus and Mesacyclops leuckarti during 1986–1989 to M. leuckarti and Megacyclops viridis in...
Article
Cyclops vicinus is reported to enter summer diapause triggered by day length in order to survive food scarcity and fish predation. Development ceases and the fourth or fifth copepodid stages persist in the sediment for several weeks. In Lake Søbygård, however, a small eutrophic lake in Denmark, C. vicinus is found in the sediment as well as in the...
Article
Cyclops vicinus is the only copepod species in the pelagic zone of Lake Søbygård and can be found there all year round. We studied the population dynamics of this copepod over a one-year period. In contrast to earlier studies we included the copepods in the pelagic zone as well as the copepods resting in the sediment. Cyclops vicinus was found not...
Article
1. The relative importance of zooplankton grazing and nutrient limitation in regulating the phytoplankton community in the non-stratified Lake Kvie, Denmark, were measured nine times during the growing season. 2. Natural phytoplankton assemblage bioassays showed increasing importance of nutrient limitation during summer. Growth rates at ambient nut...
Article
1. The role of seasonal phenology in the emergence of zooplankton from diapause in patterns of seasonal abundance in the water column was investigated in Oneida Lake, New York. Replicate emergence traps, placed in contact with the lake sediments at two locations (one at a shallow site and one at a deep site), were monitored between May and August....
Article
The impact of a cyclopoid copepod population on the protozoa community (two ciliate categories and Cryptomonas ) was assessed weekly during the spring cohort of Cyclops vicinus (one month duration) in hypereutrophic Lake Søbygård by in situ gradient experiments with manipulation of ambient zooplankton abundance. As C.vicinus always made up >92% of...
Article
The effects of major reductions in organic matter, total phosphorus (TP), and total nitrogen (TN) loading on the chemical environment, trophic structure, and dynamics of the hypertrophic, shallow Lake Søbygård were followed for 18 years. After the reduction in organic matter loading in 1976, the lake initially shifted from a summer clear-water stat...
Article
We studied the effects of food limitation on the population dynamics of the freshwater cyclopoid copepod Diacyclops thomasi in Oneida Lake, New York. In the field population, maximum juvenile abundance coincided seasonally with high phytoflagellate concentration. During the clear-water phase (a seasonal period of low algal density), D. thomasi disa...
Article
Populations of the copepod Cyclops vicinus in two Danish lakes differed in their life cycles. In Lake Vng C. vicinus was absent during summer, whereas in Lake Sbygrd it continued producing distinct cohorts throughout summer. A comparison between the lakes showed that in the lake where C. vicinus was absent during summer, food limitation generally e...
Article
Laboratory experiments were conducted to determine whether the two cyclopoid copepods, Cyclops vicinus and Mesocyclops leuckarti, exploit the same food resources. The food requirements of juveniles of the two cyclopoid copepods were investigated. Moreover, the importance of algae for the predaceous adults was studied. Nauplii of both M.leuckarti an...
Article
The seasonal cycle of Cyclops vicinus was studied during a 5 year period in the shallow and hypertrophic Lake Søbygård. The annual number of generations varied between three and six and sometimes included midsummer generations. Naupliar and copepodite density was extremely high, the maximum recorded being 1313 and 745 1−1 respectively. The seasonal...

Citations

... Macrophytes provide refugia and food for zooplankton and promote species richness for microcrustaceans and rotifers (Lougheed & Chow-Fraser, 2001;Bagella et al., 2010;Xue et al., 2014). The loss of macrophyte cover is typically followed by a shift towards rotifers and small-bodied zooplankton (Hansen & Jeppesen, 1992;Hanson & Butler, 1994) and the release of phytoplankton from top-down control (Schriver et al., 1995). ...
... The most common species were the rotifer, such as Polyartha vulgaris, Kelicotia longispina and Keratella hienalis, characterized by a short, complex life cycle. Populations develop via parthenogenesis during favorable conditions; and then by sexual reproduction with restingegg production occurring during later, unfavorable conditions in late summer and autumn (Hairston et al. 2000). For the copepods, such as Cyclops scutifer and Bosmina longispina, the development may take from less than 1 week to as long as 1 year, and the life span of a copepod ranging from 6 months to 3 years (Elgmork 1981(Elgmork , 2004. ...
... Cyclopoid copepods have three foraging patternspredation, scraping and omnivory (Song and Zhang 1979), and smaller cyclopoids tend to be plankton feeders. Food threshold concentrations also differ and are generally higher for advanced stages of cyclopoids than for calanoids (Santer 1994;Hansen and Santer 1995). Besides the impact of changes in fish predation (Jeppesen et al. 2000), a dominance of calanoids in oligotrophic water has been attributed to reduced predation pressure from cyclopoids, which are affected by high cyclopoid nauplii mortality due to low algal densities (Santer 1994;Anneville et al. 2007). ...
... Positive effects sizes and negative effects sizes are represented in red and black, respectively. these two littoral habitats still belong to the low nutrient category (Supplementary Table 1), and we did not find any sign of regime shift from clear to turbid water caused by nutrient released to water columns (Jeppesen et al., 1998), Hence, even though the biomass of phytoplankton did increase, t Cladophora in NH probably quickly incorporates most additional nutrients near shoreline development. The unnatural Cladophora blooms in this clear lake can be explained by the availability of nutrients and substrata. ...
... Rotifers, in contrast to larger microcrustaceans, graze on a narrow size window of phytoplankton, leaving them more sensitive to changes in the phytoplankton community (Padial et al. 2012). The lowest level of congruence was generally found for copepods, which is to be expected, as several of the cyclopoid species present in Danish lakes are predators or facultative predators in their advanced stages (Hansen and Jeppesen 1992). These findings are also consistent with previous studies showing weakening congruence in richness of organisms with increasing difference in body sizes in both terrestrial (Sandom et al. 2013) and aquatic (Velghe and Gregory-Eaves 2013) ecosystems. ...
... The development of algal blooms is expected to be a spatially heterogeneous phenomenon Butitta, Carpenter, Loken, Pace, & Stanley, 2017;Pace et al., 2017;Serizawa, Amemiya, & Itoh, 2008) due to both local heterogeneity in nutrient limitation, zooplankton grazing, and temperature (Davis, Berry, Boyer, & Gobler, 2009;Hansen, Andersen, & Jensen, 1997) and population scale heterogeneity due to wind (George & Heaney, 1978). Algal blooms can have a negative effect on ecosystem services, and therefore are often a target for ecosystem monitoring and management. ...
... Winter diapausing is considered to be a common strategy to overcome periods of limited food resources, as well as low temperature and oxygen conditions in Northern European lakes (Elgmork 1980, Elgmork et al. 1990Naess et al. 1993). On the other hand, summer diapause in cyclopoids is seen as a long-term decline in metabolic processes providing encysted or passive dormant stages with the capability to survive in cold and oxygen-depleted deep waters of thermally stratified lakes and avoid food resource limitation and fish predation (George 1973;Gliwicz and Rowan 1984;Wyngaard 1988;Santer and Lampert 1995;Hansen 1996;Santer and Boldt 1998;Kobari and Ban 1998;Santer and Hansen 2006;Alekseev et al. 2007). However, diapausing cyclopoids may suffer from predation by invertebrates, such as chaoborids, that migrate and survive in cold and anoxic deepwater zones. ...
... During hydroperiods, the temporary lakes are inhabited by organisms that developed adaptations allowing them to withstand dry phases, which usually involve dormant or diapause structures (Bruno et al. 2001;Bayly 2001;Wallace et al. 2005), such as the Environmental Research, (ISSN: 0719-3726), 7(3), 2019: 261-280 DOI: http://dx.doi.org/10.7770/safer-V0N0-art1656 263 production of resting eggs (Fryer 1996;Mura & Brecciaroli 2003;Alekseev & Ravera 2004;Schröder 2005), the burial of quiescence individuals in sediments (Hairston & Bohonak 1998;Santer & Hansen 2006), or coming from other lakes (Incagnone et al. 2015). ...
... Gilbert, 1963;Kuo-Cheng Shan, 1974;Pasternak & Arashkevich, 1999) and food limitation (e.g. Scharfenberg, 1910;D'Abramo, 1980;Hansen & Hairston, 1998;Drillet, Hansen & Kiørboe, 2011) as proximate cues. However, given the typically large vertical extent (amplitude) of the migration, it is inexpedient to view most marine SVMs as a behaviour to avoid harmful irradiance or temperature (see also Banse, 1964;Marshall & Orr, 1972). ...
... Metazooplankton, both small-sized crustaceans (Agasild et al. 2013) and large-bodied crustaceans (Kalinowska et al. 2015), can strongly affect the abundance, biomass, species composition and functional role of ciliates (Sanders and Wickham 1993;Wiackowski et al. 1994;Adrian and Schneider-Olt 1999;Hansen 2000;Li et al. 2017). The impact of small-bodied crustaceans and rotifers on ciliates is selective and leads to the shifts in species structure rather than a significant reduction in numbers (Wiąckowski 2000). ...