Consequences and Correctives Related to Lake Acidification, Liming and Mercury in Fish – A Case-Study for Lake Huljesjön, Sweden, Using the LakeWeb-model

This work exemplifies how a given lake (Lake Huljesjön, Sweden) would likely respond to changes in pH-values and to liming (a standard measure against anthropogenic acidification). The basic questions are: How would a liming influence pH? How long would the changes last? How would the changes influence the structure and function of lake ecosystems? The work uses a comprehensive lake ecosystem model, LakeWeb, which accounts for production, biomasses, predation, abiotic/biotic interactions of nine key functional groups of organisms, phytoplankton, bacterioplankton, two types of zooplankton (herbivorous and predatory), two types of fish (prey and predatory), zoobenthos, macrophytes and benthic algae. LakeWeb is a dynamic model and gives weekly variations. It has been critically tested using empirical data and regressions from many lakes. Those tests are not presented here but have shown that the model can capture typical functional and structural patterns in lakes very well. This gives credibility to the results presented in this work, which would be very costly to obtain in the traditional manner by extensive field studies in one or a few lakes. This work presents for the first time predictions at the ecosystem level of how functional groups of organisms (and not individual species) are likely to respond to acidification and liming. Two existing dynamic models, one for liming, the other for Hg-concentrations in fish, have been added to the LakeWeb-model. These two models have previously been tested and proven to yield good predictions. The results presented here indicate that there are several probable changes in the structure and function of the lake foodweb related to acidification and liming. The predicted changes in macrophyte cover will influence the predation pressure on fish, and thereby the fish biomass. Reductions in primary production at low pH-values will cause reductions in fish biomass. There are several interesting compensatory effects between factors that increase fish biomass and factors that tend to decrease the biomass. Such matters can be handled quantitatively by the LakeWeb-model.     

Variation in Assemblages of Small Fishes and Microcrustaceans After Inundation of Rarely Flooded Wetlands of the Lower Okavango Delta, Botswana

Water extraction from floodplain river systems may alter patterns of inundation of adjacent wetlands and lead to loss of aquatic biodiversity. Water reaching the Okavango Delta (Delta), Botswana, may decrease due to excessive water extraction and climate change. However, due to poor understanding of the link between inundation of wetlands and biological responses, it is difficult to assess the impacts of these future water developments on aquatic biota. Large floods from 2009 to 2011 inundated both rarely and frequently flooded wetlands in the Delta, creating an opportunity to examine the ecological significance of flooding of wetlands with widely differing hydrological characteristics. We studied the assemblages of small fishes and microcrustaceans, together with their trophic relationships, in temporary wetlands of the lower Delta. Densities of microcrustaceans in temporary wetlands were generally lower than previously recorded in these habitats. Microcrustacean density varied with wetland types and hydrological phase of inundation. High densities of microcrustaceans were recorded in the 2009 to 2010 flooding season after inundation of rarely flooded sites. Large numbers of small fishes were observed during this study. Community structure of small fishes differed significantly across the studied wetlands, with poeciliids predominant in frequently flooded wetlands and juvenile cichlids most abundant in rarely flooded wetlands (analysis of similarity, P < 0.05). Small fishes of <20 mm fed largely on microcrustaceans and may have led to low microcrustacean densities within the wetlands. This result matched our prediction that rarely flooded wetlands would be more productive; hence, they supported greater populations of microcrustaceans and cichlids, which are aggressive feeders. However, the predominance of microcrustaceans in the guts of small fishes (<20 mm) suggests that predation by fishes may also be an important regulatory mechanism of microcrustacean assemblages during large floods when inundated terrestrial patches of wetlands are highly accessible by fish. We predict that a decline in the amount of water reaching the Delta will negatively affect fish recruitment, particularly the cichlids that heavily exploited the rarely flooded wetlands. Cichlids are an important human food source, and their decline in fish catches will negatively affect livelihoods. Hence, priority in the management of the Delta’s ecological functioning should be centred on minimising natural water-flow modifications because any changes may be detrimental to fish-recruitment processes of the system.     

Pollen foraging: learning a complex motor skill by bumblebees (<Emphasis Type="Italic">Bombus terrestris</Emphasis>)

To investigate how bumblebees (Bombus terrestris) learn the complex motor skills involved in pollen foraging, we observed naïve workers foraging on arrays of nectarless poppy flowers (Papaver rhoeas) in a greenhouse. Foraging skills were quantified by measuring the pollen load collected during each foraging bout and relating this to the number of flowers visited and bout duration on two consecutive days. The pollen standing crop (PSC) in each flower decreased drastically from 0530 to 0900 hours. Therefore, we related foraging performance to the changing levels of pollen available (per flower) and found that collection rate increased over the course of four consecutive foraging bouts (comprising between 277 and 354 individual flower visits), suggesting that learning to forage for pollen represents a substantial time investment for individual foragers. The pollen collection rate and size of pollen loads collected at the start of day 2 were markedly lower than at the end of day 1, suggesting that components of pollen foraging behaviour could be subject to imperfect overnight retention. Our results suggest that learning the necessary motor skills to collect pollen effectively from morphologically simple flowers takes three times as many visits as learning how to handle the most morphologically complex flowers to extract nectar, potentially explaining why bees are more specialised in their choice of pollen flowers.     

Microscale genetic differentiation in a sessile invertebrate with cloned larvae: investigating the role of polyembryony

Microscale genetic differentiation of sessile organisms can arise from restricted dispersal of sexual propagules, leading to isolation by distance, or from localised cloning. Cyclostome bryozoans offer a possible combination of both: the localised transfer of spermatozoa between mates with limited dispersal of the resulting larvae, in association with the splitting of each sexually produced embryo into many clonal copies (polyembryony). We spatially sampled 157 colonies of Crisia denticulata from subtidal rock overhangs from one shore in Devon, England at a geographic scale of ca. 0.05 to 130 m plus a further 21 colonies from Pembrokeshire, Wales as an outgroup. Analysis of molecular variance (AMOVA) revealed that the majority (67%) of genetic variation was distributed among individuals within single rock overhangs, with only 16% of variation among different overhangs within each shore and 17% of variation between the ingroup and outgroup shores. Despite local genetic variation, pairwise genetic similarity analysed by spatial autocorrelation was greatest at the smallest inter-individual distance we tested (5 cm) and remained significant and positive across generally within-overhang comparisons (<4 m). Spatial autocorrelation and AMOVA analyses both indicated that patches of C. denticulata located on different rock overhangs tended to be genetically distinct, with the switch from positive to negative autocorrelation, which is often considered to be the distance within which individuals reproduce with their close relatives or the radius of a patch, occurring at the 4–8 m distance class. Rerunning analyses with twenty data sets that only included one individual of each multilocus genotype (n = 97) or the single data set that contained just the unique genotypes (n = 67) revealed that the presence of repeat genotypes had an impact on genetic structuring (PhiPT values were reduced when shared genotypes were removed from the dataset) but that it was not great and only statistically evident at distances between individuals of 1–2 m. Comparisons to a further 20 randomisations of the data set that were performed irrespective of genotype (n = 97) suggested that this conclusion is not an artefact of reduced sample size. A resampling procedure using kinship coefficients, implemented by the software package GENCLONE gave broadly similar results but the greater statistical power allowed small but significant impacts of repeat genotypes on genetic structure to be also detected at 0.125–0.5 and 4–16 m. Although we predict that a proportion of the repeat multilocus genotypes are shared by chance, such generally within-overhang distances may represent a common distance of cloned larval dispersal. These results suggests that closely situated potential mates include a significant proportion of the available genetic diversity within a population, making it unlikely that, as previously hypothesised, the potential disadvantage of producing clonal broods through polyembryony is offset by genetic uniformity within the mating neighbourhood. We also report an error in the published primer note of Craig et al. (Mol Ecol Notes 1:281–282, 2001): loci Cd5 and Cd6 appear to be the same microsatellite. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Potassium, phosphorus, or nitrogen limit root allocation, tree growth, or litter production in a lowland tropical forest

We maintained a factorial nitrogen (N), phosphorus (P), and potassium (K) addition experiment for 11 years in a humid lowland forest growing on a relatively fertile soil in Panama to evaluate potential nutrient limitation of tree growth rates, fine-litter production, and fine-root biomass. We replicated the eight factorial treatments four times using 32 plots of 40 x 40 m each. The addition of K was associated with significant decreases in stand-level fine-root biomass and, in a companion study of seedlings, decreases in allocation to roots and increases in height growth rates. The addition of K and N together was associated with significant increases in growth rates of saplings and poles (1-10 cm in diameter at breast height) and a further marginally significant decrease in stand-level fine-root biomass. The addition of P was associated with a marginally significant (P = 0.058) increase in fine-litter production that was consistent across all litter fractions. Our experiment provides evidence that N, P, and K all limit forest plants growing on a relatively fertile soil in the lowland tropics, with the strongest evidence for limitation by K among seedlings, saplings, and poles.     

Landscape Development During a Glacial Cycle: Modeling Ecosystems from the Past into the Future

Understanding how long-term abiotic and biotic processes are linked at a landscape level is of major interest for analyzing future impact on humans and the environment from present-day societal planning. This article uses results derived from multidisciplinary work at a coastal site in Sweden, with the aim of describing future landscape development. First, based on current and historical data, we identified climate change, shoreline displacement, and accumulation/erosion processes as the main drivers of landscape development. Second, site-specific information was combined with data from the Scandinavian region to build models that describe how the identified processes may affect the site development through time. Finally, the process models were combined to describe a whole interglacial period. With this article, we show how the landscape and ecosystem boundaries are affected by changing permafrost conditions, peat formation, sedimentation, human land use, and shoreline displacement.     

Importance of natural sedimentation in the fate of microcystins

Sedimentation processes of microcystins (MCs), cyanobacterial toxins, were studied in three reservoirs located in Central Spain in which the cyanobacterial community was dominated by the genus Microcystis. MCs were detected in the sediment traps deployed in all reservoirs. In Santillana reservoir, MCs were identified in sediment traps even though they could not be found in the pelagial samples. In the other reservoirs studied, sedimentation rates for MC-containing particles during the bloom period ranged from 0.43 to 2.53 mg m⁻² d⁻¹. Interestingly, this very high sedimentation of toxic biomass is not exclusively related to decaying blooms or autumnal sedimentation due to a drop in water temperature. Instead, it seems that MC-containing colonies may be settling constantly during the bloom period and we were able to estimate that during such a Microcystis dominated bloom, around 4.5% of pelagial MCs may be involved in sedimentation. Further, these settling colonies seem to maintain good cell integrity and MCs seem not to be excreted massively. A certain loss of toxin content along the vertical settling may be attributed to minor losses due to cell lysis or to variations in MC cell quota explained by reduced production or internal consumption. Our results for the first time establish specific settling rates for MC-containing particles in freshwaters and definitely identify sedimentation as a major destination for these toxins. These data may contribute to improve managing strategies concerning risks associated with MCs.