We conducted a survey of 50 thermally stratified lakes with similar nutrient concentrations and morphometries in Michigan to examine the direct and indirect effects of dreissenid mussels on the ...biomass and community composition of microzooplankton and macrozooplankton. Twenty-five lakes were infested with dreissenid mussels (invaded), while 25 lakes were dreissenid free (uninvaded). In invaded lakes, phytoplankton biomass was 24% lower, and water clarity was 21% greater. Total microzooplankton biomass was 44% lower, with ciliate and rotifer biomass 39% and 45% lower, respectively, in invaded lakes. Total macrozooplankton biomass was 33% lower, largely driven by a 40% lower biomass of Daphnia spp. in invaded lakes. In contrast, dreissenid status had no significant influence on total copepod biomass, calanoid biomass, or cyclopoid biomass. Our microzooplankton results are similar to those of previous studies conducted in shallow, well-mixed systems, although the magnitude of the dreissenid influence in our study was smaller, as might be expected in thermally stratified systems. On the other hand, ours is the first study to document lower biomass of Daphnia spp. and reduced rotifer diversity in invaded lakes. In contrast, we found no difference in macrozooplankton community structure. Dreissenids likely affected zooplankton directly through predation (microzooplankton) and indirectly through resource competition (micro-and macrozooplankton). Understanding how dreissenid mussels affect both microand macrozooplankton will help us to identify the potential mechanisms by which higher trophic levels (e.g., fish) are influenced by these invaders.
Animals can be important in nutrient cycling in particular ecosystems, but few studies have examined how this importance varies along environmental gradients. In this study we quantified the nutrient ...cycling role of an abundant detritivorous fish species, the gizzard shad (Dorosoma cepedianum), in reservoir ecosystems along a gradient of ecosystem productivity. Gizzard shad feed mostly on sediment detritus and excrete sediment-derived nutrients into the water column, thereby mediating a cross-habitat translocation of nutrients to phytoplankton. We quantified nitrogen and phosphorus cycling (excretion) rates of gizzard shad, as well as nutrient demand by phytoplankton, in seven lakes over a four-year period (16 lake-years). The lakes span a gradient of watershed land use (the relative amounts of land used for agriculture vs. forest) and productivity. As the watersheds of these lakes became increasingly dominated by agricultural land, primary production rates, lake trophic state indicators (total phosphorus and chlorophyll concentrations), and nutrient flux through gizzard shad populations all increased. Nutrient cycling by gizzard shad supported a substantial proportion of primary production in these ecosystems, and this proportion increased as watershed agriculture (and ecosystem productivity) increased. In the four productive lakes with agricultural watersheds (>78% agricultural land), gizzard shad supported on average 51% of phytoplankton primary production (range 27-67%). In contrast, in the three relatively unproductive lakes in forested or mixed-land-use watersheds (>47% forest, <52% agricultural land), gizzard shad supported 18% of primary production (range 14-23%). Thus, along a gradient of forested to agricultural landscapes, both watershed nutrient inputs and nutrient translocation by gizzard shad increase, but our data indicate that the importance of nutrient translocation by gizzard shad increases more rapidly. Our results therefore support the hypothesis that watersheds and gizzard shad jointly regulate primary production in reservoir ecosystems.
We investigated how watershed land use (a gradient of agricultural vs. forested land) relates to phytoplankton primary production (PPr) and photosynthetic parameters in 12 reservoirs in Ohio and ...examined spatial variation in these parameters. Shallow sites near stream inflows had higher light attenuation, total phosphorus (TP), chlorophyll, nonvolatile suspended solids (NVSS), light-saturated photosynthesis (PmB), and volumetric PPr than deeper sites near dam outflows, but areal PPr and the initial slope of the photosynthesis-irradiance curve (αB) were not significantly different between sites. Mean mixed layer irradiance and the severity of light limitation did not differ between sites because shallower depths compensated for higher light attenuation at inflow sites. Watershed land use (percent agriculture) was only weakly (but significantly) related to mean annual PPr, TP, and chlorophyll, but there was a well-defined upper limit to the effect of land use on all three of these parameters. Multiple regression showed that inclusion of additional watershed factors (the ratio of watershed land area to reservoir volume and the ratio of cropland area to number of livestock) greatly increased the variance explained compared to land use alone. TP and chlorophyll were highly correlated with each other and with PPr. Comparison of our TP-chlorophyll, TP-PPr, and chlorophyll-PPr regressions with those of other studies suggests that reservoirs have lower PPr per unit TP than natural lakes, probably because of lower light intensity and higher concentrations of nonalgal P in reservoirs.
We investigated whether concentrations of the cyanobacterial toxin microcystin were positively associated with Dreissena polymorpha invasion by conducting surveys of 39 inland lakes in southern ...Michigan with low to moderate total phosphorus concentrations (≤20 µg·L
-1
). Lakes with D. polymorpha had 3.3 times higher microcystin concentrations and 3.6 times higher biomass of Microcystis aeruginosa (a major producer of microcystin) than comparable lakes without D. polymorpha. In contrast, the biomass of Anabaena spp. (another potential producer of microcystin) was 4.6 times higher in lakes without D. polymorpha. We also conducted a large-scale enclosure manipulation of D. polymorpha density in Gull Lake, a low-nutrient lake containing D. polymorpha. The experiment revealed a positive effect of D. polymorpha on microcystin concentrations and M. aeruginosa biomass. The congruence between survey and experimental results provides strong evidence that D. polymorpha invasion causes an increase in toxin concentrations in lakes with low to moderate nutrients. An increase in M. aeruginosa biomass may negatively impact food webs and public health because microcystins are known to be toxic to aquatic and terrestrial organisms.
We asked if intraspecific variation within a population of the toxic, bloom-forming phytoplankter, Microcystis aeruginosa, leads to differential vulnerability to grazing by the invasive, ...filter-feeding zebra mussel (Dreissena polymorpha). We performed two series of laboratory feeding experiments in which D. polymorpha were presented with several different sympatric M. aeruginosa clones in a two-species mixture with the high-quality, nutritious alga, Ankistrodesmus falcatus. Mean selectivity across M. aeruginosa clones ranged from near zero (i.e., no feeding on M. aeruginosa) to near one (equal feeding on the two algal species), evidence of maximal variation in grazing vulnerability across twenty clones of M. aeruginosa—a species assumed to be largely ‘inedible’ to grazers—from the same population. This range of vulnerability is essentially equal to that typically measured across all phytoplankton species. Large intraspecific variation in grazing vulnerability, and its ecological consequences, could influence the promotion or control of noxious blooms of toxigenic cyanobacteria.
Blooms also like it cold Reinl, Kaitlin L.; Harris, Ted D.; North, Rebecca L. ...
Limnology and oceanography letters,
August 2023, Letnik:
8, Številka:
4
Journal Article
Recenzirano
Odprti dostop
Cyanobacterial blooms have substantial direct and indirect negative impacts on freshwater ecosystems including releasing toxins, blocking light needed by other organisms, and depleting oxygen. There ...is growing concern over the potential for climate change to promote cyanobacterial blooms, as the positive effects of increasing lake surface temperature on cyanobacterial growth are well documented in the literature; however, there is increasing evidence that cyanobacterial blooms are also being initiated and persisting in relatively cold‐water temperatures (< 15°C), including ice‐covered conditions. In this work, we provide evidence of freshwater cold‐water cyanobacterial blooms, review abiotic drivers and physiological adaptations leading to these blooms, offer a typology of these lesser‐studied cold‐water cyanobacterial blooms, and discuss their occurrence under changing climate conditions.
We report a reversal in the sign of the herbivore-phytoplankton interaction between the zebra mussel (Dreissena polymorpha) and Microcystis aeruginosa, a harmful planktonic cyanobacterium. A pair of ...large-scale manipulations of mussel density in the same lake in consecutive years showed that when phosphorus concentrations were very low (mean total phosphorus TP ∼ 3 μg L-1), the effect of Dreissena on the biomass of M. aeruginosa was monotonically negative across the full range of sustainable mussel densities. When the enclosures were fertilized with phosphorus (mean TP ∼ 9 μg L-1), there was a monotonically positive effect of Dreissena on M. aeruginosa across the same mussel gradient. These contrasting results indicate that D. polymorpha feeds on M. aeruginosa, as shown in previous laboratory feeding experiments, but that the positive effects of D. polymorpha on M. aeruginosa can be larger than the negative effects of consumption. A sign reversal in the interaction between these two species is congruent with highly variable patterns in the response of M. aeruginosa to D. polymorpha invasion across lake and river systems in North America.
Abstract
In recent decades, lakes have experienced unprecedented ice loss with widespread ramifications for winter ecological processes. The rapid loss of ice, resurgence of winter biology, and ...proliferation of remote sensing technologies, presents a unique opportunity to integrate disciplines to further understand the broad spatial and temporal patterns in ice loss and its consequences. Here, we summarize ice phenology records for 78 lakes in 12 countries across North America, Europe, and Asia to permit the inclusion and harmonization of
in situ
ice phenology observations in future interdisciplinary studies. These ice records represent some of the longest climate observations directly collected by people. We highlight the importance of applying the same definition of ice-on and ice-off within a lake across the time-series, regardless of how the ice is observed, to broaden our understanding of ice loss across vast spatial and temporal scales.
Summary
1. Elevated allochthonous inputs of nutrients and sediments to aquatic ecosystems are associated with eutrophication and sedimentation. Reservoirs receive substantial subsidies of nutrients ...and sediments from catchments due to their large catchment : lake area ratios. We examined the effect of elevated subsidies of sediments and/or dissolved nutrients on the success (survival, growth, biomass and condition factor) of larval gizzard shad (Dorosoma cepedianum), a widespread and dominant omnivorous fish in reservoir ecosystems.
2. We simulated allochthonous agricultural subsides by manipulating dissolved nutrients and sediment inputs in a 2 × 2 factorial design in experimental mesocosms. We predicted that larval fish success would be greater under elevated nutrients. However, we propose two alternative hypotheses with respect to the overall effect of allochthonous sediment inputs. If sediment inputs negatively affect larval gizzard feeding success, larval success would be highest when only nutrients are added and lowest when only sediments are added (+N > +N+S ≥ C > +S). If high turbidity enhances larval foraging activity (due to greater contrast between prey and background), we predict that larval success would be highest when both subsidy types (nutrients and sediment) are elevated, intermediate when either nutrients or sediments are added and the lowest when no subsidies are added (+N+S > +N ≥ +S > C).
3. Our results indicate that elevated nutrient and sediment conditions enhanced larval gizzard shad biomass, but the overall nutrient addition effect was greater than the sediment addition effect (+N ∼ +N+S > +S > C). We observed differential effects of nutrient and sediment inputs on larval survival, growth and condition factors.
4. The enhancement of fish biomass in elevated nutrients (+N, +N+S) relative to control conditions was associated with improved gizzard shad survival and not greater growth. The enhancement of fish biomass in the elevated sediment treatment (+S) relative to the control conditions was caused by an increase in survival that more than compensated for a negative effect of sediment addition on growth.
5. Our findings support the recommendation that reservoir management practices must consider the links between land use practices and food web dynamics. Our results suggest that reduction of subsidies of nutrients and sediments to productive reservoirs would decrease survival of larval gizzard shad due to lower food availability.
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