Effects of zebra mussels on cladoceran communities under eutrophic conditions

The purpose of this study was to determine how zebra mussels affected cladoceran community structure under eutrophic conditions. We conducted a mesocosm study where we manipulated the presence of zebra mussels and the presence of large-bodied Daphnia (Daphnia magna and Daphnia pulicaria). We also conducted a complimentary life-table experiment to determine how water from the zebra mussel treatment affected the life history characteristics of the cladoceran species. We anticipated that small- and large-bodied cladoceran species would respond differently to changes in algal quality and quantity under the effects of zebra mussels. Large-bodied Daphnia successfully established in the zebra mussel treatment but failed to grow in the control. We did not observe positive relationships between food concentrations and cladoceran abundances. However, the phosphorus content in the seston indicated that food quality was below the threshold level for large-bodied cladocerans at the beginning of the experiment. We believe that zebra mussels quickly enhanced the phosphorus content in the seston due to the excretion of inorganic phosphorus, thus facilitating the development of large-bodied Daphnia. In conclusion, our results suggest that zebra mussels can alter the phosphorus content of seston in lakes and this can affect the dynamics of crustacean zooplankton

Factors of dynamics of plankton crustacean communities under eutrophic conditions.

Текст статьи не публикуется в открытом доступе в соответствии с политикой журнала.Показано, что основным драйвером динамики обилия ветвистоусых и веслоногих ракообразных в эвтрофных условиях являются хищничество (рыбы), количество или качество пищи, выражаемое в содержании эйкозапентаеновой кислоты, фосфора и азота в сестоне. В результате исследований по динамике обилия веслоногих и ветвистоусых ракообразных в присутствии и отсутствии рыбы в экспериментальных мезокосмах с эвтрофными условиями установлено, что рыбы в эвтрофных условиях не влияют на количество и качество пищевых ресурсов для ракообразных. Однако во второй половине наших экспериментов наблюдался переход доминирования от веслоногих к ветвистоусым ракообразным. Это было связано не с влиянием рыбы, а с улучшением качества пищи для ветвистоусых ракообразных, определяемое соотношением углерода к фосфору в сестоне. Рыбы в эвтрофных условиях понижали биомассу как ветвистоусых, так и веслоногих ракообразных, не меняя соотношение между ними

Transfer efficiency of carbon, nutrients, and polyunsaturated fatty acids in planktonic food webs under different environmental conditions

Abstract The trophic transfer efficiency (TTE) is an important indicator of ecosystem functioning. However, TTE data from freshwater food webs are ambiguous due to differences in time scales and methods. We investigated the transfer of essential substances (carbon, nutrients, and polyunsaturated fatty acids) through plankton communities in 30 Polish lakes with different trophic status in the middle of summer. The results of our study revealed that different essential substances were transferred from phytoplankton to zooplankton with varying efficiencies. The average TTE of C, N, P, and the sum of ω‐3 PUFA were 6.55%, 9.82%, 15.82%, and 20.90%, respectively. Our results also show a large mismatch between the elemental and biochemical compositions of zooplankton and their food during the peak of the summer stagnation, which may further promote the accumulation of essential substances. There were also large differences in TTEs between trophic conditions, with the highest efficiencies in oligotrophic lakes and the lowest in dystrophic and eutrophic lakes. Therefore, our study indicates that disturbances like eutrophication and dystrophication similarly decrease the TTE of essential substances between phytoplankton and zooplankton in freshwater food webs

Direct and indirect impacts of fish on crustacean zooplankton in experimental mesocosms

Understanding the factors that regulate phytoplankton and zooplankton is an important goal of aquatic ecologists; however, much remains unknown because of complex interactions between phytoplankton, zooplankton, and fish. Zooplankton, in particular cladocerans, can be regulated by bottom–up factors either via food quantity or food quality in terms of polyunsaturated fatty acids (PUFA) or phosphorus (P) contents in phytoplankton. Fish can recycle nutrients and in turn change the PUFA and P contents of algal resources, thus modifying bottom–up regulation. Furthermore, fish can change phytoplankton structure through consumption of cladocerans which selectively graze phytoplankton. We conducted a mesocosm (300 L) experiment to determine how trophic state and fish affected crustacean dynamics. The mesocosms were filled with water containing natural plankton from the eutrophic Lake Jorzec and mesotrophic Lake Majcz (Northeastern Poland), and we manipulated fish presence/absence. We also conducted a complementary life-table experiment to determine how trophic state and fish nonconsumptively affected demographic parameters of the dominant cladocerans in the mesocosms. Small and large cladoceran species responded differently to food quantity and quality. Small-bodied Ceriodaphnia were regulated mainly by resource concentrations (i.e., food quantity), while large species were limited by PUFAs (i.e., food quality). Fish likely increased food quality in terms of PUFA, primarily eicosapentaenoic acids (EPA), thus providing conditions for more successful development of Daphnia than in the fish-free treatments. Phosphorus in the seston was likely limiting for zooplankton. However, food quality in terms of phosphorus was likely less important than PUFA because zooplankton can accumulate nutrients in their body

The stoichiometric ratios (C:N:P) in a pelagic food web under experimental conditions

Interactions between phytoplankton and zooplankton affect the overall functioning of lakes. Herbivores are habitually confronted with food of inferior quality, usually a result of low nutrient concentrations in plant material. Large-bodied cladocerans are better competitors for food than small-bodied species but they are more vulnerable to low food quality. Understanding the effects of food quality on zooplankton structure and competition between small – large bodied herbivorous is of considerable interest. We want to find out how differences in C:N:P ratios between phytoplankton and zooplankton communities affect their abundances in a freshwater food web. We want also to assess the role of phytoplankton and zooplankton as sinks of the phosphorus and nitrogen. Therefore, we conducted a 31-day mesocosms experiment with water from a mesotrophic and a eutrophic lake (with natural plankton communities). To simulate changes in the plankton communities large-bodied Daphnia magna and Daphnia pulicaria were added. Samples for zooplankton, phytoplankton and water chemistry were taken every 10 days. Samples for elemental analysis (C:N:P) of seston and zooplankton were collected on the first, and on the final day of the experiment. Our mesocosms experiment showed mismatch in C:P between seston (high) and zooplankton (low), which suggests that most of the phosphorus is incorporated in zooplankton biomass. This evidenced that zooplankton is an effective sink of phosphorus, while nitrogen is accumulated mainly by primary producers. Our results also indicated more stability in stoichiometry with increasing trophic levels of organisms. However, there were significant changes in the zooplankton structure. The increasing dominance of large Daphnia resulted in reduction of C:P ratio in zooplankton. Low food quality (C:P) did not limit the growth of large Daphnia in the experimental conditions, which competed effectively with small planktonic cladocerans and with Rotifera. Over time, inedible algae began to dominate resulting in increase of relative biomass of periphyton grazers, which suggests that plankton community is transformed into littoral system in mesocosms for about 30 days

Direct and Indirect Impacts of Fish on Crustacean Zooplankton in Experimental Mesocosms

Understanding the factors that regulate phytoplankton and zooplankton is an important goal of aquatic ecologists; however, much remains unknown because of complex interactions between phytoplankton, zooplankton, and fish. Zooplankton, in particular cladocerans, can be regulated by bottom–up factors either via food quantity or food quality in terms of polyunsaturated fatty acids (PUFA) or phosphorus (P) contents in phytoplankton. Fish can recycle nutrients and in turn change the PUFA and P contents of algal resources, thus modifying bottom–up regulation. Furthermore, fish can change phytoplankton structure through consumption of cladocerans which selectively graze phytoplankton. We conducted a mesocosm (300 L) experiment to determine how trophic state and fish affected crustacean dynamics. The mesocosms were filled with water containing natural plankton from the eutrophic Lake Jorzec and mesotrophic Lake Majcz (Northeastern Poland), and we manipulated fish presence/absence. We also conducted a complementary life-table experiment to determine how trophic state and fish nonconsumptively affected demographic parameters of the dominant cladocerans in the mesocosms. Small and large cladoceran species responded differently to food quantity and quality. Small-bodied Ceriodaphnia were regulated mainly by resource concentrations (i.e., food quantity), while large species were limited by PUFAs (i.e., food quality). Fish likely increased food quality in terms of PUFA, primarily eicosapentaenoic acids (EPA), thus providing conditions for more successful development of Daphnia than in the fish-free treatments. Phosphorus in the seston was likely limiting for zooplankton. However, food quality in terms of phosphorus was likely less important than PUFA because zooplankton can accumulate nutrients in their body