Long‐term changes in a zooplankton community revealed by the sediment archive

Abstract

To reconstruct changes in zooplankton communities in response to past anthropogenic perturbations, one possibility is to use the sedimentary records. We analyzed the sediments at a coastal site in the Northern Baltic Sea to relate changes in the zooplankton community to anthropogenic eutrophication and the invasion of a predatory cladoceran, Cercopagis pengoi. We sampled 30‐cm laminated sediment cores and dated the sediment layers back to the 1950s. From each 1‐cm layer, we measured eutrophication indicators (δ13C, δ15N, TC, TN, TP) and identified and counted zooplankton resting eggs (cladoceran, calanoid copepod, rotifer). In addition, we estimated the abundance of the cladoceran Bosmina (Eubosmina) maritima by counting subfossils (carapaces, headshields, and ephippia) and estimated the experienced stress as the relationship between sexual and asexual reproduction. Using redundancy and variance partitioning analyses, we found ∼ 16% of the variation in the zooplankton community to be explained by eutrophication, and 24% of the variation in B. (E.) maritima abundance and reproduction mode to be explained by eutrophication and the introduction of the alien predator. Our results show a long‐term shift from calanoid copepods and predatory cladocerans toward small‐sized zooplankton species, like rotifers. Furthermore, the results indicate that the invasion of C. pengoi induced a short‐term increase in sexual reproduction in B. (E.) maritima. The results indicate that anthropogenic eutrophication since the 1950s has altered the zooplankton community toward smaller species, while the invasion of the predatory cladoceran had only a transitory influence on the community during its expansion phase.

Functional shifts in estuarine zooplankton in response to climate variability

“…Also, the complexity of the organisms changed from more complex groups (Copepoda) to a community dominated by cladocerans and rotifers. Rotifers are known to increase in murky lakes (Leech, Pollard, Labou, & Hampton, 2018); they also respond to warming (Daufresne et al., 2009) and to eutrophication (Vehmaa, Katajisto, & Candolin, 2018). The Gulf of Riga is one of the most eutrophicated basins in the Baltic Sea (HELCOM, 2018), which is a likely reason for the strong increase in rotifers.…”

“…Vehmaa et al. (2018) demonstrated that food quantity (given as chlorophyll a and total organic carbon) increased following eutrophication, using sediment core analysis. However, food quality is also altered by eutrophication (O'Neil et al., 2012), as harmful algae blooms are known to increase in frequency, magnitude, and duration (Huisman et al., 2018), also in the Gulf of Riga as shown by Jurgensone, Carstensen, Ikauniece, and Kalveka (2011).…”

“…The Gulf of Riga is one of the most eutrophicated basins in the Baltic Sea (HELCOM, 2018), which is a likely reason for the strong increase in rotifers. Vehmaa et al (2018) showed that small-bodied cladoceran such as Bosmina (Eubosmina) coregoni also respond to eutrophication by increasing their abundance. Even though we could not include phytoplankton data in the current paper, numerous studies have shown how microalgal communities have changed during the past decades in the Baltic Sea.…”

Mechanisms behind bottom-up effects: eutrophication increases fecundity by shortening the interspawning interval in stickleback

“…In addition, a range of other perturbations have occurred in the area that could interact with eutrophication, such as climate change (particularly warming), the overfishing of top predators, and the invasion of alien species ( Casini et al, 2008 ; Meier et al, 2019 ; Ojaveer et al, 2010 ; Rutgersson et al, 2014 ). Yet, how these different disturbances influence biodiversity, directly and indirectly, and their individual and combined effects, are poorly known ( Meier et al, 2019 ; Vehmaa, Katajisto & Candolin, 2018 ). This is hampering our ability to evaluate and mitigate the effects of eutrophication on the ecosystem, calling for more research into the topic.…”

Peer Review #1 of "Mechanisms behind bottom-up effects: eutrophication increases fecundity by shortening the interspawning interval in stickleback (v0.1)"

“…In addition, a range of other perturbations have occurred in the area that could interact with eutrophication, such as climate change (particularly warming), the overfishing of top predators, and the invasion of alien species (Casini et al 2008;Meier et al 2019;Ojaveer et al 2010;Rutgersson et al 2014). Yet, how these different disturbances influence biodiversity, directly and indirectly, and their individual and combined effects, are poorly known (Meier et al 2019;Vehmaa et al 2018). This is hampering our ability to evaluate and mitigate the effects of eutrophication on the ecosystem, calling for more research into the topic.…”