Trophodynamics and seasonal cycle of the copepod Pseudocalanus acuspes in the Central Baltic Sea (Bornholm Basin): evidence from lipid composition

Marine aggregates of biogenic origin, known as marine snow, are considered to play a major role in the ocean's particle flux and may represent a concentrated food source for zooplankton. However, observing the marine snow−zooplankton interaction in the field is difficult since conventional net sampling does not collect marine snow quantitatively and cannot resolve so-called thin layers in which this interaction occurs. Hence, field evidence for the importance of the marine snow−zooplankton link is scarce. Here we employed a Video Plankton Recorder (VPR) to quantify small-scale (metres) vertical distribution patterns of fragile marine snow aggregates and zooplankton in the Baltic Sea during late spring 2002. By using this non-invasive optical sampling technique we recorded a peak in copepod abundance (ca. 18 ind. l −1 ) associated with a pronounced thin layer (50 to 55 m) of marine snow (maximum abundance of 28 particles l −1 ), a feature rarely resolved. We provide indirect evidence of copepods feeding on marine snow by computing a spatial overlap index that indicated a strong positively correlated distribution pattern within the thin layer. Furthermore we recorded images of copepods attached to aggregates and demonstrating feeding behaviour, which also suggests a trophic interaction. Our observations highlight the potential significance of marine snow in marine ecosystems and its potential as a food resource for various trophic levels, from bacteria up to fish.

Section: Trophic Interactions Between Marine Snow and Zooplanktonmentioning

confidence: 58%

Marine snow, zooplankton and thin layers: indications of a trophic link from small-scale sampling with the Video Plankton Recorder

Moeller

John²,

Temming

et al. 2012

“…With nothing (or occasionally small remains of food) in their stomachs, the sprat in the present study appeared to starve in late winter because their main food, planktonic copepods, were still overwintering and at the lowest densities of their annual cycle during the study period (Peters et al 2006(Peters et al , 2013. This is consistent with the findings of Arrhenius (1998), that sprat in the Baltic Sea feed little and lose body energy during the winter months (November to March), and of Kaartvedt et al (2009), that sprat in a Norwegian fjord feed on dormant copepods during daytime, or do not feed at all.…”

Section: Feeding and Vertical Distribution Dynamics Of Spratmentioning

confidence: 51%

Diel vertical interactions between Atlantic cod Gadus morhua and sprat Sprattus sprattus in a stratified water column

Andersen¹,

Lundgren²,

Neuenfeldt³

et al. 2017

Information about species interactions at a spatial scale comparable to the perceptive abilities of the involved species is crucial for establishment of predictive food consumption models at the population level. Nevertheless, such information is sparse due to methodological constraints. We studied the diel vertical dynamics of species interactions between Atlantic cod Gadus morhua and its major clupeid prey, sprat Sprattus sprattus, at a location in the Bornholm Basin of the central Baltic Sea during late winter. This was accomplished by combining acoustic information on diel vertical fish distribution, time of ingestion of individual sprat estimated from cod stomach content data and observed vertical profiles of salinity, temperature and oxygen content. Predation by cod took place primarily at dusk and dawn during ascent and descent of sprat associated with school dissolution and formation, respectively. Cod resided close to the bottom outside these temporal predation windows. Sprat schools were located at the same depth as cod in the daylight hours, whereas at night dispersed sprat were situated higher in the water column. These vertical dynamics could be explained by fitness optimization using bioenergetics and trade-offs between temperature, oxygen saturation of the water and predation risk. This study forms a first step towards providing a mechanistic background for the predatory impact of cod at the basin scale and beyond.

“…Investigations using lipid biomarkers showed a high importance of ciliates in addition to diatoms, dinoflagellates, and cyanobacteria (Peters et al 2006). No reliable estimates of the food sources for P. acuspes were available for our investigation period.…”

Section: Hydro-climatic Variables and Predation Pressurementioning

confidence: 99%

“…This dependence of the new generation on the overwintering stock has been shown for Pseudocalanus sp. in Dabob Bay (Ohman 1985) and also the Baltic Sea using a seasonally resolved 2 yr data set (Peters et al 2006). Subsequent offspring (N) production in spring, generally a critical phase in copepod dynamics, depends almost exclusively on the developing F abundance.…”

Section: Pseudocalanus Acuspes Life Cyclementioning

confidence: 99%

“…The observed decrease of dia toms and increase of dinoflagellates in the Gotland Basin in recent years (Wasmund & Uhlig 2003) could have had implications for the food quality important for growth and reproduction (Gulati & Demott 1997). While older stages of P. acupses are known to feed mainly on heterotrophic organisms like small flagellates and ciliates as well as detritus (Peters et al 2006), younger stages near the surface could more likely be influenced by poor quality of phytoplankton species.…”

Section: Effects Of Hydro-climatic Driversmentioning

confidence: 99%

See 1 more Smart Citation

Interactions among density, climate, and food web effects determine long-term life cycle dynamics of a key copepod

Otto¹,

Kornilovs²,

Llope³

et al. 2014

Increasing pressure on animal populations through climate change and anthropogenic exploitation fuel the need to understand complex life cycle dynamics of key ecosystem species and their responses to external factors. Here, we provide a novel, integrative study on the long-term population dynamics of Pseudocalanus acuspes, a key species in the Baltic Sea, explicitly considering its distinct life-history stages, and testing for linear, non-linear, and non-additive climate and food web effects. Based on a unique data set of stage-specific abundance covering almost 5 decades of sampling (1960 to 2008, with 1408 samples), we use generalized additive modeling (GAM) and its respective non-additive threshold (TGAM) formulation to test for (1) density effects on subsequent life-history stages within the internal life cycle, (2) the effect of exogenous bottom-up (i.e. hydro-climatic) and top-down (i.e. predation) pressures, and (3) changes between bottom-up and top-down regulation. We show that linear density effects are always present, explaining a high proportion of interannual variability, while effects of external pressures are nonlinear or non-additive and strongly stage-and season-specific. In general, younger stages of P. acuspes are more affected by atmospheric winter conditions and water temperature, whereas older stages are influenced by conditions of deepwater salinity and predation pressure. These bottom-up processes, however, are not necessarily stable, and can depend on the level of top-down predation pressure. Our study demonstrates the complex and non-stationary interplay between internal and external factors regulating long-term animal population dynamics.