Marine Research Findings of the VECTORS Project

This website provides access to the research results of the VECTORS project, which can be used to support marine management decisions, policies and governance as well as future research and investment. VECTORS was a large scale project that brought together more than 200 expert researchers from 16 different countries. It examined the significant changes taking place in European seas, their causes, and the impacts they will have on society.

Functional responses of juvenile herring and sprat in relation to different prey types

Planktivorous fish play a key role in the pelagic ecosystem as they have a marked impact upon their prey communities and are an important source of food for piscivorous predators. The intermediate trophic level can exert a major control on whole ecosystems, namely in upwelling regions1 and in the Baltic Sea with sprat and herring as dominant pelagic fish. Information on the relationship between sprat’s and herring’s per capita feeding rates and prey concentrations (functional response2) is therefore of particular interest to understand their top-down control of the zooplankton community. Functional response has been implemented in marine ecosystem models like ATLANTIS to model fish and plankton population interactions. With a newly developed experimental set up we were able to observe feeding rates at different prey concentrations. We present functional response curves for sprat and herring from experiments with two different prey types. 
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Sprat and herring clearly show a functional response type II. Furthermore, feeding rates of both predators are strongly affected by the escape ability of prey (Fig. 1).

A type II response implies a high extinction risk for the prey as predation risk per prey capita increases with decreasing prey concentrations. Furthermore, clupeids are able to store large amounts of food items in their gastric cecum, which enables the sustained exploitation of high prey concentrations3. Hence, it appears possible that schools of sprat and herring are able to deplete local zooplankton patches within relative short times given the combination of high maximum biting rates (approximately 1 copepod s-1), the high storage capacity and the type II functional response. Thus, we assume that sprat and herring are able to exert strong local top-down effects on prey populations. Non-evasive Artemia nauplii was used as prey to estimate the maximum biting rate of both predators.

In contrast, the copepod Acartia tonsa with a high escape ability was used as a realistic prey type. The feeding efficiency of sprat and herring was significantly higher with Artemia nauplii than with A. tonsa. Both fish species showed a special S-shape curvation of the body before biting when they were feeding on the copepod A. tonsa but not when they preyed on the non-evasive Artemia nauplii (Fig.2). The obtained parameters of the functional response model can be implemented in region-specific spatially resolved ecosystem models in WP4 and WP5, which will be the foundation of any integrated ecosystem assessment and evaluation of ecosystem management strategies.

References

Lead Author:

Rini Brachvogel
(rini.brachvonospamgel@uni-hamburg.de)
University of Hamburg (UHAM)
Date of research: October 2012

Related articles:

Population dynamics of sprat in the Baltic Sea 

Fish distributions and spatial management measures 

The drivers of a common sole population 

Changes in the upper trophic level: impact on fish

Cod, recruitment, temperature and zooplankton

Early life stage survival of Baltic cod

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This project has received funding from the European Union’s Seventh Framework Programme for research, technological development and demonstration under grant agreement no 266445
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