When more is less: phytoplankton abundance drives behavior mediated cascades in marine food webs

Thursday 07 Feb 19


Rodrigo Almeda
DTU Aqua


Thomas Kiørboe
DTU Aqua
+45 35 88 34 01

Our traditional view of the interactions between marine organisms is conceptualized as food webs where species interact with one another mainly via direct consumption. However, non-consumptive interactions, such as behaviorally mediated indirect interactions (BMIIs), can influence marine ecosystems as much as consumptive effects. Here we show the first experimental evidence and quantification of bottom-up BMIIs in plankton food webs.

We used observational, modeling and experimental approaches to investigate how behavioral responses to resource availability influence predation mortality on copepods with different foraging strategies (ambushing vs. active foraging). A three-level food chain was used: phytoplankton as resource (“initiator”), copepods as grazers (“transmitter”) of phytoplankton, and a large copepod as predator (“receiver”).

Our results show that active foragers are able to decrease their foraging activity with increasing phytoplankton abundance, reducing mortality due to predation up to 50 %. Ambush feeders, on the other hand, showed little change in foraging activity and no reduction of predation mortality with increasing resource availability.

Therefore, an increase in resources (“initiator”) causes behavioral changes in active grazers (“transmitter”), which ultimately negatively affects predator (“receiver”) consumption rates. This suggests that an increase in phytoplankton abundance may result in decreasing energy transfer to higher trophic levels and that behaviorally mediated interactions drive marine food web dynamics differently than predicted by only density-mediated or consumptive interactions. 

Read the paper here

van Someren Gréve H., Kiørboe T., Almeda R. Bottom-up behaviourally mediated trophic cascades in plankton food webs. Proc. R. Soc B. https://doi.org/10.1098/rspb.2018.1664

Contact: Hans van Someren Gréve, Postdoc, Roskilde University, hvsg@ruc.dk
26 APRIL 2019