Role of dimethyl sulphide (DMS) in pelagic tritrophic interactions

Lead Research Organisation: Plymouth Marine Laboratory
Department Name: Plymouth Marine Lab

Abstract

The oceans contain only about 1.5% of terrestrial biomass. However, they provide a similar amount of total annual production to that on land and the turnover time for organic matter is 1000-times faster in marine in comparison to terrestrial ecosystems. This highlights that grazing by zooplankton is disproportionally important and competition among grazers is high. It is not surprising that phytoplankton have evolved mechanisms to protect themselves from grazers. These include morphological defences such as grazing-resistant shells, for example in 'armoured' dinoflagellates, and chemical defences such as sophisticated chemical deterrence that influence the selectivity of grazers. Over the years we have accumulated a good understanding of the role of chemical defences in the bitrophic interactions between predators and their prey. However, it is also well known that land plants use another cunning defence strategy that involves the production of volatile signalling compounds (so called infochemicals) that attract the enemy of their predators. This in turn reduces the number of herbivores and releases the plants from excessive grazing pressure. Surprisingly, such infochemical-mediated tritrophic interactions have not been documented for oceanic plankton and our proposed research will rectify this shortcoming. We will focus our activities on one particular marine volatile: dimethyl sulphide (DMS). This compound is probably the best-studied of all marine trace gases, because much interest in DMS research concerns its role in regulating climate. We are starting to appreciate that DMS also has ecological importance and find that many organisms can use plumes of DMS as directional cue for their orientation. For example, some sea birds use DMS to locate areas of high food density. Recently, we also found that zooplankton copepods react to DMS gradients. Copepods are dominant consumers of microzooplankton protists (unicellular ciliates and flagellates) that are important grazers of many small phytoplankton species. In biogeochemical terms ciliates account for, on average, 30 % of the carbon consumed by copepods, representing approximately 5 % of total oceanic primary production and 100 fold the annual fisheries catch (~ 100 Mt yr-1 live weight) in carbon terms. However, these estimates may be considerably higher if other components of the microzooplankton, in particular dinoflagellates, are included. Interestingly, grazing by microzooplankton can result in a dramatic increase of DMS production and this is dependent on the ability of the phytoplankton to make this gas. Hence, phytoplankton may actively influence the 'smelliness' of their predators and this likely makes their enemies more susceptible to copepod attack. It is then not surprising that many of the DMS-producing phytoplankton species are competing successfully and can produce algal blooms that are large enough to be seen from space (for example the coccolithophore Emiliania huxleyi) or can be harmful to other organisms (for example toxic dinoflagellates). Our project will use laboratory experiments where we will quantify grazing of microzooplankton and copepods in relationship to the ability of phytoplankton to make DMS. These data will enable a first assessment of grazing-induced production of DMS in a tritrophic framework. We will also conduct field experiments with freshly collected plankton to verify our laboratory results with data from coccolithophore-dominated waters off Plymouth and in the North-East Atlantic. Our data will inform modelling efforts that aim to predict the effect of differential production of DMS on the susceptibility of microzooplankton to copepod grazing and the fecundity of copepods. This part of our project will be realised through a tied PhD studentship.
 
Description Mathematical simulation of the interactions between three trophic levels of plankton: phytoplankton, grazing microzooplankton and predatory mesozooplankton suggest that the inclusion of a grazing-induced dimethyl sulfide (DMS) production term has a stabilizing effect on the system dynamics. This feedback between trophic levels can potentially lead to the formation of a phytoplankton bloom.
Exploitation Route Our findings suggest that marine trace gases may have important biological roles beyond their function as climate-active compounds. The model provides a suitable framework for further study into the possible role of DMS in the ecology of marine food webs beyond its recognised role as a climate-cooling gas.
Sectors Environment

Pharmaceuticals and Medical Biotechnology

 
Description Through publications and the 'SET for Britain' initiative, we feel that our findings have increased knowledge and provided stakeholders with increased awareness of the important role of the climatically active gas DMS in marine microbial cycling,
First Year Of Impact 2013
Sector Chemicals,Environment
Impact Types Societal

 
Title Copepod and microzooplankton grazing preference in Arctic waters 
Description Data set of copepod and microzooplankton DMSP-specific grazing rates in response to gradients in DMS, in a transect off the Greenland Shelf during research cruise JR288 (funded through the NERC DMS tritrophic interactions project NE/H008535/1) part of the larger NERC-funded consortium ACCACIA. 
Type Of Material Database/Collection of data 
Year Produced 2013 
Provided To Others? Yes  
Impact Data set prepared for publication 
 
Description Grazing-induced production of DMS can stabilize food-web dynamics and promote the formation of phytoplankton blooms in a multitrophic plankton model 
Organisation University of Leicester
Country United Kingdom 
Sector Academic/University 
PI Contribution New collaborations with Andrew Morozov (Uni Leicester) and Jon Pitchford (Uni York) resulted in this publication
Start Year 2011
 
Description Grazing-induced production of DMS can stabilize food-web dynamics and promote the formation of phytoplankton blooms in a multitrophic plankton model 
Organisation University of York
Country United Kingdom 
Sector Academic/University 
PI Contribution New collaborations with Andrew Morozov (Uni Leicester) and Jon Pitchford (Uni York) resulted in this publication
Start Year 2011
 
Description Presentation at SET for Britain, House of Commons, UK 
Form Of Engagement Activity Participation in an activity, workshop or similar
Part Of Official Scheme? Yes
Geographic Reach National
Primary Audience Policymakers/politicians
Results and Impact As part of the SET for Britain initiative a science presentation was given to a range of politicians and a panel of expert judges at the House of Commons, March 2012, which stimulated lots of discussion and increased awareness.

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Increased public awareness of DMS emissions and their potential impact on climate
Year(s) Of Engagement Activity 2013
 
Description Presentation at microbe meeting, France 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? Yes
Geographic Reach International
Primary Audience Other academic audiences (collaborators, peers etc.)
Results and Impact Oral presentation: Fast Food: Quantifying the feeding behaviour of copepods in response to grazing-induced DMS-production. Lots of discussion during questions after the presentation.

Increased ideas flow between scientific colleagues
Year(s) Of Engagement Activity 2013
 
Description Presentation at microbe meeting, Les Houches, France 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? Yes
Geographic Reach International
Primary Audience Other academic audiences (collaborators, peers etc.)
Results and Impact Approx. 50 people visited the poster which stimulated lots of discussion and ideas sharing.

Increased knowledge sharing and increased awareness of the role of DMS in microbial food web cycling
Year(s) Of Engagement Activity 2013