Basic outline of research
Dr. Field's is a zooplankton ecologist. The Fields' laboratory studies the role of zooplankton (particularly copepods) in transferring organic matter through the food web and in mediating bio-geochemical cycling in the oceans. Our approach is to understand how the mechanisms that occur at the level of the individual animal drive regional and global scale distribution patterns in zooplankton. This work incorporates general data of zooplankton ecology (classical grazing experiments, egg production and developmental rates) as well as data from small-scale fluid mechanics, neurophysiology and animal behavior.
Research Council of Norway - The sensory biology of host detection in the parasitic salmon lice Lepeophtheirus salmonis: electrophysiological and behavioral investigations. The project investigates the sensory cues (visual and olfactory) associated with host location in the salmon louse. Our longer-term goal is to generate sufficient information to establish a basis for disruption of the louse life cycle by interfering with their ability to locate a host.
NSF- Bio Oce. Ocean Acidification-- Effects of ocean acidification on Emiliania huxleyi and Calanus finmarchicus; insights into the oceanic alkalinity and biological pumps. Ocean acidification is one of the most pressing marine science issues of our time, with potential biological impacts spanning all marine phyla and potential societal impacts affecting man’s relationship to the sea. Rising levels of atmospheric pCO2 are increasing the acidity of the world oceans. It is generally held that average surface ocean pH has already declined by 0.1 pH units relative to the pre-industrial level (Orr et al., 2005), and is projected to decrease 0.3 to 0.46 units by the end of this century, depending on CO2 emission scenarios (Caldeira and Wickett, 2005). The overall goal of this work is to parameterize how changes in pCO2 levels could alter the biological and alkalinity pumps of the world ocean. Specifically, the direct and indirect effects of ocean acidification will be examined within a simple, controlled predator/prey system containing a single prey phytoplankton species (the coccolithophore, Emiliania huxleyi) and a single predator (the oceanic metazoan grazer, Calanus finmarchicus). The experiments are designed to elucidate both direct effects (i.e. effects of ocean acidification on the individual organisms only) and interactive effects (i.e. effects on the combined predator/prey system). Interactive experiments with phytoplankton prey and zooplankton predator are a critical starting point for predicting the overall impact of ocean acidification in marine ecosystems. To meet these goals, a state-of-the-art facility will be constructed with growth chambers that are calibrated and have highly-controlled pH and alkalinity levels. The strength of this approach lies in meticulous calibration and redundant measurements that will be made to ensure that conditions within the chambers are well described and tightly monitored for DIC levels. Growth and calcification rates in coccolithophores and the developmental rates, morphological and behavioral effects on copepods will be measured. The PIC and POC in the algae and the excreted fecal pellets will be monitored for changes in the PIC/POC ratio, a key parameter for modeling feedback mechanisms for rising pCO2 levels. In addition, 14C experiments are planned to measure calcification rates in coccolithophores and dissolution rates as a result of grazing. These key experiments will verify closure in the mass balance of PIC, allowing the determination of actual dissolution rates of PIC within the guts of copepod grazers.
NSF- Chem Oce. Assessing the chemical speciation and bioavailability or iron regenerated by marine zooplankton. Iron is required for numerous biological processes in the upper ocean and is recognized as a limiting nutrient in many marine ecosystems. Iron limitation impacts phytoplankton community structure, as well as C fixation and export from surface waters. While external Fe inputs constrain the export of this element over longer timescales, Fe is rapidly cycled in surface waters through biological uptake and regeneration. Indeed, by far the largest direct source of Fe for phytoplankton growth in the open ocean is regeneration via zooplankton grazing. Digestion of phytoplankton biomass in protistan vacuoles and metazoan guts is expected to result in chemical redox and speciation changes, but these alterations remain largely unstudied and untested. Only one study to date has quantified Fe-binding ligands produced during grazing, and the results are somewhat equivocal and complicated by complex trophic interactions during the experiment. The bioavailability of regenerated Fe has been studied largely with model ligands, and the few studies to examine availability of grazer-produced ligands reach conflicting conclusions. Here we propose a comprehensive laboratory and field investigation into the mechanisms of zooplankton regeneration of Fe and the consequences for chemical speciation and bioavailability. We have four science objective: (a) determine pH and redox state in the digestive vacuole/guts of protistan and metazoan zooplankton; (b) determine the effect of prey – grazer pairing on organic and redox speciation of regenerated Fe; (c) determine the bioavailability of regenerated Fe to Felimited cultures of model phytoplankton; and (d) determine Fe regeneration, speciation and bioavailability in field experiments using natural prey – grazer assemblages from a temperate coastal system and an open ocean system. These will be accomplished through grazing experiments with a suite of ecologically representative and biogeochemically-important model organisms (bacterial, diatom and coccolithophore prey; heterotrophic ciliate and dinoflagellate protozoa grazers; small and large copepod grazers), as well as with natural coastal (Gulf of Maine) and open ocean (Southern Ocean) plankton communities. Regenerated Fe and ligands will be chemically characterized (Fe(II), soluble/colloidal size fractionation, ligand concentration and conditional stability constant), and bioavailability directly assayed via uptake by Fe-limited phytoplankton cultures (diatom, coccolithophore and cyanobacterial strains). This will enable broad application of these results to existing datasets, Further, chemical conditions (pH, redox) within grazer vacuoles/guts will be directly assayed with fluorescent dyes and microelectrode measurements, with the goal of providing a mechanistic understanding of taxonomic variations in regeneration. The proposed experiments will significantly advance our understanding of zooplankton Fe regeneration processes, a critical and understudied component of the ocean Fe cycle.
NOAA - Implications of ocean acidification on carbon export in a simplified planktonic food chain: Experiments using Acartia and Pleurochrysis. Rising levels of atmospheric pCO2 are increasing the acidity of the world oceans. It is generally held that average surface ocean pH has already declined by 0.1 pH units relative to the pre-industrial level 1, and is projected to decrease 0.3 to 0.46 units by the end of this century, depending on CO2 emission scenarios 2. The overall goal of this work is to parameterize how changes in pCO2 levels could alter the carbon export of the world ocean. Specifically, the direct and indirect effects of ocean acidification (OA) will be examined within a simple, controlled predator/prey system using a single prey phytoplankton species (coccolithophore, Pleurochrysis sp.) and a single predator (mesopelagic grazer, Acartia tonsa). The experiments are designed to elucidate both direct effects (i.e. effects of OA on the individual organisms only) and interactive effects (i.e. effects on combined predator/prey system). Such interactive experiments have never been done before and are a critical starting point for predicting the overall impact of OA in marine ecosystems. To meet these goals, a state-of-the-art facility will be constructed with growth chambers that are calibrated and have highly-controlled pH and alkalinity levels. The strength of this work lies in the meticulous calibration and redundant measurements that will be made to ensure that the conditions within the chambers are well described and tightly monitored for DIC levels. Growth and calcification rates in coccolithophores and the developmental rates, morphological and behavioral effects on copepods will be measured. The PIC and POC in the algae and the excreted fecal pellets will be monitored for changes in the PIC/POC ratio, a key parameter for modeling feedback mechanisms for rising pCO2 levels. These key experiments will verify closure in the mass balance of PIC, allowing the determination of actual dissolution rates of PIC within the guts of copepod grazers. Data will be disseminated through NOAA’s NODC data base. The proposal incorporates four undergraduate students during the three-year project and will provide them with exceptional opportunities to receive hands-on research experience learning sophisticated culturing techniques, the fundamentals of optics and micro-videography.
Moore Foundation - Carbon and gene flow mediated by virus. The perennial debate on whether viruses are alive has been livened up recently with the discovery of a new class of giant viruses that have genomes larger than the smallest bacteria and a range of genes analogous to those found in eukaryote organisms. The most remarkable aspect of giant viruses is their repertoire of novel and typically non-virus genes, many which encode central cellular functions and metabolic pathways. It has been provocatively suggested that these viruses form the fourth domain of life, although the most controversial aspect of this suggestion is there are less than a handful of representative viruses in the domain. There are numerous other bioinformatic and philosophical reasons they should not be included as a fourth domain, it is clearly highly controversial and arguably improbable; however, the discovery of viruses that contain many more genes than the smallest bacteria re-opens the age-old debate on what ‘life’ is. Virus life: One of the more persuasive arguments for viruses as life is to think of the infected cell as a novel organism that produces virions. Hence, it is the infected cell (the virus, or ‘viriocell’) that is the 2nd form of life, rather than thinking of virions (virus progeny) as life. It is akin to a multicellular organism producing genetic material in the form of sperm. Forterre (2010) describes the 2 forms of life as ribosome encoding organisms (cells) and capsid encoding organisms (viruses) The infected cell (viriocell) is a multifaceted life form ranging from retroposons that do not appear to have any effect on cells; latent infections that only produces virions under certain environmental insults; through chronic infections where virions are slowly released over time and finally, to lytic infections where the virions are released rapidly converting the infected cell into dissolved organic matter. Virus life is eaten: One significant recent discovery is that infected cells can be selectively grazed. Preferential grazing of infected cells in the ocean would sequester more carbon in particulate form, making it available to higher trophic levels. This has implications for modeling the ocean carbon budget. In addition, grazing of infected cells may transfer genes through the trophic levels. One hypothesis is that virion infected phytoplankton actually act as vectors for infection through the trophic levels (a virus-infected phytoplankton cell is grazed by a zooplankton that is then infected by its progeny virions). Many of the marine virion genomes sequenced to date have up to 80% unknown genes, we can only speculate as to the function and evolutionary origin of these genes, but one source and potential target for these genes could be higher trophic level organisms. One starting point would be to assess zooplankton. The zooplankton link: Copepods occupy and important ecological bottle neck in marine trophodynamic. Either directly or indirectly as secondary consumers, copepods ingest between 70-90% of all ocean primary productivity and provide a conduit for the flow of organic matter up the food chain and to the sediments in the form of fecal pellets. Since the first discovery of a crustacean-infecting virus, research has focused mainly on the effects of viruses on economically important crustacean species, chiefly shrimps and crabs. Nearly nothing is known about the effects of viruses on copepods species or on their potential effects on the population dynamics of higher trophic levels. Recent studies on the cosmopolitan copepod Acartia tonsa suggest that copepods populations are not directly impacted by viral infections, however they may act as vectors for transmission up the food chain. The dearth of information on copepod– virus interactions is arguably the result of a lack of investigation, rather than a lack of infection of copepods by viruses.
NSF – Bio Oce -REU Site: Bigelow Laboratory for Ocean Sciences: Undergraduate Research Experience in the Gulf of Maine and the World Oceans - 2012.
Sensory ecology and neurophysiology of marine zooplankton.
We study the characteristics of the setal motion (and the required fluid motion and force) that gives rise to the neurophysiological response in copepod mechanoreceptors. The work aims to how copepods differentiate among the myriad of fluid signals in their environment and how copepods code these complex signals in a rapid yet highly accurate manner.
Impact of global climate change on zooplankton populations.
We study effects of natural and anthropogenic changes on the energy transfer between trophic levels. Specifically we focus on grazing, respiration, reproduction and fecal pellet production rates of copepods under different climate scenarios.