Dinoflagellate competition under global change
Dinoflagellates are a diverse group of protists exhibiting a complex life cycle including resting cyst formation. We focus on toxic and calcifying autotrophic dinoflagellates, and their responses towards climate change. In particular, the aim of our research is to obtain a process-based understanding of dinoflagellate community responses towards rising CO2. This we investigate by means of laboratory CO2 and nutrient perturbation experiments in monoclonal and competition experiments in dilute batch and continues cultures. Furthermore, we investigate to what extend dinoflagellate cysts may serve as a proxy for the past climate. This combined approach of dinoflagellate community responses to the climate of the past, and resource perturbations of the present will allow predictions of community responses to future climate change.
Different dinoflagellate species; (a) a toxic Alexandrium tamarense, (b) a calcifying Scrippsiella trochoidea, and (c) a calcifying Thoracosphaera heimii (Photo’s: DB Van de Waal).
Good tidings for red tides?
With higher atmospheric CO2 levels, more CO2 will react with water forming carbonic acid. This immediately dissociates into bicarbonate, releasing a proton, and may dissociate further to carbonate, releasing another proton. The higher concentration of protons in the water will cause the pH of the water to drop. This process is referred to as ocean acidification. Dinoflagellates may respond positive to the higher CO2 availability in the water (green arrow), but may respond negative to the lower pH of the water (red arrow). Climate-driven changes on the physiology (1) and subsequent species interaction of dinoflagellates (2) may have consequences for the food web (3) and the isotopic composition of settling cysts (4).
High nutrient concentrations in coastal waters may lead to excessive dinoflagellate growth. These events can result in coloration of the water, which is then referred to as red-tide. Some dinoflagellate species produce the neurotoxin saxitoxin, and can form harmful algal blooms (HABs). Photosynthetic activity during blooms may cause pH levels to reach values above 9 and occasionally even up to 9.75. Such high pH levels may affect the competitive interactions between phytoplankton species, because some species are more sensitive to elevated pH than others. The reason for difference in pH sensitivity among dinoflagellate species is unknown, but a number of different suggestions have been put forward, including limitation by inorganic carbon.
With rising atmospheric CO2 levels, more inorganic carbon will become available for phytoplankton growth. This may alleviate inorganic carbon limitation in dense algal blooms. Higher CO2 concentrations in the water are accompanied by a reduction in pH, i.e. ocean acidification. Some dinoflagellates are calcareous, and produce calcite cysts. Because the solubility of calcite increases with reduced pH, the calcification rates of calcareous dinoflagellates may be affected in the future ocean.
What are the implications of rising atmospheric CO2 levels on dinoflagellate communities? To answer this question, we study the responses of toxic and calcareous dinoflagellates to varying CO2 concentrations according to climate scenarios predicted by the IPCC. Included parameters are dinoflagellate growth, carbon acquisition, elemental composition, isotopic composition, gene transcription, and toxin production. Furthermore, we study the competitive interactions between a variety of toxic and calcareous dinoflagellate species. Knowing the eco-physiological responses of the individual species, we aim at obtaining a process-based understanding of dinoflagellate community responses towards rising CO2.
Archives of the future (Mirja Hoins, Utrecht University)
Atmospheric CO2 levels have varied over geological time scales, influencing the Earth’s climate and ecosystems in the past. Since the industrial revolution atmospheric CO2 levels have increased to 380 ppmv and are expected to reach up to ~1400 ppmv by the year 2100. Dinoflagellates are among the most important phytoplankton groups which inhabit the global oceans since the Triassic (>200 Ma BP). Some dinoflagellate species are able to produce organic walled cysts as a part of their life cycle. These cysts are immobile and sink to the seafloor. As they are very resistant against degradation, they may provide ideal geological archives for past environmental conditions.
In this project, we aim to describe and understand the relationship between CO2 and the isotopic composition (13C) of the dinoflagellate species Gonyaulax spinifera and Protoceratium reticulatum. Experiments are performed in dilute-batch cultures in combination with bio-assays. Following this approach should yield a process-based understanding of 13C fractionation. All in all, the work should lead to a new and reliable proxy for past atmospheric CO2 levels, and support hypotheses for changes dinoflagellate communities in the future.
Student opportunities
If you are interested to do an internship as part of your studies, please don’t hesitate to contact one of us (Dedmer or Mirja). There are plenty of opportunities on varying subjects.
Collaborations
Uwe John (AWI), Maarten Boersma (AWI), Appy Sluijs (University of Utrecht, the Netherlands), Per Juel Hansen (University of Copenhagen, Denmark)
Related publications
Competition between toxic and non-toxic cyanobacteria:
Van de Waal et al. 2011 (ISME J). This paper was highlighted in Nature Climate Change (Wilhelm and Boyer, 2011: Healthy competition, NCC 1: 300-301)
Climate change and ecological stoichiometry in aquatic ecosystems:
Van de Waal et al. 2010 (Front Ecol Environ)
Inorganic carbon availability and pH effects on red tide dinoflagellates:
Rost et al. 2006 (Plant Cell Environ), Hansen et al. 2007 (Mar Ecol Prog Ser)
