Competition for phosphorus between two dinoflagellates: A toxic Alexandrium minutum and a non-toxic Heterocapsa triquetra

Abstract

The understanding of the dominance of one species with respect to others is a pertinent challenge in HAB growth dynamics studies and the nutrient supply mode is one of the factors potentially involved. The competition for phosphorus (P) between a toxic species, Alexandrium minutum, and a non-toxic species, Heterocapsa triquetra, was studied (1) along a gradient of P depletion, (2) testing different P depletion degrees before a single PO4 supply and (3) experimenting different PO4 supply frequencies. In conditions of PO4 depletion, H. triquetra stopped growing after two days both in monospecific and mixed batch cultures whereas A. minutum grew progressively from day 2 until the end of the experiment. This time-lag growth of A. minutum is associated to its ability to store P intracellularly and then mobilize it for cell division when P depletion becomes severe. Heterocapsa triquetra outcompeted A. minutum when it was submitted to less than three days of P depletion before the pulse. In contrast, A. minutum outcompeted H. triquetra after more than three days of depletion. This transition was related to the capacity for A. minutum to increase its cell PO4 uptake rate in a higher proportion to face potential PO4 supply. As a result of this physiological acclimatation to P starvation, A. minutum consumed the whole PO4 pulse supplied after 3 to 10 days of P depletion. This resulted in a reduction of H. triquetra growth. These two acclimatations were confirmed in a P limited semi-continuous culture experiment testing several PO4 supply frequencies (1, 2, 4, 6 day intervals). These experiments revealed that A. minutum is a "storage specialist" species for P, which uptakes PO4 pulses for luxury consumption, survives depletion periods and, then, utilizes P for cell growth. In contrast, H. triquetra is more a "velocity adapted" species, which utilizes PO4 just after supply to increase their cell division rate.

Growth- and nutrient-dependent gene expression in the toxigenic marine dinoflagellate Alexandrium minutum

“…3C) than the canonical Redfield ratios (Redfield, 1958) of mol C:N:P = 106:16:1 considered to represent balanced growth conditions in natural populations. Similar to other Alexandrium species, A. minutum is known to be a specialist for intracellular storage of P (Labry et al, 2008), and to a lesser extent of N (Flynn et al, 1996;Maguer et al, 2007), during nutrient pulses. The nutrients stored during the periods of ''luxury consumption'' can later be mobilized for growth when extracellular nutrients are depleted.…”

Reassessment of the cell surface area limitation to nutrient uptake in phytoplankton

“…Laboratory experiment data on growth rates (μ, divisions d ) were obtained from published reports and articles (Sakshaug & Hansen 1977, Sakshaug et al 1984, Montagnes et al 1994, Maldonado & Price 1996, Bertilsson et al 2003, Ho et al 2003, Marchetti & Harrison 2007, Labry et al 2008, Marañón et al 2013). All considered phytoplankton were grown in nutrient-replete, light-saturated or near-saturated conditions.…”

Resource Competition Affects Plankton Community Structure; Evidence from Trait-Based Modeling

“…The study was applied in the Bay of Brest due to the fact that since summer 2012, the bay has been affected by one of the most problematic organisms, i.e., the dinoflagellate Alexandrium minutum (ErardLe Denn, 1997), which gives rise to toxic events. The selection of this species was driven by the large set of physiological parameters provided by the literature and previous studies with local strains (Labry et al, 2008). We focused on the simulated timing of A. minutum and its maximal intensity values for comparison with in-situ observations.…”