Abstract
Allelopathy is wide spread among marine phytoplankton, including diatoms, which can produce cytotoxic secondary metabolites such as polyunsaturated aldehydes (PUA). Most studies on diatom-produced PUA have been dedicated to their inhibitory effects on reproduction and development of marine invertebrates. However, little information exists on their impact on key herbivores in the ocean, microzooplankton. This study examined the effects of dissolved 2E,4E-octadienal and 2E,4E-heptadienal on the growth rates of natural ciliate and dinoflagellate populations in the Chesapeake Bay and the coastal Atlantic waters. The overall effect of PUA on microzooplankton growth was negative, especially at the higher concentrations, but there were pronounced differences in response among common planktonic species. For example, the growth of Codonella sp., Leegaardiella sol, Prorodon sp., and Gyrodinium spirale was impaired at 2 nM, whereas Strombidium conicum, Cyclotrichium gigas, and Gymnodinium sp. were not affected even at 20 nM. These results indicate that PUA can induce changes in microzooplankton dynamics and species composition.
Highlights
Allelopathy is wide spread among phytoplankton ([7,8] and references therein) and has been repeatedly invoked as a crucial mechanism that leads to remarkable recruitment success in diatoms (e.g., [7])
The experimental samples collected in the Chesapeake Bay (Experiment, Exp. 1–3) were characterized by low salinity and temperature compared to the Atlantic coastal waters (Exp. 4 and 5)
The growth rates of ciliates and dinoflagellates observed in control samples were within the range reported for natural microzooplankton populations in temperate and polar waters ([36] and references therein)
Summary
They contribute 40% of the total ocean primary production and ca. 20% of global CO2 fixation [1,2,3] Due to their relatively small surface to volume ratios, diatoms tend to dominate phytoplankton communities under nutrient-replete conditions, such as in coastal waters and upwelling zones [4], where they form the base of food webs and fisheries. Allelopathy (here production of chemicals by algae to inhibit the growth of competitors and deter grazers) is wide spread among phytoplankton ([7,8] and references therein) and has been repeatedly invoked as a crucial mechanism that leads to remarkable recruitment success in diatoms (e.g., [7]). Fourteen oxylipin derivatives have been structurally identified in marine planktonic diatoms [11].
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