Abstract
Vitamin B1 is an essential exogenous micronutrient for animals. Mass death and reproductive failure in top aquatic consumers caused by vitamin B1 deficiency is an emerging conservation issue in Northern hemisphere aquatic ecosystems. We present for the first time a model that identifies conditions responsible for the constrained flow of vitamin B1 from unicellular organisms to planktivorous fishes. The flow of vitamin B1 through the food web is constrained under anthropogenic pressures of increased nutrient input and, driven by climatic change, increased light attenuation by dissolved substances transported to marine coastal systems. Fishing pressure on piscivorous fish, through increased abundance of planktivorous fish that overexploit mesozooplankton, may further constrain vitamin B1 flow from producers to consumers. We also found that key ecological contributors to the constrained flow of vitamin B1 are a low mesozooplankton biomass, picoalgae prevailing among primary producers and low fluctuations of population numbers of planktonic organisms.
Highlights
Vitamin B1 is necessary for the proper functioning of the majority of organisms because it serves as a cofactor that associates with a number of enzymes involved in primary carbohydrate and amino acid metabolism[1]
In scenarios resulting in high concentrations of vitamin B1 in planktivorous fish, the biomass of consumers and primary producers fluctuates over time, and over the season, different size groups of primary producers contribute to the total biomass of primary producers (Fig. 2b,c)
In scenarios resulting in low vitamin B1 concentrations in planktivorous fish, picoalgae biomass is high and relatively stable over time; it does not drop to the minimal levels of biomass observed in scenarios with planktivorous fish rich in vitamin B1 for most of the simulated time
Summary
Vitamin B1 (thiamin) is necessary for the proper functioning of the majority of organisms because it serves as a cofactor that associates with a number of enzymes involved in primary carbohydrate and amino acid metabolism[1]. Unicellular taxa producing or taking up dissolved vitamin B1 (or its precursors) in the Baltic Sea are very diverse with respect to taxonomy, cell size and mass-specific vitamin B1 content[7,31,32,33] Those with smaller cells have higher carbon-specific vitamin B1 levels than those with large cells[31]. High nutrient loads and changes in light attenuation due to elevated inputs of riverine soluble substances and anthropogenic pressures are expected to affect the species composition of primary producers[43] This is expected to affect the size spectra of vitamin B1-containing unicellular taxa in the Baltic Sea. As a general trend, the phytoplankton size spectrum in the Baltic Sea has shifted toward smaller primary producers in recent years[44], but the effect on vitamin B1 provisioning to zooplankton, fish and other consumers is unknown. To identify the drivers of the seasonal and yearly variation in vitamin B1 concentration in planktivorous fish and top consumers, we need to understand the transport pathways of this essential substance from the unicellular planktonic taxa up to the different parts of the aquatic food web
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