Interspecific competition in phytoplankton drives the availability of essential mineral and biochemical nutrients

Abstract

The underlying mechanisms and consequences of competition and diversity are central themes in ecology. A higher diversity of primary, producers often results in higher resource use efficiency in aquatic and terrestrial ecosystems. This may result in more food for consumers on one hand, while, on the other hand, it can also result in a decreased food quality for consumers; higher biomass combined with the same availability of the limiting compound directly reduces the dietary proportion of the limiting compound. Here we tested whether and how interspecific competition in phytoplankton communities leads to changes in resource use efficiency and cellular concentrations of nutrients and fatty acids. The measured particulate carbon: phosphorus ratios (C:P) and fatty acid concentrations in the communities were compared to the theoretically expected ratios and concentrations of measurements on simultaneously running monocultures. With interspecific competition, phytoplankton communities had higher concentrations of the monounsaturated fatty acid oleic acid and also much higher concentrations of the ecologically and physiologically relevant long-chain polyunsaturated fatty acid eicosapentaenoic acid than expected concentrations based on monocultures. Such higher availability of essential fatty acids may contribute to the positive relationship between phytoplankton diversity and zooplankton growth, and may compensate limitations by mineral nutrients in higher trophic levels.

Linking primary producer diversity and food quality effects on herbivores: A biochemical perspective

“…Total sterol concentrations in communities were calculated using sterol concentrations from algae monocultures, because the harvested biomass was not sufficient to determine the sterol concentration of every community. The carbon-based sterol concentrations of the monocultures were converted into biovolume-based sterol concentrations ( M j ) and related to the microscopically determined biovolumes ( BV j ) of each species ( j ) and the number of species in the community (I) to calculate the total expected sterol concentration ( E ) of the whole community (Equation 2 ) 28 . …”

“…In order to account for the effects of phytoplankton species competition, e.g. for light or phosphorus, on the nutritional quality of the communities 28 we allowed the species to develop their own communities rather than to artificially assemble mixtures of given species proportions to obtain a more realistic scenario.…”

Light-Induced Changes in Fatty Acid Profiles of Specific Lipid Classes in Several Freshwater Phytoplankton Species

“…Interspecific interactions between different phytoplankton species may further influence their light acclimation and will also change their biochemical composition. This is indicated by a recent study showing that, under competitive stress, algae produced either lower or higher amounts of specific fatty acids depending on the species examined (Wacker et al, 2015b ). Although the mechanistic drivers actually at play still have to be identified, we expect that changes in incident light and nutrient availability affected the concentration and composition of pigments (Richardson et al, 1983 ; Striebel et al, 2009 ), the photosynthetic efficiency (Wacker et al, 2015a ), as well as the cellular FA and sterol composition (Piepho et al, 2010 , 2012a , b ).…”

“…Second, phytoplankton species have been shown to be highly variable with respect to their FA composition and sterols when nutrient concentration, light intensity and temperature fluctuate (Piepho et al, 2010 , 2012a , b ). Consequently, changing environmental conditions may cause alterations in relative availabilities of mineral and biochemicals that are essential for higher trophic levels (Striebel et al, 2012 ; Wacker et al, 2015b ).…”

The Species-Specific Responses of Freshwater Diatoms to Elevated Temperatures Are Affected by Interspecific Interactions

“…Interspecific interactions may directly affect the growth of species. Competition for resources (nutrients, space, and light) is the most common interactions between species, and weak competitors for those resources often end up being eliminated due to growth constraints [ 34 ]. Unfavorable conditions for algal species may also arise if they interact with each other via secondary metabolites that affect cell physiology and growth of their competitors [ 35 ].…”