Absence of sterols constrains food quality of cyanobacteria for an invasive freshwater bivalve

Abstract

The accumulation of cyanobacterial biomass may severely affect the performance of aquatic consumers. Here, we investigated the role of sterols in determining the food quality of cyanobacteria for the invasive clam Corbicula fluminea, which has become a common benthic invertebrate in many freshwater ecosystems throughout the world. In standardized growth experiments, juvenile clams were fed mixtures of different cyanobacteria (Anabaena variabilis, Aphanothece clathrata, Synechococcus elongatus) or sterol-containing eukaryotic algae (Cryptomonas sp., Nannochloropsis limnetica, Scenedesmus obliquus). In addition, the cyanobacterial food was supplemented with different sterols. We provide evidence that somatic growth of C. fluminea on cyanobacterial diets is constrained by the absence of sterols, as indicated by a growth-enhancing effect of sterol supplementation. Thus, our findings contribute to our understanding of the consequences of cyanobacterial mass developments for benthic consumers and highlight the importance of considering sterols as potentially limiting nutrients in aquatic food webs.

Effects of cyanobacteria, fish kairomones, and the presence of ostracods on the demography of Simocephalus vetulus (Cladocera)

“…; Basen et al. ). Zooplankton often show low growth rates on cyanobacterial diets and tend to avoid them when offered alternatives (Schmidt & Jonasdottir ).…”

“…In experimental vessels, we often find S. vetulus feeding on semi-digested algae in the feces of H. incongruens. We also frequently find both taxa together in shallow lakes and ponds, often with high densities of cyanobacteria, in spite of the fact that studies indicate that the nutritional quality of cyanobacterial diets is low (Ahlgren et al 1992;Basen et al 2010).…”

Nitrogen Fixed By Cyanobacteria Is Utilized By Deposit-Feeders

“…The biomass of the spring bloom, which is the most important input of high quality organic matter to the sub-thermocline soft-bottom community [13],[4],[5], has decreased, while magnitude of the summer bloom of cyanobacteria has increased [14],[15]. Although deposit-feeders in experiments consume cyanobacteria [16],[10],[11], the diatoms largely constituting the spring bloom are superior in supporting growth of benthic animals, probably because the cyanobacteria contain toxins, have low content of essential fatty acids [7],[17] and lack sterols [18]. Cyanobacteria are, however, rich in nitrogen and phosphorous [19], amino acids [20] and vitamins [21], and could, therefore, be a complementary and, perhaps, crucial food source when the high quality spring bloom input to the sediments has been exhausted.…”

Compound‐specific δ13C analyses reveal sterol metabolic constraints in an aquatic invertebrate

“…The green alga Scenedesmus obliquus (SAG 276‐3a) and the eustigmatophyte Nannochloropsis limnetica (SAG 18.99) were cultivated semi‐continuously at a dilution rate of 0.2 day −1 in aerated 5 L vessels containing Cyano medium (20 °C, illumination at 120 µmol quanta m −2 s −1 ) . These species were chosen because they are known to have different sterol compositions and none of the measured sterols are abundant in both species . Algae were harvested in the late‐exponential growth phase.…”