Effect of a cyanobacterial diet on the competition between rotifers: a case study in Lake Albufera of Valencia, Spain

Abstract

Effect of a cyanobacterial diet on the competition between rotifers: a case study in Lake Albufera of Valencia, SpainBrachionus havanaensis is predominantly distributed in the Nearctic and Neotropical regions. It is now found even in the Palearctic and Oriental regions. During the summer of 2015 we found high densities (> 500 ind./l) of this species and low numbers of Brachionus angularis in Lake Albufera where the cyanobacterium (Microcystis aeruginosa) was dominant in the phytoplankton community. We hypothesized that the cyanobacterium was toxic to B. angularis but not to B. havanaensis hence the latter would outcompete the former in the presence of this cyanobacterium. To test the hypothesis, we conducted competition experiments between two coexisting rotifer species (B. angularis and B. havanaensis) from the Lake Albufera of Valencia using as food the green alga (Nannochloropsis oculata) and sonicated colonies of M. aeruginosa (single cells), separately and together (1:1 ratio based on biomass). The competition experiments using the population growth approach showed that B. havanaensis in controls had higher population abundances than B. angularis. However, when grown both together, B. havanaensis had a reduced population growth (nearly 50 %) in relation to B. angularis, in the absence of Microcystis in the diet. This reduced growth was more than that in the treatment of B. havanaensis alone when grown on a mixed diet of Microcystis and Nannochloropsis oculata. Brachionus havanaensis in all treatments (alone or in the presence of B. angularis) died completely when cultured on 100 % M. aeruginosa. The population growth rates of B. angularis, alone or in competition with B. havanaensis, were similar when Microcystis was excluded from the diet. However, Microcystis alone or together with Nannochloropsis was highly detrimental for the population growth of B. angularis. Our results showed the differences in the competitive outcome between the rotifers depending on the presence or absence of toxic cyanobacteria in the diet. Our study also showed that an exclusive diet of this cyanobacterium was toxic to both rotifers.

Experimental Studies on Zooplankton-Toxic Cyanobacteria Interactions: A Review

“…Rotifers are common in eutrophic tropical and temperate lakes and reach high densities in spite of the presence of cyanobacteria [ 59 , 60 ]. Although feeding experiments and demographic studies on rotifers such as Brachionus calyciflorus, B. havanaensis, Hexarthra mira, Keratella cochlearis , and Synchaeta pectinata , among others, indicate their ability to feed on cyanobacteria such as Microcystis aeruginosa, Anabaena flos aquae , and Anabaena affinis [ 5 , 61 , 62 ], their feeding and clearance rates are not enough to effectively reduce cyanobacterial blooms.…”

“…These are bacterivores, probably avoiding the adverse effects of cyanotoxins since they cannot ingest large colonies or filaments. Brachionus havanaensis , which is native to the neotropical region [ 64 ], has recently been reported from L’Albufera, Valencia, where it is an exotic species, feeding on cyanobacteria when offered in the sonicated form [ 60 ].…”

“…Laboratory studies on competition involving toxic cyanobacteria as diet confirm the relative competitive abilities of two or more zooplankton species for limited resources. The competition study by Sarma et al [ 60 ] indicates the ability of the exotic Brachionus havanaensis to outcompete the native B. angularis , especially on Microcystis diets; this cyanobacterium forms dense blooms in L’ Albufera. Demographic studies on the effect of extracts from phytoplankton blooms using rotifers provide valuable insights into natural interactions.…”