The effects of physicochemical variables and tadpole assemblages on microalgal communities in freshwater temporary ponds through an experimental approach

Abstract

Background: In freshwater systems, microalgae are the major biomass of microorganisms. They occur in ecosystems that are largely structured by the climatic regime, the physical and chemical environments with which they interact, and the biological interactions that occur within them. Amphibian larvae are most present in standing water habitats where they are important primary and secondary consumers and even predators. Studies conducted in America and Europe have shown that tadpoles play an important role in the regulation of the algal community structure and water quality in ecosystems. This article aimed to study the effects of the physicochemical variables and tadpole assemblages of four species on microalgae in artificial freshwater ponds using an experimental approach in the Pendjari area, a flora and fauna reserve located in the extreme north-west of Benin.

Results: The species of phytoplankton and periphyton recorded in ponds were among the taxonomical groups of chlorophytes, cyanophytes, euglenophytes, diatoms and dinoflagellates. Chlorophytes were the dominant group in the algal communities. Physicochemical variables affected the biomass of the different communities of algae in temporary freshwater ponds. Transparency and pond size were the most determinative variables of the structure of microalgae communities in ponds. Tadpoles of Kassina fusca, Ptychadena. bibroni, and Phrynomantis microps were important for the regulation of the water quality and algal community structure by grazing and filter-feeding.

Conclusions: A decrease in the tadpole population in the artificial temporary ponds due to predation by carnivorous tadpoles of Hoplobatrachus occipitalis caused a disturbance of the algal community structure. This means that the decline of the amphibian population will critically lead to the impoverishment of ecosystems, thereby negatively influencing aquatic and terrestrial ecosystems.

Keywords: Experimental approach; Microalgae; Periphyton; Physicochemical variables; Phytoplankton; Tadpoles assemblages.

Figure 1

Comparisons of the survival rate of the respective tadpole species in treatments of varying species compositions [ 19 ]. A: H. occipitalis, B: K. fusca, C: P. bibroni, D: P. microp; a) Survival rate of K. fusca in large tanks, b) K. fusca in small tanks), c) P. bibroni in large tanks, d) P. bibroni in small tanks, e) P. microps in large tanks (N = 59), f) P. microps in small tanks. Small letters indicate significant differences between treatments.

Figure 2

Differences and similarities of variables between tadpole assemblages in small ponds after comparison using a t-test. Small letters indicate significant differences between treatments.

Figure 3

Differences and similarities of variables between tadpole assemblages in large ponds after comparison using a t-test. Small letters indicate significant differences between treatments.

Figure 4

NMS ordination of ponds based on species structure in freshwater artificial ponds containing tadpoles. 1: small ponds; 2: large ponds A: Hoplobatrachus occipitalis; B: Kassina fusca; C: Ptychadena bibroni; D: Phrynomantis microps

Figure 5

RDA indicating position of algal groups and vectors of environmental variables. Chloro: Chlorophytes, Cyano: Cyanophytes, Diatomo: Diatomophyceae (Diatoms), Dino: Dinoflagellates (Dinophytes), Eugleno: Euglenophytes; ec: Electrical conductivity, Dep: depth, transp: transparency, nit: nitrates, Phos: phosphates-phosphorus, amm: ammonium, oxy: dissolved oxygen.

Figure 6

Comparison of community biomass between tadpole assemblages using a t-test. 1: abundance of chlorophytes from periphyton in large ponds; 2: abundance of euglenophytes from periphyton in large ponds; 3: abundance of chlorophytes within periphyton in small ponds; 4: abundance of cyanophytes within periphyton in small ponds. A: Hoplobatrachus occipitalis; B: Kassina fusca; C: Ptychadena bibroni; D: Phrynomantis microps. Small letters indicate significant differences between treatments.

Figure 7

Study area.

Figure 8

Photograph of small artificial temporary ponds (volume: 90 L).

Figure 9

Photograph of large artificial temporary ponds (volume: 200 L).