The effect of habitat complexity on the contribution of some littoral–benthic Cladocera to the pelagic food web

Abstract

Littoral zones of lakes are settled by typical littoral animals, but they are also explored by mobile vertebrate and invertebrate predators. The relative importance of habitat complexity on the availability of littoral–benthic species of Cladocera, including Alonella exigua, A. excisa and A. nana (Chydoridae), to planktonic predators (Leptodora and cyclopoid copepods) was investigated in a series of laboratory experiments and under natural conditions (Lake Piaseczno, eastern Poland). The laboratory experiments showed that invertebrate predators influenced the density of cladocerans, but that predatory success was related to spatial complexity. A treatment imitating a habitat of water milfoil provided the highest survival rate, whereas a treatment imitating a habitat of macroalgae provided the lowest survival rate of the Alonella species, independently of the type of predators. Leptodora showed a higher predation pressure than did the cyclopoid copepods in a treatment imitating a habitat of common reed. In the field research, inverse correlations between the density of Alonella and potential invertebrate predators in distinct habitats were found. The species most strongly preyed on under the experimental conditions showed the highest fecundity, thus suggesting that the predation pressure by planktonic invertebrates influences the demography and life-history trade-offs of juvenile Alonella individuals in the lake. The obtained results extend our knowledge on the type and magnitude of interactions between the littoral–benthic and pelagic food webs.