Cascading effects of predatory fish exclusion on the detritus-based food web of a lake littoral zone (Lake Vico, central Italy)

Abstract

An exclosure experiment was carried out in the reed-dominated littoral zone of a volcanic lake (Lake Vico, central Italy) to test whether the impact of predatory fish on benthic invertebrates cascades on fungal colonisation and breakdown of leaf detritus. The abundance, biomass, and Shannon diversity index of the invertebrate assemblage colonising Phragmites australis leaf packs placed inside: (1) full-exclosure cages, (2) cages allowing access only to small-sized fish predators, and (3) cageless controls, were monitored over a 45-day period together with the mass loss and associated fungal biomass of leaf packs. The species composition of the fungal assemblage was further assessed at the end of the manipulation. In general, invertebrate predators did not show any significant response to fish exclusion, either on a trophic guild or on a single taxon level. In contrast, the exclusion of large predatory fish induced a diverse spectrum of changes in the abundance and population size-structure of dominant detritivore taxa, ultimately increasing the biomass and Shannon diversity index of the whole detritivorous guild. These changes corresponded with significant variations in leaf detritus decay rates as well as in the biomass and assemblage structure of associated fungal colonisers. Our experimental findings provide evidence that in Lake Vico effects of fish predators on invertebrate detritivores influence the fungal conditioning and breakdown of the detrital substrate. We conclude that in lacustrine littoral zones predator-driven constraints may structure lower trophic levels of detritus-based food webs and affect the decomposition of leaf detritus originated from the riparian vegetation.

Detritus Processing in Tri‐Trophic Food Chains: a Modelling Approach

“…Finally, according to our simulations, shredders play a negligible role in leaf decomposition. This finding is probably due to the low abundance on leaf detritus of specimens belonging to the tropho-functional group, fully consistent with field data (MANCINELLI et al, 2005) yet rather unusual compared with other studies (VARGA, 2001;MANCINELLI et al, 2002; VAN DOKKUM et al, 2002). In the field, low leaf pack colonization rates by invertebrates might be related to the characteristics of the lagoon.…”

On the Influence of Temporal Resolution in Mesh Bag Decomposition Studies

“…Our results highlight a significant effect of sampling resolution on the detection of differences in reed decomposition patterns between the experimental sites. The observed loss of significance is obviously linked to the simultaneous decrease in the number of ANOVA degrees of freedom, but it is noticeable, however, how the loss of significance of the test occurred with a number of samplings similar to, or even higher than, other decomposition studies of Phragmites characterised by a temporal extent comparable to that of the present study (e.g., MANCINELLI et al, 2002). In this perspective, it is plausible to hypothesize that many studies may have provided a highly conservative estimate of actual inter-site, inter-system or inter-treatment differences.…”

Food web responses to low-level nutrient and 15 N-tracer additions in the littoral zone of an oligotrophic dune lake

“…Results of mixing model analyses of the relative contribution of periphyton, riparian vegetation (rip veg), and seston sources of carbon to the diets of aquatic consumers in Lake McKenzie. Analyses conducted with the two-isotope, three source mixing model of Phillips and Koch (2002 gotrophic lakes suggest that despite the prevalence of terrestrial detritus and emergent macrophytes in lake littoral zones, few littoral zone food webs are driven by allochthonous carbon through detritivorous pathways (Mancinelli et al 2002). Instead, consumers tend to show a disproportionate reliance on periphyton carbon, even when standing biomass is low (Hecky and Hesslein 1995;James et al 2000a).…”