Leaf choice by crustaceans in a mangrove forest in Queensland

Abstract

The feeding behaviour of leaf eating crustaceans feeding on leaves shed by Avicennia marina, Bruguiera gymnorhiza and Rhizophora stylosa in the mangrove forest at Myora Springs, Queensland, Australia was studied between 1980 and 1984.Individual Sesarma erythrodactyla (carapace > 9 mm long), one of the most abundant species of crabs in the forest, processed approximately half a leaf from any of the three species of mangroves in 24 h under laboratory conditions. Of the amount of leaf material processed, 20% was lost from the mandibles due to "sloppy feeding", 68% was egested as faeces and 12% converted into crab biomass. Crabs processed more leaf material at 30 °C than at 20 °C. S. erythrodactyla preferred leaves of A. marina to those of the other two species, probably because leaves of A. marina have a lower tannin and a higher nitrogen content. Of the other two species, B. gymnorhiza was preferred to R. stylosa. Among leaves of R. stylosa, S. erythrodactyla exerts a strong preference for aged rather than freshly fallen, and for thick rather than thin leaves. The mesofauna (carapace length < 9.0 ram) which processed dead mangrove leaves comprised juveniles of S. erythrodactyla, the crab Ilyograpsus paludicola, the isopod Exosphaeroma alata and the amphipods Orchestia sp. and Melita sp. These species processed between 0.2 and 24.7 mg dry wt of a leaf per individual over a period of 4 d. Of this, 72 to 85% was egested as faeces. The significance of leaf eating crabs to nutrient cycling in mangrove forests is discussed. I conclude that leaf processing by crustaceans shortens the time span between leaf fall and consumption of leaf material by organisms. This may have the effect of conserving leaf biomass inside the mangrove forest.

Decomposition of Avicennia marina (Forsk.) Vierh. Foliage under field and laboratory conditions in the backwaters of Karachi, Pakistan

“…However, laboratory aerobic condition (LAC) replicates the field aerobic conditions except that it excludes herbivores. The low decay rate under LAC may be due to the exclusion of some of the consumers (<1 mm 2 ), such as, isopods, polycheates, flatworms, nematodes, insect larvae, some gastropods and crabs which play a significant role in the initial stages of decomposition (Robertson 1986, Camilleri 1992. Similarly, very low decomposition rate observed in LAAC may be due to the lack of both oxygen and herbivores.…”

Litter degradation and CN dynamics in reforested mangrove plantations at Gazi Bay, Kenya

“…Amphipods were the dominant group suggesting that they were relatively more important in enhancing litter breakdown. This faunal component has been found to enhance degradation by feeding directly on detritus (Camilleri, 1992;Poovachiranon et al, 1986) and this directly influences the rate of decomposition (Basaguren and Pozo, 1994). No amphipods were however observed in the R. mucronata bare treatment litter bags, which had the lowest decay rate.…”

Effects of habitat modification in mangroves on the structure of mollusc and crab assemblages

“…Localised increases in the abundance of crabs in areas where there is reduced physical heterogeneity may have important implications for other components of mangrove systems. Mangrove crabs, including sesarmids such as Parasesarma erythrodactyla, are important seed-predators, especially in tropical systems (Smith, 1987;Camilleri, 1992), so increases in their abundance may influence the recruitment of mangrove seedlings and their capacity to recolonise areas after disturbance. Mangrove crabs are also important in determining the rates of accumulation of decaying leaf litter (Robertson and Daniel, 1989), and hence have the potential to influence the biomass of material available for export to nearshore coastal systems (e.g.…”