Abstract
Mangrove crabs influence ecosystem processes through bioturbation and/or litter feeding. In Brazilian mangroves, the abundant and commercially important crab Ucides cordatus is the main faunal modifier of microtopography establishing up to 2 m deep burrows. They process more than 70% of the leaf litter and propagule production, thus promoting microbial degradation of detritus and benefiting microbe-feeding fiddler crabs. The accelerated nutrient turn-over and increased sediment oxygenation mediated by U. cordatus may enhance mangrove tree growth. Such positive feed-back loop was tested in North Brazil through a one year crab removal experiment simulating increased harvesting rates in a mature Rhizophora mangle forest. Investigated response parameters were sediment salinity, organic matter content, CO2 efflux rates of the surface sediment, and reduction potential. We also determined stipule fall of the mangrove tree R. mangle as a proxy for tree growth. Three treatments were applied to twelve experimental plots (13 m × 13 m each): crab removal, disturbance control and control. Within one year, the number of U. cordatus burrows inside the four removal plots decreased on average to 52% of the initial number. Despite this distinct reduction in burrow density of this large bioturbator, none of the measured parameters differed between treatments. Instead, most parameters were clearly influenced by seasonal changes in precipitation. Hence, in the studied R. mangle forest, abiotic factors seem to be more important drivers of ecosystem processes than factors mediated by U. cordatus, at least within the studied timespan of one year.
Highlights
Burrowing crabs are ecosystem engineers and their importance for sediment processes has been discussed for many years [1,2,3,4,5], along with effects of their feeding activities on forestPLOS ONE | DOI:10.1371/journal.pone.0167375 December 1, 2016Ucides cordatus Removal ExperimentInstituto do Estudos Costeiros (IECOS) of the Federal University of Para (UFPa)
It proved logistically feasible to set up to approximately 400 nylon nets per sampling day and per removal plot, which initially covered around 50% of all U. cordatus burrows and, at six months of the experiment, around 90–100% of all U. cordatus burrows
The carapace width of the captured U. cordatus specimens decreased over time in removal plot 1 (F-value = 50.4, df = 1, p-value < 0.001) and 3
Summary
Burrowing crabs are ecosystem engineers and their importance for sediment processes has been discussed for many years [1,2,3,4,5], along with effects of their feeding activities on forestPLOS ONE | DOI:10.1371/journal.pone.0167375 December 1, 2016Ucides cordatus Removal ExperimentInstituto do Estudos Costeiros (IECOS) of the Federal University of Para (UFPa). Burrowing crabs are ecosystem engineers and their importance for sediment processes has been discussed for many years [1,2,3,4,5], along with effects of their feeding activities on forest. Instituto do Estudos Costeiros (IECOS) of the Federal University of Para (UFPa). The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript
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