Burrows of the Semi-Terrestrial Crab Ucides cordatus Enhance CO2 Release in a North Brazilian Mangrove Forest

Abstract

Ucides cordatus is an abundant mangrove crab in Brazil constructing burrows of up to 2 m depth. Sediment around burrows may oxidize during low tides. This increase in sediment-air contact area may enhance carbon degradation processes. We hypothesized that 1) the sediment CO2 efflux rate is greater with burrows than without and 2) the reduction potential in radial profiles in the sediment surrounding the burrows decreases gradually, until approximating non-bioturbated conditions. Sampling was conducted during the North Brazilian wet season at neap tides. CO2 efflux rates of inhabited burrows and plain sediment were measured with a CO2/H2O gas analyzer connected to a respiration chamber. Sediment redox potential, pH and temperature were measured in the sediment surrounding the burrows at horizontal distances of 2, 5, 8 and 15 cm at four sediment depths (1, 10, 30 and 50 cm) and rH values were calculated. Sediment cores (50 cm length) were taken to measure the same parameters for plain sediment. CO2 efflux rates of plain sediment and individual crab burrows with entrance diameters of 7 cm were 0.7–1.3 µmol m−2 s−1 and 0.2–0.4 µmol burrows−1 s−1, respectively. CO2 released from a Rhizophora mangle dominated forest with an average of 1.7 U. cordatus burrows−1 m−2 yielded 1.0–1.7 µmol m−2 s−1, depending on the month and burrow entrance diameter. Laboratory experiments revealed that 20–60% of the CO2 released by burrows originated from crab respiration. Temporal changes in the reduction potential in the sediment surrounding the burrows did not influence the CO2 release from burrows. More oxidized conditions of plain sediment over time may explain the increase in CO2 release until the end of the wet season. CO2 released by U. cordatus and their burrows may be a significant pathway of CO2 export from mangrove sediments and should be considered in mangrove carbon budget estimates.

Mangrove Crab Ucides cordatus Removal Does Not Affect Sediment Parameters and Stipule Production in a One Year Experiment in Northern Brazil

“…However, our rH results do not support a general, i.e. far-reaching effect of the burrows on sediment reduction state, probably due to the limited reach of aeration effects at individual burrows [63] in combination with the relatively low burrow densities (also in our control plots). Under these conditions, overlap between oxidized zones around burrows is minimal.…”

“…Pülmanns et al [63] showed such an effect at least for the immediate neighborhood of U . cordatus burrow walls.…”

Sediment properties and CO<sub>2</sub> efflux from intact and cleared temperate mangrove forests

“…Davidson . Soil temperature is one of the key abiotic factors influencing both the autotrophic and heterotrophic activity (Raich and Schlesinger, 1992).…”

“…The global net primary productivity in mangrove forests has been estimated at 218 ± 72 Tg C a −1 , which includes the rate of litterfall and above-and below-ground biomass production . An important component of the C cycle is the efflux of carbon dioxide (CO 2 ) from the sediment into the atmosphere (Raich and Schlesinger, 1992). Sediment CO 2 efflux is the total of CO 2 released through root/mycorrhizae respiration (autotrophic respiration) and microbial respiration (heterotrophic respiration) associated with the decomposition of organic matter .…”

Seasonal and latitudinal variations in the energy reserves of the mud fiddler crab Uca pugnax: implications for the response to climate change

“…Any range shift in this species has ecosystem-wide consequences: deposit feeding and burrowing by U. pugnax impact infaunal species densities (Hoffman et al 1984), plant growth (Bertness 1985, Smith & Tyrrell 2012, Gittman & Keller 2013, decomposition rates (Thomas & Blum 2010), and sediment accumulation or erosion, depending on site-specific characteristics (Katz 1980, Smith & Green 2015. Also, burrow excavation is an activity that has been found to enhance carbon flux in other systems with burrowing semi-terrestrial crabs (Pülmanns et al 2014). Finally, adult and larval U. pugnax are consumed by many other species, including larval and adult fishes, birds, and other crabs (Crane 1975).…”