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Burrows of the semi-terrestrial crab Ucides cordatus enhance CO2 release in a North Brazilian mangrove forest.

Pülmanns N, Diele K, Mehlig U, Nordhaus I - PLoS ONE (2014)

Bottom Line: This increase in sediment-air contact area may enhance carbon degradation processes.Sediment cores (50 cm length) were taken to measure the same parameters for plain sediment.More oxidized conditions of plain sediment over time may explain the increase in CO2 release until the end of the wet season.

View Article: PubMed Central - PubMed

Affiliation: Department of Ecology, Leibniz Center for Tropical Marine Ecology (ZMT), Bremen, Germany.

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.

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Vertical and horizontal sampling scheme of the sediment surrounding U. cordatus burrows for the rH measurements.
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pone-0109532-g003: Vertical and horizontal sampling scheme of the sediment surrounding U. cordatus burrows for the rH measurements.

Mentions: In the study area U. cordatus is the only large burrowing crab (max. carapace width of 9.9 cm in the Caeté estuary, [29]). An average density of 1.7 ind. m−2 was reported for the Furo Grande area in R. mangle dominated forests [30]. U. cordatus prefers to construct its burrow around the root system of R. mangle, because large roots structure the sediment and thereby increase sediment stability and provide shelter against predators [31]. Burrows of U. cordatus can have various forms. They can be simple burrows with one opening and one corridor, U-shaped with more than one opening, or even more complex structures with a maximum of three openings [32]. In northeast Brazil simple burrows are the most common type (more than 85% of all investigated burrows, n = 735) [32]. In the Furo Grande area simple burrows are also the most common burrow type (unpublished observation). Such burrows have the following morphology: Their corridors initially descend with a slight slope and then bend vertically downwards until forming a terminal burrow chamber ([14], Figure 3). At our study site at the Furo Grande total burrow corridor lengths (initial horizontal and vertical part) ranged from 73 to 219 cm with an average of 123±32 cm (mean ± standard deviation, n = 30, own data). The inner walls of the burrows of U. cordatus have no conspicuous inner mucus layer such as known from Polychaetes (e.g. reviewed by Kristensen and Kostka [33]). The burrows of the other crab species, for example sympatric fiddler crabs, also seem to be unlined (own observation, [34]).


Burrows of the semi-terrestrial crab Ucides cordatus enhance CO2 release in a North Brazilian mangrove forest.

Pülmanns N, Diele K, Mehlig U, Nordhaus I - PLoS ONE (2014)

Vertical and horizontal sampling scheme of the sediment surrounding U. cordatus burrows for the rH measurements.
© Copyright Policy
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4196909&req=5

pone-0109532-g003: Vertical and horizontal sampling scheme of the sediment surrounding U. cordatus burrows for the rH measurements.
Mentions: In the study area U. cordatus is the only large burrowing crab (max. carapace width of 9.9 cm in the Caeté estuary, [29]). An average density of 1.7 ind. m−2 was reported for the Furo Grande area in R. mangle dominated forests [30]. U. cordatus prefers to construct its burrow around the root system of R. mangle, because large roots structure the sediment and thereby increase sediment stability and provide shelter against predators [31]. Burrows of U. cordatus can have various forms. They can be simple burrows with one opening and one corridor, U-shaped with more than one opening, or even more complex structures with a maximum of three openings [32]. In northeast Brazil simple burrows are the most common type (more than 85% of all investigated burrows, n = 735) [32]. In the Furo Grande area simple burrows are also the most common burrow type (unpublished observation). Such burrows have the following morphology: Their corridors initially descend with a slight slope and then bend vertically downwards until forming a terminal burrow chamber ([14], Figure 3). At our study site at the Furo Grande total burrow corridor lengths (initial horizontal and vertical part) ranged from 73 to 219 cm with an average of 123±32 cm (mean ± standard deviation, n = 30, own data). The inner walls of the burrows of U. cordatus have no conspicuous inner mucus layer such as known from Polychaetes (e.g. reviewed by Kristensen and Kostka [33]). The burrows of the other crab species, for example sympatric fiddler crabs, also seem to be unlined (own observation, [34]).

Bottom Line: This increase in sediment-air contact area may enhance carbon degradation processes.Sediment cores (50 cm length) were taken to measure the same parameters for plain sediment.More oxidized conditions of plain sediment over time may explain the increase in CO2 release until the end of the wet season.

View Article: PubMed Central - PubMed

Affiliation: Department of Ecology, Leibniz Center for Tropical Marine Ecology (ZMT), Bremen, Germany.

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.

Show MeSH
Related in: MedlinePlus