Mangrove carbon sink. Do burrowing crabs contribute to sediment carbon storage? Evidence from a Kenyan mangrove system

Abstract

Mangrove ecosystems are acknowledged as a significant carbon reservoir, with a potential key role as carbon sinks. Little however is known on sediment/soil capacity to store organic carbon and the impact of benthic fauna on soil organic carbon (SOC) stock in mangrove C-poor soils. This study aimed to investigate the effects of macrobenthos on SOC storage and dynamic in mangrove forest at Gazi Bay (Kenya). Although the relatively low amount of organic carbon (OC%) in these soils, they resulted in the presence of large ecosystem carbon stock comparable to other forest ecosystems. SOC at Gazi bay ranged from 3.6 kg m −2 in a Desert-like belt to 29.7 kg m −2 in the Rhizophora belt considering the depth soil interval from 0 cm to 80 cm. The high spatial heterogeneity in the distribution and amount of SOC seemed to be explained by different dominant crab species and their impact on the soil environment. A further major determinant was the presence, in the subsoil, of horizons rich in organic matter, whose dating pointed to their formation being associated with sea level rise over the Holocene. Dating and soil morphological characters proved to be an effective support to discuss links between the strategies developed by macrobenthos and soil ecosystem functioning.

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

“…In our study, slightly lower rH values were recorded at the sediment surface during the wet season (Fig 2). Consequently, waterlogged and more anoxic sediment conditions in the upper sediment layers may have led to reduced carbon oxidation rates, resulting in lower CO 2 release (Fig 1) as observed elsewhere [1,70,75]. Overall, our results suggest that seasonal changes in precipitation are more important drivers for the measured parameters than the U .…”

“…low tide, dry season), when burrow walls are more oxidized due to contact with atmospheric oxygen. Consequently, carbon oxidation is facilitated by the presence of burrows, resulting in diminishing sediment organic matter [1,62]. A decreasing number of crabs would therefore affect both (antagonistic) processes and could potentially result in a zero net change.…”

“…Burrowing crabs are ecosystem engineers and their importance for sediment processes has been discussed for many years [1–5], along with effects of their feeding activities on forest structure and nutrient cycling [2,6–11]. To determine the ecological roles and ecosystemic importance of burrowing crabs, addition or exclusion and removal experiments have been performed.…”

Interference competition as a key determinant for spatial distribution of mangrove crabs

“…Although the relative frequency of crab species can change in the distinct parts of the forest, the most common crab species are Neosarmatium smithi , N. malabaricum , N. asiaticum (formerly N. meinerti ) [50, 51], Muradium tetragonum , Perisesarma dusumieri , Parasesarma bengalense and P. plicatum . Crab species of the genera Neosarmatium and Muradium feed on fallen leaves, collect them and store litter into their burrows, enhancing the carbon sink function of mangrove forests soils [31]. …”

Effect of Anthropogenic Activities on Mangrove Crab Diversity in Cameroon Atlantic Coast

“…By consuming litter, crabs can promote nutrient mineralization and recycling within the forest. Furthermore, their role as bioturbators doubtlessly contributes to alter physiochemical characteristics of the soil and enhance its capability to retain organic carbon [12,13]. More recently, the beneficial effect of Uca spp.…”