The interactions of mangrove trees with soil and associated microorganisms are complex. Mangrove trees must cope with a harsh, waterlogged environment, being anchored in soils colonized by highly abundant, productive, and diverse microbial assemblages. The soil horizons are usually dominated by biogenic structures, usually crab burrows and deep tree roots, and are often pockmarked with cracks and fissures. These structures and their activities, coupled with drainage and recharge of interstitial water by tides, foster spatially complex patterns of organic matter decomposition within the forest floor. Except for biogenic structures, oxygen penetrates only a few millimeters into the soil, so anaerobic processes dominate early diagenesis. Sulfate reduction is often the major anoxic process, occurring to a soil depth of at least 1 m and relating to root uptake and exudation of dissolved materials. Recent evidence suggests that iron and manganese reduction may be important in close association with roots and crab activities. Mangrove soils are a source of microbially mediated gases, such as CO2, CH4, N2, and N20. The driving factor of plant-soil relations in mangrove forests is the high nutrient and water requirements needed to fuel high rates of tree photosynthesis. Close and highly efficient tree-microbe-soil interrelationships are a major factor in explaining why mangroves are highly productive forests in oligotrophic environments.

Mangrove-microbe-soil relations

Structurally complex mangrove roots are thought to provide foraging habitat, predation refugia, and typhoon protection for resident fish, shrimp, and crabs. The spatially compact nature of Micronesian mangroves results in model ecosystems to test these ideas. Tidal creek nekton assemblages were compared among mangrove forests impacted by Typhoon Sudal and differing in stand structure. Structurally complex Rhizophora spp. stands were predicted to support higher densities and different communities of nekton and to provide greater protection from typhoons compared to less complex Sonneratia alba/Bruguiera gymnorrhiza stands. Lift net data revealed that structural complexity did not support greater nekton densities, but did support significantly different nekton assemblages. The cardinalfish Apogon ceramensis and goby Oxyurichthys lonchotus had significantly higher densities in S. alba/B. gymnorrhiza mangrove creeks, whereas the silverside Atherinomorus lacunosus and diogenid crabs had significantly higher densities in Rhizophora spp. creeks. Similar nekton densities 17 and 4 months after the typhoon in Rhizophora spp. creeks provided indirect evidence that structural complexity increased protection for resident nekton from disturbances. Findings indicate that studies of structural complexity and nekton densities may be better served when individual species are compared and that diverse mangrove tree assemblages will support diverse nekton assemblages that may be more resilient to disturbance.

https://www.fs.fed.us/psw/publications/mackenzie/psw_2012_mackenzie002.pdf

Stand structure influences nekton community composition and provides protection from natural disturbance in Micronesian mangroves

We compared the mollusc assemblages of planted mono-specific Rhizophora mangroves of known different ages. As forest age increased, there was a shift in species composition, abundance and biomass of mollusc assemblages for all faunal types (infauna, epifauna and arboreal fauna). This shift was correlated with the changes in vegetation (increasing forest cover and above-ground biomass) and sediment characteristics (increasing organic matter and decreasing sand content). Some species dominate in young plantations ( 15 years; Terebralia sulcata, Nerita planospira). The two former groups of species are mostly species of infaunal and epifaunal habitats, while the latter group is mainly composed of arboreal species. The shift in mollusc species composition and dominance may serve as a useful indicator of restoration patterns in planted mangroves.

Colonization and shift of mollusc assemblages as a restoration indicator in planted mangroves in the Philippines

Baseline community assemblages and diversity of macrozoobenthic infauna in soft-bottomed intertidal flats at Bodo Creek on the upper reaches of the Andoni–Bonny estuarine system were determined spatially and in relation to sediment particle characteristics for two years from May 2006 to April 2008. Interstitial water temperature, pH, dissolved oxygen and conductivity varied, while biological oxygen demand at the sites was similar. A total of 7 742 specimens belonging to 47 genera and 29 families of macrofauna were recovered from the samples. Density ranged between 8 and 1 583 m−2, while Shannon–Wiener diversity varied from 0.102 to 1.052. A Hutcheson t-test revealed significant inter-site diversity differences, except for Station 2 vs Station 5 and Station 4 vs Station 5. Canonical correspondence analysis (CCA) revealed that the nature of substratum accounted for 34% of the taxa distribution and abundance in the study area; variances for the first and second axes were 77.8% and 21.2%, respectively. The CC...

Spatial variability of macrozoobenthic diversity on tidal flats of the Niger Delta, Nigeria: the role of substratum

Environmental factors strongly affect mangrove crabs, and some factors modulate population structure and habitat partitioning during the crabs’ life cycle. However, the effect of these environmental factors on habitat selection by mangrove crabs is still unknown. We evaluated habitat selection by the mangrove crab Ucides cordatus in mangrove forests with different degrees of predominance of Rhizophora mangle, Laguncularia racemosa or Avicennia schaueriana, two tidal flooding levels (less- and more-flooded), and two biological periods (breeding and non-breeding seasons). Sampling was conducted in four mangrove forests with different influences of these biotic and abiotic parameters. We used the data for sex ratio to explain environmental partitioning by this species. Females predominated in R. mangle mangroves, independently of the biological period (breeding or non-breeding seasons), and males predominated only in the less-flooded L. racemosa mangroves. The flooding level affected the sex ratio of U.
 cordatus, with a predominance of males in less-flooded mangroves, independently of the biological period; and a gender balance in the more-flooded mangroves only during the breeding season. Outside the breeding season, the largest specimens were recorded in the R. mangle mangroves, but in the breeding season, the largest crabs were recorded in the L. racemosa mangroves with a higher level of flooding. These results suggest that tree-species composition and tidal flooding level can have a significant effect on the habitat partitioning of sexes and sizes of the mangrove crab U. cordatus both during and outside the breeding season.

/pdf/mangrove-habitat-partitioning-by-ucides-cordatus-ucididae-3z9qj2mez3.pdf

Mangrove habitat partitioning by Ucides cordatus (Ucididae): effects of the degree of tidal flooding and tree-species composition during its life cycle

A. Sasekumar

Papers

6. Benthic Communities