Fatty acids in decomposing mangrove leaves: microbial activity, decay and nutritional quality

Abstract

Changes in lipid content and fatty acid (FA) composition in decomposing mangrove leaves of Bruguiera gymnorrhiza (L.) Lamk and Kandelia candel (L.) were investigated in a subtropical mangrove forest on Okinawa Island, Japan (26.5°N, 128°E) by field experiments for 18 wk (July to November 2000), using yellow senescent leaves, and compared with FAs in the green leaves and mangrove sediments. We tested the hypothesis that changes in FA composition during decomposition can indicate the state of leaf decay and periods of high and low microbial activity, and that bacteria may rapidly degrade polyunsaturated fatty acids (PUFAs). During decay, FA composition in the yellow leaves changed in 2 wk from predominantly saturated FAs to monounsaturated FAs, and to the more branched FAs typical of bacteria, and lipid and N increased due to microbial colonization. However, the microbial decomposition of leaves did not alter the concentrations of long-chain fatty acids (LCFAs), suggesting that these vascular plant-markers remain unchanged in mangrove detritus and surface sediments for more than 4 mo. Furthermore, bacteria did not degrade PUFAs as we had hypothesized, indicating that during decomposition of mangrove leaves, bacteria tend to conserve PUFAs (as they do nitrogen), thus enriching the detritus with nutrients. Comparison of ω3 and ω6 PUFAs between the 2 species showed that nutritional quality varies greatly with the state of the leaf material, increasing through time in B. gymnorrhiza and decreasing through time in K. candel.

Impacts of exotic mangrove forests and mangrove deforestation on carbon remineralization and ecosystem functioning in marine sediments

“…These results highlight the very labile nature of the added algal-C-source and suggest that the measured SOC and total daily DIC efflux values may be higher than background values without algal addition. Nevertheless, SOC rates measured in the PHM experiments were quite similar to those found in previous mangrove studies (Nedwell et al, 1994;Middelburg et al, 1996;Alongi et al, 2000;Alongi, 2009), and overall rates were strongly correlated with total benthic (macrofauna and bacteria) biomass, which is consistent with other studies (e.g., Bolam et al, 2002). This strong correlation suggests that the significantly elevated bacterial biomass in sediment cores from the PHM and KBR sites, in addition to the large macrofauna biomasses found in sediments from both removal sites, played a major role in stimulating sediment O 2 demand in the mangrove and removal site experiments.…”

“…Mangroves also act as major ecosystem engineers by reducing water flow and trapping sediments, which can lead to enhanced densities of deposit feeding fauna (Demopoulos, 2004;Demopoulos and Smith, 2010), as well as limiting coastal erosion, and providing a buffer to tropical storms and tsunamis (Environmental Justice Foundation report 2006). They also effectively sequester nutrients (Middelburg et al, 1996;Bouillon et al, 2008), and may enhance water quality in surrounding habitats by reducing eutrophication and turbidity (Valiela and Cole, 2002;Victor et al, 2004).…”

Small-scale variability in geomorphological settings influences mangrove-derived organic matter export in a tropical bay

“…The different dominant vegetation in Kidogoweni and Kinondo creeks (Avicennia marina vs. Rhizophora mucronata; Neukermans et al, 2008) may also affect the magnitude of organic matter export from mangrove forest. Higher export from forests dominated by Avicennia sp., compared to those dominated by Rhizophora sp., has been observed in Brazil and related to different detritus decomposition rates (Lacerda et al, 1995).…”

“…The dominant mangrove species along the creek fringes at Gazi Bay are Rhizophora mucronata, Ceriops tagal, Sonneratia alba and Avicennia marina (Hemminga et al, 1994;Neukermans et al, 2008). Seagrass beds mixed with macroalgae cover both the creeks and the bay up to the seaward mouth (Githaiga et al, 2016).…”

“…The main goal of this study was to assess the fate of mangrove-derived organic matter, the dominant terrestrial source in Gazi Bay (Bouillon et al, 2007;Neukermans et al, 2008), in relation to the small-scale variability in geomorphological settings of the area, using combined elemental, isotopic and fatty acid analyses. In particular, following a preliminary characterisation of primary producers, sediment (SOM) and suspended particulate organic matter (SPOM), we estimated the contribution of dominant primary producers to SOM and SPOM pools based on quantitative (isotope mixing models) and semi-quantitative (fatty acid profiles) approaches.…”