Abstract
Abstract. Organic matter (OM) exchanges between adjacent habitats affect the dynamics and functioning of coastal systems, as well as the role of the different primary producers as energy and nutrient sources in food webs. Elemental (C, N, C : N) and isotope (δ13C) signatures and fatty acid (FA) profiles were used to assess the influence of geomorphological setting in two climatic seasons on the export and fate of mangrove OM across a tidally influenced tropical area, Gazi Bay (Kenya). The main results indicate that tidal transport, along with riverine runoff, plays a significant role in the distribution of mangrove organic matter. In particular, a marked spatial variability in the export of organic matter from mangroves to adjacent habitats was due to the different settings of the creeks flowing into the bay. Kinondo Creek acted as a mangrove retention site, where export of mangrove material was limited to the contiguous intertidal area, while Kidogoweni Creek acted as a flow-through system, from which mangrove material spreads into the bay, especially in the rainy season. This pattern was evident from the isotopic signature of primary producers, which were more 13C-depleted in the Kinondo Creek and nearby, due to the lower dilution of the dissolved inorganic carbon (DIC) pool, typically depleted as an effect of intense mangrove mineralisation. Despite the trapping efficiency of the seagrass canopy, suspended particulate OM showed the important contribution of mangroves across the whole bay, up to the coral reef, as an effect of the strong ebb tide. Overall, mixing model outcomes indicated a widespread mixed contribution of both allochthonous and autochthonous OM sources across Gazi Bay. Moreover, FAs indicated a notable contribution of brown macroalgae and bacteria in both sediment and suspended pools. These results suggest that ecological connectivity in Gazi Bay is strongly influenced by geomorphological setting, which may have far-reaching consequences for the functioning of the whole ecosystem and the local food webs.
Highlights
Mangrove forests are known to be among the most productive ecosystems worldwide, with a crucial role in the carbon budget (Alongi, 2014; Dittmar et al, 2006; Kristensen et al, 2008)
Δ13C of sedimentary organic matter (δ13CSOM) increased drastically along the land-to-sea transects (Fig. 3a). δ13C of sedimentary organic matter (δ13CSOM) of the landward stations (M, intertidal area (IA)) was lower overall in transect B than in A, while it was more homogeneous in the other stations and showed a marked increase in the coral reefs (CR)
Using elemental and stable isotope (SI) signatures, together with fatty acid (FA) profiles, this study showed that small-scale variability in the environmental settings of the mangrove forest has a crucial role in influencing the export of mangrove-derived organic matter to adjacent habitats
Summary
Mangrove forests are known to be among the most productive ecosystems worldwide, with a crucial role in the carbon budget (Alongi, 2014; Dittmar et al, 2006; Kristensen et al, 2008). A considerably large amount of mangrove-derived carbon in the form of leaves, particulate detritus and dissolved organic and inorganic matter is exported to adjoining ecosystems, subsidising coastal waters and influencing nutrient biogeochemical cycling (Dittmar et al, 2006; Duarte and Cebrián, 1996). With the “outwelling hypothesis”, Odum and Heald (1972) first suggested that leaf detritus exported from mangrove forests would represent an important trophic source contributing to secondary production in adjacent offshore areas.
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
