Organic Matter Fate and Trophic Functioning of Arid Mangroves in Abu Dhabi (UAE)

Background and Rationale

Mangroves rank among the most productive coastal ecosystems globally, functioning as critical blue carbon sinks and as primary sources of organic matter (OM) sustaining complex intertidal food webs. Over the past two decades, fatty acid (FA) profiling and stable isotope analysis have been established as robust biochemical tools for tracking the origin, transformation, and fate of OM across mangrove-associated trophic networks. Recent work has shown that allochthonous OM inputs — such as macroalgal wrack deposition events — can substantially redirect microbial activity, reorient benthic invertebrate metabolism, and enhance sedimentary blue carbon storage. This highlights how the quality and diversity of OM subsidies regulate both trophic functioning and carbon sequestration efficiency in mangrove sediments.

Yet the mechanistic understanding of these processes derives overwhelmingly from tropical and subtropical systems characterized by high rainfall, elevated nutrient availability, and multi-species canopies — conditions that contrast sharply with those of the Arabian Gulf, where mangroves persist at one of the most extreme arid limits in the world.

An Understudied Arid Mangrove

Abu Dhabi supports approximately 55–60 km² of mangroves — the largest stand in the UAE and a major share of total Arabian Gulf coverage — dominated exclusively by Avicennia marina, the only species tolerant of the region’s exceptional environmental constraints. These include annual rainfall below 100 mm, air and sediment temperatures ranging from 8°C to 45°C, persistent hypersalinity regularly exceeding 50 ppt, carbonate-rich and nutrient-poor substrates, and a near-total absence of freshwater or riverine inputs. Under these conditions, A. marina develops as a dwarf form (2–4 m canopy height) with slow growth rates, reduced litter production, and constrained below-ground carbon dynamics.

This extreme abiotic context raises fundamental and unresolved questions: How is the benthic food web sustained under such resource limitation? What are the primary OM sources — autochthonous leaf litter, microphytobenthos, phytoplankton, or allochthonous marine subsidies? And do the mechanistic links between OM quality, microbial processing, macrofaunal assimilation, and blue carbon storage — well-documented in more productive systems — hold under arid conditions? Current reviews identify the food web ecology and OM dynamics of Gulf mangroves as a critical knowledge gap with direct implications for conservation and carbon accounting.

Actual Study Framework

Drawing on established FA-tracing and blue carbon methodologies, a study of Abu Dhabi’s arid mangroves could address four interconnected objectives.

The first concerns the characterization of OM sources and their seasonal variability. Using FA profiles alongside stable isotopes (δ¹³C, δ¹⁵N), the relative contributions of A. marina leaf litter, microphytobenthos, pelagic phytoplankton, and benthic microalgae to sediment OM pools would be quantified across the system’s wide thermal range.

The second involves tracing OM through the benthic food web. FA and stable isotope compositions of dominant macrofauna — grapsid and ocypodid crabs, bivalves, polychaetes — would be analyzed to resolve trophic pathways and identify which OM sources actually sustain secondary production under arid stress.

The third objective links OM quality to blue carbon storage. Sediment core analyses (lipid classes, organic carbon, bulk isotopes) would test whether reduced litter input and constrained microbial activity under aridity result in proportionally higher or lower carbon preservation efficiency relative to tropical analogues.

The fourth addresses the role of marine subsidies. Given the near-absence of terrestrial OM inputs, the hypothesis that marine-derived material — pelagic detritus, macroalgal wrack — plays a disproportionate role in sustaining the food web would be furtherly investigated, drawing on evidence that allochthonous subsidies can restructure benthic metabolism even in mangroves with abundant in situ production.

Scientific Significance

Abu Dhabi’s mangroves represent a natural ecosystem for testing the generality of current OM cycling models under extreme abiotic stress. Results would refine blue carbon accounting for arid-zone systems — currently uncertain due to their structural and biogeochemical atypicality — and provide baseline trophic data essential for evidence-based conservation under accelerating climate pressures in the Arabian Gulf, including rising sea surface temperatures and increasing salinity stress.