Carbon and Nitrogen Deposits of Macroalgal Origin on a Tropical Seagrass Meadow

Abstract

How would the biodiversity of macroalgae modify carbon (C) and nitrogen (N) stocks within a blue carbon habitat? We addressed this knowledge gap by quantifying biomass stocks of macroalgal origins across the seascape of a seagrass meadow. Such information is warranted due to the paucity of data on macroalgal deposits that function as allochthonous inputs into an ecosystem’s pool of organic matter. Macroalgae were collected from the Merambong seagrass shoal (Johor, Malaysia) in December 2020 to February 2021. C and N analyses were performed on organic matter, and biomass measurements were upscaled to represent seascape estimates. Stocks of macroalgal origin across the meadow were estimated at 10.71 ± 1.3 Mg C and 0.75 ± 0.11 Mg N. The biodiversity of macroalgae was heterogeneous, which was similarly reflected in taxa-specific variability of up to 44.7% C and 4.9% N. The highest cumulative stocks were contributed by members of Ulvaceae for C and N. Corallinaceae and Lithophyllaceae contributed the highest organic C among the calcifying species. The morphology and habit of the 35 macroalgal species found in the meadow provided indicators of their autochthonous versus allochthonous nature based on benthic or drifting tendencies. Predictors of C and N stocks factored by biodiversity indices were not evident, although Evenness index partially explained it at the spatial level. The spatial model was still able to pinpoint clusters of C and N hotspots across the meadow, allowing management measures for the protection of C reserves while mitigating release of excess N.