Abstract
We investigated the influence of seagrass canopies on the benthic biodiversity of bacteria and macroinvertebrates in a Red Sea tropical lagoon. Changes in abundance, number of taxa and assemblage structure were analyzed in response to seagrass densities (low, SLD; high, SHD; seagrasses with algae, SA), and compared with unvegetated sediments. Biological and environmental variables were examined in these four habitats (hereafter called treatments), both in the underlaying sediments and overlaying waters, at three randomly picked locations in March 2017. Differences between treatments were more apparent in the benthic habitat than in the overlaying waters. The presence of vegetation (more than its cover) and changes in sedimentary features (grain size and metals) at local scales influenced the observed biological patterns, particularly for macroinvertebrates. Of note, the highest percentage of exclusive macroinvertebrate taxa (18% of the gamma diversity) was observed in the SHD treatment peaking in the SA for bacteria. Benthic macroinvertebrates and bacteria shared a generally low number of taxa across treatments and locations; approximately, 25% of the gamma diversity was shared among all treatments and locations for macrofauna, dropping to 11% for bacteria. Given the low overlap in the species distribution across the lagoon, sustaining the connectivity among heterogeneous soft sediment habitats appears to be essential for maintaining regional biodiversity. This study addresses a current scientific gap related to the relative contributions of vegetated and unvegetated habitats to biodiversity in tropical regions.
Highlights
We investigated the influence of seagrass canopies on the benthic biodiversity of bacteria and macroinvertebrates in a Red Sea tropical lagoon
A substantial fraction of photosynthate is released as dissolved compounds contributing to dissolved organic matter (DOM) stocks[44], the major organic matter and energy source for free-living heterotrophic prokaryotes
Important variables contributing to differences between samples were related to grain size, dissolved inorganic nutrients ( NO3− and PO43−pw), productivity and other nutrients (Chl a, total organic carbon (TOC), total dissolved nitrogen (TDN), dissolved organic carbon (DOC))
Summary
We investigated the influence of seagrass canopies on the benthic biodiversity of bacteria and macroinvertebrates in a Red Sea tropical lagoon. Seagrass beds, mangroves and coral reefs are often linked through physical, chemical and biological processes[1,2,3,4]. These interconnected habitats form what is often referred to as “the tropical seascape”[5], which contributes to a variety of ecosystem goods and services essential for human well-being[2,6,7]. Release of bioavailable DOM occurs through seagrass leaves and through their roots feeding both pelagic and benthic heterotrophic prokaryotes/bacteria[45,46] Their high metabolic rates, provide a vital link in the transfer of bioavailable DOM to higher trophic levels, supporting the rich benthic food webs[43,47]. Despite the clear linkages between macroinvertebrates and microbes, these two fundamental biological components of seagrass biotopes are rarely analyzed together
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