The role of seagrass vegetation and local environmental conditions in shaping benthic bacterial and macroinvertebrate communities in a tropical coastal lagoon

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. In tropical coastal waters, seagrass beds, mangroves and coral reefs are often linked through physical, chemical and biological processes 1-4. 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. Among the typical triad of tropical key marine habitats, seagrass meadows are considered one of the most productive 8,9. Their presence increases habitat complexity and ecological niches 10-12 , enhancing biodiversity. By reducing current velocity and wave action, seagrasses promote organic and inorganic matter deposition 13,14 .

Inter-annual variability patterns of reef cryptobiota in the central Red Sea across a shelf gradient

“…Which could keep cryptobenthic communities between reefs distinct even when perturbed by extensive bleaching events or the associated increased in temperature. A high turnover in the cryptobiome amongst reefs is present in all time periods which was previously observed prior to the coral bleaching 16 and is typical of other environments including soft bottom communities in the central Red Sea 73 and in tropical coastal habitats 74 , 75 .…”

The Seagrass Holobiont: What We Know and What We Still Need to Disclose for Its Possible Use as an Ecological Indicator

“…Only a small fraction of the bacterial species can be readily cultivated in microbiology laboratories, hence, studies assessing the composition of different microbial communities, including those growing on seagrass, have gradually moved away from the culture related approaches [37,105,199,200], to culture-independent molecular based techniques [35,36,99,161,162,201] and, ultimately, to next-generation sequencing (NGS) approaches [23][24][25][27][28][29]31,32,38,39,96,97,191,202]. This paradigm change has been necessary because bacterial growth is inhibited in vitro, if crucial factors of their natural environment are not properly replicated in the laboratory.…”

Cloud Processing for Simultaneous Mapping of Seagrass Meadows in Optically Complex and Varied Water

“…Poor water quality or deep water reduce or negate the ability to penetrate the water column, obscuring the meadows from view [15][16][17]. Additionally, seagrasses frequently occur as patches of low-density cover [18], and there are substantial species-specific differences with respect to size, color and shape [19] all of which contribute to the difficulty of defining seagrass meadows and their constituents via remote sensing [15,20,21]. In addition to these challenges, effective monitoring requires the application of a consistent methodology that enables comparison between successive mapping efforts [22].…”