Benthic foraminifera associated with seagrass as a model ecosystem for monitoring environmental changes

<p>Seagrasses and benthic foraminifera are present in a wide range of habitats over the globe. These organisms are considered ecosystem engineers and bio-indicators of coastal marine environments. In tropical waters, seagrass meadows are a favorable habitat for benthic foraminifera that benefit from this unique environment. Although each one of these organisms has been studied extensively and has been shown to be sensitive to changes within their environment, much less is known about their association with each other, particularly with respect to climate change and anthropogenic pressures.&#160;</p><p>This study was designed to ecologically characterize the benthic foraminiferal assemblages associated with the meadows of the tropical seagrass <em>Halophila stipulacea</em> as a model ecosystem for monitoring anthropogenic and natural changes in the Gulf of Aqaba-Eilat. The study was based on 11 sampling campaigns (January 2020- April 2021) in two sites that differ in their conditions: the North Beach (NB) site (10 m depth) representing a meadow near to a heavily urbanized coast,&#160; and the South beach (SB) site (10 m depth) which is found in an undisturbed area of the shoreline The ecological examination included characterization of the foraminiferal assemblages from three microhabitats at each site: leaf microhabitat (L), seagrass sediment (sediment inside meadows- SIM), and non-seagrass sediment (sediment outside meadows- SOM). In addition, sediment grain size distribution and leaf surface area were measured as the environmental parameters that characterize each site.&#160;</p><p>Our study provides multiple ecological pieces of evidence that highlight the biological importance of <em>H. stipulacea</em> seagrass meadows as a favored habitat for tropical benthic foraminifera. First, the foraminiferal biomass and diversity within the seagrass environments were significantly higher than that found outside the seagrass meadows. Specifically, the highest numbers of individuals were found on the leaf microhabitats, which were populated by epiphytic foraminifera species that were considerably less common or rare within sediment microhabitats.&#160;</p><p>The anthropogenic footprint of the urban area in the northern shore (the NB Site) was reflected by 1) The significantly lower abundances of the total living foraminifera at the NB Site compared to the SB Site, 2). The very low abundances of the two common GoA taxa, soritids, and <em>A. lobifera,</em> at the NB Site, and 3). An exceptionally higher abundance of <em>O. ammonoides</em> and <em>Ammonia </em>spp.<em> </em>(known to be affiliated with eutrophic environments) at the NB Site relative to the SB Site.</p><p>Our study demonstrates the importance of seagrass meadows as both autogenic and allogenic ecosystem engineers for benthic foraminifera by providing a substrate and other ecological resources. However, this association is delicate and could be damaged by anthropogenic stressors, as indicated by the decreased abundances of foraminifera in the NB impacted site.&#160;</p>