A low cost field‐survey method for mapping seagrasses and their potential threats: an example from the northern Gulf of Aqaba, Red Sea

Abstract

1. In the Gulf of Aqaba (GoA), coral reefs are considered the dominating ecosystem, while seagrass meadows, recognized worldwide as important ecosystems, have received little attention. Absence of comprehensive seagrass maps limits awareness, evaluations of associated ecosystem services, and implementation of conservation and management tools.2. Presented here are the first detailed maps of seagrass meadows along the Israeli coast of the northern GoA. Mapping was performed by snorkelling along transects perpendicular to the shore above meadows growing at 15-25 m. Measurements along these transects included position, meadow depth and visual estimations of seagrass cover. Shallow boundaries of meadows, parallel to shore, were recorded by GPS tracking. Supplementary work included drop-camera boat surveys to determine the position of the deeper edge of meadows. In addition, GIS layers were created that indicated shoreline infrastructures, near-shore human activities and potential pollution threats. Ecosystem services of seagrass meadows mapped were valuated using a benefit transfer approach.3. In total, 9.7 km of the 11 km shoreline were surveyed and 2830 data points collected. Seagrasses were growing along 7.5 km of the shoreline, with shallow (15-25 m) meadows found to cover an area of 707 000 m 2 and valued at more than US$ 2 000 000 yr -1 in associated ecosystem services. Pilot drop-camera surveys (additional 283 data points) indicated that meadows can extend down to 50 m in some places. Coastal uses and threats varied in character and location. A municipality runoff point and drainage canal located close to the largest meadow were identified as the main threats to local seagrasses. 4. These low-cost methods enhance our understanding of seagrass distribution in the northern GoA. They demonstrate a GIS-based tool for assessing how environmental changes might affect the cover and state of seagrasses, improving efforts to conserve seagrass, and have particular relevance to seagrass mapping in developing countries and/or island nations.

Ecophysiological Plasticity and Bacteriome Shift in the Seagrass Halophila stipulacea along a Depth Gradient in the Northern Red Sea

“…Although high water clarity was observed throughout most of the water column in the meadow (Kd = 0.115), at the deepest site (28 m) the available PAR reduced to about 5% of the surface PAR. Low levels of PAR can limit growth in seagrasses (e.g., Duarte, 1991), but maybe not so much in H. stipulacea which grows deeper than 40 m in the study site (Sharon et al, 2011; Winters et al, 2016). H. stipulacea plants showed clear morphological and biochemical variation, in response to changing environmental conditions along the depth gradient.…”

“…At this site, the shoreline is almost pristine, with very little coastal infrastructure or anthropic pressure (Mejia et al, 2016). This H. stipulacea meadow is considered healthy and harbors a rich and diverse community of corals (Winters et al, 2016). During the study (October 2013), the meadow had an area of about 61,900 m 2 commencing at 4–5 m and extending to depths greater than 50 m (Sharon et al, 2011; Winters et al, 2016).…”

“…Sampling was conducted using SCUBA along 50 m transect lines placed, parallel to the shore, at 4, 9, 18, and 28 m (see Figure 1 ). The sampling depths, selected based on recent mapping of the meadow (Winters et al, 2016), cover the different parts of the meadow, as follows: at 4 m, near the coral reef and the shallow edge of the meadow, at 9 m along the flat part of the sea bottom, before the drop to deeper waters, at 18 m, along the actual slope of the meadow, and at 28 m around the area where the slope straightens out again. To characterize the environment, three sediment samples were collected at random sites along the transect line with minicorers (3.0 cm diameter and 50 ml volume) and used for grain size (granulometry) measurements and Total Organic Carbon (%TOC) content analyses.…”

“…It is the most dominant seagrass species in the northernmost Gulf of Aqaba (GoA), forming discontinuous meadows (Angel et al, 1995; Al-Rousan et al, 2011; El Shaffai, 2011; Sharon et al, 2011; Mejia et al, 2016) in both shallow and deep environments (1–50 m depth; Sharon et al, 2009, 2011; Winters et al, 2016), and constituting an integral component of the coral reef ecosystem (El Shaffai, 2011; Winters et al, 2016). This seagrass is a putative Lessepsian migrant to the Mediterrian Sea, and over the last 150 years it has become established in many parts of the Mediterranean Sea (reviewed by Gambi et al, 2009; Sghaier et al, 2011).…”

Differences in flowering sex ratios between native and invasive populations of the seagrass Halophila stipulacea

“…The seagrass Halophila stipulacea (Forssk.) Asch is a dioecious tropical plant species, growing in both shallow and deep environments (1-50 m depth; Sharon et al 2011, Winters et al 2017. It is native to the Red Sea, Persian Gulf and Indian Ocean (den Hartog 1970).…”