Seagrass Sensitivity to Collapse Along a Hydrodynamic Gradient: Evidence from a Pristine Subtropical Intertidal Ecosystem

El-Hacen, El-Hacen M.; Bouma, Tjeerd J.; Govers, Laura L.; Piersma, Theunis; Olff, Han

doi:10.1007/s10021-018-0319-0

Cited by 11 publications

(19 citation statements)

References 100 publications

(28 reference statements)

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“…Tidal hydrodynamics influence the nutrient flow, sedimentation rate, and physical stability of the seagrass beds ( Lanuru et al, 2018 ). Increasing wave force elevates the degree of physical stability but reduces the nutrient availability in the seagrass bed sediment ( El-Hacen et al, 2019 ). Changes in hydrodynamic regime combined with eutrophic waters may have affected the macrophytes composition at the Merambong shoal.…”

Section: Discussionmentioning

confidence: 99%

“…As a result, seagrasses in MA had more significant leaf dimensions than MC, possibly due to the reduced water current velocity as suggested by Schanz & Asmus (2003) and Peralta et al (2006) . According to Schanz & Asmus (2003) and El-Hacen et al (2019) , the seagrasses are constantly affected by hydrodynamic forces, i.e ., strong tidal currents and waves, which directly affect seagrass morphology and physiology. Additionally, because sediment is deposited on seagrass beds due to their ability to decrease current velocities and weaken wave energy ( Gambi, Nowell & Jumars, 1990 ), seagrass presence may enhance macroalgae growth, especially U. reticulata on the soft sediments Buapet et al (2008) .…”

Section: Discussionmentioning

confidence: 99%

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Morphological and biochemical responses of tropical seagrasses (Family: Hydrocharitaceae) under colonization of the macroalgae Ulva reticulata Forsskål

Emmclan

Zakaria

Ramaiya

et al. 2022

PeerJ

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Background Coastal land development has deteriorated the habitat and water quality for seagrass growth and causes the proliferation of opportunist macroalgae that can potentially affect them physically and biochemically. The present study investigates the morphological and biochemical responses of seagrass from the Hydrocharitaceae family under the macroalgal bloom of Ulva reticulata, induced by land reclamation activities for constructing artificial islands. Methods Five seagrass species, Enhalus acoroides, Thalassia hemprichii, Halophila ovalis, Halophila major, and Halophila spinulosa were collected at an Ulva reticulata-colonized site (MA) shoal and a non-Ulva reticulata-colonized site (MC) shoal at Sungai Pulai estuary, Johor, Malaysia. Morphometry of shoots comprising leaf length (LL), leaf width (LW), leaf sheath length (LSL), leaflet length (LTL), leaflet width (LTW), petiole length (PL), space between intra-marginal veins (IV) of leaf, cross vein angle (CVA) of leaf, number of the cross vein (NOC), number of the leaf (NOL) and number of the leaflet (NOLT) were measured on fresh seagrass specimens. Moreover, in-situ water quality and water nutrient content were also recorded. Seagrass extracts in methanol were assessed for total phenolic content (TPC), total flavonoid content (TFC), 2,2-diphenyl-1-picrylhydrazyl radical scavenging activity (DPPH), 2,2′-azino-bis(3-ethylbenzthiazoline-6-sulfonic acid radical cation scavenging activity (ABTS), and ferric reducing antioxidant power (FRAP). Results Seagrasses in the U. reticulata-colonized site (MA) had significantly higher (t-test, p < 0.05) leaf dimensions compared to those at the non-U. reticulata colonized site (MC). Simple broad-leaved seagrass of H. major and H. ovalis were highly sensitive to the colonization of U. reticulata, which resulted in higher morphometric variation (t-test, p < 0.05) including LL, PL, LW, and IV. Concerning the biochemical properties, all the seagrasses at MA recorded significantly higher (t-test, p < 0.05) TPC, TFC, and ABTS and lower DPPH and FRAP activities compared to those at MC. Hydrocharitaceae seagrass experience positive changes in leaf morphology features and metabolite contents when shaded by U. reticulata. Researching the synergistic effect of anthropogenic nutrient loads on the interaction between seagrasses and macroalgae can provide valuable information to decrease the negative effect of macroalgae blooms on seagrasses in the tropical meadow.

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Section: Discussionmentioning

confidence: 99%

Section: Discussionmentioning

confidence: 99%

Morphological and biochemical responses of tropical seagrasses (Family: Hydrocharitaceae) under colonization of the macroalgae Ulva reticulata Forsskål

Emmclan

Zakaria

Ramaiya

et al. 2022

PeerJ

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“… Wave energy: We used the wave energy model developed for the PNBA by El‐Hacen and his collaborators (see El‐Hacen et al 2019 for more details). From the range of relative wave energy (J/m) in the PNBA, we assigned a score of 4 to villages exposed to the most energetic waves and 1 to villages exposed to the lowest wave energy.…”

Section: Methodsmentioning

confidence: 99%

Coastal protection assessment: a tradeoff between ecological, social, and economic issues

et al. 2021

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Marine coastal ecosystems are crucial to human populations in reducing disaster risk. Least Developed Countries are particularly vulnerable to the effects of climate change, such as sea-level rise and storm surges. The Mauritanian coast, West Africa, ranks among the most vulnerable worldwide to sealevel rise, and coastal communities in the National Park of Banc d'Arguin (PNBA) are particularly at risk. Here, we assessed the service of coastal protection in PNBA by (1) mapping the coastal marine ecosystems with Sentinel-2 imagery and determining their spatial wave height attenuation rates; (2) assessing the vulnerability of villages and natural habitats to coastal hazard risk; and (3) assessing the applicability of coastal protection measures in the PNBA. We found that a total of 83% of the populated coastline presents a moderate to high risk of flooding and erosion, with Iwik and R'Gueiba being the most threatened villages in the PNBA. As for the ecological risk, two low-elevated islands, which support breeding colonies of birds, are particularly vulnerable to sea-level rise. However, in other areas, the rupture in the dune cord created new lagoons that present valuable ecological and economic interests like the Lagoon of Bellaat. Improving the comprehension of wave attenuation provided by coastal habitats, combined with identifying the vulnerability and applicability of coastal protection measures, is essential for achieving the Sendai Framework for Disaster Risk Reduction goals. In the PNBA, relocation of identified villages at risk is probably the best cost-effective solution with the least disturbance to both breeding and wintering birds. Protection of coastal ecosystems will also ensure a continued provision of other ecosystem services, including food supply for sea dependent populations, and contribute to achieving the Paris Agreement and Sustainable Development Goals.

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“…Sampling locations were chosen to represent different hydrodynamic regimes: exposed, intermediate, and sheltered from wave energy (El-Hacen et al, 2019). At each location (Figure 1), a sediment push core was taken in January 2015.…”

Section: Sample Collectionmentioning

confidence: 99%

“…The age-depth model (cal. yr. BP, ± 2s) of core LV-6 was extrapolated to the core collected at the wave exposed site due to their proximity and similarity in wave energy index (El-Hacen et al, 2019). Similarly, the age-depth model of core LV-2 was extrapolated to the cores of the intermediate and wave sheltered sites.…”

Section: Sample Collectionmentioning

confidence: 99%

Fossilized diatoms as indirect indicators of the origin of carbon stored in intertidal flats

El-Hacen

Mens²,

Bouma³

et al. 2022

Front. Mar. Sci.

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Coastal systems store enormous carbon quantities in their sediment, which originates from various autochthonous and allochthonous sources. Carbon fluxes in coastal ecosystems have a strong effect on the recipient food-webs and carbon emission offsets. Yet, the relative importance of autochthonous vs. allochthonous C inputs to coastal carbon budget is still challenging to identify. Here, we combine diatoms preserved in the sediment with geochemical analyses to identify the sources of carbon stored in Africa’s largest intertidal seagrass beds at Banc d’Arguin, Mauritania. The area lies between an active ocean upwelling and the ‘Sahara-dust hotspot’ systems. The extensive seagrass beds of the area are thus expected to receive C from these neighboring systems in addition to producing C in-situ. Three sediment cores (50 cm) were collected at three intertidal sites with different hydrodynamic regimes, and analyzed for diatom composition, total organic carbon (TOC), total nitrogen (TN), total phosphorus (TP), and carbon isotopic signatures (δ13C). Diatom taxa are grouped into three guilds: (1) benthic (epiphyte, epipelon, and epipsammon), (2) planktonic, and (3) freshwater. Benthic diatoms are considered to be autochthonous, while typical oceanic and freshwater diatoms are considered to be allochthonous. Benthic diatoms are the most diverse and abundant group, while allochthonous freshwater (i.e., dust imported) and typical upwelling (i.e., tidal imported) taxa ranked last in both abundance and species’ richness. Structure equation modelling shows that variation in the stored carbon is best explained by the total abundance of diatoms and guild composition. We conclude that the C stored in the intertidal seagrass beds of Banc d’Arguin is predominantly autochthonous. Our method provides an effective way to identify historical carbon sources in coastal systems.

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Seagrass Sensitivity to Collapse Along a Hydrodynamic Gradient: Evidence from a Pristine Subtropical Intertidal Ecosystem

Cited by 11 publications

References 100 publications

Morphological and biochemical responses of tropical seagrasses (Family: Hydrocharitaceae) under colonization of the macroalgae Ulva reticulata Forsskål

Morphological and biochemical responses of tropical seagrasses (Family: Hydrocharitaceae) under colonization of the macroalgae Ulva reticulata Forsskål

Coastal protection assessment: a tradeoff between ecological, social, and economic issues

Fossilized diatoms as indirect indicators of the origin of carbon stored in intertidal flats

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