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Monocotyledons I
Published in Donald H. Les, Aquatic Monocotyledons of North America, 2020
2.3.4.1. Halophila decipiens Ostenf. inhabits coastal marine communities in waters ranging from 24.3‰ to 38.0‰ salinity and extends from subtidal zones to depths as great as 85 m (in clear waters). The plants are ruderal and able to survive in reduced or fluctuating light; however, deeper water populations are intolerant of high irradiance levels (>1000 μE m−2 s−1) and reduced salinity (<35 ppt). Typical water depths are 10–30 m with temperatures ranging from 21.0°C to 36.0°C. Plant cover diminishes noticeably when illumination falls below 10% of surface incident light. The plants thrive in sites where disturbance has eliminated competition by ordinarily more persistent species. The substrates can include coral, limestone, muddy coral sand, muddy sand, sand, shell hash, and silt. The plants are monoecious and the flowers are protandrous. Flower density can vary from 50 to 1925 m−2. Pollination is hypohydrophilous, occurring entirely underwater. In North America, flowering has been reported from July to September with fruiting from July to August. The flowers typically are open during a 9-hr period extending from first light until mid-afternoon. On average the fruits contain 36.8 seeds, which readily sink into the substrate. Large seed banks (to 13,500 seeds m−2) have been observed within the upper 3 cm of sediments; more typical values range from 134 to 3,414 seeds m−2. Seed germination has been observed from October to January. Buried seeds germinate well (to 86%) within 2–9 days after exposure to light, but will remain dormant in the dark at 24°C. Seed germination occurs at salinities from 25% to 34% but is inhibited at 42%. Although the seeds are deposited locally, their movement en masse within large quantities of sediment dislodged by disturbance (e.g. hurricanes) can result in far greater dispersal distances. Seedling densities are highest during the winter. The biomass attained by the plants varies widely, ranging from 0.02 to 12 g m−2; it is lowest during fall and winter. Production rates (e.g., 0.023 g C m−2 day−1) can reach a total of 4.56 × 108 g C day−1 during the peak growing season. The ratio of aboveground to belowground biomass is higher in shallow sites, with more storage occurring in underground organs at deeper sites. The plants can occupy extensive ranges of 7,500 km2 or more. The foliage decomposes rapidly, losing more than 50% of its original mass within 3 days. The plants have been cultured successfully in vitro. Reported associates:Halodule wrightii, Halophila engelmannii, Halophila ovalis, Ruppia maritima, Syringodium filiforme, Thalassia testudinum.
Discrete element numerical analysis for bearing characteristics of coral sand foundation considering particle breakage
Published in Marine Georesources & Geotechnology, 2023
Fenghui Hu, Xiangwei Fang, Chunni Shen, Zhihua Yao, Ganggang Zhou, Zhiqiang Wang
Coral sand, also known as calcareous sand, mainly comprises coral detritus and other marine biological debris of calcium carbonate greater than 90%. Coral sand has unique engineering properties owing to its unique material composition, structure, and developmental environment (Fang et al. 2020; Fang et al. 2023). The particle size, shape, gradation, compactness, and moisture content of coral sand affect the strength and deformation of coral sand (Sun and Huang 1999; Zhang 2014). In addition, coral sand particles are easily broken because they have various types of internal pores, and particle breakage is considered an important factor affecting the mechanical properties of coral sand (Coop 1990; Zhang et al. 2005; Wang et al. 2009; Hu et al. 2023). Meanwhile, the particle breakage of coral sand affects the stress-strain relationship, volumetric deformation, and final gradation (Wei et al. 2018; Chen et al. 2018); furthermore, coral sand with uniform gradation is more easily broken than sand with good gradation (Lv, Li, and Wang 2020; Weng et al. 2019). The particle breakage of coral sand could be reduced by some special methods, and one of the most representative methods is microbial-induced carbonate precipitation (Fu, Saracho, and Haigh 2023; Wang et al. 2023).
Large-scale triaxial tests of reinforced coral sand with different grain size distributions
Published in Marine Georesources & Geotechnology, 2023
Jian-Feng Chen, Stephen Akosah, Chao Ma, Solomon S. R. Gidigasu
Coral sand, also known as carbonate sand, is found in marine environments that are composed of the skeletal debris of marine organisms. They are widely located between 30°N and 30°S latitudes in the coastal areas including the South China Sea, the western Indian Ocean and the Bath Strait (Wang et al. 2011; Liu et al. 2021). Due to the mineral composition and formation, coral sand has unique geotechnical properties that are quite different from that of the siliceous sand (Datta, Gulhati, and Rao 1979; Coop 1990; Brandes 2011). It is revealed that coral sand is characterized by irregular grain shape (Salem, Elmamlouk, and Agaiby 2013; Wang, Wu et al. 2020) and a large number of intraparticle voids (Hyodo et al. 1996; Sharma and Ismail 2006). The internal voids within the coral sand particles are responsible for the high fragmentation and compressibility (Shahnazari et al. 2016). Moreover, the particle breakage has a significant effect on the mechanical properties (Hassanlourad, Salehzadeh, and Shahnazari 2008; Shahnazari and Rezvani, 2013; Yu 2019; Wang, Wang et al. 2020; Wang et al. 2021). In recent years, geotechnical constructions near the coastal areas have grown steadily for the sake of developing tourism, fishery, and mineral resources (Brandes 2011; Goodarzi and Shahnazari 2019). However, foundation stability and the associated structural safety are firmly focused on the mechanical properties of coral sand (Tian and Cassidy 2011; Wang et al. 2011). To improve the strength of coral sand aggregates and ensure the safety of upper structures, it is necessary to find an effective reinforcement method.
Experimental and Numerical Study on Dynamic Response of Underground Structure in Coral Sand Under Earthquakes
Published in Journal of Earthquake Engineering, 2023
Qi Wu, Xuanming Ding, Yanling Zhang, Yiwen Xin
Generally, terrigenous sands are composed of minerals and tiny rock fragments, which are mainly formed by erosion and weathering. The most common component of the terrigenous sand is silica in inland (e.g. desert) and non-tropical coastal (e.g. sandy) environments. Typically, silicon exists in the form of quartzite. There are also other components of sand, such as feldspar sandstone, which is a type of sand with a high content of aluminum silicate, usually formed by the weathering and erosion of nearby granite. Different from common terrigenous sand, coral sand is a special marine sand distributed near the equator and formed by the long-term handling and stacking action of marine life skeletons (Rajesh and Choudhury 2016; Xiao et al. 2018). The main component of the coral sand is calcium carbonate, and the content of which can reach more than 90%. Therefore, the coral sand particles are porous, irregular in shape, and prone to particle breakage under larger loads (Lv, Wang, and Zuo 2019; Wang et al. 2011). With the development of engineering construction, coral sand foundations are often encountered in engineering construction on the coastline of Mexico, the north coast of Australia, and the south coast of Egypt (Ding et al. 2021; Xiao et al. 2018).