Seagrass

Seagrass shoot density and compages influences how the aboveground vegetation slows flow velocities, traps sediment, and attenuates waves and turbulence (Fonseca and Fisher, 1986;

From: Treatise on Geomorphology , 2013

Productivity and Biogeochemical Cycling in Seagrass Ecosystems

Marianne Holmer , in Coastal Wetlands, 2019

five Future Perspectives and Conclusions

Seagrass ecosystems are facing a global crisis because of human pressures in the littoral zone ( Orth et al., 2006; Waycott et al., 2009; Short et al., 2011). This affiliate examines several examples of how altered sediment biogeochemistry is linked to observed seagrass refuse. The most pronounced touch of human activeness on sediment biogeochemistry is the reduction of sediment redox potential. Redox potential decreases when sediment oxidation from root exudates declines every bit a effect of decreased seagrass production. Seagrass production ofttimes declines as a result of decreased levels of dissolved oxygen in the h2o cavalcade, which is often the result of organic enrichment associated with eutrophication. Cumulative impacts of multiple stressors also atomic number 82 to seagrass decline and this is an agile area of current research. Seagrass outcomes nether increasing homo pressures are challenging to predict, considering the limited knowledge of multiple stressors (Koch and Erskine, 2001; Koch et al., 2007b). Another important attribute of seagrass pass up and areal loss is the bear on of their loss on the residue of the coastal system. Some examples tin be seen in systems that were subject to wasting affliction in Z. marina in the northern hemisphere during the 1930s. In these places there were major increases in coastal erosion, loss of fisheries habitat, and declining fisheries product. Many of the systems experiencing wasting disease had not fully recovered before new seagrass losses started to occur in response to littoral eutrophication (Frederiksen et al., 2004; Boström et al., 2014). Losses of slow-growing species, such as P. oceanica in the Mediterranean (Marbà et al., 2014), may be even more dramatic considering of their irksome regrowth rates. It is hard to predict whether better coastal zone land management and reduced nutrient loading will allow Z. marina recolonization of Danish coastal waters considering of many other concurrent pressures (Kuusemäe et al., 2016). In some areas the organic enrichment of the sediments during eutrophication in the 1970 and 1980s led to repeated oxygen depletion events that prevented recolonization (Frederiksen et al., 2004). Full recovery may accept decades, if at all (Valdemarsen et al., 2014). In some areas, a faster colonization past the blueish mussel Mytilus edulis into degraded areas has hampered seagrass recolonization (Vinther et al., 2008). To be able to sympathize, manage, and conserve seagrass meadows, it will be necessary to expand biogeochemical studies to a wider geographical extent and for more than seagrass species. One important objective should exist to make up one's mind ecological thresholds for seagrass performance in ecosystems under human pressures and then that further losses of seagrasses can be avoided through wiser and improve direction.

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Volume iv

Dinusha R.G. Jayathilake , Mark J. Costello , in Encyclopedia of the World'southward Biomes, 2020

Conservation

Seagrass cover has been declining globally at a rate of 0.9% per year earlier 1940 and seven% per yr after 1990 ( Waycott et al., 2009). For the last 125 years, more than 51,000   kmii expanse of seagrass meadows has been lost due to natural and anthropogenic disturbances (Orth et al., 2006; Waycott et al., 2009). These are also vulnerable to natural disasters at both regional (storms, cyclones, floods, hurricanes, earthquakes, disease, grazing by herbivores) and global (warming) scales (Brusk and Wyllie-Echeverria, 1996; Curt and Neckles, 1999; Marbà and Duarte, 2010). Human-induced disturbance such as dredging, sedimentation, eutrophication, habitat fragmentation, boat anchoring and propeller scars accelerate seagrass loss (Short and Wyllie-Echeverria, 1996; Montefalcone et al., 2010). Because of their ecological importance as one of the well-nigh productive littoral vegetation, it is essential to understand in the local and global distribution, uses, threats, management and conservation values. Thus, in some areas agile seagrass restoration has been undertaken. For case, fishermen in Japan created a Marine Protected Area where they banned dredging and replanted seagrass to assistance restore fisheries (Tsurita et al., 2017). Like active seagrass restoration has been used to help coastal ecosystems recover from eutrophication, pollution, and dredging (van Katwijk et al., 2016).

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The Coastal Marine Ecosystem of Due south Florida, United States

Diego Lirman , ... Jerome J. Lorenz , in World Seas: an Environmental Evaluation (Second Edition), 2019

17.4.2.ane Status and Trends

While seagrass coverage remains extensive, most seagrass habitats in Florida have lost area over the past several decades. A recent study past Yarbro and Carlson Jr. (2012) on the status of the seagrass beds of Due south Florida showed that limited changes take taken place in Florida Bay (where a i% increase in coverage was recorded from 2004 to 2010), Biscayne Bay (where a 0.three% increment in coverage was recorded from 1992 to 2004), and the Florida Keys (where a 0.v% increment in coverage was recorded from 1992 to 2006). However, it is important to note that the years evaluated in this mapping exercise do not include the seagrass mass bloodshed events that caused significant seagrass losses in Florida Bay where >   forty   kmii of dense Thalassia beds were lost in 1987–90 and >   40   km2 were lost once again in 2015–16 (Hall et al., 2016) (Fig. 17.7). More recently, a rapid loss of seagrass (Syringodium) was recorded in northern Biscayne Bay, and its extent and causes are still being evaluated.

Fig. 17.7

Fig. 17.7. Images of a good for you Thalassia bed (left) and a similar bed during the seagrass mass mortality event of 2015–16 (right) in Florida Bay where >   40   km2 of seagrasses were lost due to high salinity and loftier temperatures. The prototype on the correct showing seagrass mortality was graciously provided by Penny Hall, Florida Fish and Wild animals Enquiry Found, Florida Fish and Wild fauna Conservation Commission.

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Toward Realizing the Sustainable use of and Healthy Marine Environments in an Open up-Type Enclosed Bay

Teruhisa Komatsu , ... Osamu Nishimura , in Integrated Coastal Direction in the Japanese Satoumi, 2019

2.2.2.one Seagrass Beds

Seagrass species are land plants that returned to the sea. Some mature shoots become longer and reproduce, producing flowers and fruits, while other shoots are immature and remain small. In Shizugawa Bay, wide seagrass beds were distributed near river mouths and in the port on June 25, 2010 ( Fig. 2.2A ). Subsequently the tsunami in 2011, they disappeared until 2014 (Fig. ii.iiB and C). In 2015, pocket-sized patches of seagrass appeared off the river mouth of the Mizushiri River (Fig. 2.twoD) for the first time since the tsunami. The seagrass beds recovered slowly because of the lack of light near the river mouths and seashores caused past the turbid water brought by construction, such every bit seawalls, river embarkments, and grounds elevated >   viii   thou above the bounding main level for the safety of houses from tsunamis (Komatsu et al., 2014). Information technology is estimated that a decrease in turbidity promoted a recovery of seagrass patches in 2015 (Komatsu et al., 2018a).

Fig. 2.2

Fig. 2.two. Seagrass (white areas indicated with white arrows in the sea) beds and ponds filled with brackish h2o (blackness areas on land) extracted from and overlaid onto satellite images from June 25, 2009 (upper left panel), March 14, 2011 (upper right console), March 19, 2012 (lower left panel), and June 1, 2015 (lower right panel) provided by NASA and Digital Globe past Google Earth.

Field surveys in October 2011 showed that sites where seagrasses of Zostera marina L. and Z. caulescens Miki survived the tsunami were in the areas sheltered from the wave (Fig. 2.1) (Komatsu et al., 2017). The contributions of the seeds buried in the sand beds from previous years the seeds produced by remaining seagrasses were important for the recovery of the seagrasses. Seagrass beds can recover faster by protecting the seagrasses distributed in sheltered areas as a source of seed supply (Komatsu et al., 2017).

To secure the growth of germinated seeds to recover seagrass beds, information technology is necessary to protect the current vegetative and reproductive shoots that produce seeds and remove the droppings remaining on the lesser. Because turbid water retards the recovery of seagrass, fences against the diffusion of turbid water are useful for seagrass recovery (Komatsu et al., 2014).

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The Gulf of Mannar Marine Biosphere Reserve, Southern India

Nochyil South. Magesh , Subbiah Krishnakumar , in World Seas: an Ecology Evaluation (Second Edition), 2019

8.5.2 Seagrasses

Seagrass productivity is high and these also support a variety of other species. The seagrass beds provide shelter to a large number of species of crustaceans, echinoderms, gastropods, molluscs, and worms. Moreover, they provide support to epiphytic micro and macroalgae as well. Seagrasses occur between the mainland and islands of the surface area and there are 15 species altogether. Halodule uninervis is extensively found in the Gulf of Mannar and it is a dominant intertidal species. They by and large occur in a monospecific community but are sometimes associated with other seagrass species such every bit Enhalus acoroides, Cymodocea serrulata, Cymodocea rotundata, and Halophila ovalis. Seagrass beds are constitute in patches of varied size, they are dense, closely packed, and healthy. The sediments accompanying the seagrass beds are rich in organic content and provides habitat to numerous polychaetes. The seagrass vegetation is a sediment accumulator and stabilizer, thus giving stability to the islands. Species like Cymodocea serrulata provide feeding grounds for the endangered dugong. Other species such as Thalassia hemprichii and Halodule uninervis provide habitat for Holothurids. Many seagrass meadows provide feeding ground for marine turtles such every bit the green turtle (Chelonia mydas), hawksbills (Eretmochelys imbricata), leather backs (Dermochelys coriacea), loggerhead (Caretta caretta), and olive ridleys (Lepidochelys olivacea).

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Remote Sensing for Marine Direction

Merv Fingas , in World Seas: an Environmental Evaluation (Second Edition), 2019

5.2.4.v Seagrass

Seagrass is a universal grouping of plants that functions as a shoreline protector and a nursery for the young of many species as well equally an oxygen source for marine life. There are several varieties and species. The location, distribution, and aerial coverage of seagrasses constitute of import monitoring parameters. These parameters are frequently monitored using Landsat information ( Bakirman, Gumusay, & Tuney, 2016), an instance of which is shown in Fig. 5.vii. Typically, radiance and reflectance data are collected from the satellite epitome and subjected to algorithms that provide the necessary density values of the seagrass. One of the current concerns is the reject in seagrasses all around the earth (York et al., 2017). The utilise of WorldView2 to delineate seagrasses was noted past Elso, Manent, Luque, Ramdani, and Robaina (2017), while Nobi and Dinesh Kumar (2014) used visible imagery from the Indian remote sensing satellite, IRS P6 LISS Iv, to map sandy areas, corals, and seagrass in tropical India. Reshitnyk, Costa, Robinson, and Dearden (2014) used a combination of high-resolution satellite imagery (WorldView-2) and a single-beam acoustic basis discrimination system (QTC View V) for mapping the distribution of submerged aquatic vegetation in a temperate region. Yamakita, Watanabe, and Nakaoka (2011) used digital photography over a 26-term to report the dynamics of seagrasses in Tokyo Bay.

Fig. 5.7

Fig. five.7. NASA paradigm of a portion of the Cherry-red Sea showing the bigotry of seagrasses from corals (https://eol.jsc.nasa.gov/DatabaseImages/EO/lowres/ISS016/ISS016-Eastward-19394.JPG).

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Ecology of seagrass beds in Sulawesi—Multifunctional cardinal habitats at the risk of devastation

Harald Asmus , ... Dody Priosambodo , in Scientific discipline for the Protection of Indonesian Coastal Ecosystems (SPICE), 2022

half-dozen.2.ii The construction of tropical seagrass bed systems

Seagrass systems represent communities or even ecosystems distinctly separated from adjacent benthic assemblages such equally bare sand flats or coral reefs. They include the main structural elements of an ecosystem in one organization, such as master producers, consumers, decomposers, and abiotic parameters. Seagrass meadows course a special 3-dimensional structure depending on the item seagrass assemblage. This construction is adult poorly in pioneer assemblages dominated by minor genera such as Halophila and Halodule. However, it can exert a distinct blueprint as in those consisting of a mixture of tall Enhalus acoroides plants and Thalassia hemprichii every bit understory. Throughout the Indonesian Archipelago, multispecies or mixed seagrass beds consisting of up to eight species are of a relatively common occurrence (Ambo-Rappe, 2016). This is i of the key structural features clearly distinguishing Indonesian seagrass communities from those of the Caribbean, where monospecific beds are mutual.

In seagrass beds of the Spermonde Archipelago, Southwest Sulawesi, biomass of seagrasses ranged betwixt 270 m and 7.5 1000 dw m−ii depending on, to the particular community, the water depth, the exposure to currents, and the position of the seagrass bed at the shelf too as the flavor (personal observations). In the SPICE project, biomass of seagrasses was recorded during rainy and dry season from two transects at each season and 3 islands showing a different position at the shelf expanse of the Spermonde Archipelago. At the nigh coastal location, the island of Barrang Lompo, four species, E. acoroides, T. hemprichii, Cymodocea serrulata, and Cymodocea nodosa, could exist detected dominating the biomass at an average of 63 ± 30 k dw yard−two. In both transects, biomass was decreasing from the beach down to the reef edge, from 106 ± 47 k dw k−2 to but 10 ± xvi g grand−2, respectively. Species diversity did not evidence a singled-out trend forth transects; however, species richness of seagrasses was higher in the upper stations close to the embankment. In contrast to that, Erftemeier and Herman (1994) found a higher biomass range for E. acoroides (800 to 1441 one thousand dw g−2) and T. hemprichii (100 to 308 g dw m−2) at the same island with maximum values in July and lower values in August to the finish of the year. Vonk et al. (2008) found, at the island Bone Batang in the Spermonde Archipelago, a hateful leaf and belowground biomass of 118 and 625 g dw m−2 in dumbo, and 47 and 506 thou dw m−2 in sparse seagrass beds.

Further offshore to the central shelf, at the isle Sarappokeke, the large seagrass E. acoroides is missing. In full general, seagrass biomass there is in a range between 71 ± 69 to eight ± 7 g dw m−2 (i.e., 47 ± 35 on boilerplate); simply in some very dense patches of T. hemprichii, it may attain a biomass of up to 124 ± 68 thou yard−ii. Although average biomass is lower, the species richness per transect is on average college compared with the more coastal site Barrang Lompo. The highest biomass of seagrasses we establish surprisingly in islands situated at the seaward shelf edge (outer rim) of the Spermonde Archipelago at the island of Kapoposang. The big seagrass E. acoroides was present at the nearshore stations of the transects, and thus, biomass was on average 111 ± 53 g dw grand−two, and on one transect, it reached up to 270 one thousand dw grand−2.

Comparing the seagrass biomass with nutrient data bachelor for that year, we advise a congruence between the high seagrass biomass with higher nutrients at the coast of Sulawesi, lower nutrients and also biomasses of seagrasses in the fundamental shelf area, and again higher food levels at the shelf edge. The higher nutrient levels at the outer shelf edge were due to local upwelling from the adjacent deep-water regions of the strait of Makassar as a result of the currents parallel to the coast and the prevailing offshore winds. Yet, nosotros need more bear witness particularly from CN analyses of seagrass fabric to be sure whether a general nutrient slope or factors at a minor or local scale are responsible for this pattern.

Because of the nifty number of leaves per unit area, seagrasses enlarge the surface surface area for settling of primary producers such as micro- and macroalgae or sessile zoobenthos from different taxa by a factor of 20 (Couchman, 1987, p. 4). In the Spermonde Archipelago, associated micro- and macroalgae augment the primary producer biomass past on average 17% related to dry out mass. Calcareous algae and diatoms grade the base for epiphyte growth, followed by red and green filamentous algae. The distribution of epiphyte biomass over the shelf area followed the aforementioned pattern equally observed for seagrass biomass showing maximum values at the shelf edge (14.seven ± 8.9 g dw m−2) and minimum values at the key shelf (v.ii ± 8.four one thousand dw 1000−2) while increasing toward the coast (10.3 ± ten.ane g dw m−two).

The consumer assemblage of a tropical seagrass bed is highly various and consists of both very specialized residents and animals spending only parts of their life cycle inside a seagrass bed. In the seagrass beds of the Spermonde Archipelago, we sampled 158 different taxa of macroinvertebrates, but only 86 of them could exist identified to genus and even species level.

Macrobenthic animals are important components of tropical seagrass beds, and they settle either in the sediment of seagrass beds (infauna) or attached to the different parts of the plants (sessile epifauna). Other creature components are mobile and live either at the sediment surface or move along the leaves or swim within the seagrass rug. Well-nigh of the invertebrate faunal aggregation in the investigated sites of the Spermonde Archipelago is consisting of mollusks (52 species) and echinoderms (35 species), whereas hydrozoans (mainly corals and soft corals, 24 species), crustaceans (12 species), polychaetes, or other groups are less species rich. In our investigated sites likewise, sponges probably may accomplish high numbers of species (36), merely we could not identify most of the species. The consumer assemblage represents non only many commercially important species, just likewise species that are endangered and already extinct in many places.

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Ecogeomorphology

S. Fagherazzi , ... D.Due south. Johnson , in Treatise on Geomorphology, 2013

12.xiii.3.1 Modification of Near-Bed Hydrodynamics

Seagrass shoot density and architecture influences how the aboveground vegetation slows menstruation velocities, traps sediment, and attenuates waves and turbulence ( Fonseca and Fisher, 1986; Gambi et al., 1990; Gacia et al., 1999); and the extensive belowground roots and rhizomes assistance to stabilize the sediment and increase resistance to storm and moving ridge disturbance. Almost studies on the consequence of seagrasses on hydrodynamics and sediment transport have focused on larger subtidal species, such as Zostera marina, Thalassia testudinum, Syringodium filiforme, and Posidonia oceanica (Fonseca and Fisher, 1986; Gambi et al., 1990; Gacia et al., 1999). However, smaller intertidal species (e.g., Zostera novazelandica) also tin can have a significant event on sediment suspension (Heiss et al., 2000). Seagrass densities vary from patchy or depression-density meadows (<100 shoots per square meter) in areas that are physically disturbed, have low water quality, or have been recently restored, to very dense meadows (>grand shoots per square meter). In flume studies, Peterson et al. (2004) showed that at that place were greater flow reductions inside the canopy with increasing vegetation density, and that there were pregnant differences in flow on the edges of meadows. Their model showed that the 'edge effect,' or the zone in which flow decelerates, is a failing part of vegetation density, and this influences the variation in mean electric current menstruation between seagrass patches of different sizes. Flow speeds within seagrass canopies typically are 2–10 times slower than outside the meadow (Gambi et al., 1990; Gacia et al., 1999), and also less variable (Heiss et al., 2000). Specific water velocities are often <ten   cm   southward−1, but tin can be equally loftier as 100   cm   southward−1 (Koch, 2001).

Although there is general agreement that the slowing of current velocities enhances particle deposition within seagrass meadows, there are few straight measurements of sediment degradation and memory. Gacia et al. (1999) used sediment traps in Mediterranean P. oceanica meadows and showed that seagrass canopies slowed current velocities with intensities proportional to the canopy peak, and that particle retention was up to fifteen times college than unvegetated sediment. They found that the particle trapping capacity of the meadow was related to the surface expanse of the leaves, leaf bending, and particle zipper to the leaf surface.

The effect of the seagrass awning on wave attenuation is nevertheless not well understood (Koch et al., 2006). Wave attenuation is likely highest when the canopy occupies a large proportion of the water cavalcade (Ward et al., 1984; Fonseca and Cahalan, 1992), but reduction in wave energy also has been documented in deep meadows (Verduin and Backhaus, 2000; Granata et al., 2001). In wave-swept environments, seagrasses are exposed to more circuitous flows than when unidirectional flows are dominant. A long flexible shape is advantageous, every bit the leaves can sway back and forth with the water motion and thus minimize forces on the root/rhizome systems that anchor the plants in the sediment (Koch et al., 2006).

Benthic algal populations too can stabilize tidal flat sediments at times of year when the algae are growing actively and populations are physically stable. Dense populations of mat-forming species such equally Ulva rigida and Enteromorpha intestinalis stabilize sediments by decreasing shear flow at the sediment surface (Escartin and Aubrey, 1995) and reducing sediment pause (Sfriso and Marcomini, 1997; Romano et al., 2003). Thick mats (equivalent to 3.5–six.ii   kg wet weight per square meter) displace velocities vertically and tin can deflect every bit much as xc% of the menstruation over the mat, with only ten% of the menstruation traveling through the mat (Escartin and Aubrey, 1995). Benthic microalgal mats as well stabilize surface sediments past producing and extruding EPS (e.g., Paterson, 1989; de Brouwer et al., 2006). EPS bind sediment particles together and so that the shear stress needed for erosion of the sediment is increased. This sediment stabilization is a seasonal miracle at least in temperate systems, and the deposited cloth may be resuspended at times of the year when the microalgae are less productive (Widdows et al., 2002).

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Distribution of seagrass communities n of Barcelona, Northwestern Mediterranean Body of water

Thou. Canals , ... J. Ylla , in Seafloor Geomorphology equally Benthic Habitat (Second Edition), 2020

Abstruse

Seagrass communities are known to occur on inner shelves of the Mediterranean Sea, where they course meadows down to 40–45  m under optimal weather condition. These communities play a central ecosystemic office and yield a number of services including water quality comeback, COtwo absorption, and sediment production for seafloor and embankment stabilization. North of Barcelona is the Maresme shelf extending forth 50   km, where the presence of seagrasses has been investigated using multibeam bathymetry and in situ ground truthing. Predictive modeling has been carried out based on environmental predictors to produce habitat maps of seagrasses. Recurrent seafloor dredging for embankment nourishment and other coastal interventions, together with event-driven river discharge, appear to exist the master causative factors for a pregnant reduction of the potential depths and extension of seagrasses in the study area. At present seagrasses are mainly plant in the 10–twenty   m depth range of the central segment of the Maresme inner shelf, which is capped past coarse sediment atop a relict morphology.

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Estuarine food webs

Eric Wolanski PhD, DSc, FTSE, FIE Aust , in Estuarine Ecohydrology, 2007

five.7 SEAGRASS AND CORAL REEFS

Seagrass and coral reefs are oft found nearly the mouth of less turbid estuaries and in their coastal waters. Their health is determined by the rate at which fine sediments and nutrients are sequestrated in the estuary, primarily in the turbidity maximum zone and in the tidal wetlands, and to the efficiency of the bacterial loop in the estuary to procedure the nutrients. The remaining mud and nutrients are flushed out to ocean. If human activities increment the sediment and nutrient load, the seagrass beds and the coral reefs degrade. An immediate reason is lite attenuation past increased turbidity, as is evident for seagrass beds that progressively dice off in waters made more turbid by human activities (e.g. Schoellhamer 1996, and Onuf, 1994, for the example of dredging-induced turbidity; eastward.g. Knuckles and Wolanski, 2001, for the case of farming-induced turbidity in coastal waters).

Coral reefs are usually located further offshore than seagrass beds. Seagrasses have roots and are established in softer substrate. They tin can help protect the reefs past trapping mud and backlog nutrients, provided the quantities are not excessive (Fig. 5.10a; Kitheka, 1997; Wolanski et al., 2001).

FIGURE 5.10. (a) The trapping of sediment by seagrass growing in soft substrates between the estuary and the coral reef helps shield coral reefs from riverine sediment. (b) Seaweeds growing over a coral substrate trap mud trapped by seaweeds. This mud is harmful to corals considering information technology ultimately falls on the coral.

 Photos courtesy of L. McCook.

Past contrast, seaweeds have no roots and attach themselves unto solid substrates, such as coral reefs. Any mud that they trap ultimately lands on the reef and kills the coral, and does not protect it (Fig. five.10b; Fabricius, 2005).

The fraction of a reef substrate covered past live coral naturally fluctuates because some corals are occasionally killed by natural events such as river floods and storms or tropical cyclones. The storms or tropical cyclones kill the corals by mechanic forces (Washed, 1992a). The river plumes kill corals by bringing freshwater, fine sediment and excess nutrients to the reefs (McCook 1999; McCook et al., 2001; Wolanski et al., 2003a and 2004b). The empty infinite is readily colonized by fast growing algae (Fig. 5.11a). The corals can recolonise that space later on several years provided that h2o quality and the quality of the substrate remains skillful in the recovery period. The length of the recovery menstruation depends on the water and substrate quality. This is because (1) suspended sediments cloud the water column and coats the substrate, thereby reducing photosynthesis, and (two) coral larvae recruit by attaching themselves to the reef and growing into adult colonies, and they are unable to do so in areas of high sedimentation or sediment buildup. Therefore, inshore reefs commonly take higher coral cover than offshore reefs, located further away from the oral cavity of estuaries (Birkeland, 1997). The recovery menstruation is shorter offshore than inshore due to higher water clarity (Fig. 5.11b).

FIGURE five.xi. Sketch of the space war between coral and algae on a coral reef. (a) Algae quickly colonise empty infinite made vacant by the death of corals following a major disturbance such equally a river flood or a storm. Coral slowly recolonises that lost space by displacing the algae. (b) Coral cover decreases following such a major disturbance and the recovery menstruation is longer in inshore than offshore reefs, considering the quality of the h2o and the substrate is lower inshore than offshore.

The impact of the river arrival of freshwater and mud on coastal coral reefs is long lasting because of the long residence fourth dimension of mud (Fig. 5.12). During the river flood, a river plume is formed that tin impact straight on the reef. The suspended mud settles out, a fraction falls directly on the coral and smothers it. The remaining mud settles on the lesser around the reef to grade a settled layer that tin be either compacter or un-compacted (a nepheloid layer). This mud is resuspended during storms and decreases photosynthesis by reducing visibility. Some of that resuspended mud settles on the coral and harms it, and this occurs fifty-fifty without river runoff. As a upshot of this frequent sedimentation, fleshy and filamentous algae overgrow the coral and prevent coral recruitment (Fig. v.11a). The impact disappears but after the mud is flushed away. The impact is long-lived because the residence time of mud is much larger than the residence time of water (Fig. 3.17b; Wolanski et al., 2003a and b, 2004b and 2005; Golbuu et al., 2003; Victor et al., 2006). This can pb to an ecological phase shift, whereby the corals dice and the substrate is entirely covered past algae, a process that is facilitated if nutrients are arable (Done, 1992b).

FIGURE 5.12. Sketch of the processes controlling the affect on coastal coral reefs from river inflow of freshwater and mud.

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