Alcuéscar ( Spanish: [alˈkwes.kaɾ] ) is a municipality located in the province of Cáceres , Extremadura , Spain. The town is on the Silver Route (the Via de la Plata) branch of the Camino de Santiago, the pilgrimage trail to the burial place of St. James the Apostle.
109-470: The most noticeable feature of the small town is a convent and affiliated care facility for the disabled. The convent and church have large gardens. The services are very beautiful, and include special blessings for travelers and pilgrims. The convent is known for its hospitality, running an albergue (pilgrim's shelter), including a donativo (donation suggested) meal. They are also one of the primary sources of pilgrim's shells for people walking this route of
218-539: A positive feedback cycle , where the decomposition of organic matter further decreases the amount of oxygen present in the water column. Possible seagrass population trajectories have been studied in the Mediterranean sea . These studies suggest that the presence of seagrass depends on physical factors such as temperature, salinity, depth and turbidity, along with natural phenomena like climate change and anthropogenic pressure. While there are exceptions, regression
327-481: A combination of natural factors, such as storms and disease, and anthropogenic in origin, including habitat destruction , pollution , and climate change . By far the most common threat to seagrass is human activity. Up to 67 species (93%) of seagrasses are affected by human activity along coastal regions. Activities such as coastal land development, motorboating, and fishing practices like trawling either physically destroy seagrass beds or increase turbidity in
436-453: A detectable difference in anaerobic energy expenditure than those without encrustation. In the absence of barnacle encrustation, individual scallops swim significantly longer, travel further, and attain greater elevation. The family name Pectinidae, which is based on the name of the type genus, Pecten , comes from the Latin pecten meaning comb , in reference to a comb-like structure of
545-481: A given animal is "facing" requires detailed information about its valves. The model scallop shell consists of two similarly shaped valves with a straight hinge line along the top, devoid of teeth, and producing a pair of flat wings or "ears" (sometimes called "auricles", though this is also the term for two chambers in its heart) on either side of its midpoint, a feature which is unique to and apparent in all adult scallops. These ears may be of similar size and shape, or
654-563: A group of green algae . Seagrasses then evolved from terrestrial plants which migrated back into the ocean. Between about 70 million and 100 million years ago, three independent seagrass lineages ( Hydrocharitaceae , Cymodoceaceae complex, and Zosteraceae ) evolved from a single lineage of the monocotyledonous flowering plants. Other plants that colonised the sea, such as salt marsh plants, mangroves , and marine algae , have more diverse evolutionary lineages. In spite of their low species diversity, seagrasses have succeeded in colonising
763-438: A hospitable environment for sediment-dwelling organisms . Seagrasses also enhance water quality by stabilizing heavy metals, pollutants, and excess nutrients. The long blades of seagrasses slow the movement of water which reduces wave energy and offers further protection against coastal erosion and storm surge . Furthermore, because seagrasses are underwater plants, they produce significant amounts of oxygen which oxygenate
872-457: A local scale. Also, in an ever growing human population, there is a need to balance the needs of the people while also balancing the needs of the planet. Lastly, it is challenging to generate scientific research to support conservation of seagrass. Limited efforts and resources are dedicated to the study of seagrasses. This is seen in areas such as India and China where there is little to no plan in place to conserve seagrass populations. However,
981-419: A mixed biotic-abiotic strategy. Crustaceans (such as crabs, Majidae zoae , Thalassinidea zoea ) and syllid polychaete worm larvae have both been found with pollen grains, the plant producing nutritious mucigenous clumps of pollen to attract and stick to them instead of nectar as terrestrial flowers do. Seagrasses form dense underwater seagrass meadows which are among the most productive ecosystems in
1090-414: A number of ecosystem services . Seagrasses are considered ecosystem engineers . This means that the plants alter the ecosystem around them. This adjusting occurs in both physical and chemical forms. Many seagrass species produce an extensive underground network of roots and rhizome which stabilizes sediment and reduces coastal erosion . This system also assists in oxygenating the sediment, providing
1199-486: A nursery grounds for commercially and recreationally valued fishery species, including the gag grouper ( Mycteroperca microlepis ), red drum, common snook , and many others. Some fish species utilize seagrass meadows and various stages of the life cycle. In a recent publication, Dr. Ross Boucek and colleagues discovered that two highly sought after flats fish, the common snook and spotted sea trout provide essential foraging habitat during reproduction. Sexual reproduction
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#17327655462501308-526: A physical barrier around byssal openings to prevent sea stars from inserting their digestive membranes. Sponge encrustation protects C. hastata from barnacle larvae settlement, serving as a protection from epibionts that increase susceptibility to predators. Thus, barnacle larvae settlement occurs more frequently on sponge-free shells than on sponge-encrusted shells. In fact, barnacle encrustation negatively influences swimming in C. hastata . Those swimming with barnacle encrustation require more energy and show
1417-726: A polyphyletic group of marine angiosperms with around 60 species in five families ( Zosteraceae , Hydrocharitaceae , Posidoniaceae , Cymodoceaceae , and Ruppiaceae ), which belong to the order Alismatales according to the Angiosperm Phylogeny Group IV System. The genus Ruppia , which occurs in brackish water, is not regarded as a "real" seagrass by all authors and has been shifted to the Cymodoceaceae by some authors. The APG IV system and The Plant List Webpage do not share this family assignment. Seagrass populations are currently threatened by
1526-529: A popular object to collect among beachcombers and vacationers. The shells also have a significant place in popular culture. Scallops inhabit all the oceans of the world, with the largest number of species living in the Indo-Pacific region. Most species live in relatively shallow waters from the low tide line to 100 m, while others prefer much deeper water. Although some species only live in very narrow environments, most are opportunistic and can live under
1635-401: A row before becoming completely exhausted and requiring several hours of rest. Should a swimming scallop land on its left side, it is capable of flipping itself over to its right side via a similar shell-clapping movement called the righting reflex. So-called singing scallops are rumored to make an audible, soft popping sound as they flap their shells underwater (though whether or not this happens
1744-873: A single species) or in mixed beds. In temperate areas, usually one or a few species dominate (like the eelgrass Zostera marina in the North Atlantic), whereas tropical beds usually are more diverse, with up to thirteen species recorded in the Philippines . Seagrass beds are diverse and productive ecosystems , and can harbor hundreds of associated species from all phyla , for example juvenile and adult fish , epiphytic and free-living macroalgae and microalgae , mollusks , bristle worms , and nematodes . Few species were originally considered to feed directly on seagrass leaves (partly because of their low nutritional content), but scientific reviews and improved working methods have shown that seagrass herbivory
1853-520: A tourist attraction and a significant source of income for many coastal economies along the Gulf of Mexico and in the Caribbean. The concept of the holobiont , which emphasizes the importance and interactions of a microbial host with associated microorganisms and viruses and describes their functioning as a single biological unit, has been investigated and discussed for many model systems, although there
1962-529: A variety of anthropogenic stressors . The ability of seagrasses to cope with environmental perturbations depends, to some extent, on genetic variability , which is obtained through sexual recruitment . By forming new individuals, seagrasses increase their genetic diversity and thus their ability to colonise new areas and to adapt to environmental changes. Seagrasses have contrasting colonisation strategies. Some seagrasses form seed banks of small seeds with hard pericarps that can remain in
2071-557: A vital defense mechanism for avoiding predators. Though rather weak, their series of eyes can detect surrounding movement and alert precaution in the presence of predators, most commonly sea stars, crabs, and snails. Physiological fitness and exercise of scallops decrease with age due to the decline of cellular and especially mitochondrial function, thus increasing the risk of capture and lowering rates of survival. Older individuals show lower mitochondrial volume density and aerobic capacity, as well as decreased anaerobic capacity construed from
2180-456: A wide variety of conditions. Scallops can be found living within, upon, or under either rocks, coral, rubble, sea grass , kelp , sand, or mud. Most scallops begin their lives as byssally attached juveniles, an ability that some retain throughout their lives while others grow into free-living adults. Very little variation occurs in the internal arrangement of organs and systems within the scallop family, and what follows can be taken to apply to
2289-514: Is a characteristic that has evolved within the lineage. In a 2008 paper, Puslednik et al. identified considerable convergence of shell morphology in a subset species of gliding Pectinidae, which suggests iterative morphological evolution may be more prevalent in the family than previously believed. There have been a number of efforts to address phylogenetic studies. Only three have assessed more than ten species and only one has included multiple outgroups. Nearly all previous molecular analyses of
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#17327655462502398-440: Is active or how seeds can remain anchored to and persist on substrate until their root systems have completely developed. Seagrasses occurring in the intertidal and subtidal zones are exposed to highly variable environmental conditions due to tidal changes. Subtidal seagrasses are more frequently exposed to lower light conditions, driven by plethora of natural and human-caused influences that reduce light penetration by increasing
2507-544: Is an important link in the food chain, feeding hundreds of species, including green turtles , dugongs , manatees , fish , geese , swans , sea urchins and crabs . Some fish species that visit/feed on seagrasses raise their young in adjacent mangroves or coral reefs . Seagrasses trap sediment and slow down water movement, causing suspended sediment to settle out. Trapping sediment benefits coral by reducing sediment loads, improving photosynthesis for both coral and seagrass. Although often overlooked, seagrasses provide
2616-526: Is based on molecular phylogeny using mitochondrial (12S, 16S) and nuclear (18S, 28S, and H3) gene markers by Yaron Malkowsky and Annette Klussmann-Kolb in 2012. Palliolinae (in part) [REDACTED] Palliolinae (in part) and Camptonectinae Chlamydinae [REDACTED] (70 mya) Pecten [REDACTED] Flexopecten [REDACTED] (247 mya) Aequipecten [REDACTED] Limidae (file shells) [REDACTED] other Pteriomorphia ( oysters , mussels ) [REDACTED] Scallops are
2725-479: Is controlled by three paired ganglia located at various points throughout their anatomy, the cerebral or cerebropleural ganglia, the pedal ganglia, and the visceral or parietovisceral ganglia. All are yellowish. The visceral ganglia are by far the largest and most extensive of the three, and occur as an almost-fused mass near the center of the animal – proportionally, these are the largest and most intricate sets of ganglia of any modern bivalve. From this, radiate all of
2834-543: Is declining worldwide. Ten seagrass species are at elevated risk of extinction (14% of all seagrass species) with three species qualifying as endangered . Seagrass loss and degradation of seagrass biodiversity will have serious repercussions for marine biodiversity and the human population that depends upon the resources and ecosystem services that seagrasses provide. Seagrasses form important coastal ecosystems . The worldwide endangering of these sea meadows, which provide food and habitat for many marine species , prompts
2943-592: Is extremely energetically expensive to be completed with stored energy; therefore, they require seagrass meadows in close proximity to complete reproduction. Furthermore, many commercially important invertebrates also reside in seagrass habitats including bay scallops ( Argopecten irradians ), horseshoe crabs , and shrimp . Charismatic fauna can also be seen visiting the seagrass habitats. These species include West Indian manatee , green sea turtles , and various species of sharks. The high diversity of marine organisms that can be found on seagrass habitats promotes them as
3052-639: Is found in modern scallops only; both putative ancestors of modern scallops, the entoliids and the Aviculopectinidae, did not possess it. Like the true oysters (family Ostreidae ), scallops have a single central adductor muscle, thus, the inside of their shells has a characteristic central scar, marking the point of attachment for this muscle. The adductor muscle of scallops is larger and more developed than those of oysters , because scallops are active swimmers; some species of scallops are known to move en masse from one area to another. In scallops,
3161-517: Is generally anoxic , seagrass must supply oxygen to their below-ground roots either through photosynthesis or by the diffusion of oxygen in the water column. When the water surrounding seagrass becomes hypoxic, so too do seagrass tissues. Hypoxic conditions negatively affect seagrass growth and survival with seagrasses exposed to hypoxic conditions shown to have reduced rates of photosynthesis, increased respiration, and smaller growth. Hypoxic conditions can eventually lead to seagrass die-off which creates
3270-435: Is now Blessed, and is expected to be confirmed as a Saint in the near future. This article about a location in the autonomous community of Extremadura, Spain is a stub . You can help Misplaced Pages by expanding it . Shell of Saint James See text Pectenidae Scallop ( / ˈ s k ɒ l ə p , ˈ s k æ l ə p / ) is a common name that encompasses various species of marine bivalve mollusks in
3379-495: Is one of the largest marine bivalve families and contains over 300 extant species in 60 genera. Its origin dates back to the Middle Triassic Period, approximately 240 million years ago; in terms of diversity, it has been a thriving family to the present day. Evolution from its origin has resulted in a successful and diverse group: pectinids are present in the world's seas, found in environments ranging from
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3488-408: Is open to some debate). Other scallops can extend their foot from between their valves, and by contracting the muscles in their foot, they can burrow into sand. Most species of the scallop family are free-living, active swimmers, propelling themselves through the water through the adductor muscles to open and close their shells. Swimming occurs through the clapping of valves for water intake. Closing
3597-411: Is sometimes equivocal, and information about phylogeny and relationships of the species are minimal, not the least because most work has been based only on adult morphology . This family's earliest and most comprehensive taxonomic treatments were based on macroscopic morphological characters of the adult shells and represent broadly divergent classification schemes. Some level of taxonomic stability
3706-415: Is substantial criticism of a concept that defines diverse host-microbe symbioses as a single biological unit. The holobiont and hologenome concepts have evolved since the original definition, and there is no doubt that symbiotic microorganisms are pivotal for the biology and ecology of the host by providing vitamins, energy and inorganic or organic nutrients, participating in defense mechanisms, or by driving
3815-630: The Camino de Santiago , and their style of shells are distinctive. The church itself dates to the turn of the twentieth century, but has classical architecture, appearing to be a castle. Like an older castle, this building was mostly constructed by hand. This church has a proud place in history as a place of succor for the poor and starving during the Spanish depression, World War I, and under Franco's regime. The priest who served in Alcuéscar in that era
3924-563: The D'Entrecasteaux Channel in the south of Tasmania dredging was banned in 1969, and since then divers have caught them in this area. Attempts to use lighted pots to attract lobster and crab led to the discovery that they were effective in attracting scallops. Sea grass See Taxonomy Seagrasses are the only flowering plants which grow in marine environments. There are about 60 species of fully marine seagrasses which belong to four families ( Posidoniaceae , Zosteraceae , Hydrocharitaceae and Cymodoceaceae ), all in
4033-414: The adductor muscle , that is sold as seafood . The brightly coloured, symmetric, fan-shaped shells of scallops with their radiating and often fluted ornamentation are valued by shell collectors, and have been used since ancient times as motifs in art, architecture, and design. Owing to their widespread distribution, scallop shells are a common sight on beaches and are often brightly coloured, making them
4142-641: The chlorophyll a/b ratio to enhance light absorption efficiency by using the abundant wavelengths efficiently. As seagrasses in the intertidal and subtidal zones are under highly different light conditions, they exhibit distinctly different photoacclimatory responses to maximize photosynthetic activity and photoprotection from excess irradiance. Seagrasses assimilate large amounts of inorganic carbon to achieve high level production. Marine macrophytes , including seagrass, use both CO 2 and HCO − 3 ( bicarbonate ) for photosynthetic carbon reduction. Despite air exposure during low tide, seagrasses in
4251-412: The heterokonts and dinoflagellates . Some scallops, including Chlamys hastata , frequently carry epibionts such as sponges and barnacles on their shells. The relationship of the sponge to the scallop is characterized as a form of mutualism, because the sponge provides protection by interfering with adhesion of predatory sea-star tube feet, camouflages Chlamys hastata from predators, or forms
4360-476: The subtidal zone adapt to reduced light conditions caused by light attenuation and scattering due to the overlaying water column and suspended particles. Seagrasses in the deep subtidal zone generally have longer leaves and wider leaf blades than those in the shallow subtidal or intertidal zone, which allows more photosynthesis, in turn resulting in greater growth. Seagrasses also respond to reduced light conditions by increasing chlorophyll content and decreasing
4469-537: The taxonomic family Pectinidae , the scallops. However, the common name "scallop" is also sometimes applied to species in other closely related families within the superfamily Pectinoidea , which also includes the thorny oysters . Scallops are a cosmopolitan family of bivalves found in all of the world's oceans, although never in fresh water. They are one of the very few groups of bivalves to be primarily "free-living", with many species capable of rapidly swimming short distances and even migrating some distance across
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4578-663: The Pectinidae have only utilized mitochondrial data. Phylogenies based only on mitochondrial sequence data do not always provide an accurate estimation on the species tree. Complicated factors can arise due to the presence of genetic polymorphisms in ancestral species and resultant lineage sorting. In molecular phylogenies of the Bivalvia, both the Spondylidae and the Propeamussiidae have been resolved as sister to
4687-515: The Pectinidae. The following are recognised in the family Pectinidae: The largest wild scallop fishery is for the Atlantic sea scallop ( Placopecten magellanicus ) found off the northeastern United States and eastern Canada. Scallops are harvested using scallop dredges or bottom trawls. Most of the rest of the world's production of scallops is from Japan (wild, enhanced, and aquaculture) and China (mostly cultured Atlantic bay scallops). In
4796-788: The ability to synthesise sulfated polysaccharides was regained by marine angiosperms. Another unique feature of cell walls of seagrasses is the occurrence of unusual pectic polysaccharides called apiogalacturonans . In addition to polysaccharides, glycoproteins of the hydroxyproline -rich glycoprotein family, are important components of cell walls of land plants. The highly glycosylated arabinogalactan proteins are of interest because of their involvement in both wall architecture and cellular regulatory processes. Arabinogalactan proteins are ubiquitous in seed land plants and have also been found in ferns , lycophytes and mosses . They are structurally characterised by large polysaccharide moieties composed of arabinogalactans (normally over 90% of
4905-581: The abundance of species within the Pectinidae has varied greatly over time; Pectinidae was the most diverse bivalve family in the Mesozoic era , but the group almost disappeared completely by the end of the Cretaceous period . The survivors speciated rapidly during the Tertiary period . Nearly 7,000 species and subspecies names have been introduced for both fossil and recent Pectinidae. The cladogram
5014-587: The amount of glycogen stored in muscle tissue. Environmental factors, such as changes in oxidative stress parameters, can inhibit the growth and development of scallops. Seasonal changes in temperature and food availability have been shown to affect muscle metabolic capabilities. The properties of mitochondria from the phasic adductor muscle of Euvola ziczac varied significantly during their annual reproductive cycle. Summer scallops in May have lower maximal oxidative capacities and substrate oxidation than any other time in
5123-409: The anatomy of any given scallop species. The shell of a scallop consists of two sides or valves , a left valve and a right one, divided by a plane of symmetry . Most species of scallops rest on their right valve, and consequently, this valve is often deeper and more rounded than the left (i.e., upper) valve, which in many species is actually concave. With the hinge of the two valves oriented towards
5232-455: The animal sense its position in the surrounding environment. They are connected to the pedal ganglia by short cerebral-pedal connectives. The pedal ganglia, though not fused, are situated very close to each other near the midline. From the pedal ganglia, the scallop puts out pedal nerves which control the movement of, and sensation in, its small muscular foot. Scallops have a large number (up to 200) of small (about 1 mm) eyes arranged along
5341-428: The anterior ear may be somewhat larger (the posterior ear is never larger than the anterior one, an important feature for distinguishing which valve is which). As is the case in almost all bivalves, a series of lines and/or growth rings originates at the center of the hinge, at a spot called the " beak " surrounded by a generally raised area called the " umbo ". These growth rings increase in size downwards until they reach
5450-633: The byssus as they grow larger. A very few species go on to cement themselves to a hard substrate (e.g. Chlamys distorta and Hinnites multirigosus ). However, the majority of scallops are free-living and can swim with brief bursts of speed to escape predators (mostly starfish ) by rapidly opening and closing their valves. Indeed, everything about their characteristic shell shape – its symmetry, narrowness, smooth and/ or grooved surface, small flexible hinge, powerful adductor muscle, and continuous and uniformly curved edge – facilitates such activity. They often do this in spurts of several seconds before closing
5559-464: The cell walls of seagrasses seem to contain combinations of features known from both angiosperm land plants and marine macroalgae together with new structural elements. Dried seagrass leaves might be useful for papermaking or as insulating materials, so knowledge of cell wall composition has some technological relevance. Despite only covering 0.1 - 0.2% of the ocean’s surface, seagrasses form critically important ecosystems. Much like many other regions of
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#17327655462505668-485: The combined sensitivity of both retinas to light entering the eye and light retro-reflected from the mirror grants scallops exceptional contrast definition, as well as the ability to detect changing patterns of light and motion. Scallops primarily rely on their eyes as an 'early-warning' threat detection system, scanning around them for movement and shadows which could potentially indicate predators. Additionally, some scallops alter their swimming or feeding behaviour based on
5777-500: The common backbone structure of land plant arabinogalactan proteins is conserved, the glycan structures exhibit unique features suggesting a role of seagrass arabinogalactan proteins in osmoregulation . Further components of secondary walls of plants are cross-linked phenolic polymers called lignin , which are responsible for mechanical strengthening of the wall. In seagrasses, this polymer has also been detected, but often in lower amounts compared to angiosperm land plants. Thus,
5886-570: The concentric rings of their shells. Many scallops are hermaphrodites (having female and male organs simultaneously), altering their sex throughout their lives, while others exist as dioecious species, having a definite sex. In this case, males are distinguished by roe-containing white testes and females with roe-containing orange ovaries. At the age of two, they usually become sexually active, but do not contribute significantly to egg production until four. The reproduction process occurs externally through spawning, in which eggs and sperm are released into
5995-574: The conservation and restoration of seagrass may contribute to 16 of the 17 UN Sustainable Development Goals . In a study of seagrass conservation in China, several suggestions were made by scientists on how to better conserve seagrass. They suggested that seagrass beds should be included in the Chinese conservation agenda as done in other countries. They called for the Chinese government to forbid land reclamation in areas near or in seagrass beds, to reduce
6104-537: The continental shelves of all continents except Antarctica. Recent sequencing of the genomes of Zostera marina and Zostera muelleri has given a better understanding of angiosperm adaptation to the sea. During the evolutionary step back to the ocean, different genes have been lost (e.g., stomatal genes) or have been reduced (e.g., genes involved in the synthesis of terpenoids ) and others have been regained, such as in genes involved in sulfation . Genome information has shown further that adaptation to
6213-406: The curved ventral edge of the shell. The shells of most scallops are streamlined to facilitate ease of movement during swimming at some point in their lifecycles, while also providing protection from predators. Scallops with ridged valves have the advantage of the architectural strength provided by these ridges called "ribs", although the ribs are somewhat costly in weight and mass. A unique feature of
6322-615: The density of suspended opaque materials. Subtidal light conditions can be estimated, with high accuracy, using artificial intelligence, enabling more rapid mitigation than was available using in situ techniques. Seagrasses in the intertidal zone are regularly exposed to air and consequently experience extreme high and low temperatures, high photoinhibitory irradiance , and desiccation stress relative to subtidal seagrass. Such extreme temperatures can lead to significant seagrass dieback when seagrasses are exposed to air during low tide. Desiccation stress during low tide has been considered
6431-468: The dormancy stage for several months. These seagrasses are generally short-lived and can recover quickly from disturbances by not germinating far away from parent meadows (e.g., Halophila sp., Halodule sp., Cymodocea sp., Zostera sp. and Heterozostera sp.). In contrast, other seagrasses form dispersal propagules . This strategy is typical of long-lived seagrasses that can form buoyant fruits with inner large non-dormant seeds, such as
6540-444: The edge of their mantles. These eyes represent a particular innovation among molluscs, relying on a concave, parabolic mirror of guanine crystals to focus and retro-reflect light instead of a lens as found in many other eye types. Additionally, their eyes possess a double-layered retina, the outer retina responding most strongly to light and the inner to abrupt darkness. While these eyes are unable to resolve shapes with high fidelity,
6649-445: The epiphytes and invertebrates that live on and among seagrass blades. Seagrass meadows also provide physical habitat in areas that would otherwise be bare of any vegetation. Due to this three dimensional structure in the water column, many species occupy seagrass habitats for shelter and foraging. It is estimated that 17 species of coral reef fish spend their entire juvenile life stage solely on seagrass flats. These habitats also act as
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#17327655462506758-483: The evolution of the host. Although most work on host-microbe interactions has been focused on animal systems such as corals, sponges, or humans, there is a substantial body of literature on plant holobionts . Plant-associated microbial communities impact both key components of the fitness of plants, growth and survival, and are shaped by nutrient availability and plant defense mechanisms. Several habitats have been described to harbor plant-associated microbes, including
6867-512: The family Poaceae . Like all autotrophic plants, seagrasses photosynthesize , in the submerged photic zone , and most occur in shallow and sheltered coastal waters anchored in sand or mud bottoms. Most species undergo submarine pollination and complete their life cycle underwater. While it was previously believed this pollination was carried out without pollinators and purely by sea current drift, this has been shown to be false for at least one species, Thalassia testudinum , which carries out
6976-412: The family Pectinidae is monophyletic, developing from a single common ancestor. The direct ancestors of Pectinidae were scallop-like bivalves of the family Entoliidae. Entoliids had auricles and a byssal notch only at youth, but they did not have a ctenolium, a comb-like arrangement along the margins of the byssal notch in Pectinidae. The ctenolium is the defining feature of the modern family Pectinidae and
7085-420: The family Pectinidae, marine bivalve molluscs within the superfamily Pectinoidea . Other families within this same superfamily share a somewhat similar overall shell shape, and some species within some of the related families are also commonly referred to as "scallops" (for example, Propeamussiidae , the glass scallops). The family Pectinidae is the most diversified of the pectinoideans in present-day oceans. It
7194-412: The food is digested in the digestive gland, an organ sometimes misleadingly referred to as the "liver, " which envelops part of the oesophagus, intestine, and entire stomach. Waste is passed on through the intestine (the terminus of which, like that of many mollusks, enters and leaves the animal's heart) and exits via the anus. Like all bivalves, scallops lack actual brains. Instead, their nervous system
7303-584: The genera Posidonia sp., Enhalus sp. and Thalassia sp. Accordingly, the seeds of long-lived seagrasses have a large dispersal capacity compared to the seeds of the short-lived type, which permits the evolution of species beyond unfavourable light conditions by the seedling development of parent meadows. The seagrass Posidonia oceanica (L.) Delile is one of the oldest and largest species on Earth. An individual can form meadows measuring nearly 15 km wide and can be hundreds to thousands of years old. P. oceanica meadows play important roles in
7412-507: The intertidal zone can continue to photosynthesize utilizing CO 2 in the air. Thus, the composition of inorganic carbon sources for seagrass photosynthesis probably varies between intertidal and subtidal plants. Because stable carbon isotope ratios of plant tissues change based on the inorganic carbon sources for photosynthesis, seagrasses in the intertidal and subtidal zones may have different stable carbon isotope ratio ranges. Seagrass beds /meadows can be either monospecific (made up of
7521-500: The intertidal zone to the hadal depths. The Pectinidae play an extremely important role in many benthic communities and exhibit a wide range of shell shapes, sizes, sculptures, and cultures. Raines and Poppe listed nearly 900 species names of scallops, but most of these are considered either questionable or invalid. Raines and Poppe mentioned over 50 genera, around 250 species, and subspecies . Although species are generally well-circumscribed, their attribution to subfamilies and genera
7630-407: The maintenance of the geomorphology of Mediterranean coasts, which, among others, makes this seagrass a priority habitat of conservation. Currently, the flowering and recruitment of P. oceanica seems to be more frequent than that expected in the past. Further, this seagrass has singular adaptations to increase its survival during recruitment. The large amounts of nutrient reserves contained in
7739-600: The marine habitat was accomplished by radical changes in cell wall composition. However the cell walls of seagrasses are not well understood. In addition to the ancestral traits of land plants one would expect habitat-driven adaptation process to the new environment characterized by multiple abiotic (high amounts of salt) and biotic (different seagrass grazers and bacterial colonization) stressors. The cell walls of seagrasses seem intricate combinations of features known from both angiosperm land plants and marine macroalgae with new structural elements. Today, seagrasses are
7848-418: The molecule) which are covalently linked via hydroxyproline to relatively small protein/peptide backbones (normally less than 10% of the molecule). Distinct glycan modifications have been identified in different species and tissues and it has been suggested these influence physical properties and function. In 2020, AGPs were isolated and structurally characterised for the first time from a seagrass. Although
7957-502: The muscular foot, used to attach to a firm support, such as a rock. Some can also be found on the ocean floor, moving with an extendable foot between their valves or burrowing themselves in the sand by extending and retracting their feet. Scallops are highly sensitive to shadows, vibrations, water movement, and chemical stimuli. All possess a series of 100 blue eyes, embedded on the edge of the mantle of their upper and lower valves that can distinguish between light and darkness. They serve as
8066-427: The natural world. This allows for misconceptions and a lack of understanding of seagrass ecology and its importance. Additionally, it is a challenge to obtain and maintain information on the status and condition of seagrass populations. With many populations across the globe, it is difficult to map the current populations. Another challenge faced in seagrass conservation is the ability to identify threatening activities on
8175-423: The need for protection and understanding of these valuable resources. Around 140 million years ago, seagrasses evolved from early monocots which succeeded in conquering the marine environment. Monocots are grass and grass-like flowering plants (angiosperms), the seeds of which typically contain only one embryonic leaf or cotyledon . Terrestrial plants evolved perhaps as early as 450 million years ago from
8284-409: The nerves which connect the visceral ganglia to the circumpallial nerve ring which loops around the mantle and connects to all of the scallop's tentacles and eyes. This nerve ring is so well developed that, in some species, it may be legitimately considered an additional ganglion. The visceral ganglia are also the origin of the branchial nerves which control the scallop's gills. The cerebral ganglia are
8393-407: The next-largest set of ganglia and lie distinct from each other a significant distance dorsal to the visceral ganglia. They are attached to the visceral ganglia by long cerebral-visceral connectives, and to each other via a cerebral commissure that extends in an arch dorsally around the esophagus. The cerebral ganglia control the scallop's mouth via the palp nerves and connect to statocysts which help
8502-603: The number and size of culture ponds, to control raft aquaculture and improve sediment quality, to establish seagrass reserves, to increase awareness of seagrass beds to fishermen and policy makers and to carry out seagrass restoration. Similar suggestions were made in India where scientists suggested that public engagement was important. Also, scientists, the public, and government officials should work in tandem to integrate traditional ecological knowledge and socio-cultural practices to evolve conservation policies. World Seagrass Day
8611-533: The ocean floor, where they attach themselves to objects through byssus threads. Byssus is eventually lost with adulthood, transitioning almost all scallop species into free swimmers. Rapid growth occurs within the first several years, with an increase of 50–80 % in shell height and quadrupled size in meat weight, and reaches a commercial size at about four to five years of age. The lifespans of some scallops have been known to extend over 20 years. Scallops are known to be infected by viruses , bacteria , microalgae of
8720-480: The ocean floor. A small minority of scallop species live cemented to rocky substrates as adults, while others attach themselves to stationary or rooted objects such as seagrass at some point in their lives by means of a filament they secrete called a byssal thread . The majority of species, however, live recumbent on sandy substrates, and when they sense the presence of a predator such as a starfish , they may attempt to escape by swimming swiftly but erratically through
8829-482: The ocean, seagrasses have been faced with an accelerating global decline. Since the late 19th century, over 20% of the global seagrass area has been lost, with seagrass bed loss occurring at a rate of 1.5% each year. Of the 72 global seagrass species, approximately one quarter (15 species) could be considered at a Threatened or Near Threatened status on the IUCN’s Red List of Threatened Species. Threats include
8938-404: The order Alismatales (in the clade of monocotyledons ). Seagrasses evolved from terrestrial plants which recolonised the ocean 70 to 100 million years ago. The name seagrass stems from the many species with long and narrow leaves , which grow by rhizome extension and often spread across large " meadows " resembling grassland ; many species superficially resemble terrestrial grasses of
9047-480: The physical, chemical, and biological environments of coastal waters. Though seagrasses provide invaluable ecosystem services by acting as breeding and nursery ground for a variety of organisms and promote commercial fisheries , many aspects of their physiology are not well investigated. There are 26 species of seagrasses in North American coastal waters. Several studies have indicated that seagrass habitat
9156-864: The potential to induce widespread seagrass loss. An additional threat to seagrass beds is the introduction of non-native species. For seagrass beds worldwide, at least 28 non-native species have become established. Of these invasive species , the majority (64%) have been documented to infer negative effects on the ecosystem. Another major cause of seagrass disappearance is coastal eutrophication . Rapidly developing human population density along coastlines has led to high nutrient loads in coastal waters from sewage and other impacts of development. Increased nutrient loads create an accelerating cascade of direct and indirect effects that lead to seagrass decline. While some exposure to high concentrations of nutrients, especially nitrogen and phosphorus , can result in increased seagrass productivity, high nutrient levels can also stimulate
9265-435: The primary factor limiting seagrass distribution at the upper intertidal zone. Seagrasses residing the intertidal zone are usually smaller than those in the subtidal zone to minimize the effects of emergence stress. Intertidal seagrasses also show light-dependent responses, such as decreased photosynthetic efficiency and increased photoprotection during periods of high irradiance and air exposure. In contrast, seagrasses in
9374-411: The rapid overgrowth of macroalgae and epiphytes in shallow water, and phytoplankton in deeper water. In response to high nutrient levels, macroalgae form dense canopies on the surface of the water, limiting the light able to reach the benthic seagrasses. Algal blooms caused by eutrophication also lead to hypoxic conditions, which seagrasses are also highly susceptible to. Since coastal sediment
9483-398: The rhizoplane (surface of root tissue), the rhizosphere (periphery of the roots), the endosphere (inside plant tissue), and the phyllosphere (total above-ground surface area). The microbial community in the P. oceanica rhizosphere shows similar complexity as terrestrial habitats that contain thousands of taxa per gram of soil. In contrast, the chemistry in the rhizosphere of P. oceanica
9592-474: The scallop family is the presence, at some point during the animal's lifecycle, of a distinctive and taxonomically important shell feature, a comb-like structure called a ctenolium located on the anterior edge of the right valve next to the valve's byssal notch. Though many scallops lose this feature as they become free-swimming adults, all scallops have a ctenolium at some point during their lives, and no other bivalve has an analogous shell feature. The ctenolium
9701-409: The sea floor between each contraction of its valves, whereas a swimming scallop stays in the water column for most or all of its contractions and travels a much greater distance (though seldom at a height of more than 1 m off the sea bed and seldom for a distance of greater than 5 m). Both jumping and swimming movements are very energy-intensive, and most scallops cannot perform more than four or five in
9810-620: The seeds of this seagrass support shoot and root growth, even up to the first year of seedling development. In the first months of germination , when leaf development is scarce, P. oceanica seeds perform photosynthetic activity, which increases their photosynthetic rates and thus maximises seedling establishment success. Seedlings also show high morphological plasticity during their root system development by forming adhesive root hairs to help anchor themselves to rocky sediments. However, many factors about P. oceanica sexual recruitment remain unknown, such as when photosynthesis in seeds
9919-474: The shell entirely and sinking back to the bottom of their environment. Scallops are able to move through the water column either forward/ventrally (termed swimming) by sucking water in through the space between their valves, an area called the gape, and ejecting it through small holes near the hinge line called exhalant apertures, or backward/dorsally (termed jumping) by ejecting the water out the same way it came in (i.e. ventrally). A jumping scallop usually lands on
10028-412: The shell shape tends to be highly regular, and is commonly used as an archetypal form of a seashell . Scallops possess fast ( striated ) and slow ( smooth ) adductor muscles , which have different structures and contractile properties. These muscles lie closely apposed to one another but are divided by a connective tissue sheet. The striated adductor muscle contracts very quickly for swimming, whereas
10137-565: The shell which is situated next to the byssal notch. The fossil history of scallops is rich in species and specimens. The earliest known records of true scallops (those with a ctenolium) can be found from the Triassic period , over 200 million years ago. The earliest species were divided into two groups, one with a nearly smooth exterior: Pleuronectis von Schlotheim, 1820, while the other had radial ribs or riblets and auricles: Praechlamys Allasinaz, 1972. Fossil records also indicate that
10246-401: The smooth catch adductor muscle lacks striations, and contracts for long periods, keeping shells closed with little expenditure of energy. Scallops are filter feeders , and eat plankton . Unlike many other bivalves, they lack siphons . Water moves over a filtering structure, where food particles become trapped in mucus. Next, the cilia on the structure move the food toward the mouth. Then,
10355-404: The top, one side corresponds to the animal's morphological anterior or front, the other is the posterior or rear, the hinge is the dorsal or back/top region, and the bottom corresponds to the ventral or (as it were) underside/belly. However, as many scallop shells are more or less bilaterally symmetrical ("equivalved"), as well as symmetrical front/back ("equilateral"), determining which way
10464-488: The trends they identified appear to be part of a large-scale trend worldwide. Conservation efforts are imperative to the survival of seagrass species. While there are many challenges to overcome with respect to seagrass conservation there are some major ones that can be addressed. Societal awareness of what seagrasses are and their importance to human well-being is incredibly important. As the majority of people become more urbanized they are increasingly more disconnected from
10573-399: The turbidity or clarity of the water, by detecting the movement of particulate matter in the water column. Scallops are mostly free-living and active, unlike the vast majority of bivalves, which are mostly slow-moving and infaunal. All scallops are thought to start out with a byssus , which attaches them to some form of substrate such as eelgrass when they are very young. Most species lose
10682-426: The valves propels water with a strong force near the hinge via the velum, a curtain-like fold of the mantle that directs water expulsion around the hinge. Scallops swim in the direction of the valve opening unless the velum directs an abrupt change in course direction. Other species of scallops can be found on the ocean floor attached to objects by byssal threads. Byssal threads are strong, silky fibers extending from
10791-414: The water column. These meadows account for more than 10% of the ocean's total carbon storage. Per hectare, it holds twice as much carbon dioxide as rain forests and can sequester about 27.4 million tons of CO 2 annually. Seagrass meadows provide food for many marine herbivores. Sea turtles, manatees, parrotfish, surgeonfish, sea urchins and pinfish feed on seagrasses. Many other smaller animals feed on
10900-503: The water during mating season and fertilized ova sink to the bottom. After several weeks, the immature scallops hatch and the larvae, miniature transparent versions of the adults called "spat", drift in the plankton until settling to the bottom again (an event called spatfall) to grow, usually attaching by means of byssal threads. Some scallops, such as the Atlantic bay scallop Argopecten irradians , are short-lived, while others can live 20 years or more. Age can often be inferred from annuli ,
11009-425: The water using jet propulsion created by repeatedly clapping their shells together. Scallops have a well-developed nervous system, and unlike most other bivalves all scallops have a ring of numerous simple eyes situated around the edge of their mantles . Many species of scallops are highly prized as a food source, and some are farmed as aquaculture . The word "scallop" is also applied to the meat of these bivalves,
11118-416: The water, causing seagrass die-off. Since seagrasses have some of the highest light requirements of angiosperm plant species, they are highly affected by environmental conditions that change water clarity and block light. Seagrasses are also negatively affected by changing global climatic conditions. Increased weather events, sea level rise , and higher temperatures as a result of global warming all have
11227-514: The water. Spawning typically occurs in late summer and early autumn; spring spawning may also take place in the Mid-Atlantic Bight . The females of scallops are highly fecund, capable of producing hundreds of millions of eggs per year. Once an egg is fertilized, it is then planktonic, a collection of microorganisms that drift abundantly in fresh or salt water. Larvae stay in the water column for four to seven weeks before dissipating to
11336-403: The world. They function as important carbon sinks and provide habitats and food for a diversity of marine life comparable to that of coral reefs . Seagrasses are a paraphyletic group of marine angiosperms which evolved in parallel three to four times from land plants back to the sea. The following characteristics can be used to define a seagrass species: Seagrasses profoundly influence
11445-477: The year. This phenomenon is due to lower protein levels in adductor muscles. The scallop family is unusual in that some members of the family are dioecious (males and females are separate), while others are simultaneous hermaphrodites (both sexes in the same individual), and a few are protoandrous hermaphrodites (males when young then switching to female). Female scallops have red roe and male scallops have white roe. Spermatozoa and ova are released freely into
11554-617: Was a general trend in many areas of the Mediterranean Sea. There is an estimated 27.7% reduction along the southern coast of Latium , 18%-38% reduction in the Northern Mediterranean basin, 19%-30% reduction on Ligurian coasts since the 1960s and 23% reduction in France in the past 50 years. In Spain the main reason for regression was due to human activity such as illegal trawling and aquaculture farming. It
11663-476: Was achieved when Waller's studies in 1986, 1991, and 1993 concluded evolutionary relationships between pectinid taxa based on hypothesized morphological synapomorphies, which previous classification systems of Pectinidae failed to do. He created three Pectinidae subfamilies: Camptonectinidae, Chlamydinae and Pectininae. The framework of its phylogeny shows that repeated life habit states derive from evolutionary convergence and parallelism. Studies have determined
11772-408: Was dominated by the presence of sugars like sucrose and phenolics. Seagrass cell walls contain the same polysaccharides found in angiosperm land plants, such as cellulose However, the cell walls of some seagrasses are characterised by sulfated polysaccharides, which is a common attribute of macroalgae from the groups of red , brown and also green algae . It was proposed in 2005 that
11881-464: Was found that areas with medium to high human impact suffered more severe reduction. Overall, it was suggested that 29% of known areal seagrass populations have disappeared since 1879. The reduction in these areas suggests that should warming in the Mediterranean basin continue, it may lead to a functional extinction of Posidonia oceanica in the Mediterranean by 2050. Scientists suggested that
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