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👩‍🎓 | Swimming in the dark and tracking fish The University of Tokyo elucidates the migratory ecology of nocturnal fish using the world's first method


The University of Tokyo elucidates the migratory ecology of nocturnal fish using the world's first method of swimming in the dark and tracking fish

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At night, it returned to the coral reef to excrete feces, and it was found that it plays an important role in the energy circulation of the ecosystem inside and outside the coral reef.

A research group led by Assistant Professor Keita Koeda of the University of Tokyo is the world's first hand to swim and track in the dark with a tag that shines on fish ... → Continue reading

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Coral reef

Coral reef(Coral reef,coral reef,Coral reef,Coral reef) IsReef coral OfCanopyMade byterrainone of.熱 帯Facing the open seacoastalWell developed.


Suitable for breeding reef-building corals海Is as high as 25-30 ℃Water temperature, As high as 3-4%Salinity, Even deepWater depthIt is a shallow and beautiful sea area of ​​about 30m.equatorialIn the vicinityTrade windBy westwardWarm currentOccurs from high latitudesCold snapHas entered after that.The Pacific Ocean,Indian Ocean,大西洋This is the reason why coral reefs are concentrated on the west side and rarely seen on the east side.Also, even on large coral reefsEstuaryIt can be seen that it takes the form of avoiding the area.

in JapanNansei Islands,Izu Islands,Ogasawara IslandsCoral reefs can be seen in the southern islands, but coral reefs are formed up to a water temperature of about 18 ° C, so if they are small in mainland Japan,Tsushima StraitsSouthBoso PeninsulaIt can be found in various parts of the south.

The islands on which coral reefs are based are disappearing not because of global warming but because of the subsidence of the coral reefs themselves.

There are hundreds of types of reef-building coral, such as, but these are less than 100 cm in diameter.Sea anemoneSmall similar toPolypGathered a lotgroupMany polyps are unique to each type of coral in various shapes.骨 格Is formed.

Coral polypsplanktonPrey on, but in the bodyphotosynthesisI doZooxanthellaeTheSymbiosisYou can also get the nutrients.The grown polypSplitAnd increase in seawatercarbon dioxide,calciumIncorporateCalcium carbonateCreate a skeleton whose main component is.As a result of many reef-building corals performing life activities, it is thick under the coralsLimestoneThe coral itself grows further up and offshore.

Near the coral reef砂 浜Becomes whitish, including coral debris that has been broken by waves or bitten by animals.Othershellfish,Uni,ForaminiferaDead husks are also deposited on the coast.Thus, most of the sand on coral reef beaches is of biological origin and most of it is calcareous.These limes are deposited, and a part of them melts and hardens again, resulting in rocks containing sand grains.Beach rock.

The accumulation of these creatures and natural activities over a long period of time results in the formation of large coral reefs due to the limestone bedrock, which changes the terrain.Looking at the sea area with coral reefs from the sky, the shallow waters of the coral reefs emerge in light blue and emerald green in the indigo sea.


Coral reefs can be roughly divided into three types, the Great Barrier Reef, the Great Barrier Reef, and the Atoll, depending on their form.

Coral reefs that have developed in contact with the coast are called skirt reefs.The inside of the reef surrounded by the outer reef (the edge of the coral reef) becomes a shallow reef, which looks light blue when viewed from above.CurrentJapanMost of the coral reefs in Japan are foot reefs.

Outer reefbreakwaterSurrounding the island in a ring like, a slightly deep reef lake between the reef and the islandLagoonThe one with) is called the Great Barrier Reef.Chuuk Island(Truck Islands) is an example.The Great Barrier Reef is not only the one that surrounds the central island, but also the one that surrounds the continent.It is famous because it surrounds the continent.Australia OfGreat Barrier Reef(Great Barrier Reef).

Those with no island in the center of the reef, only circular outer reefs and lagoonsAtoll(Kansho).Murloa Atoll,OkinotorishimaIs given as an example.

Such differences in coral reef morphology are thought to be due to island subsidence or sea level rise.Regarding the formation process of the Great Barrier Reef and Atoll, the island with the foot reefCrustal movement,ErosionIt is assumed that it has subsided and changed to a great barrier or atoll.Subsidence theoryWhen,Last glacial period OfSea level fluctuationIt is assumed that the skirt reef created by the sea level has changed to a reef or atoll due to the rise in sea level.Glacier constraint theoryBoth have a certain reputation.Especially the subsidence theoryCharles DarwinBy, nowPlate tectonicsIs linked with.

Coral reefs may become islands due to uplift and sea level descent.Miyakojima,OkinoerabujimaFor example, the island is characterized by its flat shape as a whole.Also,Kitadaito IslandとMinami Daito IslandThe center of the island is dented, and there is a high part surrounding it.It is believed to be a raised atoll.

In addition,パラオEtc. are big in the coral reefLimestone caveHowever, since the limestone cave can only be formed on land, it used to be on land.This is because coral reefs appeared on the surface of the sea due to the descent of the sea level, eroded to form a limestone cave, and became the seabed when the sea level rose again, and the part that is now an island remains uneroded. Is.

Coral reef composition and fossils

It is not always the case that coral reefs are formedReef coralnot only.If there are other substances that greatly develop the calcareous skeleton, they can be factors that form coral reefs.In today's coral reefsRed algaeThere are some places that dominate, though it is a kind.In addition, although it is not necessarily involved in the formation of coral reefs, it is involved in the accumulation of calcareous substances in coral reefs because it forms calcareous shells.clamsKindGiant clamOr largeForaminiferaIsMarginopora,HoshizunaIs inhabited in large numbers.Hoshizuna is a coral reef砂 浜In some places, you can find sandy beaches that are almost exclusively for Hoshizuna.Coral reefs as fossilsfossil ThePaleozoicSince then, it has appeared frequently.In particular,Reef coralIncluding fossils ofLimestoneTake the form of.

Today's coral reefs appear only in shallow waters, mainly in the tropics, where they are warm and transparent.The reason for this is the reef-building coralZooxanthellaeUnicellular algaeSymbiosisBecause it is letting you.This is not just a coincidence or nutritional need, but of zooxanthellaephotosynthesisIt is believed that this is the reason why the coral calcareous skeleton can maintain such a growth rate.By the way, giant clams and Hoshizuna also coexist with zooxanthellae.From this, it is probable that there was a similar situation in the past coral reefs.Therefore,Coral reef fossilsIf, it can be determined that the place at that time was a tropical or subtropical, warm and shallow sea area.Thus, with the discovery of that fossil, that place of the eraEnvironmentIf you can determine such fossilsPhase-indicating fossilI'm calling.

However, the formation of coral reefsSubsidence theoryAs mentioned in, the subsidence of the island and the movement of the ocean plate are greatly involved.It is also necessary to consider the possibility that the sea area where coral reefs are formed and the point where they are found as fossils will change significantly, and that they will be taken into other strata and appear.

Coral reef environment and life

The outside of the reef is suddenly deep and the waves are high, but the reefs and reefs surrounded by the outer reefs are natural to stop the violent waves of the outer reefs.breakwaterTherefore, the waves are calm.The coral gaps are convenient for hiding small creatures, and large animals that prey on them also gather.Furthermore, inside and outside the lagoon砂 浜,EelgrassSince there is also a place, if these are included, a truly diverse environment will be created on the coral reef, and many organisms will inhabit it.Coral reefbiodiversityIt can be said that it is an important place from the viewpoint of.

Here are just a few of the creatures that live on coral reefs.


Since the rocky shores and sandy beaches near the coral reefs contain a lot of lime, peculiar plants adapted to the lime-rich soil grow naturally.HerbWell thenKusato Bella,Sedum formosanumSuch,KimotoThen.Hibiscus tiliaceus,AkoAnd so on.In the shade of these treesHermit crab,Coconut crabInhabits animals such as.In addition, the gap between the rocksSea snakesIt will be a roost and spawning ground.

On the beachBindweed,Gunbai Hirugao,Zoysia tenuifoliaEtc. grow naturally, and near the shore where plants do not growSnaganiInhabits.In addition, the sandy beachウ ミ ガ メIt is a spawning ground for species.

Inside the reef

Many creatures live inside the reef where the waves are calm.Large fish that normally live outside the reef may enter the inside of the reef for spawning and foraging.

Seagrass bed

From the shallow part of the tide zone to the depth of several meters in the lagoon,SeaweedOvergrownSeaweed bedIs formed in various places.For example, in OkinawaEnhalusThere are several types of seagrass inhabiting.Seagrass beds serve as habitats for various small animals and as a base for fry of fish.furtherBlue-green algaeBy inhabiting a large amount ofNitrogen fixationIt is also a place where coral reefs are held, supporting the high productivity of coral reefs.

Outside the reef

After passing the outer reef, the water depth suddenly becomes deeper.Many corals spread their branches on the slopes, and there are small fish as well as inside the reef, but around themQuintoki,Striped jack,Snappers,GrouperLarge fish can be seen,Onite mackerel,Hammerhead sharkEtc. also appear.

Dangerous creatures

Coral reefs colored with colorful corals and creatures, but these creatures have thorns andpoisonThere are many creatures with sickness and ferocious creatures, and some of them are poisonous enough to be life-threatening.

Also, attention should be paid to edible fish.Puffer fishPoisons of the same kind are well known, but inhabit coral reef areasYellow-edged lyre,Lutjanus bohar,Flatfish,Striped beakfish,Spotted knifejawLarge fish such as are derived from algaeCiguatoxinThe poison is stored in the body.Small individuals are less dangerous, but care must be taken when eating large individuals.

Coral reef ecosystem

Coral reefs are an environment in which extremely diverse organisms live at high densities.Even if you take a peek, you can see colorful fish dancing.On the rockSea cucumberKind is rugged, and even if you look under the coral gaps and boulders, there are variousInvertebrateCan be seen.There are several possible reasons why such diverse organisms can live at high densities.

  • Be warm throughout the year.It is a tropical subtropical area with high water temperatures throughout the year.In general, biodiversity is higher in environments where there are no harsh physicochemical conditions such as cold seasons.
  • The coral skeleton that fills the seabed has a wide variety of sediments andscaffoldTo supply.Plate-shaped and branch-shaped coral create gaps of various sizes, which provide dendrites for creatures of various sizes.In addition, the skeleton of coral is softer than that of ordinary rocks, making it easier for various creatures to live in it.The structure of the entire coral reef also supports it.
  • Coral reefs are highly transparent and shallow seas, so the sunlight is strong, which is whyEcosystemSupport the wholeProductionIt can be said that it is backing.However, high transparency is oligotrophic and yetplanktonThis means that there is little production, which is a disadvantage in securing production.Moreover, it is large on coral reefsSeaweedIs not often seen.So on the coral reefProducerSpeaking of what, it is still coral.Coral is an animal, but in the bodyZooxanthellaeTheSymbiosisTherefore, it has a practical role as a producer.However, not many animals eat coral directly.Parrotfish that bite together with the coral skeleton,Crown-of-thorns starfishIs to some extent.outside,ButterflyfishIt seems that they eat like coral polyps by pinching the soft part.Other than that, there aren't many people who eat coral directly.Then, how it is used is that coral secretes from the body surface.mucusSeems to be used quite a bit.
  • In addition to factors directly related to photosynthesis, factors that limit the amount of production by producers include the amount of fertilizer such as nitrogen and phosphorus.In this respect as well, coral reefs do not seem to have a large supply of them.Regarding nitrogen, it is said that blue-green algae living on the sand surface of the lagoon fix nitrogen.
  • There are many kinds of fish, and there are many similar species in butterflyfish and parrotfish, and they coexist in different patterns.It is also said that the species are identified by visual information.
  • In addition, various small invertebrates inhabit the coral crevices.Among them are coralSymbiosisYou can also see what you are doing.
  • Fish that live on coral reefs generally have a bad color.Tatsuo MotokawaAccording to the report, the coral reef, which is a limited space, is crowded with various types, the water is transparent, and the shaded color is a means of communication between fish. Because it has to be identified.

Coral reef crisis

Red soil outflow

Due to overdevelopment on land, etc.soilNot only does the water become muddy and the coral is not exposed to light when it flows into the sea, but when it settles, mud accumulates on the surface of the coral, which can choke the coral.Therefore, measures such as creating a reservoir on the land side to settle and remove mud are being taken.However, it is peculiar to tropical and subtropical soilsLateriteVery small amount that does not easily settle on (red soil)粘土It contains a large amount of particles and easily flows out into the sea during heavy rains.Therefore, it causes the destruction of a wide range of coral reefs.


When the zooxanthellae escape from the coral, the coral loses its color and the calcareous skeletonwhiteOnly the colors will stand out.This is called coral bleaching (bleaching phenomenon).The bleaching may return to normal, but if it continues for a long time, the coral polyps will eventually die.The bleaching phenomenon itself has been known since ancient times, but in recent years it tends to occur on a large scale.

According to the 2016 Ministry of the Environment survey, some areas have 100% to 90% bleaching.[1].. 2018年度のXNUMXScienceAccording to the survey results of 100 locations around the world from 1980 to 2016 in the paper "Spatial and temporal patterns of mass bleaching of corals in the Anthropocene" published in the journal, the recovery period from the bleaching period is short due to global warming. The current situation is reported to be difficult[2][3].


Coral reefs originally face the open sea and are necessary for photosynthesisInorganic saltsBecause it is a poor environmentSeaweed,PhytoplanktonIs few.Zooxanthellae in the body of coral can photosynthesize using waste products produced by coral in an environment with few rivals, and can also feed the host coral.
When the sea becomes eutrophicated, phytoplankton floating in the sea becomes more advantageous for photosynthesis, so that the transparency of seawater decreases due to the growth of phytoplankton, and zooxanthellae cannot survive.
Rising water temperature
In addition, zooxanthellae may not be retained in the coral tissue due to an increase in water temperature.[2]..The mechanism in this case iseutrophicationWhen the water temperature rises in the seawater, the photosynthetic activity of zooxanthellae increases remarkably and absorbs light energy that cannot be used for carbon dioxide assimilation.Active oxygenIt is thought that a large amount of zooxanthellae is generated and damages the body tissue of coral, leading to the discharge of zooxanthellae.
Included in sunscreenParabenIt has been confirmed that such components trigger bleaching of coral even at low concentrations, and at the same time, it has been confirmed that it induces the growth of viruses harmful to blue-green algae.[4].
Micro plasticThere is also a research result that symbiosis with zooxanthellae does not go well with coral that has taken in[5].

Destruction of coral reefs by living things

Crown-of-thorns starfish
In coral reefs around the worldCrown-of-thorns starfishbyReef coralEating damage is also a problem.The crown-of-thorns starfish is large and has poisonous spines all over its body, making it difficult to remove.Crown-of-thorns starfishNatural enemy TheReef coralSo, the planktonic larvae of the crown-of-thorns starfishReef coralPolyps eat and become mutual natural enemies.There is a theory that the conch shell is a natural enemy of the crown-of-thorns starfish, but it is said that it takes a week to digest one crown-of-thorns starfish in addition to preying on sea cucumbers and sea urchins, and it can be a natural enemy in front of the outbreak of crown-of-thorns starfish. Absent.Moreover, the conch shells are delicious and edible, and the shells are clean, so they are traded at a high price, and there is a fact that these have led to a decrease in conch shells.The technology for producing seedlings of conch shells has not been established.
Coral food roll shellfish
Eating damage by shellfish of the genus Reishia bronni causes more damage than crown-of-thorns starfish in some places.[6].
Terpios OfspongeMay cover and suffocate coral reefs[6].

Man-made disaster

Potassium cyanide
DiverIs a kind of admiration forHumphead wrasse(Napoleon fish) is also famous as a high-class food.To catch thisPotassium cyanideThere are fishermen who use (potassium cyanide) for that purposeIndonesiaCoral reefs such as are ragged.
Bomb fishing method
dynamiteA fishing method that kills and raises fish usingBlast fishing) Is practiced all over the world because it catches more than normal fishing methods, but it can also severely destroy coral reefs and kill reef-building coral.
Skin care products such as sunscreen
SunscreenIngredients contained in skin care products such as are harmful to coral reefsHawaii[7][8],Palau[9],Kingdom of Thailand[10]Those containing harmful substances are prohibited.
The main banned chemicals areEthylhexyl methoxycinnamate(Also known as octinoxate), and other substances such as butylparaben and methylbenzylenecanfa.

World Coral Reef Situation

The situation of coral reefs in 2012 is as follows.[11].

RegionTotal area (thousand km2)Area in crisis (%)
Middle East14.465
Indian Ocean31.566
Southeast Asia69.694
The Pacific Ocean66.048
World total249.761

Coral transplantation / planting

Many companies are easy to publicize by the message in the video and the number and area of ​​plants.Environmental protectionActivities andEnvironmental educationAs an event: ・ We are planting.However, scientifically, if the environmental conditions of the transplanted sea area are not favorable for the growth of coral, the coral will eventually die and the parent coral (donor) may be damaged. Not.

In November 2004, published "Guidelines for Transplanting Reef-building Corals"[12].

Coral reef survey and monitoring activities

  • (Reef Check) --A diver's survey of coral reefs around the world.
  • (CoralWatch)-Monitors bleaching without damaging the coral and determines coral health.
  • Monitoring Site 1000 (Important Ecosystem Monitoring Area Monitoring Promotion Project)[13] --Ministry of the Environment Natural Environment BureauBiodiversity Center

Major Japanese companies engaged in coral reef conservation activities


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