A coral reef has more in common with a forest than you might think. When sunlight strikes a group of trees, some parts tend to get more sun than others.

Leaf tissue somewhat compensates for this by scattering light outward, helping to illuminate other leaves. A similar thing happens with coral. When scientists shone a laser at a coral, the coral’s colorful tissue spread the light, generally redistributing it to other parts. Coral’s white calcium carbonate skeleton also gets in on the action. But it tends to spread light less, helping instead to focus it on specific areas that would otherwise be in the shade. 

Coral can also rearrange themselves depending on the circumstances, expanding to increase the spread of light or contracting to minimize it. Yet even with all of these tricks, light can only penetrate so far into coral tissue; it tends to drop off the deeper you go, as in forests, making getting by more difficult for cells at the bottom of tissue. 

So just as different cells in a leaf contain different amounts of chlorophyll, coral cells seem to house different amounts of the photosynthetic algae that makes their food, Symbiodinium. Cells specialized for low light to still make decent amounts of food in dim conditions, as measurements of photosynthesis, showed. Snorkelers visiting coral may not notice the canopy below, a much smaller and subtler affair than the lofty bowers of forests on land. But the researchers argue that understanding it is crucial for understanding how life gets by on the sea floor.

New algae species helps corals survive in the hottest reefs on the planet

A new species of algae has been discovered in reef corals of the Persian (Arabian) Gulf where it helps corals to survive seawater temperatures of up to 36 degrees Celsius - temperatures that would kill corals elsewhere.

Researchers from the University of Southampton and the New York University Abu Dhabi identified the symbiotic algae in corals from Abu Dhabi, United Arab Emirates, the world’s warmest coral reef habitat.

The paper, which reports the breakthrough discovery, is published in the journal Scientific Reports from where it can be freely accessed via

“We found that commonly applied molecular methods did not give enough resolution to distinguish the dominant symbionts of Gulf corals from those in other parts of the world’s oceans,” explains Professor Jörg Wiedenmann, Professor of Biological Oceanography and Head of the Coral Reef Laboratory at the University of Southampton. “However, when analysed by alternative molecular biological approaches, we found pronounced differences that set this heat tolerant species clearly aside. We named it Symbiodinium thermophilum in reference to its ability to survive unusually high temperatures.”

However, the symbiotic association is vulnerable to changes in environmental conditions, in particular to increases in seawater temperature. Heat-stress induced loss of the algal partners from the coral host can result in the often fatal process known as ‘coral bleaching’.

“Understanding how corals survive under the extreme temperatures in the Gulf will give us important insights into the ability of reef corals to handle the heat stress, which is threatening their survival in the oceans that are warming up in response to climate change,” explains Professor Wiedenmann.

Reefs are made up of many coral species, most of which live in a mutually beneficial relationship with microscopically small algae hosted in their tissue. These symbiont algae produce sugars that contribute to the diet of the coral in return for shelter and nutrients that are vital for algal growth.

Read more here.

Provided by the University of Southampton

Image: Welcoming Persian Gulf (Credit: Hamed Saber on Flickr)

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Mangrove Jellyfish | ©Seth Patterson

An up-side down jellyfish found in Yal Ku Lagoon, Akumal, Quintana Roo, Mexico (Caribbean).

The up-side down jellyfish, Cassiopea xamanchana, does not have the typical physical characteristics of jellyfish. Often it has a somewhat green or gray/blue coloration. This display is the result of numerous densely packed symbiotic zooxanthellae, Symbiodinium microadriaticum.

The medusa, the dominant adult phase of the life cycle, possesses four branching tentacles that extend from the body, up into the water column. These structures are used in feeding and provide nutrients in combination with what is made available by the photosynthetic dinoflagellates. The large, dome shaped exumbrella of the medusa contains a central depression that is used mainly for attachment purposes as the up-side down jellyfish remains sedentary throughout a majority of its lifecycle.

Animalia - Cnidaria - Scyphozoa - Rhizostomeae - Cassiopeidae - CassiopeaC. xamachana

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“Giant Green Anemone” (Anthopleura xanthogrammica)

Also known as the Green Surf Anemone, Green Anemone, Solitary Anemone, Rough Anemone, and the Giant Tidepool Anemone, Anthopleura xanthogrammica is a species of Actiniid sea anemone that inhabits low to mid intertidal zones in the Pacific Ocean, ranging from Alaska to Southern California and rarely down to Panama. Like other sea anemones A. xanthogrammica sports several nemoatocyst lined tentacles which are used to paralyze and capture prey that wanders too close. Phoyosynthetic algae of the genus Zoochlorella and dinoflagellates of the genus Symbiodinium live in the tissue and gut of A. xanthogrammica, in this symbiotic relationship they will provide nutrients to the anemone via photosynthesis (partly giving the anemone its green coloration) and in turn they get a safe place to reside. 


Animalia-Cnidaria-Anthozoa-Hexacorallia-Actinaria-Nyantheae-Thenaria-Actiniidae-Anthopleura-A. xanthogrammica

Image: Stan Shebs
The Microbe That Invaded Caribbean Coral Reefs
Think of giant pythons from southeast Asia, ending up in the Florida everglades and suffocating any small mammal they could find. Think of cane toads from South America, relentlessly marching over ...
By Ed Yong

Think of giant pythons from southeast Asia, ending up in the Florida everglades and suffocating any small mammal they could find. Think of cane toads from South America, relentlessly marching over …

By Ed Yong

SKETCHY SUNDAY: Symbiodinium spp.

Corals have developed an important symbiotic relationship with photoautotrophic dinoflagellates, i.e. zooxanthellae, which live inside coral tissue for protection and inorganic nutrients. In return, the algae produce a photosynthate that provides the coral with energy to complete growth, reproduction, and calcification processes.

This is a drawing of an individual Symbiodinium, which populate a coral along the lines of hundreds of thousands per square centimeter.

Drawing by Stacy Peltier, 2013

New Algae Species Helps Coral Stand the Heat

It’s no secret that the world’s coral reefs are rapidly declining, taking the one-two punch that is warming temperatures and mounting ocean acidification. However, there is hope, and it’s coming straight from an unknown member of the natural world. Researchers have just discovered a new species of algae, and it’s one that seems to be able to help corals survive otherwise deadly temperatures.

That’s at least according to a study recently published in the journal Scientific Reports, which details how a previously unknown species of algae (Symbiodinium thermophilum) found in the waters of Abu Dhabi, of the United Arab Emirates, is what likely facilitates what is the warmest known coral reef habitat.

Continue Reading.


The Pink-tipped Anemone or Aggregating Anemone - Anthopleura elegantissima

This anemone is commonly found in the intertidal zone in coastal regions of the Eastern Pacific. The tips of the tentacles in this anemone are often bright pink, but the rest of the body is actually colourless. The green and brown colours are due to microscopic algae living inside its tissues called zooxanthellae and zoochlorellae.

Brown hues are due to the zooxanthellae Symbiodinium californium and S. muscatinei, while green hues are due to the zoochlorella Elliptochloris marina. When the anemone grows in dark places, the algae in its tissues cannot survive, and the anemone remains white.

Pteraeolidia ianthina

…a strikingly marked species of of Facelinid nudibranch which is known to occur among shallow coral reefs throughout the Western Pacific Ocean, from Hawaii to the Philippines, to the waters of northeast Australia and parts of New Zealand. It is also known from the Red Sea. P. iathina is known to feed almost exclusively on hydroids, generally those which contain Symbiodinium spp. These dinoflagellates are “farmed” in the digestive diverticula of P. iathina allowing the sugars they photosynthesize to be used. 


Animalia-Mollusca-Gastropoda-Heterobranchia-Euthynerua-Nudipleura-Nudibranchia-Dexiarchia-Cladobranchia-Aeolidida-Aeolidioidea-Facelinidae-Pteraeolidia-P. ianthina 

Image: Richard Ling