And the colours fade to grey: What is coral bleaching?

By Stephan Kamrad

Hermatypic corals may look like lifeless rocks but they are really living creatures which belong to the animal phylum Cnidaria, together with jellyfish and sea anemones. Many members of the Cnidaria have tentacles equipped with specialised stinging cells that contain venom. These are used for self-defence and to prey on small fish and crustaceans. Hermatypic corals, however, have no stinging cells; they defend themselves with a rock-like, calcareous exoskeleton that is slowly deposited over years. Nor are they predators, instead they live in association with photosynthetic plankton from the genus Symbiodinium, often called zooxanthellae, and the photosynthetic pigments of these unicellular algae give corals their bright colours! Members of the Symbiodinium belong to the Dinoflagellates, a group only very distantly related to land plants and green algae. They are endosymbiotic, meaning they are completely engulfed by the coral’s plasma membrane and live inside their cells. The coral provides the algae with a protected environment and a number of nutrients, like ammonium and phosphate, which it filters out of the water. In return, the Dinoflagellates fix CO2 dissolved in the water to provide the coral with sugar.


Bleached coral (credit Acropora)

Coral reefs are found in tropical oceans, usually only few kilometres off the coast or on sand banks where the ocean is still shallow enough for light to reach the photosynthetic corals at the ground. They are globally rare, covering only about 0.1% of ocean surface but are the habitat of over a quarter of all known marine species! Their incredible biodiversity make coral reefs a valuable resource. Millions of people depend on the reefs as rich fishing grounds. Additionally, reefs physically protect the coastline form incoming waves and prevent erosion. The great reefs of Australia, Florida and the Caribbean yearly attract hundreds of thousands of tourists. When considering their social and economic importance, ecologists speak of ‘ecosystem services’ provided by coral reefs and it turns out their monetary value is immense!

It is thus very concerning that we have seen an immense decline of coral reefs over the last decades. The Caribbean for example has suffered an 80% loss of their coral populations over the last thirty years! The underlying phenomenon known as coral bleaching is a process during which the usually so beautifully coloured corals expel their symbiotic algae causing them to turn white and die. The picture shows a bleached, white coral in the foreground and a healthy coral in the background. Coral bleaching is associated with high peak water temperatures and increasing water acidity, both of which are a direct consequence of rising CO2 levels in the atmosphere.

A group from the University of Georgia recently published new detailed insights into the bleaching process. The research team was able to observe a bleaching event as it was happening at a reef off the coast of Mexico. Their key findings, published in the Journal of Limnology and Oceanography, shows how coral/algae populations can adapt to changes and sometimes even recover from bleaching events. There are many different species of endosymbiotic Dinoflagellates, classified into 9 major clades, and it turns out some of them are more resistant to high temperatures than others. Single corals often host three different algae species at once and their relative abundance determines the temperature tolerance. Furthermore, bleached corals do not die immediately; they can be repopulated and their new composition of Dinoflagellate species is significantly different to their pre-bleached one.

The symbiotic relationship between corals and Symbiodinium is an active area of research. The hope is that through a deepened understanding, we might find ways to protect reefs from bleaching and dying.

Reference: Dustin W. Kemp et al. (2014) Community dynamics and physiology of Symbiodinium spp. before, during, and after a coral bleaching event. Limnol. Oceanogr., 59(3), 2014, 788-797 DOI: 10.4319/lo.2014.59.3.0788

Fluffy Horror

By Nathan Smith

As a general rule, the fluffier a pet is the better. Fluffy things are cuter, more cuddly, and funnier when they move; it’s a win-all situation. But like all general rules, there are always exceptions. In this case the exception is fish.

Fish, as many will have already noticed, are not usually fluffy. Indeed it would be reasonable to put forward the hypothesis that fish and fluffiness are mutually exclusive and, for healthy fish, this is certainly the case. Unfortunately fish cannot always be healthy and sometimes unhealthy fish go fluffy.

Not a happy fish (credit Émilie Proulx)

Not a happy fish (credit Émilie Proulx)

The cause of such fluffiness is an oomycete, or water mould; a type of organism which looks like a fungus but is closely related to kelp. Specifically, it is caused by the oomycete Saprolegnia parasitica, which infects freshwater fish. S. parasitica causes grey/white cotton wool like patches on the skin and gills of infected fish and can coat up to 80% of the host’s body. These patches are external signs of destruction of the host’s skin and underlying tissue and this result in lethargy of the host, making it more susceptible to predation. If the host avoids predation, symptoms of late stage infection are impaired osmoregulation, which is caused by increased haemodilution due to the large scale surface wounds. This is followed by respiratory failure, caused by the extensive infection of the gills. Organ failure is the final result. A closely related species, S. diclina, also infects fish eggs.

Despite the bizarre symptoms, infection by Saprolegnia is no niche occurrence. Whilst it is generally not an issue for wild fish, generally only infecting wounded or otherwise immunocompromised individuals, it is a considerable problem in aquaculture hatcheries and farms, due in part to the overly high densities in which fish are kept. In these environments, losses of more than 10 % due to Saprolegnia are commonplace and as high as 50% in some more extreme cases. Furthermore, it has a significant economic impact, with conservative estimates putting the losses due to Saprolegnia infection at five million pounds per year in Scotland alone.

That Saprolegnia infection is so endemic in aquaculture indicates generally low health in the fish population and highlights issues within the industry. Fluffy fish may not be cute but they can’t be ignored.

Packaging: Is there mushroom for change?

By Sophie Harrington

It’s nearly Christmas and nowadays that seems to mean lots of online shopping. There’s nothing quite so convenient as avoiding the crowds, anxiety, and Christmas music on loop in favour of leisurely browsing from the comfort of your couch. For the most part, deliveries these days are highly reliable, even when you’ve ordered something that doesn’t do well with rough handling—perhaps a new set of glasses, or a bottle of champagne. It’s thanks to the use of packing materials such as polystyrene that we can even consider ordering such fragile items online.

A new use for corn stalks? (Credit Phoebe Baker)

A new use for corn stalks? (Credit Phoebe Baker)

Yet despite their convenience, there are a whole host of environmental concerns that come with traditional packing materials. Most people have heard that this sort of packaging never breaks down, and while that isn’t strictly true, polystyrene discarded in landfills, or left as litter will not degrade for hundreds of years. Our love for packing peanuts and Styrofoam has left us with a mass of polystyrene clogging up our landfills and environment.

But what if there was a better option? Enter mushroom materials, the brainchild of Ecovative. As an alternative to the petroleum-based polystyrene that forms a majority of the packing market, mushroom materials use only natural agricultural waste, such as cornstalks, and mycelium, or the “roots” of fungi. The agricultural waste is placed into a specific mould, through which the mycelium are able to grow, turning the material into a solid block. After growth is completed, the material is fully sterilised before being shipped out to their growing base of customers.

The use of agricultural waste in producing the blocks is only the beginning of their environmental benefits. Not only is this a use for otherwise discarded waste products from farming, but the products themselves are fully compostable at home. No need for expensive processing or complicated techniques to degrade the blocks—just break them up and leave in your garden.

Not just good for eating (Credit Christine Majul)

Not just good for eating (Credit Christine Majul)

Besides the obvious market in packaging materials, Ecovative are branching out into other areas, including furniture and even surfboards! There materials are perfect as light-weight foam cores and fins for surfboards, with the added benefit of being entirely degradable in a marine environment if the board is lost. The materials are also being developed for use as structural biocomposites, using “Myco Foam” that has been heat and pressure treated to compress into “Myco Board” for use in furniture that has no need for the addition of resin (and thus the use of formaldehyde), unlike traditional wood composites such as MDF. Who knew fungi could be so much fun?

Intrigued? Wish you could get involved in the “mushroom age”? Turns out you can even grow your own mushroom materials via the “Grow It Yourself” kit available from Ecovative. This might just make Christmas shopping even easier…

Thar She Blows: of Saharan Dust and Marine Productivity

By Charlie Whittaker

The Sahara Desert is not something you would usually associate with abundant life and vibrant algal blooms. It is one of the most arid and inhospitable areas in the world, representing the largest subtropical hot desert on the planet. And at well over 9,400,000 square kilometres- i.e. about the size of the United States, it is perhaps one of the most inhospitable areas globally. To say that it is unwelcoming to life is an understatement of epic proportions.

The Sahara Desert (credit mtsrs)

The Sahara Desert (credit mtsrs)

However, the desert is in fact one of the cornerstones of continued survival of one of the most abundant groups of organisms on the planet: the phytoplankton. This vast swathe of barren land is actually responsible for a dazzlingly complex and diverse ecosystem albeit thousands of miles away.

Tiny flecks of sand, red in colour due to the abundance of the element iron, are picked up the winds floating across the sand dunes, and in turn, carried thousands of miles westwards on the air currents. These tiny grains of iron rich sand then land in the ocean off the West coast of Africa, where they are responsible for sustaining a astounding array of life. Though individually insignificant and of little relevance, the sheer scale of their deposition makes them a globally relevant input- it is estimated that something in the region of 1015g/year get deposited courtesy of these Saharan winds Westwards. That’s 1012kg, or 1 billion tonnes!

A phytoplankton bloom in the Southern Ocean (credit ESA)

A phytoplankton bloom in the Southern Ocean (credit ESA)

But why all the fuss about iron though? Iron represents a fundamental micronutrient required as a cofactor for the enzymes of a ubiquitous number of different phytoplankton, from cyanobacteria to coccolithophores and diatoms to dizaotrophs. In particular, iron acts as an essential constituent of the enzyme nitrogenase, responsible for the fixation of atmospheric nitrogen. The photosynthetic organisms present in this group are globally significant in terms of the fixation of carbon dioxide from the atmosphere. These so called “forests of the ocean” contribute as much to the control of CO2 levels as tropical rainforests.

Given their dependence on iron then, there has been considerable interest in the concept of “iron seeding” the oceans as a means of generating blooms of these photosynthetic organisms. Such a sudden population rise would lead to increased CO2 drawdown and may have the potential to mitigate, at least in part, some of the consequences of continual anthropogenic mediated CO2 release into the atmosphere. Efforts doing this are still in progress but who would have thought the Sahara Desert, byword for desolate, bleak and lifeless, may have acted as the inspiration for one of the most ambitious biogeoengineering projects currently underway.