Arxiu d'etiquetes: coral bleaching

Why do we need ocean?

Fortunately, society is more concerned about the state of conservation of the environment due to human activities, both on land and at sea. In case there are still who think we do not need sea at all, this article aims to show what benefits gives us the sea.


Did you know that some studies suggest that the entire surface of the seas and oceans of the Earth is hit by some human activity? In fact, 41% of the surface is affected by more than a factor of anthropogenic origin.

According to the United Nations Environment Programme (UNEP), there are several anthropic impacts at sea:

  • Ocean acidification.
  • Coral bleaching [More information here].
  • Chemical contamination.
  • Global change [You can read about the effects of global change on plants, whales, corals, reptiles and the current sea level rise].
  • Increase in toxic algae.
  • Increased invasive species [Discover what is an invasive species!].
  • Increase of jellyfish [If you want to know how are jellyfish and want to learn to identify the species of the Mediterranean, visit this article].
  • Loss of biodiversity.
  • Loss of habitats.
  • Nutrient overload.
  • Overexploitation of species with commercial interests.
  • Dead zones.
problemas mar contaminación
There are many anthropic impacts at sea, like pollution by several types of products and materials (Picture: NOAA, Creative Commons).

Not only do they affect marine ecosystems, but also affects the human population because the ecosystem services promote our welfare. So we can ask: why do we need the sea?


According to TEEB, ecosystem services are all those direct and indirect ecosystem and biodiversity contributions to human welfare. These services are: supply services, cultural services and regulation services.


All those contributions of ecosystems that take place directly or indirectly to human welfare, whether they have a biological or geological origin, are part of supply services.

Foods that the sea provides is one of the most important supply services to humans, including fish, shellfish and algae. An example of this is the fact that supplies 20% of the animal protein intake to 3,000 million people and that more than 120 million tons of fish were consumed in 2010. For all this, the current situation of exploited populations is critical in many cases, as you can read in this article.

Sea supplies 20% of the animal protein intake to 3,000 million people  (Picture: Pixabay).

Sea is also a source of renewable energy because it is the source of many weather events (like wind) and tides and currents. Thus, sea provides wind energy and tidal power (generated by tides, currents and waves).

Another benefit that we get is different biotic or geologic materials, such as salts, ornamental materials and mineral resources. Without going into the details of the high environmental impact of extracting marine mineral resources, materials such as sand, diamonds, metals such as gold and tin, coal, gas hydrates, oil, gas and some others are exploited [can read more in this document of the International seabed Authority (ISA)].

The exploitation of marine geologic resources, which is not free of impacts, lets obtain many diverse resources (Picture: National Geographic).

In addition, we benefit from certain substances and organisms that have some beneficial property to humans, such as medicines and cosmetics.


Cultural services are those that are obtained through direct experience with ecosystems. Although they are not the most important, we must also taken into consideration.

Ecosystems help to the creation and maintenance of cultural identity and sense of belonging to a community. What would we be without our festivities and without the different types of food?

Marine ecosystems enable developing advocacy and awareness by sea. They also contribute to the increase of scientific knowledge through research of different types. If you’re a biologist, would you like to discover a new species?

Research in marine environment let obtain useful knowledge for society (Picture: Perplex Me Not).

It is also the basis for many recreational activities such as whale watching, diving, tourism, recreational fishing and navigation activities [Do you want to know if recreational fishing is compatible in marine reserves?].

Here we could talk about more services, but I focused on the most relevant.


Last but not least, marine ecosystems are responsible for the proper functioning of ecosystems as a whole. They are the most important services because from them depend all the rest.

In marine ecosystems, it occurs a set of processes by which they maintain or improve water and sediment quality. To give an example, they are involved in the oxygenation of dead zones and to absorb waste or pollutants.

But, certainly, it is important to highlight its key role in regulating the Earth’s climate. Earth’s oceans are the largest sink for greenhouse gases because they capture  carbon dioxide away from the air and distributes it in depth. So, they help to fight against global change, but everything has its limit.

Due to the power of oceans in absorbing dioxide carbon, they play a key role in climate regulation  (Picture: El Confidencial).

On countless occasions, we have seen beaches to disappear after a storm, a hurricane and other extreme events. Do you want to know the reason? The main reason is that due to human action, our coast has lost its protective function, ie, has lost the ability to buffer natural disturbances. In a healthy beach, after a storm, it would regenerate naturally. Well, when a beach disappears, then  we have problems in promenades or houses built  at first line of the coast.

Although we could explain some more benefits, I will finish by mentioning its importance in providing the necessary nutrients for marine organisms and habitat maintenance of biodiversity.


  • FAO. (2012). The State of World Fisheries and Aquaculture. FAO. Rome.
  • Fernando Santos-Martín, Carlos Montes, Paloma Alcorlo, Susana García-Tiscar, Blanca González, María Rosario Vidal-Abarca, María Luisa Suárez, Laura Royo, Inmaculada Férriz, Juan Barragán, Juan Adolfo Chica, César López y Javier Benayas. 2015. La aproximación de los servicios de los ecosistemas aplicada a la gestión pesquera. Fondo Europeo de Pesca, Fundación Biodiversidad del Ministerio de Medio Agricultura, Alimentación y Medio Ambiente. Madrid.
  • Jackson, J.B., Kirby, M.X., Berger, W.H., Bjorndal, K.A., Botsford, L.W., Bourque, B.J., Bradbury, R.H., Cooke, R., Erlandson, J., Estes, J.A., et al. (2001). Historical overfishing and the recent collapse of coastal ecosystems. Science 293, 629–637.
  • MA (Millennium Ecosystem Assessment). (2005). Ecosystem and Human Well-being. Island Press. Washington.
  • Notes of the subject “Geología de los océanos” of the Master in Oceanography and Marine Environment Management (UB).
  • TEEB. (2012). The Economics of Ecosystems and Biodiversity in Business and Enterprise. Joshua Bishop (ed.). Earthscan, London and New York. Urquhart, J., Acott, T., Reed, M., Courtney, P. (2011). Setting an agenda for social science research in fisheries policy in Northern Europe. Fish. Res. 108,
  • UNEP. (2006). Marine and coastal ecosystem and human well-being. A synthesis report based on the finding of the Millennium Ecosystem Assesment. UNEP.
  • Main picture: Stilts fishhermen Sri Lanka (Bernard Gagnon, Creative Commons).


Ocean alert: Coral bleaching is massively happening!

We would like that the main picture of this post had been modified using Photoshop, but unfortunately this is not the case. Thanks to the project XL Catlin Seaview Survey, we now know that coral bleaching is massively happening. What causes coral bleaching? How does coral become bleached? Which is the importance of coral in the ocean ecosystems? These questions and more are answered in this post. 


Coral bleaching is the result of the expulsion of symbiotic algae living in the coral tissues (zooxanthellae), producing them to become completely white.

Coral before and after a bleaching event (Picture: Kendall Kritzik, Creative Commons).
Coral before and after a bleaching event (Picture: Kendall Kritzik, Creative Commons).

The presence of zooxanthellae is frequent in marine cnidarians, especially in species that live in shallow waters, and they are the responsible of the greenish, bluish, yellowish or brownish colour of many coral species. In fact, each cubic millimetre of tissue of the host has 30,000 algae cells. These zooxanthellae are single-celled algae, usually dinoflagellates, that are able to live in mutualism with the coral. So, if zooxanthellae and coral live in mutualism, which are the benefits of this relationship? Coral gets the products of photosynthesis, organic carbon and nitrogen; while the algae receive nutrients, carbon dioxide, protection and a good position with access to sunshine.

Diagram of the location of zooxanthellae in a coral (Picture: Ocean Portal).
Diagram of the location of zooxanthellae in a coral (Picture: Ocean Portal).


Several causes of coral bleaching have been detected:

  1. Increased ocean temperature. Climate change is the foremost responsible of the increase in ocean temperature and this is the main stress causing coral bleaching, but it is not the only one. The rise of temperatures may be also produced by El Niño phenomenon. With just an increase of 1ºC of the water for only one month, corals begin to become bleached.
  2. Reduced ocean temperature. As warmer water ocean may produce coral bleaching, colder water may also produce these events. Some proofs support this idea: in January 2010, cold water temperature in Florida might have produced coral bleaching that resulted in coral death.
  3. Runoff and pollution. Near-shore corals can be bleached due to the pollution carried by precipitation’s runoffs.
  4. Freshwater inundation. Due to a low salinity produced by a freshwater inundation, corals may start bleaching.
  5. Overexposure to sunlight. High solar irradiation causes bleaching.
  6. Extreme low tides. Long exposures to the air can produce bleaching in shallow corals.
  7. Disease. Diseases cause coral to be more susceptible.

All these causes produce a stress to the coral and, as a result, corals expel the algae living in their tissues.


When corals are in a healthy state, they are home to algae, so that they are in a symbiotic relationship. But, when corals are stressed, the photosynthetic machinery of algae produce toxic molecules that cause the corals to expel the symbionts. If the stress is not severe, corals can recover, but they become bleached in severe and prolonged stresses. As a result, corals death because they loose their main source of food and are more susceptible to disease.

Coral bleaching process (Picture: Great Barrier Reef Marine Park Authority, Australian Government).
Coral bleaching process (Picture: Great Barrier Reef Marine Park Authority, Australian Government).


Two worldwide episodes of coral bleaching were detected in the 1998 (which killed 16% of the coral reefs around the world) and 2010, but a recent study carried out by the NOAA and the University of Queensland confirm a more severe coral bleaching episode this year (2015). This new episode, which is triggered by El Niño of this year (together with the global change), is predicted to affect the 38% of the worldwide coral reefs, killing 12,000 square kilometres of reefs. The more altered zones will be Australia and the Pacific and Indian oceans.

Bleaching in American Samoa. The first picture (before) was taken in December 2014 and the second (after) in February 2015 (Picture: XL Catlin Seaview Survey).
Bleaching in American Samoa. The first picture (before) was taken in December 2014 and the second (after) in February 2015 (Picture: XL Catlin Seaview Survey).

Nevertheless, coral bleaching doesn’t only occur in massive episodes. Each year, during summer months, some limited coral bleaching is reported all over the globe.


Despite the fact that coral reefs comprise less than 1% of the underwater ecosystems, they play a major role in the ocean. One quarter of marine life depends on coral because they are the nursery of the sea, so they are an important protein source for animals and humans. Moreover, they protect shorelines from waves and tsunamis. In addition, from an economical point of view, they are one of the most important places of tourist interest and support fishing industries. In fact, they provide food and livelihoods for more than 500 million people around the world.


All the activities you do to lessen your carbon dioxide production are good to prevent the Earth from global change and, therefore, are good to avoid coral bleaching. Keep doing like that! Share with us: which are the actions that you take to prevent global change?