Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

Coral bleaching disturbs the structure of fish communities

28.10.2008
There is no longer any shadow of a doubt about the impact of global warming on coral reefs. A rise of a few degrees in sea surface temperature induces the expulsion of essential microscopic algae which live in symbiosis with the coral.

This process is the cause of coral bleaching and is well known to scientists, but few large-scale studies have dealt with its effects on the structure of communities of hundreds of species of reef-colonizing fish.

Research work reported on recently by an international research team1, including an IRD scientist, brought out evidence of the impact on the fish communities of a mass bleaching event resulting from the 1997-1998 El Niño climatic episode. The investigation was wide in scope, focusing on more than 60 coral reef sites in the Indian Ocean, including nine located in Marine Protected Areas.

Changes in diversity, size and composition of fish communities were found to follow the decline in the coral reef’s health. Nevertheless, the status of no-take Marine Protected Areas, where fishing is strictly forbidden, appeared to have little impact on the recolonization of such waters by corals. The scientists therefore recommend the setting-up of reserves specially devoted to coral reef conservation.

Reef-building coral may be defined as the result of a symbiotic relationship between microscopic dinoflagellate algae, the zooxanthellae, and an animal organism, the polyp. In terms of biodiversity, coral reefs are often compared with the tropical rain forests. The reef ecosystem harbours thousands of species, whose complex interactions are still largely unfathomed. The main destructive factor facing rain forests is deforestation. The equivalent threat to coral ecosystems is bleaching. The sea surface temperature needs to rise only by a small number of degrees for the polyp to expel the zooxanthellae, the very element that is vital for its survival. Without these microscopic algae, the coral loses its colour, no longer receives the nutrients essential for its development and hence eventually dies.

Scientists have been working on the coral bleaching process for many years, but few studies have made it possible to assess the large-scale impact on reef fish communities. Recent work by an international team in the Indian Ocean, including an IRD scientist, has provided keys to improved measurement of the consequences of a coral bleaching event, linked to a high-intensity El Niño event in 1997-1998, on fish communities. February 1998 saw temperature rises resulting from this regional climatic anomaly provoke mass bleaching - involving almost half the Indian Ocean’s corals. That represented the most severe event of this kind since biologists began to study this ecosystem.

Data concerning the size, structure, diversity and trophic composition of fish communities of 66 coral sites of seven different countries (Maldives, Chagos Archipelago, Kenya, Seychelles, Tanzania, Mauritius and Réunion Island), collected in the mid 1990s, were compared with more recent ones gathered in 2005. A regional-scale picture of the 1998 bleaching event’s impact on the coral reefs was produced by superimposing the two sets of information. Analysis showed that the decrease in the proportion of living coral and modification of its architectural complexity were two decisive factors behind changes to the structure of fish communities in the reef ecosystem.

After the corals die, turf algae and macroalgae rapidly invaded the space left free by the dead corals, leading to increased uniformity of the habitat. The mortality resulting from the bleaching particularly affects the reef-building corals. The calcareous constructions the latter build up serve as shelter and nursery for dozens of fish species. The huge decline of corals therefore affects those fish that depend closely on coral colonies, either as feeding grounds, like the polyp-eating butterflyfish, or to find protection, like the small-sized damselfish. When their numbers recede, these species are often replaced by herbivore fish (parrotfish, surgeonfish and so on) adapted to consuming certain algae proliferating on dead coral. Some, such as damselfish of the Stegastes genus, can then invade the coral reefs smothered in algae, as happened on several sites following the bleaching of 1998.

Moreover, nine out of the 60 or so sites studied are located within Marine Protected Areas where fishing has been strictly forbidden since the mid 1960s. As can be expected, the scientists have observed, after bleaching, a higher density of fish and a larger size among specimens in these marine reserves. The corals, however, did not manage to recolonize these protected zones any more rapidly than in ordinary areas. The weak level of coral regeneration appears partly linked to the fact that these strictly demarcated protection areas are close to the Equator, where the ocean warming of 1998 was most intense. These results highlight its deleterious effects on the reefs, show that it is necessary to designate marine protected areas specifically dedicated to coral conservation. The creation of a network of marine conservation zones far enough away from the Equator to limit as much as possible the global-warming related rise in sea surface temperature, could at regional level, represent refugia effective for conservation both of the corals and of the fish species closely bound to the reef ecosystem.

Grégory Fléchet – DIC

Translation - Nicholas Flay

1.This research project was run jointly with scientists from Newcastle University (United Kingdom), the Wildlife Conservation Society, New-York (USA), James Cook University, Townsville (Australia), Université de la Réunion, Université de Marseille and Université de Perpignan (France).

Grégory Fléchet | alfa
Further information:
http://www.ird.fr/fr/actualites/fiches/2008/fas305.pdf

More articles from Ecology, The Environment and Conservation:

nachricht New mathematical model can help save endangered species
14.01.2019 | University of Southern Denmark

nachricht Foxes in the city: citizen science helps researchers to study urban wildlife
14.12.2018 | Veterinärmedizinische Universität Wien

All articles from Ecology, The Environment and Conservation >>>

The most recent press releases about innovation >>>

Die letzten 5 Focus-News des innovations-reports im Überblick:

Im Focus: Energizing the immune system to eat cancer

Abramson Cancer Center study identifies method of priming macrophages to boost anti-tumor response

Immune cells called macrophages are supposed to serve and protect, but cancer has found ways to put them to sleep. Now researchers at the Abramson Cancer...

Im Focus: Ten-year anniversary of the Neumayer Station III

The scientific and political community alike stress the importance of German Antarctic research

Joint Press Release from the BMBF and AWI

The Antarctic is a frigid continent south of the Antarctic Circle, where researchers are the only inhabitants. Despite the hostile conditions, here the Alfred...

Im Focus: Ultra ultrasound to transform new tech

World first experiments on sensor that may revolutionise everything from medical devices to unmanned vehicles

The new sensor - capable of detecting vibrations of living cells - may revolutionise everything from medical devices to unmanned vehicles.

Im Focus: Flying Optical Cats for Quantum Communication

Dead and alive at the same time? Researchers at the Max Planck Institute of Quantum Optics have implemented Erwin Schrödinger’s paradoxical gedanken experiment employing an entangled atom-light state.

In 1935 Erwin Schrödinger formulated a thought experiment designed to capture the paradoxical nature of quantum physics. The crucial element of this gedanken...

Im Focus: Nanocellulose for novel implants: Ears from the 3D-printer

Cellulose obtained from wood has amazing material properties. Empa researchers are now equipping the biodegradable material with additional functionalities to produce implants for cartilage diseases using 3D printing.

It all starts with an ear. Empa researcher Michael Hausmann removes the object shaped like a human ear from the 3D printer and explains:

All Focus news of the innovation-report >>>

Anzeige

Anzeige

VideoLinks
Industry & Economy
Event News

Our digital society in 2040

16.01.2019 | Event News

11th International Symposium: “Advanced Battery Power – Kraftwerk Batterie” Aachen, 3-4 April 2019

14.01.2019 | Event News

ICTM Conference 2019: Digitization emerges as an engineering trend for turbomachinery construction

12.12.2018 | Event News

 
Latest News

Mechanical engineers develop process to 3D print piezoelectric materials

22.01.2019 | Materials Sciences

Energizing the immune system to eat cancer

22.01.2019 | Health and Medicine

Early Prediction of Alzheimer’s Progression in Blood

22.01.2019 | Health and Medicine

VideoLinks
Science & Research
Overview of more VideoLinks >>>