On our planet the World Food Program estimates approximately one billion people are starving everyday and this appalling number has led to many millions of pounds worth of aid from international charities and widespread condemnation, yet research from the National Oceanography Centre (NOC) at the University of Southampton has discovered it’s not just humans who are dying from starvation – our coral reefs are too.
Coral reefs are often regarded as the tropical rainforests of the seas. They are so diverse and yet they also support a vast number of other flora and fauna. This makes them important – not just ecologically, but anthropogenically, as they are nursery grounds for many edible sea creatures as well as being a huge carbon sink for the additional carbon dioxide we pump into the atmosphere.
Corals are made up of two organisms, polyps and algae. The polyps are the organisms which create the structure and make up the “body” of the coral. The algae (also known as zooxanthellae) lives in the polyps and helps produce the colour of the coral. The two organisms work in a symbiotic relationship because the polyp provides a home to the algae and gives the algae some of the polyp’s excess nutrients, whilst the algae gives the polyp some of products from its photosynthesis (i.e. energy for the coral to grow).
Within the scientific community, it is well established that the gradual warming of our oceans is creating chaos for the species which live within them. Scientists at the university have been attempting to find out if the demise of coral reefs by coral bleaching is purely down to temperature increases or whether other factors such as nutrient concentrations could be playing a role.
In high temperature waters, photosynthesis in the algae can stop and this leads to a build-up of toxic oxygen compounds which threaten the coral and can lead to the algae being expelled from it. It is this expulsion of the algae that cause the coral to whiten, which is why the phenomenon is also known as coral bleaching.
The tests in the university’s specialist Coral Reef Lab tested the effect of nutrients on corals. There are 2 main nutrients which control the growth of plants such as coral reefs and they include nitrogen and phosphorous; both are found naturally in the ocean, although human inputs are changing the concentrations. The test varied the levels of these nutrients and monitored whether these corals were more or less likely to suffer from heat-related coral bleaching. The results showed that if there was limited phosphorous, this could cause starvation of the algae and as a result the coral the algae lives in will die – losing its colour and becoming bleached. This happens even if there was an abundance of dissolved nitrogen.
The level of available nutrients restricts the growth of the algae and therefore of the coral. If certain nutrient levels decrease below the demand from the cells then the coral gets starved because all the nutrients go in helping the algae survive and consequently starve the polyp in the coral.
The results have helped to show that coral reefs suffer from bleaching – not just because of high water temperatures but because of a loss or depletion of nutrients.