Man Made and Natural Stresses

In this blog post I will be looking at what has the larger impact on corals- natural or man made problems. Both can cause serious damage, with natural causes including hurricanes, large storms and natural algal blooms. Man made problems can be a wide variety of things- overfishing, ocean acidification, bleaching through increased temperatures as a result of global warming and other pollutants put into the ocean by humans.

First of all let's take a look at natural impacts on corals. Hurricanes are one such an issue for corals. They are unavoidable, and happen on a repeating time scale. They are very difficult to predict however. In 1980, Jamaica experienced a category 5 Hurricane, Hurricane Allen, around 40 years after the last major storm event. The storm was incredibly damaging to jamaicas corals. 5 years after the hurricane the number of corals per m2 was still lower that pre storm levels by a factor of 10. This just shows the catastrophic impact that hurricanes can have on coral reefs. The corals found at shallow depths were the most succeptable to damage. The elkhorn and staghorn corals were the worst off after the storm. These are examples of soft coral. The hard coral species fared better, as they are better equipped to be protected against storms. The corals at depths of 10-15m were much less likely to be damaged. This meant that after the storm the area was much more densely populated with hard corals relative to soft corals than before the storm. The storm also had a secondary impact on the coral. The hurricane resulted in an algal bloom. This algal bloom transpired as a result of increased runoff of nutrients following the high rainfall and windspeeds. This bloom prevented the coral from being able to feed, as this occurs through photosynthesis which was temporarily blocked by the algae.  

This meant that the recovery of the corals was inhibited. However over time they will be able to recover. The problem in recent times is that the human factors will then come into play once corals have been weakened by a hurricane for example, and put the corals under incredible strain.

There are several ways in which human activity puts corals under stress. As we all know, anthropogenic activity has resulted in global temperatures accelerating to new levels. These elevated temperatures will result in the loss of symbiotic algae from corals. This means they can no longer feed. The bleaching effect is he loss of the algae as this is what gives the coral its colour. Corals can recover from bleaching, but this requires the temperature of the ocean to go down. It is hard to

quantify how much bleaching has been due to human activity. It is clear however that human activity has had a significant impact on coral bleaching. Scleractinia and hydro corals are particularly succeptable to bleaching. It has been predicted that a 2 degree increase in the ocean temperature will reach the upper threshold of the majority of corals. This is a very worrying statistic.

Acidification is another threat to corals. Acidification can be caused by irresponsible farming and irrigation, resulting in the runoff of fertilisers. Acidification of the oceans can also be caused by extra co2 being in the atmosphere, caused by anthropogenic sources. This then results in more acid in rainwater, which will then filter into the oceans. This prevents corals from being able to produce their protective skeleton, leaving them vulnerable to waves and storms.

Overfishing is another human impact on corals. Overfishing results in man made algal blooms,mas there are less and less fish to eat the algae and phytoplankton. The algal blooms prevent the coral from being able to feed through photosynthesis.

But what has the bigger impact on corals? Both natural and human impacts can be destructive. Natural impacts tend to be much larger in their scale and intensity, over a much shorter period of time, such as the hurricane we examined in Jamaica. There was a large drop off in the amount of coral found after this very serious event. However this was a category five hurricane, and so the majority of hurricanes and tropical storms will be at a lower magnitude than this. Corals are also well adapted to recovering from tropical storms, and complications tend to arise from human sources.

Human effects on coral seem to be less intense than tropical storms, but they ever present. A storm may last a day or two, but ocean temperatures rising is a constant worldwide. With no signs of slowing down, it would appear that human impacts are the largest threat to coral the world over. The human impacts are something that we can do something about, which means the future of corals are in our hands.





Sources
1.http://bio.classes.ucsc.edu/bio160/Bio160readings/Catastrophes,%20Phase%20Shifts.pdf
2. http://link.springer.com/article/10.1007/BF00303779