An Introduction to the Tropical Marine Environment

My last post in my “Learn Something!” column, An Introduction to Neotropical Birds, pretty much wrapped up what my series on rainforest ecology had to say. Today I’ll be beginning a new series on reef ecology, which is also very exciting and is something I’m very passionate about.

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The importance of coral reefs

When we talk about the tropical marine environment, we are mainly referring to coral reefs. Not only are coral reefs beautiful, they are also sites of abundant biodiversity. They act as both a nursery and a home to a huge variety of fish, and host a plethora of algae, rays, turtles, sponges, etc. Even though they make up a tiny percentage of the ocean floor in area, they host the most concentrated areas of life.

Coral reefs are buffers to storms. They dramatically reduce the impact of an incoming hurricane by absorbing part of it before it hits land, for example, which is undoubtedly of benefit to terrestrial life.

However, these reefs are in danger because of two reasons: a) they are highly sensitive to changes in environment, and b) they grow very slowly. Scientists estimate that at least 75% of coral reefs will be perceivably impacted by 2050.

What they are

A coral reef is essentially a mond or a ridge of living coral, coral skeletons, and calcium deposits.

There are two types of coral: soft and hard coral.

Corals are the ecosystem architects. The entire structure of the reef is basically dependent on them, although many different plants and animals also contribute to the reef’s construction, like shells of worms, snails, and clams, and bryozoans and crustaceans.

The constant battle is against erosion and algae, especially of the encrusting/coralline variety.

Reefs exist in roughly three areas:

  1. The Caribbean (10%)
  2. The Indo-Pacific
  3. The Western Indian Ocean

Of all of these, the Caribbean reefs take the most beating from storms and have the least diversity of the above.

If you look at the profile of a coastline, structurally, you can roughly divide the reef into three zones: the reef flat, a crest, and a slope. Ecologically, usually you can progress from mangrove to seagrass bed to coral reef nursery, where all the baby fish live.

Abiotic factors on the reef

  • Temperature: a temperature greater than 30° can cause bleaching (we’ll get into this later).
  • Emersion: coral reefs cannot withstand regular or irregular time out of the water
  • Light intensity: too little light will limit the photosynthesis of algae
  • Salinity: the reefs tolerate high, not low salinity (saltiness)
  • Sedimentation: if the water is not clear, it reduces light levels and smother the corals

Most reefs are oligotrophic, which means that they are low in nutrients. This means that they are the most productive ecosystems on the planet!

Marines around the world

About 93 out of 110 of the world’s countries show evidence of decline of their coral reefs. 10% of these are beyond repair, which means they are irreversibly damaged. 30% of them are severely impacted (that’s terrible!!).

In healthy reefs, the natural ecosystem processes are not affected by relative external pressures, and those sites are pristine.


About 27% of all reefs are Marine Protected Areas (MPAs), and are protected in some way, however the levels of management vary. About 71% of these are merely “paper parks”, which means they only exist on paper.

Multi-zoned management is when MPAs are divided into zones, where the zones have different permitted amounts of human activity. A no take zone (NTZ) in this case means that no extractive activity is allowed.

The SLOSS debate refers to the benefits of protecting a single large or several small due to costs and the spillover effect. For example, fish are mobile, and are therefore hard to protect simply by placing management over a small area. The overall strategy seems to be:

  1. Protect core areas
  2. Protect marine park areas, where diving and scientific research happen
  3. Protect buffer zones

MPAs can be difficult because sometimes there is not adequate funding for protection and setting up, or a lack of compliance. There often needs to be some kind of local compensation, which is why officials look to bottom-up management (community-based changes).

Because reefs are open-access, this can be a barrier to management success. Think: tragedy of the commons. People all want to take advantage of that, and sometimes there can be a lack of community awareness.

For many local communities, the reefs are a source of livelihood: economically, culturally, and for food security. Many prime fishing grounds are now marine reserves. So, to change their lifestyles (sustenance fishing, diving), management needs to find them a replacement, not an addition for income.

Ecotourism is a potential new source for income, but it is important that the local communities benefit from the business, not a businessman from the outside.

Another option is seaweed farming, which produces hydrocolloids. If the middle man is cut out, that would be even better for increasing local profit.

But that’s just protection on a local scale – globally, reefs face climate change and water acidity which threaten their existence.

To learn more about this global issue, keep your eye out for more posts to come. Thank you for reading!

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