Coral reefs in crisis?

Parrot fish, locally known as chub. (Photo courtesy Dr Robert Steneck)

If they are … if coral reefs are in crisis … why should I care? Before we draw a food web to find out, let’s learn a bit more about the players.

Hard coral that builds reefs is composed of tiny members of the animal kingdom called polyps, which live within stony calcium carbonate structures that they secrete. Living in a symbiotic relationship with these polyps are photosynthetic organisms called zooxanthellae; polyps provide safe housing and raw materials while zooxanthellae share their food produced with the aid of sunlight. It is these various types of zooxanthellae that impart a myriad of colours to different species of coral.

Near the base of our food web are the plant-like zooxanthellae and the coral polyps. As we humans on land jostle for real estate, a similar scenario occurs in the water where ‘seaweeds’ are always seeking space to expand, even if that space is on top of the coral.

If the seaweeds grow unchecked, they will block sunlight from the zooxanthellae, reducing a major food source for the polyps and thereby leading to death of the coral. To keep seaweeds in check are herbivores such as chub (parrot) fish and long-spine sea urchins (Diadema species). Larger fish and/or man are at the next level of our food web. Therefore, fisherfolk and consumers benefit from these web relationships but over-taking these chub contributes to reef decline and reduced available fish in the longer term.

The EAG’s December meeting included a short presentation by Dr Robert Steneck who discussed his work with coral reefs in the Caribbean and other regions over the past almost four decades. Dr Steneck is a Professor of Marine Biology, Marine Policy and Oceanography in the University of Maine. He is currently doing reef surveys throughout the Caribbean partly in development of a project for an Antiguan graduate student who recently joined his laboratory. Dr Steneck was last in Antigua & Barbuda in 1974 when reefs were healthy and diverse and is now sobered by the stark contrast.

Dr Steneck pointed out that the major coral bleaching event in 1998 had significant negative effects on reefs all over the world. While zooxanthellae need sunlight to photosynthesise, too much sunshine and its associated warmth can be detrimental. A rise in sea temperature, among other factors, led to coral bleaching wherein zooxanthellae died or ‘flew the coop’. Once this pigmented component was removed, the coral appeared white (bleached). Without the food that was provided by the zooxanthellae, some species of coral polyps could not source enough food on their own and subsequently died.

In some parts of the Caribbean, such as Bonaire, there has been good recovery of coral after the 1998 event. However, many of Antigua and Barbuda’s reefs have not been as fortunate and, according to Dr Steneck, “many coral reefs have become seaweed reefs”. Even though some persons place the blame for the state of our reefs on hurricanes, he thinks that other factors are much more significant. He argued that reefs can recover if baby coral have a safe space to develop, one not over-run by seaweeds.

Increased (chub) fishing pressure (and urchin removal) reduces the amount of grazing that can occur. We know on land what happens when grass it not kept mowed. Since coral reefs present ideal breeding, spawning and nursery conditions for other fish and sea-life, reef decimation can have extensive consequences. In addition, it is becoming harder to find live, diverse, colourful reefs to show our guests.

Dr Steneck revealed that some countries have banned export of chub fish, recognising the long-term impacts of not doing so, although they maintain sustainable fishing for local consumption only. In answer to the question, ‘Why should you care?’, we ask you and relevant government agencies to consider the long-term impact (on the marine environment, boat tour and dive operators, fishers, consumers) of turning a blind eye.

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