Whats with all the Algae covering the reefs in the Caribbean?

[Tjack]

What is a healthy proportion of Algae to hard corals on a Caribbean reef?

Just back from Curacao and was struck by the amount of red Algae covering some walls. Elsewhere in the Caribbean I have noticed lots of dead hard corals with Algae cover, seems like far less in the Indo-pacific.

I heard somewhere that there was an Urchin die off in the Caribbean at one point and this is a contributing factor?

Anyone know of a region in the Caribbean which is relatively Algae free?

 

[drbill]

Another reason can be serious reductions in the local herbivore populations of fish that feed on the algae that otherwise may inundate the coral

 

[beaverdivers]

Yes, it could be a combo of both lack of urchins and fish eating algae.

 

[agilis]

Dead coral is quickly covered with algae, and there is a lot of dead/dying coral in the Caribbean, the result of numerous factors that are well known and widely discussed. Most of the causative factors are connected to human activity, direct and indirect. A high level of nutrients in the water is a related phenomenon that enables particularly lush algae growth. Generally speaking, the further away from human activity the healthier the coral and the least algae cover. The thinning out of herbivorous fish populations is not an especially significant cause, despite the countless tedious graduate student research done in poor overworked Discovery Bay. In any case the reduced number of algae eating fishes is the result of human activity. The gigantic African dust storms that saturate the Caribbean every winter are growing worse and more heavily loaded with toxic fertilizer chemicals, and these affect even the most remote Caribbean locations. The reality is that the acidification of the oceans will destroy most of the worlds's corals in coming decades. Calcium production requires an alkaline environment and we have managed to compomise the very essence of oceanic chemistry. But look on the bright side: there is always Disneyland and amazingly lifelike virtual reality apps that you will be able to download.

 

[drbill]

The thinning out of herbivorous fish populations is not an especially significant cause, despite the countless tedious graduate student research done in poor overworked Discovery Bay. In any case the reduced number of algae eating fishes is the result of human activity.

As a marine biologist, I'd have to disagree with that statement. However, you are correct in identifying nutrient enrichment as a major cause of algal growth on dead coral and human activity as a major contributor.

Another factor might be the tremendous reduction in sea turtle populations over historic time. Columbus' sailors reported sea turtles so thick in the Caribbean you could practically walk across their backs to get to land. Many sea turtles are herbivorous.

 

[Tjack]

One Curacao location, the wall off of Tugboat was almost completely covered in red algae. There was a large ship moored near by, this might support the idea that nutrient enrichment or pollution is a contributing factor.

I don't recall seeing whole reefs covered in the same red algae before. What is this stuff?

 

[agilis]

The red algae is probably a type of cyano slime algae, bacterial in origin and an indicator of organic pollution.

I'm aware of the link between the decline in herbivorous fish and algae growth, but the literature I've seen is so frequently reflective of research done in Jamaica's Discovery Bay as to be almost comical.

The conventional academic position also tends to blame the severe reduction in urchin numbers due to diseases as the original primary cause for algae overgrowth, and then proceeds blame the reduction in the numbers of herbivorous fishes for failing to provide a back up for the missing urchins, a second line of defence, a reserve army that was not there. This perception undoubtedly has some merit, but perhaps not as much as is the official party line among some academics. There is, I think, a great deal more going on than is usually mentioned, and there seems to be a shameful reticence and an overly cautious approach when big money issues like construction, industrial pollution, and energy production are involved, most especially when funding for research eminates from these polluters.

It's easy and risk-free to point the finger at poor people making a marginal living with fish traps. These fisherman certainly do their share of damage, but it really irks me to see them mentioned so prominently and frequently while wealthy and powerful polluters are mentioned very carefully and diffidently, if they are mentioned at all.

I first encountered references to the huge sea turtle numbers in the early Caribbean in Archie Carr's book, 'So Excellent A Fishe'. Dr Carr was a gentleman and a scholar of the old school, and I count myself fortunate to have met him, long ago, when the world was young.

 

[drbill]

Certainly no argument with the anthropogenic causes of the problem at all ends... human activity that enhances nutrient levels (as well as higher sedimentation rates affecting corals) coupled with human-caused reductions in several herbivore populations. Glad I "live" in waters where kelp forests still thrive far away from the mainland's negative influence!

 

[Tjack]

Interesting you bring up energy production Agilis, the oil refineries on Curacao reminded me of Gary Indiana. One good reason to stay west end of the island. Actually the corals seemed least impacted the further away from Williamstead, far less algae cover. Areas with more current seemed healthier as well.

Channel Islands, now that's the kind of algae I can deal with. Love the iridescent y shaped algae in the right quantities.