Macroalgae backing off this summer?

[RickI]

... or not? I was saddened to see the extent of hard bottom coverage of algae between roughly 10 and 100 ft. two summers ago off Andros. A view of a section of reef in about 40 ft. of water appears below.

and a closer view;

This looks like it might be Dictyosphaeria sp..

Was just over diving off Big Bursa Cay near More's Island bordering Northwest Providence Channel. This is a small island some distance from any of the larger islands and obvious substantial concentrations of terrestrial runoff. It is in an outflow area from the flats of the "Marls" between GBI and Abaco in the Bahamas however.

From a few days ago. Plenty of coverage in this photo, less so in other areas however.

Although still present, it seemed to be less abundant than a couple of years ago. Is this a trend others have noticed in the Bahamas this summer or not really? This winter and related temperatures seemed to be cooler than in recent years. There is still tons of denuded rock and dead coral, just less macroalgae to go with it seems. There was one section of reef I noticed that seemed to be fairly healthy, in shallow water less than 10 ft. of water on a bar extending between two islands. Impressions?

Thanks

 

[archman]

I have not read any recent literature or reports showing improvements in water quality or coral reef health for that area.

On the other hand, I've skimmed more than a few reports showing continuing damage to coral cover and seagrass beds.

My own observations in the Bahamas regarding Dictyosphaeria mats indicate that they undergo periodic "pulses" of slough and renewal. On some reefs that I previously observed extensive cover... a month or so later the reef had shedded much of the stuff and there was sloughed algae clumps drifting all over the place.

 

[RickI]

Interesting, do you have a rough time estimate for the periods of sloughing off and renewal you've observed and have you noticed any relationship to time of year? I hadn't considered wave energy in the apparent absence or lesser presence of algal mats over the reefs I saw over the weekend. We have had an active wind season this winter and spring, perhaps more so than in 2007. Outwardly Dictyosphaeria appears to be more resistant to wave energy than some growth forms. A hurricane or strong extended cold front winds might rip some mats free from the bottom. In the case of Sargassum in SE Florida, we usually see a major development of floating mats after the first period strong cold front winds in the fall.

Yes, I agree with your conclusions about coral health in general in the area, doesn't look good. I did see some particularly large, for the most part healthy stands of A. palmata off Freeport. These were some of the largest stands I can recall seeing in some years. Uncertain whether this stand has regenerated much but perhaps persisted through the die off of the early '80's. Then again, there have been some particularly nasty hurricanes through this area since the 1980's suggesting some regrowth. Good to see it whatever the cause.