Too many Nassau groupers?

[DavidPT40]

I read an interesting article that talked about Nassau groupers eating too many parrotfish. The parrotfish are helping reefs recover from the 1998 El Nino damage by eating algae so new coral can grow. Special reserves have been set up so the parrotfish can escape being eaten by the groupers.

I'm skeptical about the special reserves. Where can a parrotfish go that a grouper can't?

Heres the article: http://www.sciencedaily.com/releases/2006/01/060106131757.htm

Just FYI, heres a parrotfish

and heres a grouper

 

[Hank49]

Where is this abundance of Nassaus? I see choke (Hawaiian slang for a lot, or many) parrot fish around here near Placencia and the cayes, but few Nassaus. Like maybe a ratio of 100 parrots to 1 nassau.

 

[DavidPT40]

Exuma Cays Sea Park

 

[liberato]

Too many parrotfish aren't very heathy for a reef either. Yeah, they graze the algae but like goats of the sea they also munch the coral itself especially newly settled polyps and anything else that happens to be there.

 

[isurus]

The bbc report on this tells a slightly different story:
http://news.bbc.co.uk/1/hi/sci/tech/4583984.stm

 

[drbill]

It is my understanding that Nassau groupers have been a fish targeted heavily by fishers in the past, especially during spawning aggregations. Current levels of Nassaus therefore may not be anywhere near pre-exploitation levels. My belief is that we have little idea of what a truly "healthy" reef ecosystem should be composed of in terms of ratios of Nassaus to other species.

In California's past the sea otter was hunted to near extinction in the 1700's and 1800's. At that point predation pressure was greatly reduced on abalone, urchins and other prey species. By the early 1900's we had a surplus of abalone (until they were over exploited by commercial and sport fishers and subjected to withering syndrome). A "healthy" ecosystem would have more otters and fewer abalone.

 

[Hank49]

It's kind of backwards as far as the path that nature usually follows. The top of the food chain is usually in abundance because there is plenty of prey....not lack of prey due to too many predators. At least not for long. The predators will die off or move on if there is no food source.

 

[DavidPT40]

I just thought of something. What if water pollution has changed the need for grazers on reefs? I know in Florida that effluent from wastewater treatment plants is causing the bleaching of reefs. I think the bleaching is from excess algae.

 

[drbill]

I just thought of something. What if water pollution has changed the need for grazers on reefs? I know in Florida that effluent from wastewater treatment plants is causing the bleaching of reefs. I think the bleaching is from excess algae.

This is true on the Great Barrier Reef and other areas where agricultural runoff has enriched nutrients in the nearshore environment. Certainly this has altered the "natural" (pre-human or pre-European) balance.

Although I'm no coral reef expert, I don't believe the increased algae creates bleaching. It kills the coral by smothering it and the dead coral is white.

 

[Hank49]

The bleaching may be from the warm water this last year. That's what happened in a lot of places world wide when water was 30C from the big El Nino of 98. Malaysia, the Philippines, the great Barrier Reef...all had white corals that died. After they died algae grew on the skeletons.
Someone reported here on SB that there was bleaching in the eastern Caribbean a few months ago. I don't see it in Belize yet. But that warm water was probably what fueled all the hurricanes too.