Wild Ocean Blue

As I mentioned in my last post, 2010 is the International Year of Biodiversity. And what better way to start things off than with a neat study from Florida telling us why some fish species are especially important.

This is the story of the red grouper.

Red grouper. by NOAA.

As their name suggest, these chaps are usually red. They can grow to over a metre from head to tail although 50cm (or nearly 2 feet) is more common. They can apparently live for up to 25 years, which is quite a lot for a fish. And like many other fish, red groupers are sex shifters: they are all born as females and after between 7 and 14 years they reajust their sexual organs, transforming into fully-functioning males.

The warm waters of the Caribbean Sea and central west Atlantic, between North Carolina and Brazil, are where the red groupers call home. And it now turns out these fish help to build and maintain their complex reefy  habitats.

“Red groupers are the Frank Lloyd Wrights of the sea floor” said the study co-author Susan Williams, from University California-Davis.

Red grouper. Photo by tiswango.

Felicia C. Coleman from Florida State University’s Coastal and Marine Laboratory led the study in the West Florida Shelf, sending both scuba divers and mini-subs down to spy on the red groupers. The researchers watched on as the fish got busy, digging great holes in the seabed to live in – up to a few metres wide and deep. The fastidious fish then keep their homes neat and tidy, ejecting mouthfuls of sand and sweeping the rocks clean with their tail.

In a series of experiments, the research team temporarily kept groupers away from their excavated abodes (by putting a cage around them), showing just how well they maintain their burrows.

And it turns out that this meticulous housekeeping creates important three-dimensional habitat that many other species rely on, giving a boost to biodiversity wherever red groupers are present; it clears areas of hard rock for corals and sponges to settle on and provides hiding places for spiny lobsters and dozens of other fish species including many that we like to eat such as snappers.

No-one has yet experimented with taking away red groupers permanently to test out this theory; somehow that doesn’t seem like a very good idea, these days.  But this study from Felicia Coleman and colleagues gives us a strong hint that all would not be well if red groupers were to disappear. In their own habitat-building way, they could well be what ecologists call “key-stone species”.

So, without the red groupers it seems likely that a whole host of other species would suffer.

And in the end that’s why red groupers really matter.

In detail:

• Red groupers – Epinephelus morio – are listed as Near Threatened on the IUCN Red List, which is a fairly low threat category but means they are certainly not safe. Many populations are considered to be overfished, especially parts of the Gulf of Mexico, and despite a few recoveries declines have been particularly bad in some areas.
• They are ambush predators, sneaking up on their prey and swallowing it whole, including shrimp, octopus, squid, fish and crabs.
• Other key-stone species include sea otters and starfish. They exert a disproportionate influence (for their size and abundance) on the rest of the ecosystem mainly because of their voracious appetites.

A pair of sea otters holding hands. Just too cute. Photo by joemess

• The red grouper paper can be downloaded for free from the Open Fish Science Journal.