Dive Dry with Dr. Bill

#314: Rhodoliths... Riddle Solved

Despite 40 years spent in part submerged under the waters surrounding Catalina, there are still many things I don't know. Heck, if I did... what fun would it be to go back under? Fortunately ecological systems are full of millions and millions of critters, and the inter-relationships between them are dynamic and changing, so I'll never run out of "discoveries." Last week I solved a riddle that had been puzzling me for about two years.

The riddle first emerged when I was diving the shallow waters around Indian Rock in Emerald Bay. That's a long distance to travel, especially when fuel prices are high, so we didn't dive there often on the King Neptune. On the inside of the rocky reef I found the soft bottom littered with round, reddish "stones." Looking closely, I realized they were actually covered with a coralline red alga, but I didn't take the time to identify them when we got back. I fell asleep editing the day's video footage.

Then last week I received an e-mail from a graduate student at the Moss Landing Marine Lab up north. The subject heading was "Catalina Island Rhodoliths." Even before I opened it, I knew that this would provide the key to solving this riddle. After all, "rhodo" translates as "red" and "lith" as "rock." I read the e-mail and the grad student was seeking my advice on the use of GIS (Geographic Information Systems) to map these red algal nodules so he could investigate certain environmental factors and disturbance elements on them. Years ago I did some pioneering research on the use of GIS to map giant kelp forests, so he probably read one of my papers and felt I could advise him.

His message stated that rhodoliths could also be found ay Cherry Cove, Fourth of July Cove, Big Fisherman's Cove and even near Avalon. Jogging my memory, I thought I may have seen them at some of these other sites back in the 1970's. They are known from Arctic to tropical waters elsewhere. Beds of these red algal nodules in other parts of the world are known to support a unique and highly diverse community of invertebrates. His work may be the first study of these red algae in the United States. They can form a layer about three feet thick over extensive areas. Individual rhodoliths are slow growing and may live more than 100 years. The dead rhodoliths erode into a form of sand.

Some marine biologists feel rhodolith beds may form one of the four top algal communities in the marine world along with kelp forests, seagrass meadows and reefs formed of other coralline algae. The French formerly referred to them as maerl, and some use that older term for smaller, twig-like structures; and the word rhodolith for the larger, more spherical ones. Because they are rounded balls, they move about with the tides and currents like pebbles and gravel on the ocean floor.

The critters associated with rhodolith beds are usually more diverse than those in surrounding soft bottom habitats at the same depth. Some live within the intricate nooks and crannies of the rhodolith itself, others bore into them while others attach to their surfaces. Since these nodules are living algae, there are also grazers that feed on them.

The scientific classification of rhodoliths is not easy. Some may be composed of several different algal species. Lithopyllum is one common genus in the Sea of Cortez and other locations. Since they are algae, their growth is a function of available light and nutrients. Depth affects the amount of light present, so this can be an additional factor. These variations in light and nutrients help produce banding in the rhodolith which can record changes in environmental parameters for scientists to interpret.

So finding the solution to my riddle once more reaffirmed my belief that natural ecosystems are incredibly diverse and complicated. I often compare ecosystems with economic systems. The latter are human constructs, and therefore one would assume they would be more comprehensible to economists. I guess recent events have proven that an ecologist may better understand economic systems than the financial analysts. I could easily foresee the potential mess our lack of financial discipline could create. Humans seem very willing to play with these economic systems without fully understanding their complexities and the ramifications. Look at how this has affected the rest of us mere mortals. That suggests to me that humans should be been even more careful with natural systems that have evolved over billions of years and are far more complex. Just proves the old adage... Don't mess with Mother Nature!

© 2008 Dr. Bill Bushing. Watch the "Dive Dry with Dr. Bill" underwater videos on Catalina Cable TV channel 49, 10:00 AM and 5:00 PM weekdays and on Charter Communications Cable channel 33 at 7:30 PM on Tuesdays in the Riverside/Norco area. Please help me climb out of self-imposed poverty... buy my DVD's (see this link). Yes, take Dr. Bill home with you... we'll both be glad you did!

A field of rhodoliths at Emerald Bay and close-ups of the nodules.

This document maintained by Dr. Bill Bushing.
Material and images © 2008 Star Thrower Educational Multimedia