Dive Dry with Dr. Bill

#482: Kelp Kondos

In the past I've referred to condos in the sea. No, I'm not referring to those in underwater cities designed by my old friend and trained architect Jean-Michel Cousteau. I'm referring to dive sites like the Bill Kroll Hi Spot (also known as the Little Gibraltar pinnacle) where the moray eels are so thick I sometimes call the site the Moray condo. I've also written about bryozoan colonies in which hundreds to many thousands individual bryozoans live each with their own home or zoecium. Today I'd like to look at the Kelp Kondos as I sometimes refer to the large holdfasts on our giant kelp (Macrocystis pyrifera).

Those who read my column regularly (and why would you want to be "irregular?") are aware that southern California kelp forests are home to many hundreds of species. Some live up in the kelp canopy near the surface. Others live among the vertical fronds that reach toward the sunlight. But a number of critters seek the shelter afforded by the twisted root-like structure at the bottom known as the holdfast. It isn't a root at all since it does not absorb water or nutrients the way a terresrtrial plant root would. Its function is just as its name suggests... to hold the kelp fast to the bottom. The many tangled root-like structures known as hapterae secrete a chemicakl tyhat glues them to the hard substrate.

Now the hapterae (singular: haptera) of the kelp holdfast do Thomas' English muffins one better. They have far more nooks and crannies for critters to creep into for protection. Brittle stars secrete their bodies within them and extend their arms out into the surrounding water to filter food. Bryozoa may grow their own colonies on the root-like structure. Shrimp are frequent residents of the crevices as are a wide range of other invertebrates... and even a few small bottom-dwelling fish!

When I first came to Catalina on August 24, 1969, I was looking for some serious scientific research to involve my marine biology students in at the Catalina Island School (then for boys only) in Toyon Bay. My mentor at Harvard, Dr. H. Barraclough "Barry" Fell suggested we start looking at drifting kelp. He had studied drift kelp in his native New Zealand, and drifting logs up on the New England coast. Barry wanted to determine what marine critters might hitchhike rides on the drifting material and travel to far off places. Since Catalina was a somewhat isolated island, we thought marine critters might find a cheap way to get to the island from the mainland. Back then the S.S. Catalina or Great White Steamer took 2 3/4 hours to cross the Channel. Of course kelp rafts would take much longer, but at least there would be no ticket to buy.

The "kelp rafting project" eventually received National Science Foundation funding thanks to Dr. Fell. For 7 1/2 years we took our 26' launch, the K.V. (named after the school's founder, Keith Vosburg), scouted for drifting kelp, dragged the huge kelp rafts up into the boat, bagged them in black plastic trash bags and took them back to my ocean front lab. There my students combed the blades and stipes looking for critters (many of which fell off of course) and "dissected" the compacted kelp holdfasts to extricate all the critters within them. In all we sampled 109 different algal rafts and found at least 127 different species of marine invertebrates on them.

So what you might rightly ask? Can't these critters just crawl or swim over to the island? After all, they do live in the ocean. Well, if you are familiar with the San Pedro Channel, you know it gets extremely deep between here and there. It's a wee bit difficult for critters that live in shallower waters (say above 130 ft, the maximum recommended depth for recreational SCUBA diving) to crawl all the way down to the deep waters where the whale skeletons abound and then all the way up the slope to the island? Without a GPS system, that would be a remarkable task for a critter less than an inch long to undertake. Might even require several lifetimes to accomplish it. As for swimming over, how many of YOU have tried swimming over to the island? I didn't think so.

Okay, so you smart readers out there might remember that Dr. Bill has written frequently of the eggs and larvae that are released into the water column when many marine critters perform the... um... ultimate requirement for the population to survive. Yep, after the "wild thing" is completed, the eggs and larvae can drift in the plankton with the currents sometimes for periods of over a year. You get a lot of "sea miles" that way (although I don't think they are redeemable at Catalina Express). OK smarty, species that broadcast spawn and have reasonably long planktonic existence can make it to sunny Catalina just by floating with the moving water.

Those of you familiar with the cruise ships that have anchored off our beautiful coast know that there is a relatively new breed of such vessels. These are the cruising condos. Members of the 1% can purchase living space on such a majestic ship and join the cruise wherever they wish in its travels around the world. Actually I'm a member of the 1% myself... but I'm referring to the bottom 1%, not the top. The point I'm trying to make is that critters on a drifting kelp holdfast are kind of like the owners of these ocean-going condos. They just cruise along, hopefully with a decent view from their particular nook or cranny.

Why might this be important as a means of dispersal for an ocean-dwelling critter? Let's say evolution kind of shorted you. You never developed a way to cast your sperm and eggs into the water and let them travel to far off places. Or if you did, the youngsters just don't have the stamina to remain in the current long enough to disperse. Perhaps you like to be a good parent and you brood your young, keeping them close to you until they can crawl off on their own close by. Maybe you never even figured out how to reproduce sexually (I did, I have a great son). You're stuck with that age old method of asexual reproduction... splitting your body into parts that then can grow into new individuals. For these critters, including ones like the asexually reproducing variable star (Linckia columbiae), the brooding star Leptasterias hexactis or anemone Epiactis prolifera; or critters like Octopus and the solitary coral Balanophyllia elegans whose youngsters just ain't got what it takes to go the distance, a dispersal mechanism like kelp rafting is just the ticket!

© 2012 Dr. Bill Bushing. Watch the "Dive Dry with Dr. Bill" underwater videos on Catalina Cable TV channel 29, 10:00 AM weekdays and on Charter Communications Cable channel 33 at 7:30 PM on Tuesdays in the Riverside/Norco area. You can also watch these episodes in iPod format on YouTube through my channel there (drbillbushing). 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!

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Kelp holdfast where it "belongs:" attached to the rock, holdfasts detached by storm and preparing for their voyage;
drifting holdfast buoyed up by the air floats on the kelp and holdfast ready for "dissection" in the Toyon lab.

This document maintained by Dr. Bill Bushing.
Material and images © 2011 Star Thrower Educational Multimedia