Dive Dry with Dr. Bill

#260: If They Can Do It... Why Can't We?

I miss my old steel high pressure 120 cubic foot SCUBA tank. It was a gas... that is, it contained enough atmospheric gas (or air as we commonly call that mixture) to give me free reign throughout the water column. Insomniacs and other regular readers of this column remember my thrilling exploits down to my basement depth of 200 feet. Unfortunately, the tank failed visual inspection due to a coating of rust on the inside walls, and I currently dive with a smaller 90 cubic feet aluminum tank. That's not enough for me to feel comfortable hitting such depths... so now I'm limited to about 160 feet with occasional descents to 180 feet.

What was it about exceeding the recreational depth limit of 130 feet that interested me? I'm no thrill seeker, nor do I have a death wish. After decades of studying our kelp forests above that limit, I've become interested in seeing what life exists and how it is adapted to the cold, dark depths. Although in clear tropical waters sunlight can penetrate to such depths, here in our more turbid, plankton-rich waters; there isn't enough light there for most algae to photosynthesize. So I have taken to entering the twilight zone... er, I mean the aphotic zone (vs the photic zone where light is sufficient for algae to photosynthesize).

I was surprised to find that there was far more algal life at these depths than I expected. Some are kelps related to our giant bladder kelp, but with huge blades (the "leaves") that spread out over the ocean floor. The broad and often very long blades are necessary to capture enough of what little light penetrates there so the kelp can photosynthesize and produce food. In other words, the alga's solar energy collectors have to increase substantially in size for the kelp to produce enough sugars and carbohydrates to survive.

This is one mechanism for dealing with the very low light levels way down under. Now if simple kelp can develop the capacity to trap solar energy at such depths, why aren't we doing it topside in Avalon? I remember looking in awe at pictures of our city in the 1920's and 1930's, and seeing the rooftops of many buildings covered with solar hot water heaters. I confirmed this recently in a conversation with long-time island resident Bill Hill, who remembers the solar water heater his father placed on their roof back in the late 1920's. If we were to return to this simpler technology, perhaps we could do our part to lower the greenhouse gas emissions and throttle down global warming... unless my readers are hoping for warm tropical beaches here in the near future.

I also see species of algae that I've never seen in shallower waters. One of them, which I usually find attached to rocks between 150 and 200 feet, has a beautiful, almost irridescent purple color. In the past I'd ask Dr. Mike Neushul, my mentor at UCSB and one of the world's experts on algae, about unusual species I encountered. He passed away years ago, but I now consult with another colleague, Dr. Kathy Ann Miller at the University of California Herbarium (and formerly with USC). I sent her a color image of this alga captured from my video footage to see if she could identify it.

Kathy quickly responded that it was the red alga Maripelta rotata. Sorry, there is no common name I'm aware of. I consulted a technical guide to California algae by Abbott and Hollenberg and found the following. This red alga was first discovered off Catalina in the 1940's. It is said to be rare, and found down to a depth of 30 meters (about 100 feet). I don't think I've ever seen it that shallow here! Its geographic range appears to be from the Carmel and Diablo Submarine Canyons up north to Catalina and south to Point Eugenia, Baja California.

Why is this deep water alga red rather than green, brown, golden-brown, or psychedelic orange and yellow for that matter? To answer this, I need to talk briefly about pigments and their interaction with the sun. Most sentient human beings are aware that land plants tend to be green, using chlorophyll to photosynthesize. They are able to use both ends of the color spectrum, the reds and the blues, reflecting back green to our eyes. Now several groups of algae use auxiliary pigments to help capture sunlight and transfer the energy to the chlorophyll in them for photosynthesis. So a red alga (or a red bandana or jacket) reflects back the red light, but can capture (or absorb) the middle ranges (green) and upper ranges (blue) of the spectrum.

As sunlight penetrates through the water column from the surface, it gets progressively dimmer as light is absorbed and scattered in the layers above. However, not all colors of light penetrate equally into the water. The lower energy reds and yellows are filtered out first, usually in the first 15-30 feet in our waters. It is the greens, and especially the higher energy blues that penetrate deepest into the ocean. If a deep water alga were green, it would reflect the greens at depth and only capture the blues since the reds have already been removed by the water. A red alga reflects what little red light reaches such depths (and usually appear black to my eye), but captures the greens and blues. Therefore it makes use of the more abundant colors of light in its photosynthetic process. Simple isn't it? Want me to repeat that explanation?

Now if alga and land plants have adapted through evolution to utilize the most optimum colors of sunlight as their energy source to photosynthesize, why can't the evolutionarily far more advanced Homo sapiens at least match their accomplishment? Instead of doing what our parents and grandparents did with solar collectors, we burn massive amounts of fossil fuels (which are the remnants of long-dead plants) that pollute our air, affecting our health, and add to global warming, which could affect the health of all other species and the Earth itself. And of course by "we," I am definitely including myself... and I certainly ought to know better! Okay, I'll step off of my soapbox and drop down to the ocean floor where no one can hear me!

© 2007 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. Please help me climb out of self-imposed poverty... buy my "Munching and Mating in the Macrocystis," "Great White Sharks of Guadalupe," "Calimari Concupiscence: Mating Squid, " "Playful Pinnipeds: California Sea Lions," "Belize It or Not: Western Caribbean Invertebrates, Fish and Turtles," "Gentle Giants: Giant Sea Bass" or "Common Fish and Invertebrates of the Sea of Cortez" DVD's. Yes, take Dr. Bill home with you... we'll both be glad you did!

The very interesting red alga Maripelta rotata at 160 feet off Sea Fan Grotto.

This document maintained by Dr. Bill Bushing.
Material and images © 2007 Star Thrower Educational Multimedia