DIVE DRY WITH DR. BILL #780: COLORLESS CNIDARIANS
Back in the 1960s when I was a lifeguard at various pools in the Chicago area, the long days in the sun bleached my hair blonde (not to mention turning my skin a rich, dark brown). The one time I tried using bleach, it turned orange. The things we did back then to enhance our image as the dashing life savers for the ladies.
Of course this column won't be about bleached hair. These days I avoid freshwater pools and prefer a close association with Mother Ocean. That's what marine biologists are supposed to do! Besides, freshwater habitats are pretty boring to me these days... well, except for the lovely bikini-clad amphibious mammals at poolside. But then there are very few pools out on Catalina Island.
I'm sure most of my readers are aware of the problem with coral bleaching in the tropics and subtropics. Coral often form a symbiotic relationship with one celled algae. The algae live within the tissues of the coral. Through their photosynthesis they produce products that can be used as an alternate food source by the coral. In turn, the coral excrete waste products that can help fertilize the algae. providing nutrients to help it grow.
However, unusually high water temperatures can force the algae to escape from the coral tissues. The coral becomes "bleached" because it no longer has the photosynthetic pigments associated with the algae. It also no longer has the supplemental food source provided by the alga's photosynthesis.
Even though we don't have reef-producing (hermatypic) corals in our somewhat chilly waters off Catalina Island, I've observed an interesting case of bleaching in a relative of the corals. On occasion during my decades of diving island waters, I'd encounter "bleached" "white" sea anemones known as the giant green sea anemone, Anthopleura xanthogrammica.
The mechanism for the bleaching observed in this species is quite different from that in warmer water corals. In the corals bleaching is caused by the departure of the algae due to elevated temperatures. In our local sea anemone, it is due to the anemone living in a place such as a deep crevice or cave that gets little sunlight. Algae need sunlight to photosynthesize, and if there isn't enough they simply will avoid such places or die.
The giant green sea anemone is normally a bluish-green due to the algae (Zoochlorellae sp.) and photosynthetic dinoflagellates (Zooxanthellae sp) in its tissues. They co-exist quite nicely in reasonably well-lit locations such as tidepools and shallow, exposed water. Back in my days as a marine biology teacher at pre-CIMI Toyon Bay, I collected a few individuals of this species from heavily shaded locations. As you can see from the images below, they appear a ghostly white.
I thought this was due to the lack of algae that often give cnidarians their color. Back in the Dark Ages that is what I was taught. However in researching this column, I discovered on the Monterey Bay Aquarium site that their green color comes from the anemone itself rather than the algae. However, the Animal Diversity Website and others state that the color of the anemone is due to the amount of sunlight the algae in it receive. Other sources say both contribute to the color. However, given my observation of bleached individuals I wonder about the color being due to the anemone's pigmentation. Now I'm really confused (doesn't take much). Looks like a project for further research.
The anemones seemed to survive fine, unlike their coral relatives. They were able to use their primary mode of feeding to sustain themselves. Of course this involved using their many tentacles to snatch a variety of prey drifting in the water above it. They will also take careless molluscs, crabs, sea urchins and small fish. Heck, if I stick my finger on the anemone's disk I can feel the little harpoons of the nematocysts penetrating even my thick skin!
© 2018 Dr. Bill Bushing. For the entire archived set of over 775 "Dive Dry" columns, visit my website Star Thrower Educational Multimedia (S.T.E.M.) Home Page
Image caption: A bleached version of the giant green anemone from a cave and one with its symbiotic algae intact.
Back in the 1960s when I was a lifeguard at various pools in the Chicago area, the long days in the sun bleached my hair blonde (not to mention turning my skin a rich, dark brown). The one time I tried using bleach, it turned orange. The things we did back then to enhance our image as the dashing life savers for the ladies.
Of course this column won't be about bleached hair. These days I avoid freshwater pools and prefer a close association with Mother Ocean. That's what marine biologists are supposed to do! Besides, freshwater habitats are pretty boring to me these days... well, except for the lovely bikini-clad amphibious mammals at poolside. But then there are very few pools out on Catalina Island.
I'm sure most of my readers are aware of the problem with coral bleaching in the tropics and subtropics. Coral often form a symbiotic relationship with one celled algae. The algae live within the tissues of the coral. Through their photosynthesis they produce products that can be used as an alternate food source by the coral. In turn, the coral excrete waste products that can help fertilize the algae. providing nutrients to help it grow.
However, unusually high water temperatures can force the algae to escape from the coral tissues. The coral becomes "bleached" because it no longer has the photosynthetic pigments associated with the algae. It also no longer has the supplemental food source provided by the alga's photosynthesis.
Even though we don't have reef-producing (hermatypic) corals in our somewhat chilly waters off Catalina Island, I've observed an interesting case of bleaching in a relative of the corals. On occasion during my decades of diving island waters, I'd encounter "bleached" "white" sea anemones known as the giant green sea anemone, Anthopleura xanthogrammica.
The mechanism for the bleaching observed in this species is quite different from that in warmer water corals. In the corals bleaching is caused by the departure of the algae due to elevated temperatures. In our local sea anemone, it is due to the anemone living in a place such as a deep crevice or cave that gets little sunlight. Algae need sunlight to photosynthesize, and if there isn't enough they simply will avoid such places or die.
The giant green sea anemone is normally a bluish-green due to the algae (Zoochlorellae sp.) and photosynthetic dinoflagellates (Zooxanthellae sp) in its tissues. They co-exist quite nicely in reasonably well-lit locations such as tidepools and shallow, exposed water. Back in my days as a marine biology teacher at pre-CIMI Toyon Bay, I collected a few individuals of this species from heavily shaded locations. As you can see from the images below, they appear a ghostly white.
I thought this was due to the lack of algae that often give cnidarians their color. Back in the Dark Ages that is what I was taught. However in researching this column, I discovered on the Monterey Bay Aquarium site that their green color comes from the anemone itself rather than the algae. However, the Animal Diversity Website and others state that the color of the anemone is due to the amount of sunlight the algae in it receive. Other sources say both contribute to the color. However, given my observation of bleached individuals I wonder about the color being due to the anemone's pigmentation. Now I'm really confused (doesn't take much). Looks like a project for further research.
The anemones seemed to survive fine, unlike their coral relatives. They were able to use their primary mode of feeding to sustain themselves. Of course this involved using their many tentacles to snatch a variety of prey drifting in the water above it. They will also take careless molluscs, crabs, sea urchins and small fish. Heck, if I stick my finger on the anemone's disk I can feel the little harpoons of the nematocysts penetrating even my thick skin!
© 2018 Dr. Bill Bushing. For the entire archived set of over 775 "Dive Dry" columns, visit my website Star Thrower Educational Multimedia (S.T.E.M.) Home Page
Image caption: A bleached version of the giant green anemone from a cave and one with its symbiotic algae intact.
