Dive Dry with Dr. Bill

#136: Turn My World Upside Down... or Downside Up!

During my second week in Florida, my dive buddy Stephanie and I drove down to Key Largo to dive there with highly rated Aqua-Nuts out of Kelly's on the Bay. With a name like that, I knew I was in for an interesting experience. Unfortunately weather blew in on our first day and the dive trips were canceled due to winds and swell. There turned out to be the proverbial silver lining in those clouds. As I walked along the small bay where the dive boats were anchored, I noticed something that excited me. It was Cassiopeia. No, not the constellation of stars in the skies but the mangrove upside-down jellyfish in the waters of the bay. Interestingly a naturalist in Belize said that the constellation itself is upside down, so the name of the jellyfish is appropriate. I guess he didn't realize that the constellations turn around the North Star, Polaris, and that Cassiopeia can be right side-up or upside-down! As Steinbeck and Ricketts wrote in the Log from the Sea of Cortez, one should "look from the tide pool to the stars and then back to the tide pool again."

I first encountered this group of unusual jellies in the Sea of Cortez while working with Lindblad Expeditions. Dr. Jim Kelley, the former president of the California Academy of Science, and I were in Zodiacs giving our passengers a tour of the mangroves. Looking down in the water, we saw something that neither of us was familiar with. Strange frilly circular life forms were lying on the muddy bottom pulsing. When we returned to the cruise ship, I checked the field guides in our library and discovered they were the mangrove upside-down jellyfish. I didn't have my wetsuit and video camera so I wasn't able to film them there before we left for our next location on the cruise.

This time I didn't hesitate. I put on my wetsuit, grabbed my camera and spent most of that day snorkeling in the very shallow bay to film these strange jellies. I did check to see how powerful their sting was, and was relieved to know they would not zap me badly. I carefully snorkeled through the bay, trying not to stir up the muddy sediment which would ruin my filming. Stephanie joined me after she finished kayaking the Bay. There were upside-down jellies all over, so I had no problem finding subjects to film. Their colors ranged from almost white to deep brown with some green and purple mixed in. Most were in the 5-8" range, although they are said to reach a foot in diameter.

The mangrove upside-down jelly is common in Florida and the Caribbean. It and other species are known from Asia and other tropical regions. After some research, I discovered the species I saw in Mexico was the same one. I found it interesting that this inhabitant of mangrove habitats was found on both sides of Central America. I had to wonder how it might have achieved this distribution? Perhaps it was already dispersed to both regions before the North and South American continents joined in past geologic time.

This species frequents shallow ( to 15') bays and lagoons with muddy or sandy bottoms. Most jellies we are familiar with drift in the ocean currents with their tentacles trailing below them. The mangrove upside-down jellies rest on the bottom with their tentacles reaching up towards the stars (Cassiopeia? or the Sun at this time of day). There is good reason for this. Inside their tissues are small, single-celled algae known as zooxanthellae. These algae need sunlight to photosynthesize, and they produce a source of food for the jellies. This same form of symbiosis is found in jelly relatives like corals. The rest of the jelly's food comes from more conventional sources- plankton, small invertebrates and fish that wander into its upright stinging tentacles. Of course Stephanie and I were too big to be on the menu!

This jelly has 15 primary "arms" of tentacles with many branches. There are eight oral arms extending from the small "mouth." It is hard to refer to that opening as a "mouth" because it also serves as the passageway for wastes excreted by the jelly. While that may be more convenient for these primitive creatures, I prefer my digestive tract to be "open" at two ends! That way I don't mix tonight's steak with yesterday's burrito!

Since these jellies sit on the bottom and pulsate, they aren't the most dynamic of subjects for filming. Like in the early Cousteau films and Marlin Perkin's Wild Kingdom TV show, film makers occasionally have to induce behavior in their subjects to create interesting footage. I readily admit that I picked up several of these jellies and released them in midwater to film their movement. It was obvious that they are not related to the house cat because most of them landed upside-down rather than on their "feet."

As I said earlier, I normally stay away from the subject of religion. However, in researching these jellies, one of the websites that Google placed on my computer screen was that of Creation magazine. In volume 25 issue 4 this publication mentioned the mangrove upside-down jellyfish as an example to discredit evolution! It cites an article contending that the species is strictly vegetarian (remember the zooxanthellae). The magazine further states that the original diet of humans and "all" animals was vegetarian and tries to answer the question why a "God of Love" would create animals with killing mechanisms like the stinging cells of some jellies. I was surprised to read that, according to the article, the Bible does not consider invertebrates to be "living creatures." I guess that means that I am not a "zoologist" in the Biblical sense according to this magazine. My readers are already aware that I "know" nothing in the Biblical sense, so that may be no surprise! Of course I accept evolution and find no inconsistency with it and the concept of a Higher Power, a topic I'll no doubt delve into in the future after reading this!

© 2005 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.

Upside-down jelly "right" side up, upside-down jelly "wrong" side up;
upside-down jelly settling down to the bottom in "proper" position.

This document maintained by Dr. Bill Bushing.
Material and images © 2005 Star Thrower Educational Multimedia