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Dive Dry with Dr. Bill

#506: Some "Exotics" Are Welcome

Now I'm old enough to remember what our waters were like back before 1977-78 when a decades-long warming trend began. I'd already been teaching marine biology at the Catalina Island School, conducting scientific research and diving here for eight years by that time. Chilly is one word for the waters back then. Luxuriant is another, at least for the kelp forests that thrived at that time. Of course I'm also old enough to forget what I went into the other room for this morning!

The El Niño event that occurred then led to a long period of warmer than average water temperatures, coupled with several other El Niño events like "The Big One" in 1982-84. Why I could free dive for two hours during those summers and only come out a pale blue instead of royal blue! When these changes occurred, scientists were assuming they were part of a "short" term oscillation between cool and warm water that fluctuated on the order of several decades. Although the concept of "global warming" (global climate change) was known by then, and taught to my classmate Al Gore by one of our Harvard professors, I don't remember it being part of mainstream thinking in that era. Certain anti-science segments of our society today are trying to return it to that status.

This year we've had unusually warm water with surface temperatures hitting 77 F in the dive park in late August. Even now I'm getting minimum temperatures in the 70s at depths of 50 to 70 ft. After the two previous summers when temperatures were cooler, this has been both a welcome change and a potential for ecological disruption.

Our giant kelp forests are dying off due to the lack of nutrients associated with the warm water. As the shade from their dense canopies disappears, the immature exotic Asian seaweed Sargassum horneri has started to reach maturity and will probably pose a significant threat to our local species as it out competes those algae for space, light and nutrients. It may once again form such dense stands that it looks like exotic wheat fields underwater, and divers will become entangled in it.

The warm waters have also brought other "invaders" into our waters. These somewhat exotic species have taken advantage of the mild temperatures and north flowing currents to travel a bit and see the world beyond their normal home range. Staff at CIMI recently "spotted" a spotted porcupinefish (Diodon hystrix) under the pier float. I observed it in their aquarium when I visited the campus with a group of my former Toyon high school students holding a reunion here a week ago. Of course I had filmed this species while working down in the Sea of Cortez a number of times. It ranges as far north as San Diego and south to Chile.

Then last weekend Ken Kurtis of ReefSeekers surfaced from a dive and told me about a strange tiny fish he had seen cavorting with a group of baby garibaldi. It had the same shape as the garibaldi, but sported an irridescent yellow-green dorsal region, deep blue body and a blue spot at the rear of its dorsal fin. I told Ken it was either a mutant garibaldi, affected by the radioactive waste from the Fukushima nuclear tragedy now drifting along the West Coast, or a damsel relative of the garibaldi from "south of the border, down Mexico way." He sent me a picture and I tentatively identified it as a baby white tail damsel (Stegastes leucorus).

The following day I did two very unusual dives. They were to an average depth of a mere five feet. Yes, you read that correctly... five feet. Ken had spotted the young damsel just below the end of the dive park stairs so I positioned myself there and filmed for 79 minutes while the surge battered my body and divers stepped on my back to get out of the water. What else could they do since I was in their way. The conditions were very poor for recording this unique species, but a few of the still images I grabbed from what little video I saved came out fairly good.

The white tail damsel is known from Guadalupe Island to Mazatlan, Mexico. An interesting fact about this damsel is that 90% of its total population lives in one small region of Mexico, the Revillagigedo Islands. Apparently it is very abundant there, but uncommon on the mainland coast of Mexico. The International Union for the Conservation of Nature (IUCN) refers to it as an insular species. Maybe that is why it found its way to our island! Its rather restricted distribution makes it all the more interesting that it found its way to our waters.

Like the garibaldi, the male white tail tends a nest of eggs laid on the bottom by the female. These eggs hatch out into larvae that then drift with the currents to disperse. Our little one must have caught an express to get this far north in the time it remains within the plankton. Although some sources stated this was a deeper water tropical fish, others list its maximum depth as only about 50 ft. At five feet, this little one was well within that range! White tail damsels are reef associated, staying close to their home, and are not migratory. They may live 19 years and reach a maximum length of 5 1/2 inches.

Although all three species entered our waters from other geographic areas, I don't consider the whitetail damsel and spotted porcupinefish to be non-native ecological "threats" like I do the Japanese seaweed. The two fish appeared here thanks to natural dispersal via ocean currents from adjacent regions. The chance a single whitetail damsel or spotted porcupinefish will reproduce and establish here is very slim indeed. It takes two to tangle... or is it tango? I ought to know because I haven't gotten tangled in a long time... except in kelp!

Even if many of their brothers and sisters arrive here in the future via currents, they would be considered a natural introduction and simply constitute an extension of their geographic range northward as our waters warm. If global climate change is true, and I believe it is, we may be seeing more of these introductions from warmer waters... and some of our cool, temperate species hightailing it to the north!

In contrast, the Sargassum horneri arrived from Japan via human intervention on the hull or in the ballast water of a human ship. It has already demonstrated its ability to become a well-established invader posing threats to our native seaweeds including giant kelp (Macrocystis). I've wanted to initiate a control effort in the dive park to remove as much of it as possible each year. After all, the park is now an official marine protected area. Unfortunately the language in the Marine Life Protection Act does not appear to distinguish between protecting native and non-native species. Way back in 1972 the Wrigley and Offield families made that distinction when forming the mission statement of our Catalina Conservancy. The California Dept. of Fish & Game is still considering my request for a permit to thin out this non-native in our marine reserve, but bureaucratic decisions come at a kelp snail's pace.

© 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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Baby damsel tentatively identified as the white tail damsel; adult white tail damsel (courtesy of
www.DiscoverLife.org) and a spotted porcupinefish I filmed in Mexico.

This document maintained by Dr. Bill Bushing.
Material and images © 2012 Star Thrower Educational Multimedia