About this time of year, when water temperatures are near their highest, our native giant kelp starts to senesce and die from starvation. No, this alga is not a vicious predator... or even a hungry herbivore. It is not starved for flesh, but for nutrients which which to photosynthesize and build or repair its cells. When the temperature exceeds 68 F for a period of a few weeks, nutrient levels in the water plummet. This temperature is known as an inflection point: below it nutrients are present, above it nutrients are depleted. Neither the giant kelp nor the phytoplankton can proliferate until things cool down a bit.
As parts of the giant kelp begin to age or senesce, they stop growing. The blades no longer are elongating before your very eyes. At this point they become a stable substrate for other living things to attach to or live on. I've already written about the baby starfish I've filmed up in the kelp canopy. Today I want to write about a species which creates "large" condo developments on top of the older blades. Well, maybe not large to the human eye since they are only about 2-3" maximum, but they do contain hundreds of single rooms that are home for a "moss animal" known as a bryozoan, the species Bugula neritina.
The kelp blades become encrusted with these shrub-like, "high rise" condos. No need to landscape the "grounds" with them around. Like developers maximizing the number of units per acre, this "moss animal" or bryozoan can literally cover the kelp blade. Since their condo colonies are constructed of calcium carbonate, the added weight of a dense development often causes the kelp blades and entire fronds to drop to the bottom under the extra load.
This bryozoan is an erect, branching, tree-like colony with a reddish-purple to brown color. The individual organisms, called zooids, have tiny homes known as a zooecium (= animal house..." but not starring John Belucci of course) that alternate on the branches of the colony. They suspension feed on bacteria, plant plankton and organic matter using a structure of 23 cilia-covered tentacles known as a lophophore. In turn they are fed upon by fish including senorita and garibaldi. I have also observed clusters of eggs laid on the colonies by a yet unidentified nudibranch (shell-less snail) whose young undoubtedly feed on them as well.
This bryozoan is very precocious, reaching sexual maturity in 6-8 weeks! The tiny critters are hermaphrodites, each containing both sex organs. However they release their eggs first, then the sperm later so they don't self-fertilize. The larvae have no mouth or digestive tract so they can't feed. Don't you wish your teenager was like that! Fortunately they only remain in the plankton for up to 10 hours, then settle and (like a butterfly's caterpillar) metamorphose into the adult form. The new adult zooid buds off others to form the colony, which may live for up to a year if they attach to something more permanent than a dying kelp blade!
I have filmed these encrusting animal colonies for many years but recently my interest in this species took an unexpected twist. I was contacted by a researcher looking for a good source to harvest Bugula neritina. He stated that this species is a source of a group of chemicals known as bryostatins which show potential for use in the treatment of cancer. The bryostatins may actually be synthesized by bacteria that live symbiotically within the bryozoa itself. The larvae of the moss animals are covered in this bryostatin which is distasteful to fish predators, so it helps protect them while drifting around in open water.
The researcher wanted to collect 100-500 pounds of the species for this research. After looking into it further via the Internet, I discovered this bryozoan was not native to our West Coast! I had always assumed that it was because it had been here when I first started diving Catalina's waters. However Bugula neritina is part of the fouling community that can attach to the hulls of boats, piers, floats and other structures. They are highly tolerant of mercury, so boat anti-fouling paints based on that would have little effect. The date of its first recorded appearance in the eastern Pacific was in 1905, but it has spread throughout much of the West Coast and temperate to tropical waters around the globe as an unintentional consequence of human activity such as trans-oceanic shipping or the importation of oysters from other regions since they also attach to oysters. No one is certain where its original geographic distribution was centered.
Of course we could harvest all the Bugula neritina we wanted and not control this exotic species, but it is good to know this non-native could be good for something after it had invaded our waters. In the past I've suggested we get biofuel manufacturers to harvest the exotic Asian seaweed Sargassum horneri that invaded Catalina during the last decade to use to fuel vehicles like the SCICo's Expedition H-1 Hummers. Maybe the good doctor should start a new business harvesting the bryozoa and the Sargassum to process into usable products to benefit both human health and the environment. Wait, me a businessman? Not very likely.
This is where the concept of an ecological baseline comes in. Marine biologists prior to 1905 would not have noted this bryozoan in our waters. Therefore when first detected in the early 1900s, it would be considered an exotic (non-native) species. Diving biologists like myself who arrived on the scene decades later would probably assume (as I did) that the species was a native, at least until they were enlightened! So my personal baseline for Catalina, back in 1969, would yield a completely different picture of what was "natural" in our waters. But you can't fool me forever!
© 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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Bugula neritina colony and several colonies on kelp blade; kelp blade encrusted with bryozoa,
and nudibranch eggs (white) laid on colony.
This document maintained by
Dr. Bill Bushing.
Material and images © 2012 Star Thrower Educational Multimedia