Last week my son Kevin flew into "Lost Angeles" from Denver and took the Express out to visit the "old man." The plan was to do some diving, including a night dive or two, and a lot of father-son bonding. His wife Mary and several of their friends joined us on Sunday for a little Blues on the Beach. But I'm not telling you this simply out of a papa's pride. These days it is not unusual for one's offspring to move away from their parents in search of better opportunities such as jobs and lower cost of living which seem like endangered species in the State of "Caleefornyia." Fortunately, my son and daughter-in-law are not dive bums like the old man... they have legitimate jobs with benefits such as paychecks. Obviously neither of them followed my example!
Likewise the offspring of marine critters often travel long distances to find new places to live in and explore. An individual organism munches to grow, then mates to ensure the continuation of the population and species. Likewise, their population often faces crowded conditions requiring offspring which can set off on perilous adventures to colonize new habitat and allow the species to expand its geographic range. A few years before I was born, Catalina approached the water's surface from below, and emerged from the sea as an island thanks to the geological processes associated with plate tectonics. As it inched into shallower water, it become excellent virgin habitat for many subtidal and eventually intertidal critters. Now all they had to do was get here from the mainland.
Most of you, especially the anglers and yachters, are aware that the San Pedro Channel separating Catalina from "the mainland" is a rather deep one. It is WAY over my head... reportedly dipping down below 3,000 feet. Pelagic fish may not find it difficult to swim across the 19.7 miles at our closest point, but Barney Barnacle attached to a rock in Laguna Beach, and Stacey Starfish over on the Palos Verdes Peninsula, can hardly be expected to crawl all the way over here... at least not in their lifetime. Although they are part of the nekton, meaning they can swim, a number of fish also don't go very far from home either. We call them "reef associated" and examples include the sheephead and garibaldi.
Critters need a way to disperse to such new habitat and colonize them. None of them that I'm aware of can afford even a one way ticket on the Express. Given their often limited mobility, or fear of the unknown beyond their reef ("what if the ocean is flat?"), it would be very helpful if they could hitchhike over here. We are aware of land plants like dandelions whose seeds spread in the wind. Other than the flying fish, there aren't many marine critters that could take advantage of that mechanism. However, the ocean currents provide an equivalent mode of transportation that many critters can utilize!
No, Barney Barnacle can't detach from his rock and Stacey Starfish is a bit too, um... plump... to be carried by the currents without sinking. However, both species produce young 'uns who are brave enough to venture out into the open ocean. These babies are actually planktonic larval forms that are capable of drifting with the currents sometimes for days, weeks or even months depending on the species. When they have munched on the plankton they encounter there. and grown a bit too big for their britches, they may metamorphose (you know, like a caterpillar into a butterfly) into a juvenile that looks more like mom or dad, and settle down. Since they do not remain in the plankton all their lives, we refer to them as meroplankton or temporary plankton. Those drifters who live their entire life in the plankton like the photosynthesizing diatoms, the "green flush" dinoflagellates and insect-like copepods are permanent plankton or "holoplankton."
The immobile or semi-mobile adults are often broadcast spawners. Thanks to chemical signals they release, the males and females simultaneously cast their gametes into the water column. With any luck, the sperm and egg will meet and fertilization will occur, creating an ovum that often begins the journey. There may be several different transitions into distinguishable larval forms that continue the voyage. For example, although abalone are known to "stampede," they too require pelagic larval forms to disperse to distant habitats. It is believed the males and females must be within about 18 inches of one another to ensure successful fertilization (I wish I could get that close). Is it any wonder we don't see many baby "abs" these days? Others, like the reef associated garibaldi, will brood their eggs in algal nests. When the eggs hatch, the larvae begin their meroplanktonic phase and disperse to colonize new reefs and enhance gene flow between different garibaldi populations.
Of course currents are fickle. A barnacle larva from Laguna may take a rather circuitous route to get to Catalina... if it even makes it to a suitable habitat at all! Most marine life must release hundreds to millions of eggs to ensure some are successful. When larvae have developed enough to settle, they may delay their metamorphosis until they sense suitable surroundings. In some cases the "smell" of the reef, especially their favorite food sources or proper substrate, may attract them. In other cases, chemical signals released from adults of their species may be the cue to come join them.
Recently the pelagic larvae of these critters has become a much more intriguing topic of study for marine biologists due to the Marine Life Protection Act process presently underway for our SoCal region. If we are to truly protect entire ecosystems and their component species, and ensure the creation of a suitable network to connect these new reserves, the duration of planktonic larval existence is an important factor to consider. If reserves are too close, the larvae dispersing between them may overshoot their destination. If reserves are too far apart, the larvae will transition too soon. Of course either "navigational error" has a positive side... those larvae that land outside of protected areas but in suitable habitat will produce the spillover that will enhance the quality of these unprotected locations and improve fishing potential.
Using this, let's look at some of the proposals for marine reserves around Catalina and see how effective they might be. The prevailing currents near shore are often from the (North)West End to the (South)East End of the island. Of course winds and tides cause variations in this and currents are fickle. If marine reserves are established on the southern end of the island, say in the vicinity of Silver Canyon, there is a good chance the increased larval flow from these protected areas will disperse beyond the island and settle "down to the bottom of the sea" where they do none of us any good. Marine reserves established further north along our coast, such as along parts of the West End or near China Point or Sea Fan Grotto, will produce larvae with a greater chance of landing elsewhere on the island rather than being lost at sea. Therefore it is important to protect these areas. However, when I travel to and from the mainland, I still take the Express. After all, my competitive swimming days ended a long time ago when I found myself swimming in the wake of Olympian Mike Troy at Harvard!
© 2009 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 and on Charter Communications Cable channel 33 at 7:30 PM on Tuesdays in the Riverside/Norco area. 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!
To return to the list of ALL of Dr. Bill's "Dive Dry newspaper columns, click here.
Barney Barnacle's baby (larva), a baby cephalopod still inside its egg; the advanced larval form of Stacey Starfish
and an unidentified fish egg drifting in the plankton (some images courtesy of Sally Bartel).
This document maintained by
Dr. Bill Bushing.
Material and images © 2008 Star Thrower Educational Multimedia