Anyone who has read my columns over the past 15 years knows that I make no bones about focusing on two primary subjects: munching and mating. They are the two fundamental activities of all creatures. Munching is necessary to ensure the individual grows and matures so it can continue the species by mating (or whatever form of reproduction evolution has given it). Yes, breathing is also a critical function... but I doubt many would bother reading my columns if I focused on that! Right?
My frequent readers also know that during summer I dive mostly after the sun goes down. There are just too many poorly supervised snorkelers in the dive park these days and they make often it a royal PITA to try to dive with them blocking the fairway out from the dive park stairs to the descent buoys or having to duck under due to their legs thrashing about above me as I try to approach to exit. Yes, there is another reason to dive after dark... there is a lot more munching and mating going on for me to film and share with you! A third rationale to dive at night is that it keeps me out of the local bars... an air fill costs less than a beer at some establishments.
Following the terrible surge from Hurricane Marie down off Baja, I did a few night dive a week later. As I entered the water, I immediately noticed that boulders were overturned and many of them were scoured of all plant and animal life. On Thursday I also noticed I was once again getting tossed around by surge. My assumption was that Hurricane Norbert was already affecting this end of the island. Strong surge, especially when coupled with a swift current, makes filming extremely difficult. In fact the current converted me into a member of the plankton several times as it took hold of me and literally dragged me along through the water!
Okay, so when are you going to tell us something interesting, Doc? Hold your sea horses... I'm getting to it. Lately I've noticed a number of abalone are out of their holes. The surge has wiped out a large portion of the giant kelp (Macrocystis pyrifera) from Long Point to the East End. Abalone love to munch on drift kelp, especially the tender and nutritious blades ("leaves"). With so little drift kelp to capture with their feet (and Mom thought MY table manners were bad), they are resorting to eating sub-prime beef... er, seaweed. Some capture the tough kelp stipes ("stems") if they can, others grasp whatever alga is within reach.
Since munching is critical to survival... and therefore to reproduction... and I want our abalone to continue their recovery from overharvesting and the withering syndrome disease, I try to feed the ones I can while I'm down under. After all, I'm a kelp forest ecologist and conservationist and I want the kelp beds here to return to the glory I knew when I first arrived here in the late 1960s. Usually there is plenty of giant kelp and I just grab a blade or two and extend it toward them. They eagerly rise up and extend their foot (which does look somewhat like a dark tongue) to capture my offering of chef's salad. I've even had them take the invasive devil weed Sargassum horneri when I offer it to them... and that alga has nasty tasting polyphenols in it.
Although the surge made this operation difficult on that fateful night, I did feed a few. The last one I approached was not very receptive to my dinner offering. It didn't look like it had eaten recently so I was surprised. Then, as I watched it with my arm extended holding my blade of kelp close, white clouds suddenly appeared out of the shell's respiratory holes. I had caught it "in the act" (my more mature readers will understand that phrase but the little kids won't... I hope).
I tried planting myself to get stable footage, but the surge was making that difficult. The green abalone (Haliotis fulgens) released its gametes in several bursts. It looked like it was smoking... during rather than after (if you get my drift). I was able to record several releases and the cloud of gametes that sometimes obscured the abalone itself as the surge and current dispersed the goodies.
Now I could have determined whether these were sperm or egg by plucking the ab and checking the color of its gonad. Males are cream colored and females are gray or greenish. However, I did not want to hurt the ab or interrupt its spawning (spawning interruptus?). Females are said to release as many as 11 million eggs! Spawning may be controlled by water temperature or daylength. The astronomical number of gametes is necessary because "infant" mortality is high (99%).
It is said abalone need to be in close proximity (perhaps about 18") to ensure fertilization. The closest ab I saw to this one was a different species, a pink abalone (Haliotis corrugata), so it was not a compatible mate for the green ab (although researchers have induced the creation of hybrids from these two species). It is reported that when an abalone spawns, it often triggers others of the same species to join in. Makes sense to me. Visibility was poor that night, but I didn't see any others release their gametes so this might have been a wasted effort.
In researching this column, I found that in laboratory studies green abalone begin to experience thermal stress at temperatures in the 77 F range. On my night dives, my minimum temperatures (at depths of about 50 ft) have been around 72-75 F. Direct stress from unusually high water temperature combined with the loss of a major food source (giant kelp) due to elevated water temperature and strong surge may be putting our abalone at some risk this summer. Apparently higher water temperatures also increase their food requirements and may delay sexual maturity, adding to the potential problem. As if that wasn't enough, spawning also diminishes the stored energy available for growth or survival. Warriors, prize fighters and athletes have been told that for years. Once again, "reproduction" can be deadly!
© 2014 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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Green abalone spawning during night dive and gamete cloud obscuring abalone.
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