DIVE DRY WITH DR. BILL #876: THE KELP NIBBLER MYSTERY
I may have solved yet another of the "mysteries of the deep" that have kept me diving for so many decades. The Magus, is one of the books I have read over and over again beginning the summer of '69 before I moved to the island. It it, author John Fowles writes "mystery has energy... it pours energy into whoever seeks an answer to it. Man... needs the existence of mysteries, not their solution."
Well after all my time in the kelp forests of Catalina I have accumulated a lot of questions and I do like answers to them even though Fowles claims that "an answer is always a form of death." Fortunately at my "mature"age, I am likely to forget the answer shortly after I receive it, so it becomes a a mystery once again. Kind of like an underwater groundhog's day.
The mystery I'm referring to in this column is the presence of many circular holes in giant kelp blades (Macrocystis pyrifera), especially the sporophylls at the bottom where the spores form to generate the tiny gametophyte ("male" and "female") stages of this species. These specialized blades must be highly nutritious to the critters that feed on them.
But what critter creates such nearly perfect circular holes when it ingests a mouthful? At first I thought it might be a snail such as Norris' top snail (aka the kelp snail). However snails feed with a scraping radula that would not create such symmetric holes. I was aware that a family of fish known as kyphosids will feed on kelp blades. These include our opaleye (Girella nigricans), halfmoon (Medialuna californiensis) and zebra perch (Kyphosus azureus). You may know them by their common name, the sea chubs.
I have observed these fish as they sample a tasty bite of salad from the giant kelp. I concluded that they couldn't be the culprit. Instead of mouthing the blade and cutting a perfect circle, these fish tear at the blade and rip it up. Such messy eaters couldn't be the creator of these very symmetric holes. Their impact would be more like when I eat and tear apart a nice flank steak with my fangs!
But then I posted one of the images you see here of a kelp blade and got as response from Selena McMillan, who is the southern California regional manager of Reef Check Foundation. A few years back I was honored by that international organization with the annual Poseidon award, joining Jean-Michel Cousteau and Dr. Sylvia Earle who were previous recipients.
Selena posted that she studied this group of kelp nibblers, the kyphosids, as part of her PhD research. That study involved analyzing the stomach contents of these fish to determine their diet. She stated that she found nearly perfectly round pieces of giant kelp blades in their stomachs. I must admit that came as a total surprise to me based on my observations of their feeding behavior.
So Selena may have solved yet another mystery of the kelp forest. Fortunately many other mysteries abound and there is no way I can solve them all before I finally kick the bucket. I'll continue to have questions to ask and mysteries to solve until the day I arrive in the great dive site in the sky. With any luck I'll end up there instead of the far warmer waters of the other place!
© 2020 Dr. Bill Bushing. For the entire archived set of over 850 "Dive Dry" columns, visit my website Star Thrower Educational Multimedia (S.T.E.M.) Home Page
Image caption: Circular holes in kelp blade and sporophyll blade; opaleye feeding on kelp blade and posing for my camera; other sea chubs... the halfmoon (aka Catalina blue perch) and zebra perch.
I may have solved yet another of the "mysteries of the deep" that have kept me diving for so many decades. The Magus, is one of the books I have read over and over again beginning the summer of '69 before I moved to the island. It it, author John Fowles writes "mystery has energy... it pours energy into whoever seeks an answer to it. Man... needs the existence of mysteries, not their solution."
Well after all my time in the kelp forests of Catalina I have accumulated a lot of questions and I do like answers to them even though Fowles claims that "an answer is always a form of death." Fortunately at my "mature"age, I am likely to forget the answer shortly after I receive it, so it becomes a a mystery once again. Kind of like an underwater groundhog's day.
The mystery I'm referring to in this column is the presence of many circular holes in giant kelp blades (Macrocystis pyrifera), especially the sporophylls at the bottom where the spores form to generate the tiny gametophyte ("male" and "female") stages of this species. These specialized blades must be highly nutritious to the critters that feed on them.
But what critter creates such nearly perfect circular holes when it ingests a mouthful? At first I thought it might be a snail such as Norris' top snail (aka the kelp snail). However snails feed with a scraping radula that would not create such symmetric holes. I was aware that a family of fish known as kyphosids will feed on kelp blades. These include our opaleye (Girella nigricans), halfmoon (Medialuna californiensis) and zebra perch (Kyphosus azureus). You may know them by their common name, the sea chubs.
I have observed these fish as they sample a tasty bite of salad from the giant kelp. I concluded that they couldn't be the culprit. Instead of mouthing the blade and cutting a perfect circle, these fish tear at the blade and rip it up. Such messy eaters couldn't be the creator of these very symmetric holes. Their impact would be more like when I eat and tear apart a nice flank steak with my fangs!
But then I posted one of the images you see here of a kelp blade and got as response from Selena McMillan, who is the southern California regional manager of Reef Check Foundation. A few years back I was honored by that international organization with the annual Poseidon award, joining Jean-Michel Cousteau and Dr. Sylvia Earle who were previous recipients.
Selena posted that she studied this group of kelp nibblers, the kyphosids, as part of her PhD research. That study involved analyzing the stomach contents of these fish to determine their diet. She stated that she found nearly perfectly round pieces of giant kelp blades in their stomachs. I must admit that came as a total surprise to me based on my observations of their feeding behavior.
So Selena may have solved yet another mystery of the kelp forest. Fortunately many other mysteries abound and there is no way I can solve them all before I finally kick the bucket. I'll continue to have questions to ask and mysteries to solve until the day I arrive in the great dive site in the sky. With any luck I'll end up there instead of the far warmer waters of the other place!
© 2020 Dr. Bill Bushing. For the entire archived set of over 850 "Dive Dry" columns, visit my website Star Thrower Educational Multimedia (S.T.E.M.) Home Page
Image caption: Circular holes in kelp blade and sporophyll blade; opaleye feeding on kelp blade and posing for my camera; other sea chubs... the halfmoon (aka Catalina blue perch) and zebra perch.
