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Dive Dry with Dr. Bill

#576: Got Milk? Why, No!

Like most of you, I was constantly admonished to drink milk as a young child. As my mother always said, it will build strong bones. I think they also told us back then that Wonder Bread would also build strong bodies. Right! I never liked the taste of milk in a glass. As a kid, I always added a humongous helping of Nestle's Quick to mine... or if that wasn't available, quickly gulped it down white while holding my nose. This continued into my Harvard years... at least until I was caught sneaking two canteens of white milk out of the dining hall to my room to add the magic elixir.

Of course the reason we were told to drink that foul tasting white fluid filled with fat was that it contained a magic ingredient known as calcium. And those of you who passed high school biology or health probably remember that calcium is important for strong bones and teeth! So what do the poor denizens of the deep do to get their calcium? Marine critters, especially vertebrates like fish, need strong bones too. Invertebrates like crabs and starfish with exoskeletons do too. Even though I spend little time studying them, there are milk givers in the sea. No, I'm not referring to cows.

Local marine mammals that give milk to feed their offspring include whales, dolphins, porpoises, seals and sea lions. I've written about the rich milk of species like the northern elephant seal which may contain 50-60% fat compared to our 1-3% (unless you drink skim milk). However, when is the last time you heard about a fish suckling at the teat of a seal... or a crab using its claws to milk a dolphin? Neither have I! Got milk in the sea? Not really... no white mustaches on most of the critters there.

If calcium is also needed by marine life, but they don't have milk readily available, how do they get it? Well, how do you think cows, goats, pigs, deer and other terrestrial mammals obtain it? Yep, through their diet. Of course marine critters don't graze on grass, or browse on bushes or even chew on my old boots (not much calcium in them anyway). But some have found rather unique ways to get it, including at least one that does it through recycling!

I finally made it out to the dive park in mid-February to enjoy the great visibility and the WARMTH of the water. I could see 50-60 feet, and the lowest temperature I got on my dive was a scalding 61 F. Quite toasty for this time of year. In fact, the winter has been so mild that I haven't even given serious thought to escaping to the tropics for a few months of warm water diving. I spent a fair bit of time analyzing the island's rainfall records when I was with the Conservancy, and found that one recurring pattern involves light early season rain, followed by a few mild and dry months and then all Hades breaks lose in March and April. If this year follows that, I'll be in the tropics then!

Yes, I know... I digressed. So which critter is it that acquires its calcium through recycling? Actually all of them do, since they obtain it from plants and animals that are their food. The calcium moves up the food chain until it is finally returned to the system when the apex predator or scavenger decomposes. However, the one I filmed on that February dive is none other than the spiny lobster, Panulirus interruptus. By the way... as a scavenger it also recycles a lot of dead stuff from the ocean floor. Think about that the next time you eat one!

I was poking my camera into a shallow but narrow cave to film a lobster when I noticed it was chewing on something white. At first I thought it might be a bivalve as I've seen them gnaw on clam and mussel shells before. Then my eyes began to focus clearly (well, as clear as they can without my glasses). It was holding a molted carapace of another lobster, the part of exoskeleton that most divers aren't interested in. Obviously this was a great way to ingest high quality calcium since their external skeletons are largely made of calcium carbonate.

For some reason the lobster didn't seem too perturbed that I was filming it and continued to gnaw, gnash and gnosh on the carapace. They use their thick mandibles to crush the calcium-rich carapace into smaller pieces that can be ingested and used by the body to build its newer, more commodious exoskeleton. Thus it recycles these cast off outer skeletons as it grows. Perhaps lobster deserve an environmental award for this.

I mentioned that lobster may also ingest calcium from the shells of bivalves like clams and mussels. They can also do so by munching on gastropod (snail) shells. I also knew that lobster are predators on sea urchins. When lobster are overfished from an area, urchins may form patches denuded of giant kelp unless they are controlled by another predator such as the sheephead.

Years ago I was diving in the park and found another lobster deep in a crevice. It was also holding something in its legs and chewing on it. I finally realized it was the test, or exoskeleton, of a sea urchin! The urchin's innards were long gone, perhaps consumed by that very bug. However, it continued to chew on the test because it too is made of calcium carbonate. Of course I'm not going to suggest that we humans start chewing on the exoskeletons of lobster or sea urchins, much less the hard shells of mussels, clams or snails. I think it best we stick to milk. I'll take mine with Nestle's Quick, thank you!

© 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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Giant sea bass with a milk mustache... NOT, and lobster chewing on wavy top snail shell,
sea urchin test and a "bug" exoskeleton. .

This document maintained by Dr. Bill Bushing.
Material and images © 2014 Star Thrower Educational Multimedia