DIVE DRY WITH DR. BILL #767: BRACHS DO IT DEEPER
I recently wrote a column about the phoronids, a group related to bryozoa which uses a feeding structure known as a lophophore. Today I'll focus on another member of that group, the brachiopods or "lamp shells." Phoronids are often ignored by divers since they are very small, but often quite numerous. Brachiopods are seldom seen in our waters because they usually live at depths beyond the recreational dive limit of 130 ft, preferring colder deep water. And they don't even need a wet- or dry-suit! Actually the temperatures I experienced at such depths were generally 50-52° F and I've experienced significantly colder waters at depths of a mere 70 fsw.
However, about a decade ago I was testing my reaction to nitrogen narcosis by doing very deep dives on air to a maximum depth of 200 fsw. Well, I did hit 201 fsw once because I couldn't stop in time. I was hoping to create an episode in my "Munching and Mating in the Macrocystis" cable TV show on "deep ecology." There are many different critters way down there, but given the extreme depth I had relatively short bottom times to find and film them.
One of the critters I did encounter and film frequently was the brachiopod. This is an ancient group, originating back in the early Cambrian which began 543 million years ago ("shortly" before I started diving). During this geological period there was an evolutionary explosion of species, some of which I studied as fossils while a Harvard undergraduate. Fascinating stuff. Back in these early daze, brachiopods were one of the dominant filter feeders and even helped build reefs. During the great Permian extinction about 252 million years ago, many brachiopod species went extinct and the group never recovered its former glory. Bivalves like clams and oysters took their place.
Brachiopods secrete a calcium carbonate shell like bivalves. However their shells are dorsal and ventral to the animal inside rather than being on the sides (lateral) as in bivalve molluscs. Like bivalves, brachiopods use sets of muscles to close the shell if predators approach or open it to feed. Brachs have two sets of muscles that close the shell... one that snaps them shut quickly and another, slower set that can hold the two shells closed for longer periods of time.
The lophophore is designed a bit differently from those in bryozoa and phoronids. It is supported by a structure made of cuticle. The lophophore cannot be retracted for protection, which is a major reason why the brachiopods have protective shells. The ones I encounter at depth in our waters reside scattered on the bottom. Some attach to hard substrates with a short pedicle and I've seen clusters attached to one another. Being exposed could make them more vulnerable to predation than the phoronids which can retract their bodies back into their tubes. Like its relatives, the lophophore is covered with cilia that create a water current allowing the brach to filter feed largely on plant plankton.
Brachs apparently have few natural predators. Their rather thin shells do not offer a lot of protection. However, it is reported their flesh is not very palatable but I don't know a single scientist who has tested that hypothesis. My marine biologist icon Ed "Doc" Ricketts reportedly tried tasting a nudibranch to see if it was true for that group. However, I doubt he ever got deep enough to sample a brach unless it was dredged and brought to the surface.
Brachiopod species may live three to 30 years. The sexes are usually separate, but a few species are hermaphroditic. I was intrigued to learn they have four gonads instead of the two we humans possess. Gametes are generally released into the water column and larvae develop from the fertilized eggs, although in some species the female broods the embryos until they hatch into larvae. In some species the larvae drift for only a few days while in others they may be planktonic for months so they can see the world.
I'm assuming the brachiopod species I've observed is Laqueus californianus. However, while researching images for that species I've seen distinctly different morphologies for it which has me a bit confused. If any brach specialist out there can confirm the identification, please e-mail me at bushing@post.harvard.edu.
© 2018 Dr. Bill Bushing. For the entire archived set of over 750 "Dive Dry" columns, visit my website Star Thrower Educational Multimedia (S.T.E.M.) Home Page
Image caption: Ancient brachiopod fossil and brachiopods from our local waters plus image of the lophophore courtesy of Lovell and Libby Langstroth © 2005 California Academy of Sciences.
I recently wrote a column about the phoronids, a group related to bryozoa which uses a feeding structure known as a lophophore. Today I'll focus on another member of that group, the brachiopods or "lamp shells." Phoronids are often ignored by divers since they are very small, but often quite numerous. Brachiopods are seldom seen in our waters because they usually live at depths beyond the recreational dive limit of 130 ft, preferring colder deep water. And they don't even need a wet- or dry-suit! Actually the temperatures I experienced at such depths were generally 50-52° F and I've experienced significantly colder waters at depths of a mere 70 fsw.
However, about a decade ago I was testing my reaction to nitrogen narcosis by doing very deep dives on air to a maximum depth of 200 fsw. Well, I did hit 201 fsw once because I couldn't stop in time. I was hoping to create an episode in my "Munching and Mating in the Macrocystis" cable TV show on "deep ecology." There are many different critters way down there, but given the extreme depth I had relatively short bottom times to find and film them.
One of the critters I did encounter and film frequently was the brachiopod. This is an ancient group, originating back in the early Cambrian which began 543 million years ago ("shortly" before I started diving). During this geological period there was an evolutionary explosion of species, some of which I studied as fossils while a Harvard undergraduate. Fascinating stuff. Back in these early daze, brachiopods were one of the dominant filter feeders and even helped build reefs. During the great Permian extinction about 252 million years ago, many brachiopod species went extinct and the group never recovered its former glory. Bivalves like clams and oysters took their place.
Brachiopods secrete a calcium carbonate shell like bivalves. However their shells are dorsal and ventral to the animal inside rather than being on the sides (lateral) as in bivalve molluscs. Like bivalves, brachiopods use sets of muscles to close the shell if predators approach or open it to feed. Brachs have two sets of muscles that close the shell... one that snaps them shut quickly and another, slower set that can hold the two shells closed for longer periods of time.
The lophophore is designed a bit differently from those in bryozoa and phoronids. It is supported by a structure made of cuticle. The lophophore cannot be retracted for protection, which is a major reason why the brachiopods have protective shells. The ones I encounter at depth in our waters reside scattered on the bottom. Some attach to hard substrates with a short pedicle and I've seen clusters attached to one another. Being exposed could make them more vulnerable to predation than the phoronids which can retract their bodies back into their tubes. Like its relatives, the lophophore is covered with cilia that create a water current allowing the brach to filter feed largely on plant plankton.
Brachs apparently have few natural predators. Their rather thin shells do not offer a lot of protection. However, it is reported their flesh is not very palatable but I don't know a single scientist who has tested that hypothesis. My marine biologist icon Ed "Doc" Ricketts reportedly tried tasting a nudibranch to see if it was true for that group. However, I doubt he ever got deep enough to sample a brach unless it was dredged and brought to the surface.
Brachiopod species may live three to 30 years. The sexes are usually separate, but a few species are hermaphroditic. I was intrigued to learn they have four gonads instead of the two we humans possess. Gametes are generally released into the water column and larvae develop from the fertilized eggs, although in some species the female broods the embryos until they hatch into larvae. In some species the larvae drift for only a few days while in others they may be planktonic for months so they can see the world.
I'm assuming the brachiopod species I've observed is Laqueus californianus. However, while researching images for that species I've seen distinctly different morphologies for it which has me a bit confused. If any brach specialist out there can confirm the identification, please e-mail me at bushing@post.harvard.edu.
© 2018 Dr. Bill Bushing. For the entire archived set of over 750 "Dive Dry" columns, visit my website Star Thrower Educational Multimedia (S.T.E.M.) Home Page
Image caption: Ancient brachiopod fossil and brachiopods from our local waters plus image of the lophophore courtesy of Lovell and Libby Langstroth © 2005 California Academy of Sciences.
