DIVE DRY WITH DR. BILL #852: CORALLINE ALGAE
Glancing over the hundreds of "Dive Dry" columns I have written over the last 20 years, I was surprised to find I had never written about a very interesting group of algae (aka seaweeds) in our waters. It is easy for many to overlook them because they tend to be fairly small... especially compared to our giant kelp (Macrocystis pyrifera). I'm referring to the many species of coralline algae seen here.
Coralline algae are not related to corals in any way. However they do possess calcium carbonate in their cell walls that is similar to what forms the "skeleton" of stony corals. There are two basic types. Crustose corallines form crust-like growths on the substrate that are generally very thin. Articulated or geniculate corallines have branches and grow up from the substrate to the incredible height of about eight inches! They are attached by a small holdfast.
Most coralline algae are pink or red in color, but some species can be purple, yellow, blue, white or gray-green. Of the approximately 10,000 species of algae, it is estimated that 65% are red algae in the Division Rhodophyta. Almost all are marine. They not only grow on rocky and coral reefs, but can attach to some shelled invertebrates and even other algae.
The process of calcification, embedding calcium carbonate in their cell walls, is energy intensive. These algae expend a good deal of their energy budget doing so. Therefore their growth rates are fairly slow and an 8" articulated coralline may be 10 years old! Compare that to our giant kelp that can grow 12-24" in a single day! The articulate corallines have uncalcified sections between the calcified ones which allows them flexibility against surf and swell.
One group of coralline algae had me stumped many years ago. I found it growing near Indian Rock at Emerald Bay. It looked like unattached spheres of red with protuberances on the surface. I did some research and found that this group is known as rhodoliths, and is composed of several distantly related types of red algae. They are found throughout the oceans of the world including the Arctic (brrr). I later found them on the bottom of Avalon Bay beneath the repair barge.
Like all algae, corallines harvest sunlight and perform photosynthesis. They do possess chlorophyll but the red pigments such as carotenoids, phycobilins, and allophycocyanins that they use as accessory pigments allow them to live much deeper than most algae. This is due to two facts. First, a red object absorbs the shorter wavelengths of light such as blue and reflects back the longer wavelengths such as red, orange and yellow. Blue and green light penetrates further in the water column, so it is available at deeper depths for photosynthesis.
They have few herbivores that feed on them. That would be like eating limestone. However there are a few species of marine snails that do chow down on this seaweed salad. They include young abalone and a chiton known scientifically as Tonicella lineata. Later in life, when the abalone become adults, they wisely choose the much softer blades of giant kelp and other seaweeds for food. In warmer waters sea urchins and parrotfish will also munch on corallines.
Crustose corallines may also have other algae that grow on their hard surfaces, and reduce light for photosynthesis. To prevent this, many species attract herbivores to graze on these encrusters while some actually slough off their outer layers to remove them. Can't have them trapping all the light for themselves!
In the tropics coralline algae can be an important component of coral reefs. They serve as a kind of cement to keep the reef together and may be even more important than the coral itself in maintaining reef structure. They can also attract marine larvae to settle on the reefs. I must admit in all the time I've spent diving coral reefs, I was not really aware of this and didn't notice these important algae.
© 2020 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: Articulate or geniculate coralline algae (left); crustose coralline algae and rhodoliths from Emerald Bay (right).
Glancing over the hundreds of "Dive Dry" columns I have written over the last 20 years, I was surprised to find I had never written about a very interesting group of algae (aka seaweeds) in our waters. It is easy for many to overlook them because they tend to be fairly small... especially compared to our giant kelp (Macrocystis pyrifera). I'm referring to the many species of coralline algae seen here.
Coralline algae are not related to corals in any way. However they do possess calcium carbonate in their cell walls that is similar to what forms the "skeleton" of stony corals. There are two basic types. Crustose corallines form crust-like growths on the substrate that are generally very thin. Articulated or geniculate corallines have branches and grow up from the substrate to the incredible height of about eight inches! They are attached by a small holdfast.
Most coralline algae are pink or red in color, but some species can be purple, yellow, blue, white or gray-green. Of the approximately 10,000 species of algae, it is estimated that 65% are red algae in the Division Rhodophyta. Almost all are marine. They not only grow on rocky and coral reefs, but can attach to some shelled invertebrates and even other algae.
The process of calcification, embedding calcium carbonate in their cell walls, is energy intensive. These algae expend a good deal of their energy budget doing so. Therefore their growth rates are fairly slow and an 8" articulated coralline may be 10 years old! Compare that to our giant kelp that can grow 12-24" in a single day! The articulate corallines have uncalcified sections between the calcified ones which allows them flexibility against surf and swell.
One group of coralline algae had me stumped many years ago. I found it growing near Indian Rock at Emerald Bay. It looked like unattached spheres of red with protuberances on the surface. I did some research and found that this group is known as rhodoliths, and is composed of several distantly related types of red algae. They are found throughout the oceans of the world including the Arctic (brrr). I later found them on the bottom of Avalon Bay beneath the repair barge.
Like all algae, corallines harvest sunlight and perform photosynthesis. They do possess chlorophyll but the red pigments such as carotenoids, phycobilins, and allophycocyanins that they use as accessory pigments allow them to live much deeper than most algae. This is due to two facts. First, a red object absorbs the shorter wavelengths of light such as blue and reflects back the longer wavelengths such as red, orange and yellow. Blue and green light penetrates further in the water column, so it is available at deeper depths for photosynthesis.
They have few herbivores that feed on them. That would be like eating limestone. However there are a few species of marine snails that do chow down on this seaweed salad. They include young abalone and a chiton known scientifically as Tonicella lineata. Later in life, when the abalone become adults, they wisely choose the much softer blades of giant kelp and other seaweeds for food. In warmer waters sea urchins and parrotfish will also munch on corallines.
Crustose corallines may also have other algae that grow on their hard surfaces, and reduce light for photosynthesis. To prevent this, many species attract herbivores to graze on these encrusters while some actually slough off their outer layers to remove them. Can't have them trapping all the light for themselves!
In the tropics coralline algae can be an important component of coral reefs. They serve as a kind of cement to keep the reef together and may be even more important than the coral itself in maintaining reef structure. They can also attract marine larvae to settle on the reefs. I must admit in all the time I've spent diving coral reefs, I was not really aware of this and didn't notice these important algae.
© 2020 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: Articulate or geniculate coralline algae (left); crustose coralline algae and rhodoliths from Emerald Bay (right).
