A New Symbiosis

19 Apr, 2013

Anthopleura artemisia, A Northeastern Pacific Actinarian Having Both Zooxanthellae And Zoochlorellae

This organism, Anthopleura artemisia, consists of at least three symbiotic organisms: a sea anemone, some zooxanthellae, and some zoochlorellae. None of those three organisms are routinely found as free-living organisms in the area where the symbiosis exists.

The First Of A Series Of Related Blogs – This One Sets The Stage.

 A New World

I was doomed from the get-go.  My really formative years were during the post-Sputnik era, when  I discovered speculative or science-fiction literature.  As a result, I would have given anything to be able to travel to other, vastly different, worlds.  At that time in the late 1950s and early 1960s speculation about the rest of the solar system knew no bounds; cloud-covered Venus, Earth’s twin, was seriously considered to be a hot wet wild world, maybe a jungle world, similar to …  well, a dinosaur utopia.  And if Mars didn’t really have canals… “What were those things on its surface, anyway”?

By the time I was in college, the Apollo program was going full steam, and probes, mostly unsuccessful, were being sent to the Moon, Mars, and Venus.  Unfortunately, the spectacular Soviet Venera probes showed that Venus was a hot hellish world with sulfuric acid clouds and surface temperature hot enough to melt lead.  About the same time the equally spectacular American Mariner and Viking probes showed that Mars was a cold and dry world, with a possibility of life…  Maybe.   And that meant I had to give up on ever seeing aliens in the flesh.  Whimper…

Time passed and as I was starting my first diving research, it took me about 10 seconds to realize the subtidal world I was coming to know WAS the different alien world I had wanted to visit as a youngster.

The general environment on this alien world, let’s call it “Marina”, is truly hostile to human life.  Humans are only able personally examine limited portions of the world’s surface and, for any but the briefest visits, a protective “space suit” is necessary along with some specialized breathing equipment.  Most of the world’s habitats are deadly to humans.  To examine these areas explorers must either remain inside mobile protective exploratory vehicles, or they must send probes into hostile environments.   The gravity is different; in those habitats that may be personally explored, the explorer is effectively weightless.  Light from the nearest star is muted and filtered through a differentially transparent medium altering the visible spectrum and making most electromagnetic communication impossible.

Marina - Earth's Wet Alter Ego

A View Of Marina, The Wet Alter-Ego Of Earth. Google Earth Image.

Marina is teeming with life, but many of the organisms are so vastly different from the life seen on the Earth’s surface that it has been difficult to understand how they live.  Additionally, many of this world’s organisms are dangerous or deadly to humans.  In many places the life on Marina is dominated by sessile predators, a category of life that is uncommon on the Earth’s surface, and often restricted to particular habitats.  Additionally, many of Marina’s life forms are neither wholly plant nor wholly animal, but a sort of weird combination of two – or more – different life forms living in a cooperative manner; definitely unlike the “good” true animals or plants, one is used to seeing on land.

Anthopleura artemisia, A Northeastern Pacific Actinarian Having Both Zooxanthellae And Zoochlorellae

This organism, Anthopleura artemisia, is a symbiosis consisting of at least three organisms: a sea anemone, some zooxanthellae, and some zoochlorellae. None of those three organisms is routinely found as a free-living organism lacking an initmate relationship to the other two species in the area where the symbiosis exists.

I could take this analogy quite a bit further, but it is surely unnecessary, except for the point that most of the exploration of Marina, the subtidal world of Earth, has occurred almost in parallel to the exploration of space.  In 1969, when Apollo 11 touched down on the Moon, if one pooled results from all of the oceanographic cruises that had ever gathered information from the deep sea, far less than 10 square miles had quantitatively examined by investigators.  At the present time, it still is a trite but true, statement that we know far more about the surface of the moon that we know about the bottom of the oceans of earth.  And most of what we do know is known from shallow waters that have been explored by SCUBA divers.

A Unique Habitat

In the early 1970s, the first wave of aquanauts exploring the habitats of “Marina”, could easily find “new” things; species that had not been scientifically described or interactions that were hitherto unknown.  This could make life pretty nice for a student, as it was easy to find interesting problems to research.  Soon it was noted that the relative amount that was known about the organisms and interactions occurring in the ocean was directly proportional to one’s distance from a marine research lab.  In other words, the farther away from a lab, the less was known.  That meant the interactions seen in marine environments near the Marine Biological Lab in Woods Hole, Massachusetts were quite familiar, similar situations were found near the University of Washington’s Friday Harbor Labs in northern Puget Sound or the German lab on Heligoland in the North Sea.  However, as far as what was going on in more distant areas, such as the polar regions or coral reefs…  Well, a map of the Mesoamerican Barrier Reef in the Gulf of Mexico or the Great Barrier Reef off Australia, could have been labeled with the notation “Terra Icognita” as far as biologists were concerned.

Urticina piscivora, the fish-eating anemone of the NE Pacific

Individuals of this sea anemone, Urticina piscivora, reach large adult sizes, the column can exceed 30 cm (1ft) in diameter.  It is a common species and found near some marine field stations/laboratories, nonetheless, it was not scientifically described until 1977.

By the late 1970s, I was working at the University of Alaska, Anchorage, and was doing research in an intertidal habitat near the town of Homer, about 250 miles south of Anchorage.  Having done my previous research in the northern Puget Sound, I was somewhat familiar with the fauna.  I’d guess about half of the animals I encountered were “familiar” to me.  I had the good fortune to discover a type of symbiosis that I think is unique.  Or, probably it would be better to say, no similar symbiosis have been discovered elsewhere to the best of my knowledge.

The Lyre Whelk, this specimen is from Puget Sound.

This is a specimen of the lyre whelk, Neptunea lyrata. While present at the Homer, Alaska site, they were not common, compared to the Pribiloff Whelk.

Neptunea pribiloffensis, the Pribiloff Whelk

This large specimen of Neptunea pribiloffensis was collected from the Bering Sea, and was more than 10.0 cm (4 inches) long. The specimens from the Homer, Alaska area were normally about half that size. This specimen shows the characteristic spiral sculpturing well.

At the time I was studying a couple of species of some relatively large whelks found in this habitat.  These predatory snails, Neptunea lyrata, and N. pribiloffensis, were typically found off shore in much deeper water.  However, my study area, an intertidal hard sandstone bench habitat west of the town of Homer, Alaska, contained a population of each species.  These animals were living in the very low intertidal zone, which given the extreme tidal range of the area was, in a very real sense, the extreme high end of the subtidal zone.  This habitat was on the northern shore of Kachemak Bay, which, in turn, was part of Cook Inlet.  Cook Inlet areas, including Kachemak Bay, have an absolutely enormous tidal exchanges.  In fact, the largest known tidal range near Homer, where my research was done, is about 28.3 feet, about 8.6m.

Homer, Alaska

This image shows the locality of my Homer, Alaska study site. The yellow arrow in the main image indicatess the town of Homer, the pink arrow indicates my study site. The inset shows Cook Inlet and the arrow there indicates Homer. Images modified from Google Earth.

Time and Tide Wait For…

In the area where I was working, ranged from a low of -6 feet to a high of + 23 feet above the mean lower low water, the U. S. tidal datum for the reckoning of sea level or a tidal height of 0.0 feet.  This was more than twice what the tidal range is in Puget Sound, and 5 to 10 times what it was in some of the coral areas I subsequently did diving on.  My study animals were found in an area near the bottom of the tidal range, and as such were exposed only a few hours during those months that had the more extreme tidal ranges.

An Example of the tidal fluctuation at Homer, Alaska.

This is an example of the typcal tidal sequences and ranges for Homer, Alaska near the time of an equinox. A full week’s tides are shown, and the progession of depths and times is apparent. The “0” tidal height, aka “sea level” is indicated by the red line. The pink areas in the cusps of the tidal graphs are the times when my study sites would have been exposed. However, given the relative length of exposure, plus the relative amount of daylight, the only tides that would have workable are indicated with a star.  This type of seqence would repeat every two weeks with the extreme lows and highs becoming more pronounced as the solstice was approached.

My study area had a tidal elevation from -6 feet to about -2 feet below tidal datum.  Only the most extreme of the lowest tides in the area were the ones where I could get to the habitats where I could reasonably expect to find my study animals.  Consequently, these were the tides for which I had to be out on the site for my research.  These extreme low tides only occurred on a couple of days during most months, although they were more frequent on the tidal sequences around the solstices. The extreme low tides were immediately followed by the lower of the two daily high tides, that could put the sea level at be more than 25 feet above them, doing research meant that keeping track of the tidal height was a real imperative.

Bluff Point Study Area, Homer, Alaska.

This image was taken on the study area near Homer, looking shoreward to the cliffs behind the beach. This beach is a hard sand stone beach.

Each research site visit involved using among other things a good eye on the clock, a copy of the predicted tides, and, especially, the water level.  Tidal height predictions are only guestimates, and atmospheric conditions, particularly barometric pressure may really alter what happens in the real world.  When the tide turned and started to flood, the water would take about 6 hours to rise the 24 feet to the highest high tide; or phrased another way, the tide would be coming in at the rate of 4 feet or 48 inches vertically per hour or about 4/5 inch per minute.  If I had my hands in the bottom of a tide pool, I could literally feel the water creep up my arm.

Just to make life more interesting, I guess, on the way to my study site, I had to climb down about a 60ft cliff and then walk about 2 miles up the beach to my study site.  Along the way, I had to wade through a tidal channel about 2 feet deeper than the surrounding beach.  That channel was about half the distance from my site to the beach access.  The beach that I worked at was bordered at the shore, at about the 0 foot tidal height, by the continuation of the cliff I had to climb down for beach access.  Here the cliff was about 100 feet high and there was no way up it.  This meant when the tide was fully in, the water level was about 25 feet vertically up the cliff from the level of the study site.  Getting stuck on the beach would have meant a long immersion in cold water, which at this locality meant… really bad news.  Consequently, when the tide turned, there was no time to spare; my assistants and I had to get hoofing up the beach and across the low spot before the incoming tide filled the channel deep enough to overtop our boots or higher.  One REALLY didn’t want to get wet in this water; remember this is Alaska, either the water is cold, or the air is cold, or both are cold, and hypothermia kills.  Additionally, at the time, there was nobody living in the area where they could see this beach.  It was a wild area.

First Observations

I had been working in the area for a few months when I noticed the Neptunea pribiloffensis female were spawning.  As a general rule, whelk egg capsules are constructed out of a tough leather-like cover encasing a small bit of a clear proteinaceous liquid called albumin (probably not the same as albumin in chicken egg) containing anywhere from a few to several thousand eggs.  These egg capsules are attached to the substrate.  Typically, over the developmental time of these animals, only one or a few of these eggs in each capsule actually develops into a juvenile.  During the development process, which normally takes a month or two, the few viable eggs in the capsule consume the non-developing eggs, which are commonly referred to as “nurse eggs”.  Eventually, the juvenile snails have developed sufficiently to make in on their own, and they cut a hole in the egg capsule and creep away.  Thus the mother’s reproductive investment is quite high.  There are the eggs which are metabolically expensive, the albumin (also expensive) and the tremendous protein investment of the proteins of the egg capsules.  Additionally, the females will have often been observed to spend some time in the vicinity of their spawn protecting the capsules from the few predators, such as fish or sea urchins that are capable of eating them. During this entire period the female may not feed.

Female Neptunea pribiloffensis whelk depositing her egg capsule mass at the Homer, Alaska study area.

A female Pribiloff whelk is depositing her egg capsule mass at my Homer, Alaska study site.  Notice the large sea anemone at the bottom left.

Neptunea pribiloffensis egg capsule masses are large and durable, and made of hundreds of rugged leather-like proteinaceous egg capsules secreted together in a characteristic “corncob-like” shape.  It didn’t take much in the way of observational skills to notice that the egg capsule masses were generally deposited within about 1 foot of some large sea anemones.  The obvious question… If you were a hot snail mama, was there some benefit to laying your eggs next to a sea anemone?  And, if so, what was it?

To be continued… 

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About the author

Ronald L. Shimek, PhD
Ronald L. Shimek, PhD

I am a marine biologist/invertebrate zoologist who got captivated by - or sucked into - the reef aquarium hobby late in the last millennium, I have written widely in the hobby press and elsewhere, mostly about invertebrates (in the context of the hobby, anything but fishes) and how to keep them alive. I reside in Wilsall, Montana, about as far from the ocean as one can get and still live in the contiguous 48 states, go figure... What can I say, it is home. :-)

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