Archive for March, 2013

A Star of The Cowlitz Cacophony

Monday, March 25th, 2013

The First Star Of The Cowlitz Cacophony…

 Luidia foliolata

 The winter in the Cowlitz Bay subtidal habitats is a time when nothing much appears to be happening, at least down to around a depth of 18m (60 ft) or so.   If large is bigger than a golf ball, then a lot of such large critters are visible; however, most of them, such as Pachycerianthus fimbriatus, the large cerianthid tube anemone, and the weathervane scallop, Patinopecten caurinus, while quite attractive and morphologically interesting, are sessile, and observing their behavioral array takes special skills or goals. 

A Weathervane scallop, Patinopecten caurinus, .  photographed in the ealry winter.

A Weathervane scallop, Patinopecten caurinus. photographed in the ealry winter.

 While both species do play noteworthy roles in the natural history drama of Cowlitz Bay, their version of a one dive’s act needs some serious augmentation to keep someone’s interest.  Individuals of neither species do much – at least overtly.  The anemone can … wait for it … retract down into its tube; … rapidly.  Wow!!  Golly gee, be still, my beating heart!  Woo… Woo… Impressive!!

Tube anemones or cerianthids are commonly found in Cowlitz Bay.  Here an individual of Pachycerianthus fimbriatus is blowing in the current at about 20 m.  The currents in this bay can common reach about 2km/hr

Tube anemones or cerianthids are commonly found in Cowlitz Bay. Here an individual of Pachycerianthus fimbriatus is blowing in the current at about 20 m. The currents in this bay can common reach about 2km/hr.  This individual was on the top of the relatively steep slope leading to much deeper water. 

These are the "mucus" and "ptychocysts" which are specialized nematocysts tubes which may extend into the sediment for a meter or more.  The animal can retract rapidly into them..

These tubes comprised of  “mucus” and “ptychocysts”, specialized nematocysts, may extend into the sediment for a meter or more. The animal can retract rapidly into them when startled.

And the scallop… well, now.  It may close its shells, an event truly worth a negative number on the excitement scale.  However, if one has been blessed by the fates, a scallop may actually swim (!) by rapidly clapping its valves together a few times.  This actually IS exciting.  Of course, probably the main reason for any excitement is that the behavior happens so rarely and it is compared to all of the other apparently non-interesting things happening in the vacinity.  Normally, Patinopecten scallops are the epitome of dull.  An individual spends its life in its little mud depression filtering water to obtain the phytoplankton it eats.  Of course, a fair-sized clam such as fully-grown weathervane scallop contains a large mass of delicious muscles along with other nutritious innards.  Consequently, the scallop is desirable prey item for any number of predators, including sea stars.  Presumably as a result, natural selection has given the scallop its rather spectacular swimming escape response.  If its mantle edge is contacted by a single tube foot from a sunflower sea star (Pycnopodia helianthoides), the scallop will usually start to clap its valves together rapidly and repeatedly, forcefully blowing water from between the closing valves forcing the clam up into the overlying water where it is blown away by the current.  In a way, calling this “swimming” is overstating the activity, it has no direction and a very limited extent.  However, currents in the area are often relatively strong, and the behavior can work to move the scallop away from the star.  And that is truly worth the show.  And then, after the scallop is done, it can be collected and become dinner for an altogether more lethal predator. 

 Normally, though, to see some interesting action in this habitat in the winter – and actually, through the rest of the year, as well – it is necessary to look for other predators at work.  Fortunately, the array of active predators on the surface, in the sediments and in the waters above the soft-sediment areas of Cowlitz Bay is rich, diverse, and impressive resulting in a lot of opportunities to see “ecology in action”.  The variety of predators ranges from diving ducks to dogfish and various other fishes from sculpins to flatfishes to sepiolid squids, nudibranchs, moon snails, and crabs.  However, perhaps the most commonly seen, abundant, and continuously active predators in the region are sea stars. 

 The most commonly seen stars are Pycnopodia helianthoides, the sunflower star, and Luidia foliolata, the snakeskin star, both of which may attain large sizes.  Sunflower star individuals have reportedly been measured at 1.5 m (5 feet) in diameter, while I have measured the average size in some Vancouver Island populations to be about 81 cm (32 inches) in diameter.   While Luidia foliolata individuals don’t commonly exceed 1 m (39 inches), they are often around 80 cm (31.5 inches) in diameter.  Pycnopodia helianthoides has been the object of a lot research, undoubtedly because of their large size and ubiquitous nature.  They are probably the most frequently encountered, relatively large, subtidal sea star in the region, and given the demonstrated importance of asteroids in ecologically controlling marine communities, they justifiably have attracted a lot of interest.  Luidia foliolata, hasn’t been investigated anywhere nearly as much, and as I spent more than a bit of time watching Cowlitz Bay’s L. foliolata, I thought this post would be a good place to introduce them.

 The Mouth That Roared, Wetly

 Asteroids are one of the most common educational poster children for invertebrates.  Back in those ancient days when I was in high school, some time in a biology class was spent dissecting and examining a poor, rather pathetic, pickled Asterias individual shipped in from the New England coast to Montana where it spent the last of its cohesive existence boring some kids who had never seen a body of water much larger than a small farm pond and who didn’t really care for any animals without fur, fins or feathers.  For those few of us who had a bit more on the ball (or so we thought), the asteroid’s pentaradiality along with its implied strangeness was really a pretty good introduction to invertebrate weirdness. 

 To even the most literate of us, a sea star was a pretty exotic critter; most of us had never seen a living one.  Had the specimen been remotely like a living animal, it really would have been a neat thing to examine, I think.  Unfortunately, the specimens reeked of formalin, and had a semi-slushy consistency resulting from much of the ossicular skeleton having dissolved in the acidic formaldehyde solution in which they had been stored.  Finally, to top everything else off, their normal purplish color had turned to a gawd-awful pale diarrhea brown.  Although the dissection wasn’t too hard, determining one tan glob from another was uninspiring to say the least.  Still… the effort was made to show us sea stars, and point out some pertinent typical features of their anatomy and biology, such as their complete gut, part of which, the so-called “cardiac stomach” could be extended into the clams that they ate, and the suckered tube feet which used suction to hang on to anything.  

 Long years later, I was trying to teach many of the same things to my students.  Fortunately, we were using specimens more freshly murdered “for the cause”, which weren’t a pasty mess.  I hoped the students were able to more carefully examine and “understand” what they were seeing in their specimens than I had been in mine so many years before.  Remembering my travails, I tried a number of different ways to make the important points.  One of these was that they got to examine other sea stars, to become aware of a bit of the diversity in this awesome group.  I always tried to have a live Luidia foliolata available in this exercise, as this was the first of a number of examples I used in my survey course to show the students that the “typical” animals they were learning about were, perhaps, not that “typical” after all.

Luidia foliolata

This specimen of the snakeskin sea star, Luidia foliolata was about 50 cm across the arms.

This close-up image, of the Luidia shown above, shows a patch of green (arrow) due to the presence of a species of endoparasitic green alga.  These infections are certainly lethal in some stars, but the outcome of such an infection is unknown in this species.

This close-up image, of the Luidia shown above, shows a patch of green (arrow) due to the presence of a species of endoparasitic green alga. These infections are certainly lethal in some stars, but the outcome of such an infection is unknown in this species.

To a careful observer, even one unfamiliar with sea stars, Luidia specimens are a bit weird.  When first observed, there is just something about them that seems “odd”; perhaps it is the spines on edges of the rays, or the odd “scale-like” pattern of plates on the top of the arms, or the non-descript brownish-grey color of the aboral surface, but they leave the impression that they are somehow “different”.   And, of course, they are (otherwise the “wily” instructor, aka “the old fart”, would not have put it out for them to examine). 

 Close examination shows that these animals lack the “suckers” or, more correctly, the “adhesive pads”, on their tube feet.  Nonetheless, they are still able to stick to surfaces and hang on to prey.  As is now known, sea stars attach themselves to substrata by a duo-gland adhesive system, not suction.  Duo-gland adhesive systems were first discovered using Luidia, in part because the stars were seen crawling up the sides of aquaria by some students who flashed on the fact that this is a star that lacks “suckers” on its tube feet, and it shouldn’t be able to climb up a vertical aquarium wall.  And if that weren’t odd enough, Luidia do not have a complete gut and do not (actually, cannot) extend their stomach into any clams that they eat.  In Cowlitz bay their primary prey are sea cucumbers, although small clams are also on the menu.  And all of the prey items are ingested.

A Luidia individual burying as it is feeding.  This image was taken in Cowlitz Bay in mid May.

A Luidia individual about 60 cm in diameter is  burying as it is feeding. This image was taken in Cowlitz Bay in mid May.

 Individuals of Luidia foliolata move over the substrate in Cowlitz Bay at a fairly good pace.  Although a big one can move along at about a meter per minute when it is, for some reason, in a hurry, normally their pace is more leisurely.   When they decide to feed, they stop, and start to burrow into the substrate.  The tube feet move sediments from beneath the arms and central disk out to beside the animal and the whole critter just slowly descends into the substrate, taking a day or so to disappear completely.  This activity leaves a large Luidia-sized star-shaped pattern on the sediment surface.   Presumably, as it descends, any potential prey items, such as individuals of sea cucumbers in the genus Pentamera, or small bivalves such as Macoma carlottensis are transported to the mouth and ingested.  I suspect they stop descending into the sediments when the tube feet have not encountered sufficient numbers of appropriate sea cucumbers for a while.  They spend some time, probably no more than a couple of days below the surface, feeding and digesting their meal.  When they are done, they rise up, emerge from the sand, regurgitate the indigestible remains of their meal, and mosey off looking for another place to feed.

 

This is depression left after the departure of a Luidia foliolata that had been feeding.  Some of the regurgitated indigestible remains of its meal are in the center area, the remainder were probably scavenged by some other animal such a large hermit crab.

This is depression left after the departure of a Luidia foliolata that had been feeding.  Some of the regurgitated indigestible remains of its meal are in the center area, the remainder were probably scavenged by some other animal such a large hermit crab.

 In Cowlitz Bay, the aboral surface of Luidia foliolata individuals is sometimes covered with a layer of the large caprellid amphipods, Caprella gracilior.  More than several hundred may be found on the back of a large star.  When the star buries in the sediment, these amphipods will be seen filling the star‑shaped pattern with a layer of pink skeleton shrimp.  The amphipods remain in place and when the asteroid rises from the sediments, they climb on their host and continue their ride.  What these are doing on the back of the asteroid is unclear.  This relationship has not been commonly reported, and I have never seen it elsewhere, although it was fairly commonly seen on my dives in Cowlitz Bay.  It was just one more thing about this place that made it a worthwhile place to work.

 

Caprella gracilior on Luidia foliolata.

Caprella gracilior on Luidia foliolata.

Caprellids waiting on the sediment for their submerged sea star to emerge.

Caprellids waiting on the sediment for their submerged sea star to emerge.

 

A mass of Caprella gracilior on the substrate over a buried Luidia foliolata.

A mass of Caprella gracilior on the substrate over a buried Luidia foliolata.

 The tale of Cowlitz Bay will continue in the future…

 Until later,

 Cheers,  Ron  

,

4 March, 2013 – “Pop”, Went The Asteroid!

Monday, March 4th, 2013

It probably says something pretty deep about my warped mind, but I find myself fascinated by the phenomena known as mass-extinctions.  Mass extinctions are killing events that have removed significant numbers of species from the tally of the Earth’s life.  Probably one of the major reasons I am interested in these awful processes, is that we are in the midst of one, and unlike almost all others, humanity is the cause of this one.  And the truly horrible thing about that is, that we know it is occurring, and that our species in aggregate shows its immaturity by actively refusing to do anything about it.  Ah, well, at my age, my own personal extinction is not all that far off, and there is little I can do about most larger issues anyway, so…

 Mass extinctions are a fact of life on Earth, but strangely enough they have only intensively been studied within the last 25 to 30 years. Back in the bad old days when I was in grad school, the greatest extinction event ever, the end-Permian extinction event, was not even recognized by many paleontologists, let alone neontologists, and although some mass extinctions were known because the faunal changes that resulted from them were used to determine geological time periods, nobody studied those mass extinctions themselves.  This all changed in the amazing kerfluffle of research following the Alvarez et al., 1980, paper proposing that the Cretaceous-Tertiary, or End-Cretaceous,  mass extinction exposition, wherein the (larger) dinosaurs perished, was caused by an asteroid impact. 

 The explosion of fuss and feathers this paper caused, I think, had to be lived through to be believed. Helen of Troy, the legendary face that launched a thousand ships, and the Alvarez et al. 1980 article launched at least a thousand research projects, and maybe ten times that many follow-up articles.  The upshot, of course, is we now know Alvarez, et al. were right; an impact with a large asteroid certainly hastened the large dinosaurs out the door, if it didn’t kill them all by itself.  And the discovery of the smoking gun, er… watery crater, the Chicxulub crater off the northern Yucatan Peninsula, lead to an awareness that the Earth was in a perpetual celestial game of dodge ball, and even though most of the really big rocks appear to have hit the planet long ago, every now and then… 

Bang…

 And, of course, that means the Earth WILL get hit again, and actually it is getting hit all the time, except the bombards are small much smaller.

 All of this has resonated with me, because I have been a fan of meteors – as small asteroids that burn up in the atmosphere are called – ever since I used to lay out our backyard at night as a kid and see the occasional “shooting star.”  I entertained the hope that one day I would be in the right (?) point at the right time, and see a really big meteor.  I have remained hopeful of that eventuality, but am more mindful now that I might not want to be too close.

 About two weeks ago, what has been estimated to be the largest object to hit the earth since the Tunguska object of 1908, arced over Russia, exploding more-or-less over Chelyabinsk, Russia, spraying small fragments that impacted on the ground west of the city.  From the sequence of things that happened during the event, the object has been since estimated to have been a small asteroid weighing about 10,000 tons and about 15m to 20m in diameter, travelling at about 18 km/sec (40,000 mph). 

 Apparently research that also ultimately resulted from Alvarez et al., 1980, showed that most stony asteroids of that size tend break up and explode rather than hit the earth.  And explode this one did, at an altitude of 15 to 20 km (9 to 16 miles) with an explosion that was considerably brighter than the sun.  Equipment in place to detect atmospheric nuclear tests nicely detected this explosion, and its size was estimated to be in the range of a blast by a thermonuclear device with a yield of about 500 kilotons, the size of a decent ICBM warhead.  Even though the explosion was at a high altitude, over 1000 people were injured and there was extensive damage due to shock waves.

Some closing thoughts, I don’t know if the rock could have held together to explode with that force nearer the ground, but if it did, the damage could have been much greater. Several people have discussed what might have happened if the position of the earth or the rock were varied by a minute or less in the relative orbits – it could have entered the atmosphere at a much steeper angle and perhaps over a larger city or populated area.  Or perhaps the best/worst thought:  Chelyabinsk was a city where a lot of weapons research was done during the cold war.  What would have been the outcome of this rock hitting near there in, say, 1978?

 I grew up in Great Falls, Montana, home of Malmstrom Air Force Base, around which in 1962 the first 150 Minuteman Ballistic Missiles were emplaced in “silos”.  Judging from the palpable tension at times in that community during “Duck and Cover” days, if an asteroid had appeared out of nowhere on a low ballistic trajectory (as this one was described by the Russian military) and exploded 10 miles above that city, I suspect there would have been trails of launching missiles visible from those missile silos for a 100 miles around the town.  I dare say, the same outcome would have occurred on the Soviet side.  The ultimate result could have been rather severely unpleasant. 

Some closing thoughts; rocks of this size are now estimated to hit the Earth every century or so, an estimate that dovetails nicely if one considers the last known impact was the Tunguska in 1908.  However, at least though most of the 20th century, large areas of the Earth, such as much of the Indo-Pacific and Antarctica, could have experienced such a meteor impact and nobody would have been the wiser. Additionally, for example there was the Grand Teton fireball of 1972, which was essentially the same size as this latest impact, but which simply grazed the atmosphere.  So.,.  Such impacts could be more frequently enjoyed events.  In any event, the regularity of such events is a statistical phenomenon, and the next one could happen tomorrow or 531 years from now.

Another Blog

I now have another blog, on the Reef2Rainforest site.  There may be some overlap between that site and this one from time to time, but if so, the material will appear on that site first.

 Reference.

Alvarez, L. W., W. Alvarez, F. Asaro, H. V. Michel. 1980. Extraterrestrial Cause for the Cretaceous-Tertiary Extinction. Science. 208. 1095-1108.

Until Later…

Cheers!!