The
very popular shells you may look for on the beach, known as sand dollars, are
actually the shells of living creatures. That’s right, sand dollars are not
just pretty shells for tourists to shell hunt for but they are living
invertebrates. When sand dollars are alive they are actually very colorful
creatures whose color can range from gray to dark purple. Sand dollars are very
abundant suspension feeders of the ocean floor and are evolutionary equipped to
be very efficient at it. First, sand dollars have tiny spine like pincers to
capture plankton floating by called pedicellariae. The now captured food in the
pedicellariae needs to be transported to the mouth or madreporite. To
accomplish this task sand dollars have cilia along their spines, not to be
confused with a vertebrate spine, which lead right to the madreporite. These cilia,
which are like tiny moving hairs, direct the food along the food grooves on the
oral side of the organism to the madreporite where food can be digested. Sand
dollars even position themselves to increase their ability of filter feeding.
When sand dollars are in calm waters they “standup” by burying a portion of
their shell under the sand and allowing the unburied portion to stand up right.
If the currents are too high the sand dollar will lay flat or even bury itself
to reduce the risk of being taken away by the current. Smaller sand dollars
will even ingest sand to act as a weight belt for further stability in rougher
waters. Sand dollars are capable of movement from tiny tube like feet that
protrude from the ambulacra, the radial areas on the oral side of the shell. So
sand dollars are living organisms but whats their importance to their
ecosystem? Well, sand dollars are very dense in population on the sea bed, even
though they lack species diversity. Sense they are so dense in population they
are high contributors in the predation of tiny planktons and crustaceans which
some feed on the algae on the sea bed. In short, they keep the populations of
these tiny organisms in check. Even more important though is that they are a
very large food source for fish and crabs. Fish and crabs are able to crush the
shell of the sand dollars and eat the actual organism. Sand dollars are much
easier prey than their close relative the sea urchin which are equipped with
sharp protruding spikey spines to defend itself, so naturally sand dollars are
a better choice. So it’s important to know that the shells we so happily
collect were ecologically valuable organisms when they were alive, but that doesn’t
mean you shouldn’t collect the shell for a keepsake!
Sunday, October 26, 2014
(Follybeach.com)
Sunday, October 19, 2014
Sea Star Wasting Syndrome: The Mystery Killer
The balance of the Pacific and Atlantic Oceans
ecosystems along the coast might soon be tilted in an unknown direction due to
a new threat, which is killing off thousands of its starfish, known as Sea Star
Wasting Syndrome. Sea Star Wasting Syndrome is the new marine disease so
devastating it has an estimated mortality rate on infected starfish of
ninety-five percent and it already affects over twenty species on the U.S. coasts.
This horrific disease causes starfish to lose entire limbs in a matter of days
leading to their inevitable death. The symptoms are well known by marine
biologists, but the actual pathogen causing the disease is not. High mortality
rates of sea stars are significant to the entire ecosystem of the species since
they are a keystone predator of many crustaceans and Mollusca. First let us
look at the symptoms of Sea Star Wasting Syndrome to grasp an understanding of
its severity.
Courtesy USCS Long Marine Lab
Marine
biologists, studying sea stars with the disease, describe the main symptom of
the syndrome to be, sea stars tearing themselves apart which is a good
interpretation of the disease in a nutshell. The disease first causes white
lesions in the ectoderm of the sea star on the body or a single limb, the
initial lesion may then spread to other areas of the organism. The sea stars
tissue begins to deteriorate around these lesions. Finally, the sea star begins
to fall apart around the lesions due to the surrounding deterioration of tissue.
The fragmentation is what leads the sea star to death, but the actual pathogen
causing the disease is still a mystery.Source 1
The first documentation of sea star syndrome was in
the summer of 2013 and the exact pathogen causing the disease has not been
found yet. Scientists have come to the assumption that: recent increase in
temperatures are aiding the pathogens infection rate by putting sea stars under
abnormal stress. This assumption is based off the fact that most of the first
infected species were in the warmest of water, like intertidal zones. Now
scientists have spotted signs of infection in colder waters and swift currents
in areas such as the Washington’s San Juan Island. San Juan Island has only
recently experienced the infection do to the rise in temperatures of its waters
during the summer, the islands are usually cooler than the adjacent continent.
This assumption that warm waters is aiding to the rise of the infection seems
to be fairly correct but, the actual pathogen is still a mystery. Scientists
believe that the pathogen is a bacteria or virus but do not know which, even
though the first documentation was over a year ago. Source 2
Credit: Melissa Miner
Sea Stars are
keystone species to many oceanic ecosystems, meaning it has a tremendous effect
on the ecosystem relative to the size of its population. Keystone species, such
as many sea star species, have a critical role in maintaining balance in their
ecosystem. Sea stars are keystone predator that feed on Mollusca and
crustaceans, and since there are many different types of Mollusca and
crustaceans for sea stars to feed on there was a high abundance in sea stars.
Now that sea stars are becoming less common, some species in California and
Florida are on the verge of extinction, there are many more of these Mollusca
and crustaceans. Scientists are skeptical on just how the ecosystem will
change, but my prediction is that there will be an increase of grazing like
organisms like snails, which are easy prey for sea stars, and subsequently a
decrease in algae. I believe that the overpopulation of these grazers will lead
to a decrease in oxygen levels in the ocean and increase carbon dioxide levels.
What this means exactly I am not very sure, but hopefully a solution can be
found (or a mutation to arise) to reset the balance in the effected ecosystems.
Further Study:
Tuesday, October 14, 2014
The Complexity of the Squid
The
complexity of the Squid.
For a time, humans have
been seen as the pinnacle of evolutionary success, or god ultimate creation.
Scientists now know that this is not the case, humans lack traits that could be
valuable to us and have faulty designs in our anatomy, squids for example have
useful traits that we lack and have a key similar trait that is anatomically
more efficient. No organism is perfect but, as far as invertebrates go, the
squid is as close as they get. The squid is a highly modified Mollusca
cephalopod that has a number of traits that make it very well fit in the
evolutionary sense. The squid has the ability to change colors in seconds to hide
from possible threats and ambush its prey. Squids also have a highly complex
eye for seeking out its prey that is better designed than our own. Squids even
share a very interesting symbiotic relationship with species of bacteria.
Source:
http://www.ryanphotographic.com/images/JPEGS/Squid%20from%20kaikoura%20montage%20copy.jpg
Certain species of squids, and other cephalopods,
have the ability to change their color drastically in a matter of seconds. This
sudden color change is made possible by the possession of cromatophores.
Cromatophores are tiny pigment filled sacs in their skin that contain different
pigments. The chromatophores are connected to muscles that run to the
cephalopods brain and when the brain signals for the turning on of the
chromatophores, these muscles relax and let out the pigment desired. The
chromatophores are limited in the colors they can produce so to reach even
further color change, the cephalopods have a second layer of skin armed with
iridophores. Iridophores are extremely fast acting, neuron controlled, pigments
that reflect certain wavelengths of light to achieve the desired color. The
mechanism in which iridophores work is not completely understood but
researchers understand that they modify the pigment expressed by the
chromotophores. It has also just been accepted in the scientific community that
iridophores do so by moving closer or further apart at a nanoscale level to
achieve the desired color. Of course the full mechanism has not been discovered
and there is much more research on this phenomena to be done. Another
astonishing anatomical feature of the squid is the complexity in the wiring of
its eye.
Certain
species of squids, and other cephalopods, have the ability to change their
color drastically in a matter of seconds. This sudden color change is made
possible by the possession of cromatophores. Cromatophores are tiny pigment
filled sacs in their skin that contain different pigments. The chromatophores
are connected to muscles that run to the cephalopods brain and when the brain
signals for the turning on of the chromatophores, these muscles relax and let
out the pigment desired. The chromatophores are limited in the colors they can
produce so to reach even further color change, the cephalopods have a second
layer of skin armed with iridophores. Iridophores are extremely fast acting,
neuron controlled, pigments that reflect certain wavelengths of light to
achieve the desired color. The mechanism in which iridophores work is not
completely understood but researchers understand that they modify the pigment
expressed by the chromotophores. It has also just been accepted in the
scientific community that iridophores do so by moving closer or further apart
at a nanoscale level to achieve the desired color. Of course the full mechanism
has not been discovered and there is much more research on this phenomena to be
done. Another astonishing anatomical feature of the squid is the complexity in
the wiring of its eye.
Neurally stimulated squid iridophore. (Credit: Wardill,
Gonzalez-Bellido, Crook & Hanlon, Proceedings of the Royal Society B:
Biological Sciences)
The squid has eyes that are anatomically more
sufficient than ours. A humans eye lined with neurons that take in light to
decipher the image given to us. A major problem with the wiring of these
neurons is that they are facing inwards towards our brain. This caused the light
to have to travel through our pupil twice to be processed by out neurons, and
eventually our brain. The squid has a similar intake of light mechanism in its
eye except the neurons a facing the outwards. The change in wiring, although
seemingly small, allows the squids neurons to take in the light instantly and
process the image. The wiring of a humans eye has another major malfunction
that is corrected by software in our brain, this is the presence of blood
vessels in front of our pupil. These blood vessels create blind spots in the
human eye that is filled in by our brain. The squid, on the other hand, has its
blood vessels behind its pupil making these blind spots nonexistent for them. At
this point it is easy to understand that the squid really is a magnificent
invertebrate adapted well by natural selection, but if that wasn’t enough some
squids even have an extremely beneficial symbiotic relationship that makes them
shine, literally!
Eye of
Giant Humboldt Squid Norbert Wu, Corbis Norbert Wu, Corbis
Some squids possess more color changing organs
located under the mantle cavity that are home to a species of luminous
bacteria. These organs are called the crypt and the lens. The crypt is the home
to these tiny luminescent microbes, the vibrio
fischeri, while the lens controls the brightness of the bacteria in the
crypt. The lens is composed of tiny reflecting plates piled together in a sack.
The lens comes in great use for a squid in hiding from potential predators.
Therefore
we should not view humans as the best designed organisms of evolution, squids
are just one example of high complexity that rivals our own. Although not all
traits that squids have would fit our lifestyles as terrestrial mammals, their
complexity should not be ignored. These
intelligent cephalopods are adapted well to predatory lifestyle with their own
unique modifications like their complex and well wired eye, designed better
than our own! They are also equipped with defense mechanisms such as color
change and some squids even have acquired a mutualistic symbiotic relationship
with bacteria. Squids are amazing feats of evolution and although much has been
discovered about them, there is still much more to learn.
Further studies on squids:
http://www.earthlife.net/inverts/mollusca.html
References:
Wei, S.L., and R.E. Young. 1989. Development of
symbiotic bacterial bioluminescence in a nearshore cephalopod, Euprymna
scolopes. Marine Biology 103:541-546.
Staaf, Danna. Quest. Aug 28, 2012. Squid Skin:Why
Pigment (but Not Glitter) Will Dance to the Beat. http://science.kqed.org/quest/2012/08/28/squid-skin-why-pigment-but-not-glitter-will-dance-to-the-beat/
Holt AL, Sweeney AM, Johnsen S, & Morse DE
(2011). A highly distributed Bragg stack with unique geometry
provides effective camouflage for Loliginid squid eyes. Journal of
the Royal Society, 8(63):1386-99
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