Sadly, much of the ecological and marine biology news over the last week has been dominated by the huge oil spill threatening the Gulf of Mexico.
Comprehensive accounts of this event are nicely summarized by my friends over at Deep Sea News here and here.
A great deal of the public media coverage will show you heartbreaking images of turtles, seabirds, and other charismatic vertebrates that will be harmed by this ecological catastrophe.
But the sad truth is that some of the animals which will be hit worst by the oil spill will probably be invertebrates. A general overview of the effect of oil on marine invertebrate communities can be found here.
Echinoderms are exclusively MARINE invertebrates, that is they ONLY live in the ocean (none in freshwater or terrestrial). There are relatively few invertebrate groups that can make that claim.
And as such, they are VERY sensitive to environmental changes. Are they the spiny, marine equivalent of the "canary in a coal mine"?
Echinoderms need reasonably good quality seawater to survive...and so, if they aren't getting that, then its safe to say that things aren't well. There's a physiological basis for that-and I'll get into that in a bit...
So, what kinds of impacts/effects will we see as crude oil spills impact the marine invertebrate communities in the Gulf of Mexico??
1. Marine Larvae will be Badly Affected. So, many if not most marine invertebrates go through a small free-floating, free-living or swimming larval stage that live in the water column.
A good photo essay of this can be seen here.
So, can happen if you saturate the water with crude oil?
A variety of possible effects: 1. Death. The oil adheres and smothers the larvae which prevents respiration, movement, creates excess weight. Not to mention the toxic effects of other chemical additives. I would imagine that there can be fairly severe larval dieoffs.
2. Defects. Some studies on purple sea urchins have shown that even minor petroleum hydrocarbons can lead to "cytogenic or cytologic anomalies". Oil can affect the larval development stage at any number of critical stages
a. It can affect abilities of the larvae to settle (including discovering settlement sites) b. It can affect attachment of that larvae to the bottom or wherever it wants to "live" as an
c. Stunts growth and ability to mature.
d. Inability to defend against/avoid predators.
2. Oil Impacts on the ADULT animals.... So that was larvae. Larvae are tiny (about 1mm if even that!) But starfish are BIG!!
How specifically are adult echinoderms vulnerable to oil spills?
Echinoderms don't do well with toxic substances.... Following a paper by Michel Jangoux (1984) and others.. a massive oil spill can "destroy echinoderm populations", sometimes for years...
Most other animals you might think of....crabs, clams, snails, worms, fish, etc. , they have internal, self-regulating kidneys, livers, and etc. that maintain a certain level of internal body chemistry that is healthy for the animal.
Unlike these other animals, echinoderms have bodies that are functionally open to seawater. Effectively echinoderms have HUGE amounts of surface area because water enters from the tube feet, the madreporite and other places throughout the body. The internal body of echinoderms are essentially in constant contact with their surroundings.
Echinoderms constantly pump essentially SEAWATER in and out of their bodies to fuel their water vascular system (i.e., their tube feet and locomotory apparatus). Millions of tiny hair like structures called CILLIA beat and create a current over the surface of the body that drive gas exchange and carry away toxins.
SO, something like crude oil would physically smother and adhere to the cilia and other body surfaces as well as block respiration (gas exchange) on the body surface.
That's not to mention the other toxic effects which the animal would be unable to remove because the oil would be clogging/blocking/interfering with the natural way the animal regulates the removal of foreign substances.
Chemical adhesion in tube feet would be blocked by oil and rendered ineffective.
This specific dependence on fresh non-toxic seawater has always been part of echinoderms' fundamental biology. They often have great sensitivity of the water around them. Speaking from experience, one doesn't usually see echinoderms where water quality is anything less then optimal.
Some have gone so far as to interpret this intrinsic link to seawater as the reason why echinoderms have never exploited freshwater and terrestrial habitats or other settings where regulating toxic substances is crucial.
Also, this is POSSIBLY why echinoderms are generally absent from natural settings where toxic chemicals are present, such as hydrothermal vents or cold seeps and is likely why crude oil SO adversely affects echinoderm biology.
So, it was pretty clear that oil was going to act as a stressor on these animals..and that's what they saw...the appetite and ability to locate food was affected as well as the stars' ability to right themselves when turned upside down.
But they applied three different oil-based substances including...
- pure crude oil,
- "dispersed oil" (i.e., oil that had been chemically treated to break up)
- and burnt oil (i.e., oil that had been set on fire and allowed to burn out)
Interestingly, the BURNT oil residue created the weakest impact. Their conclusions go on to support that the strategy of burning oil might be the best insofar as the effect of that residue on Coscinasterias (and by extension-other starfish or echinoderms) following the burn....
But bear in mind, this experiment was performed in a lab with isolated oil products. An actual burn would involve, you know..FIRE, smoke and other toxic substances that echinoderms aren't likely to handle well..
So..in Conclusion.. things don't look good for the great diversity of echinoderms and/or other marine invertebrates in the Gulf given the increasingly growing oil slick problem.
Echinoderms might be a little more vulnerable and more different then other marine invertebrates...but they are often regarded as the "model animal" for how certain marine invertebrates will fare.....and based on other studies, its probably not unreasonable to predict a massive die-off of not just echinoderms...but other marine invertebrates.