View Full Version : Marine Biology,Ecosystems and Invasive species

04-11-2008, 09:46 AM
I am looking to get information that has to do with marine biology, particularly the effect the great white shark has on the marine ecosystem and what would the damage to the system be if an invasive species higher than the shark was introduced, a species that started making sharks extinct.

Or maybe even what kind of an effect an invasiove species would have on land.

This is research i am looking to do for a possible novel and want to try and get as much information as possible on such subjects.


Greg Jeffrey

04-11-2008, 11:27 AM
hi Greg,
You may want to send a PM to NeuroFizz if he doesn't see this in the next day or so. He's your man. He will know what you need. He's the smart one. (read: he teaches marine biology at the grad level).
he'll be along hopefully sometime today. If I see him, I'll point him this direction.

04-11-2008, 11:38 AM
The usual problem with invasive species is that nothing can stop them. They have no natural predators, parasites or diseases. They increase in numbers to crazy population levels. Then food restricts them, and the population drops down to a more manageable number.

What happens to everything else varies. In a small ecosystem, like an island or lake, it is very likely that they will drive other species extinct. This happens all the time. Extinction is less likely to happen in large, complex ecosystems (like an ocean). In an ocean environment, it's more likely that things will balance out and the new species will naturalise.

What would happen if you killed off the great whites? There are many possible outcomes. Given that the great white population isn't that dense, and is already reduced from over-fishing, I doubt it would have much impact. You might see a temporary rise in prey fish populations, but this would balance out quickly as other predators make the most of the new fish.

I wouldn't predict great whites going extinct. Reduced populations perhaps, but it won't be the first time they've been lower down on the food chain. Sharks used to be eaten when reptiles ruled the oceans. I'd also expect the new predator to go after sea mammals, as a similar sized meal. So when the shark population falls, the predator moves onto mammals as the more available food... and the shark population rises again.

There isn't a right answer to this. There are other possible outcomes. Maybe sharks do go extinct, with the new predator following close behind because it only eats sharks. Maybe giant squid become the main predator of this new predator, keeping the population in check. Perhaps humans decide the new predator is tasty stuff.

Mac H.
04-11-2008, 11:53 AM
I am looking to get information that has to do with marine biology, particularly the effect the great white shark has on the marine ecosystem and what would the damage to the system be if an invasive species higher than the shark was introduced, a species that started making sharks extinct.That is already happening - at least for some sharks.

There are several factors that can lead to a predator causing something below it going extinct.

These can include:

1. The other predator is eating sharks.
2. The other predator is eating the food that the shark relies on.
3. The other predator is stuffing up other things in the shark's environment.

There is a predator on the planet that is doing all three ... humans.


04-11-2008, 08:27 PM
The immediate effect of removing an apex predator is a rebound in the numbers of the immediate prey of that predator, and a depletion of whatever that former prey eats. Of course, ecosystems are mostly about equilibria, so eventually, a new apex predator (or predators) will fill the niche of the removed one, and a new ecological equilibrium will be established. Or, if there is no replacement, a different equilibrium will be established. Many introduced, invasive species become so because they find conditions suitable for their species propagation, a lack of predators, an abundance of nutrients, or a combinations of these. In these cases, they may not form an equilibrium for years, instead they may keep spreading until they run into limiting conditions. Look up Kudzu as a plant example (very familiar to anyone who lives in the South). In the aquatic environment, look up zebra mussels (they are a problem in freshwater habitats). One chief problem that introduces species to new environments (with the potential for invasive propagation) is the ballast tanks of ships. If they fill the tanks with seawater in one place, then expel them in another, all organismsm that survive the trip are given the gift of immediate dispersal.

Basically, though, if you are going to kill off an apex predator, you should know about that animal's food webs/food chains, and either model or predict (or make up in the case of fiction) the ramifications down through the food web/chain. The world's oceans represent such wonderful buffers to all kinds of perturbations, however, it would have to be a drastic or long-term ocurrence (even slowly developing but persistent--eventually reaching a critical threshold) to produce immediate or lasting alterations that would impact humans. So, if you can couple your predator removal with some other oceanographic threshold event (like seismic events), you'd be able to create a castastrophic result.

And, as a point of interest, the show Surface was filmed in Wilmington (since there is a large film industry here, they call it Hollywood East), and in fact, a couple of the scenes of the show were filmed in my research laboratory. For example, the scene when the little know-it-all kid talks about hagfish (or whatever they were talking about) as a "primitive vertebrate that feeds on carrion," that scene was filmed in my lab. I still have the 3x5 cheat-sheet card the kid used to remember that line posted in my lab, near where they taped it for him to see. A later microscope scene was also filmed in my other lab room. Several other scenes were filmed here at the Center for Marine Science.

04-11-2008, 08:47 PM
Thanks for the replay to my post and questions. SURFACE was one of my favorite shows. The whole idea fascinated me and i wish it had continued on.

So, in theory, you would need a predator that invades and removes other predators and then have the threshold event working together to create the result. That seems to me to be just what SURFACE did and for what i was thinking about writing that kind of rules it out for me. I would have to do some more research and see if there is a different kind of angle i could take on the whole thing. Maybe take the invasive species out of the water perhaps.

04-11-2008, 09:00 PM
You can also have invasion of toxin-producing organisms (like red tide dinoflagellates) that produce massive fish kills. This could occur in freshwater drinking water sources and directly endanger humans. On the other side, you could have a "bloom" of an apex predator such that it has to go looking for alternate prey after the preferred prey is scarce. No beach would be safe to swim. If you had a change in a killer whale's preferred prey, wouldn't you just love to write the initial scene of the eco-freak who is so excited to kayak out in the calm waters where the Orcas frolic, only to have him realize their games are targeting him and his pathetic little boat (keep in kind the doral fin of a male Orca can be six feet tall). Kind of like Shamu in a steroid rage.

04-12-2008, 08:20 AM
Wouldn't even have to go out in a kayak, really. Ever seen the footage of a killer whale off Patagonia, 'body-surfing' onto the beach, grabbing a seal, then shoving himself back into the sea? At least the shark in 'Jaws' stayed in the water.

04-12-2008, 11:35 AM
This marine biology stuff fascinates me i wish i had studied it when i was in school.

This is good stuff i was reading about apex predators and they are interesting. I havew the seed of an idea but i need to try and flesh it out some. If there was a bloom of apex predators and then humans became the target i need to try and create an angle that would make it so that these new predators were engineered by a company. If i can figure out a reason for that and couple it with the creation of red tides i may have something. With red tides there could always be a terrorism angle to it, having them created as an act of terrorism.

I need to do some more work on this and find that angle im looking for.

thanks again