Gigantism in Marine Animals

[Orleander]

Is there more oxygen in cold water? Why? Is this why all those things they found down by NZ were so big?

Do I need to worry about this is warm water? Does it ever leave the water and crawl on shore?:booo:

 

[spidergoat]

Slow metabolisms let them live longer, and so grow bigger.

 

[Orleander]

Do they have fewer predators? Is that why King Crabs live there and get so big?

 

[spidergoat]

I would imagine they are less likely to get killed by a predator the larger they are. Mostly, they just age more slowly, and so they can get in more moltings.

 

[weiguxp]

the sea is huge.. lots of places to hide

 

[Roman]

Cold water does indeed contain more dissolved oxygen. Water doesn't, however, contain more oxygen than air.

Couldn't tell you why, though.

 

[Search & Destroy]

takes less energy to move

 

[draqon]

I want to float in ocean just like them, grown big and beautiful, I want to grow tentacles and glow in the dark and forget this human life, just float and drift into the depths of the ocean

nah...I want to be the ocean...



or...maybe I will settle for being the sky

 

[Asguard]

as roman said cold water carries more desolved O2 than warm water, thats one of the reasons a skimmer is required in a marine tank to bump up the O2

Of course its ALSO true that DEEP water containes LESS O2 than water close to the surface.

Its also true that its easier to move under water, which is why wales are such good preditors because they have a land species resptory system

 

[Orleander]

so is it the cold or the deep water that makes them large?

 

[synthesizer-patel]

so is it the cold or the deep water that makes them large?

In the case of this pycnogonid it's the cold - or more accurately the higher O2 concetrations that are a result of colder water.
Like many arthropods it does not have a respiratory system - O2 enters the blood from the environment simply through diffusion - as this is a relatively slow process compared to animals which have an active respiratory system (gills / lungs), natural selection will select for smaller animals. In areas where O2 concentrations of seawater this selective pressure is relaxed somewhat - allowing them to grow bigger.

You can occasionally find these around the shores of Wales where I live - but they are tiny - however I spent last summer in Alaska working on identifying marine animals trawled up from around the Berring sea and there were some real monster invertibrates - including pycnogonids as big as your hand

Gigantism can also be a common feature of some deep water invertibrates too - however the reasons for this are different and varied - if you are interested I can give you some examples but there are quite a few

 

[Fraggle Rocker]

Its also true that its easier to move under water, which is why whales are such good predators because they have a land species respiratory system

It's hard to call whales "predators" since they have no teeth and just trawl through the water sucking up krill by the ton. "Grazers" would be more accurate.

The other branch of the cetaceans, the dolphins, are true predators. Before anybody says, "Wait, what about the sperm whale," well technically it would be more accurate to group that with the dolphins since it is more closely related to them and it has teeth instead of baleen. (And hopefully everyone knows that the "killer whale" is a misnomer: the orca is just a big dolphin.)

In addition to the advantage of being an air-breather in an aquatic environment, competing with the less efficient gill-breathers, cetaceans also have the advantage of being endothermic (warm-blooded) like all mammals and birds. This more energetic metabolism allows them to use that extra oxygen to support a more complex anatomy, including a bigger brain.

 

[synthesizer-patel]

It's hard to call whales "predators" since they have no teeth and just trawl through the water sucking up krill by the ton. "Grazers" would be more accurate.

I wouldn't be so quick to judge - the co-operative hunting behaviour of Humpbacks ( a baleen whale) when they "bubble-net" herring is extremely complex.

even "lower" large plankton "grazers" like basking sharks use (probably - the research is still unpublished) a complex array of behaviours and sensory systems to detect rich patches of zooplankton

Grazing is all well and good but krill and phytoplankton density is very patchy - even in Antarctica where it is anectodally very abundant - these animals still need a very effective feeding strategy to deal with this patchiness

 

[Asguard]

your right FR i would have been better talking about the occors and dolphins

 

[Orleander]

...You can occasionally find these around the shores of Wales where I live - but they are tiny - however I spent last summer in Alaska working on identifying marine animals trawled up from around the Berring sea and there were some real monster invertibrates - including pycnogonids as big as your hand ...

Holy Crap! They do come on shore? When you say tiny, do you mean tick size or tarantula size?

 

[synthesizer-patel]

Holy Crap! They do come on shore? When you say tiny, do you mean tick size or tarantula size?

like many invertibrates, the diversity of species increases from pole to equator, and size decreases from equator to pole (NB this is a generalisation) - so while we have quite a few species of pycnogonid here in wales and in other temperate countries, I've never seen one bigger than about 20mm across over here.

As far as I know they are exclusively marine (the common name for the class pycnogonida is sea-spiders which is a big clue here think) - so whille a sharp-eyed person might find one under a rock or in a rockpool at low tide, you wont find one in crawling into your burger bun at a beach barbecue - and they pose no threat to us at all apart from the "eeeeek!" value

 

[Orleander]

if cold water saturated with oxygen makes animals big, why are there so many big ones in Asian rivers? That water doesn't look too clean, its in the tropics, and rivers aren't near as large as the ocean.