Advantages of needing salt in shrimp development?

TKD · Post by **TKD** » Fri Apr 06, 2007 10:43 pm

Hi everyone,

Why would amanos, wood, vampires and other shrimp types evolve a need for there larval to go to sea for a relatively short time (at most a few months) compared to cherries, greens and other shrimp who don’t?

I could see the advantage for fish were they stay at sea for several years (more food) but not for a few months in the case of shrimp… it seams like a waste of energy and time.

Thanks,

TKD

wijnands · Post by **wijnands** » Sat Apr 07, 2007 2:24 am

Could it be something seasonal?

Guybrush · Post by **Guybrush** » Sat Apr 07, 2007 2:43 am

If their habitat has currents that pull the larvae into the ocean or brackish areas, then I'd guess that they had to adapt to be able to survive the salt (until they're post-larvae and make their way back to freshwater). If their natural habitat isn't near any saltwater, then they would never have needed this adaptation.

Not sure why they wouldn't adapt to living in saltwater at later stages in life. Maybe it's like salmon swimming back to their place of birth to reproduce.

Note: I'm less than an amateur at this stuff, so take it as somewhat logical speculation.

zwergkrebszuechter · Post by **zwergkrebszuechter** » Sat Apr 07, 2007 3:54 am

Actually it is vice versa. Shrimp come from the sea and some managed to adapt to freshwater. First by having larvae that do not need salt and more adapted species by going through their larval stage, still attached to the female.

Invader_Xan · Post by **Invader_Xan** » Sat Apr 07, 2007 5:10 am

It's worth mentioning that a lot of shrimp naturally inhabit brackish streams and swamps and have adapted to live in fresh water.

badflash · Post by **badflash** » Sat Apr 07, 2007 6:58 am

These likely started as salt water animals, like salmon, and the adults evolved to live in fresh water to explore a new niche. You see this with lots of animals, where they have one foot in two worlds and are in a transition. Sea turtles come to land to lay their eggs, salamanders go to the water to lay thie eggs, salmon swim to fresh water to laytheir eggs, etc.

Post by **Mustafa** » Sat Apr 07, 2007 8:49 am

Yes, atyid and palaemonid (and other) shrimp seem to have originally come from saltwater. They are all "caridean" shrimp and most caridean shrimp still live in the oceans (e.g. the "cleaner shrimp" Lysmata spp.).

Anyway, to get back to the original question...it's obvious why having saltwater larvae can actually be very advantageous for a species. Whereas shrimp that don't have such larvae are very limited in their distribution and are in danger of dying out if their habitats (i.e. rivers, lakes etc.) disappear in the future (i'm talking about geological time spans here, not human), shrimp with saltwater larvae have, generally, a much wider distribution and can always colonize new habitats much more easily from the ocean (as larvae develop into postlarvae and migrate up rivers).

From what I could glean from scientific literature, there seem to be some possible advantages to having large eggs with benthic freshwater offspring. For one, if shrimp species inhabit long rivers and happen to live in the upper part of the river, its difficult for saltwater larvae to reach the ocean. The Amazon river in Peru is an extreme example of that, but there are many, many other much shorter rivers that are still "too long" for most saltwater larvae to surivive the trip to the ocean (i.e. they don't get there in time). Second, in certain areas, again at the headwaters of a river or creek, with lots of torrential rainfall (and probably lots of predatory fish in the rivermouth) it's probably advantageous to have benthic offspring, so they can cling to the rocks and not get swept away and probably get eaten by predatory fish. I.e. it's just another survival strategy...not necessarily better or worse than having larvae in my opinion.

Also, it's also possible that old shrimp species with benthic offspring that used to live in habitats further away from the sea (where their mode of reproduction with benthic offspring developed) started living closer to the sea due to geological changes over time (i.e. tectonic plate movement, changes in sea levels etc..).

Lastly, there are currently ocean shrimp species (also caridean shrimp) that have large eggs and that seem to produce either fully benthic offspring or mostly benthic larvae for various reasons (which I won't elaborate on here). It is also possible that some of the freshwater species with large eggs and benthic offspring that we see today developed from such ancestors.

This explanation should cover most bases.

TKD · Post by **TKD** » Sat Apr 07, 2007 9:10 am

Cool.

Thank you everyone.

TKD