College Coursework!

[bex1]

hey as part of my college work we have to do an end of term experiment. me and my partner have decided to look at the 'effects of differing salinity levels on crabs o2 consumption'
we are just going to collect some crabs from around the coast (UK) and put them in small containers full with water, 1 will be pure sea water, 1 will be 95% sea wter and 5% distilled water etc ...............
the crabs are going to be totally submerged in water will they be ok?
any ideas or suggestions on this experiment welcomed.
NO CRABS WILL BE HARMED DURING THIS EXPERIMENT!!! - WE HAVE VERY STRICT TUTORS WHO WILL BE SUPERVISING US AT ALL TIMES.
thanks x x

 

[pleder]

Instead of percentages you will want to look at Specific Gravity

Ocean water does have slight variations in levels of salinity, in diffeent places where rivers meet the ocean, but for the most par the ocean is presumed to be at 1.027. This reading can vary with temperature.

Most hobbist keep there tanks between 1.022 and 1.027 if they are keeping inverts. Experience has shown us tht under 1.022 inverts don't fair well and will most likely die.

Since the normal 1.027 reading can vary with temperature you could use the 36ppt to be more accurate if your inclined.

You will need to provide some sort of aeration, and some type of food, as well as filtration to remove the ammonia. If it is a temporary experiment and your not inclined to use a filter there is a product Amquel_Plus that will chemically remove the ammonia by adding beneficial bacteria.

Depending on the species of crab, it will most likely be fine completely under water.

Good Luck and please report your findings back.

 

[bex1]

hi thanks for the advice!

we are only going to be keeping the crabs for around 24hrs max so i dont think they'll need a filter or food.
we are going to do a bit of a preliminary experiment next week and then will start the proper experiment after Easter.
anymore advice welcome.
thanks x x

 

[pleder]

If it is going to be 24 hours you will need something to agitate the water. A simple air pump machine will be fine. They have models were you can attach two air hoses to the same machine so you could have one for each container.

Otherwise in a 24 hour period the crabs might suffercate.

 

[Opcn]

oceans are useually closer to 1.025 @20 C, maybe higher in tide pools and lagoons due to evaporation.

Something to keep in mind is that you have to aclimate the crabs to the lower levels of salt very slowly, no more than 0.003 a day, also you should acount for the extra O2 desolved in the lower SG water and the reduced absorbtion by the surface of the water. I'm assuming you are useing a respirometer, and know how to do it so I won't go into that, but how do you plan on accounting for the varying sizes of crabs?

Also, the Crabs should not be released back into the ocean, sell them to an aquarium shop maybe, but the stress and chemical exposure from being in a lab could weaken them and they could be exposed to exotic parasites and you could end up doing major harm to a great many critters, better to be safe than destroy the ecosystem just to feel good right.

 

[pleder]

oceans are useually closer to 1.025 @20 C,

Like I said the number will fluctuate with temperature which is why the ppt readings are more accurate, as they are constant regardless of temperature.

 

[Opcn]

Seeing s how its being done in a scientific setting its important to provide a temp with ANY Sg that you produce, if you do its acctually more acurate than PPT (i.e. ppt of which of the 70 minerals and trace elements in salt water)

 

[pleder]

How did the research go?