Importance of daily fluctuations in the crabitat

[JediMasterThrash]

(Initial disclaimer, that these are advanced crab-care techniques for those with the will and the budget. Smaller crab setups, like 10g tanks, may have the most difficulty achieving these goals. For smaller tanks and thrifty crabbers, maintaining steady levels is relatively easier, and won't in any way jeopordize the health of your crabs. But you will need more regular cleanings. The fluctuations described here will help maintain the longevity of your crabarium.).



I did some research a while back on just that, and based my current crabitat on it.

The gulf cost regions (PP, and presumably similar E climatalogy) is:

Summer daily variance:
Humidity: 60-90% (predominantly 65-85%)
Temperature: 70-100oF

Winter daily variance:
Humidity: 60-90% (predominantly 65-85%)
Temperature: 60-80oF

First thing to note: High daily fluctuation, which indicates that constant temperature and humidity is unnatural. In fact, steady states allow for hamrful bacteria to develop unabated. Fluctuations keep things better in check.

Second thing to note: Humidity is not directly perceived by hermit crabs. Rather, relative humidity is a measure of how close to saturation the water vapor content of the air is. The lower the number, the more water can evaporate and the quicker it will evaporate. As hermit crabs need to keep their gills moist, low relative humidity cuases them to dry out faster, which requires that they either stay clamped in their shells to use their shell water to keep their gills moist (less activity), or they bury into moist substrate to create microclimates of higher humidity to keep their gills from drying out (also perceived as less active crabs).

So, higher humidity means the crabs can be more active and out without drying out their gills. In practice, it seems that upper 70's is a sweet spot for most crabs.

However, climate is multivariabled. Crabs are also observed to be more active and healthy in higher temperatures, even in the presense of lower humidity. Through thermoregulation, they will use their shell water to keep cool as necessary. But their shells serve as insulators as well. So if it is too hot, they will appear more active, or to hang out of their shells more, to cool off. The evaporating water from the higher temps and lower humidity serves to cool them off well.

Some species of crabs (straws and Es) appear to enjoy warmer temps as their sweet spot (upper 80's, lower 90's), while other species appear to prefer upper 70's, lower 80's.

Not the same, but related to temp, is light. And hermit crabs are observed to increase activity with UV light, and this is probably a natural result of most animals requiring some UV light for vitamin D synthesis.



So, my conclusion is that a crabarium should provide daily fluctuation in temperature and humidity with averages near 80oF/75%. I double the amount of heat lights during the daytime to acheive this. A crabarium should provide a source of UV light, which if nothing else, kills bacteria and mold. And a crabarium does not necessarily need to have high humidity in all areas of the tank, as long as there is a water supply and damp substrate to provide microclimates. I tend to actually have a lower average relative humidity because of this. And the crabarium should be allowed to have a lower average temperature during winter months, by up to 10oF (but keep the average at least 75oF, but if it drops to lower 70's at night in the winter, it's OK). Providing insulation on the bottom and sides of the substrate (but not UTH) is probably something we should do.




The daily fluctuation should cover the whole tank - we're not talking about gradients, which would be variations among different areas of the tank at the same time.

So if you have a relative humity (RH) gauge in a fixed location, that gauge's reading should go up and down during the course of the day. I have a flukers digital, and it stores a min/max, and I occasionally reset it, and then check it in a couple of days to see what my min/max ranges are (both RH and temp).

And RH is the correct gauge to measure how fast moisture will evaporate. Absolute humidity is probably fairly constant during the day in my tank. It's the change in temperature that drives changes in RH, since warmer air can hold more water vapor. Near the ocean, the sun will evaporate more ocean water, which will drive up AH, but we don't get that effect in our tanks as much, unless you have daytime-only bubblers or misters.

Gradient or micro climate is still important for other reasons, because the crabs need places to go to obtain the conditions they want at that moment. Nature naturally fluctuates; it's crab's natural behavior to move around or bury to compensate.


Also, a note, those daily variances are maximums. It won't go up and down 30oF every single day. Crabs don't live in Minnehsootah, where it's well known to go from 70oF and shorts to 10oF and blizzard in under 24 hours. ^_^

[Guest]

Thanks JMT, so am I correct in thinking the RH is higher at night in the wild?

I'm trying to achieve this right now by using some air pumps I have lying around. Interestingly my 55 is doing very well with some fluxuations, but my 40B is sticking to it's 88, even though I have a more powerful pump in there.

[Kilimanjaro]

Wow, that's a great load of information. I currently have a 20 gallon, could I fluctuate with that? It's a bit smaller, but it is bigger than a ten gallon.

[JediMasterThrash]

Actually I've thought I might be going backwards in my tank, with the higher RH at night (due to lower temperatures). This is because the absolute humidity is constant in my tank, so RH is just inversely proportional to temp.

However, I think that at least near the beach in the wild, the sun radiating on the ocean during the day might increase absolute humidity enough to sometimes raise RH during the day. But it could depend on many factors. So far my crabs haven't been walking upside down, so it seems to be working out all right.

Kilimanjaro, you can do anything you set out to do. The main issue with smaller tanks is:
1. Temp. With a larger tank, I can take over 100w of overhead lighting, so it's easy to set extra 25 or 15watters on timers. However, for a smaller tank, 15 or 25w might be all it can take, so it's hard to find an inbetween for day/night fluctuations. A combination of a low-side-mounded UTH and light may work.
2. Humidity. With a larger tank, there's room for larger bowls, which add humidity when the lights heat them up. With a smaller tank, you may be pressed for space for larger bowls. However, a bubbler or humidifier set on timers may work.

Whatever you choose to try, report back on what you did and your results!

[troppo]

So, you've mentioned for Straws that they prefer warmer temperature ranges, what about humidity?
Can that have a large range of fluctuation as well in the wild?

[Guest]

Thank you for great info! This confirms what I have been thinking intuitively all along: nowhere in nature is climate completely stable. COnditions in my carbitat vary a lot during the course of the day or week, depending on lots of factors - what is the temperature in the house? is the air conditioning on (sucks the humidity right out of the air)? Do I have the windows open? how much is the lid covered? when did I mist last?

While we're on the subject, maybe you could offer your opinion on covered lids. My goal is to achieve optimal climate without covering the top of the tank - I just think stagnant, trapped air is unhealthy and unnatural. My light hoods cover about 70% of the opening, and rest I leave open. Humidity fluctuates, but I'm able to keep it within the acceptable range. My thinking was greatly influenced by a long post I read here or on another site by a guy who goes for all-natural conditions, and doesn't even keep his crabs in an aquarium tank.

Great topic. Other thoughts?

[Guest]

I can't beleive my 40B won't flucturate! Grrrr. Gonna try some extra lighting.

morf2540, I think I'm familiar with this crabber also. I am of the opinion that not everyone could use that method. For example in my house I couldn't, living in the desert there is just no natural humidity, going with no top would be a disaster for me.

[Guest]

Good point! I think the post I referred to was from a person living near the beach in southern california - natural heat and humidity!

[JediMasterThrash]

The humidity fluctuations listed about show that they could daily swing from 60% to 90%.

Humidity will naturally gradient in the tank as well, being higher near damp substrate and water with bubblers/falls, and lower near lights and openings.

I have not yet noticed any particular species variation in humidity requirements, but if you check in the caresheets forum, lots of members have their own opinions on the best ranges for each species.



As for stagnant air, you are absolutely correct, though that's a topic I've dealt with in different posts. Air needs to be circulated. For a small tank, propping the lid enough works, as there isn't much air to diffuse. For larger tanks, more needs to be done. I have two tropicaire humidifiers running on a 55-90g air pump. So I have a constant inflow of humid air, which pushes older air out the openings. Keeping the inflow humid helps prevent the humidity from decreasing from just opening the top more or otherwise blowing in house air.


Other ideas I toyed with before that were creating an inflow and outflow (using computer fans) on two opposite corners of the tank.

Since normal house humidity is around 35-55% in our area, opening the tank up too much isn't a good solution for me.

[troppo]

Lol Jedi. For the last few days, I've taken the lid completely off my 40 Long because the humidity keeps creeping over 85%.
Plus the windows are open and there's a ceiling fan turned on and also the UV light on over the tat to try and reduce the humidity a bit.
It's a pain in the rear trying to keep the humidity down rather than trying to increase it.

[Guest]

I'm not quite there yet.....I can't beleive how stubborn my 40B is, I would have thought the 55 would have taken longer to change the humidity. It worked with the air pump, but it took all day to get it to 80. Not practical for me, because I want to use my light too, which increases the humidity. The air pumps cause a lot of vibrating and it stirs up the crabs, which would be good if those digging to molt didn't resurface to see what is going on.......

I bought a couple of hand held fans and will mess around with those tonight. I though about using computer fans, but I don't want to buy some 30 thingy to power them.

[Kilimanjaro]

So, I understand the benefits now, but what would be the detriments to the hermits health if fluctuation isn't executed?

[Hermit_of_Hermit_Crabs]

I just use a large 5.0 Reptisun bulb during the day and the humidity is about 79 or 80 percent. At night I just leave the 75W moonglo bulb on and the humidity goes up to about 83 or 84 percent by the time I get up at 7 in the morning. The temperature fluctuates a bit as well. It is usually around 81 or 82 degrees during the heat of the day (4 to 5 p.m.) and then it drops to about 75 or 76 at night.

[JediMasterThrash]

I think that ther hermit crabs will grow hardier with regular fluctuations. I think that constant conditions make them too accustomed to it, and it makes it more difficult to deal with changes. If they're used to regular fluctuations, then an hour or day or two in a different condition might not induce stress in them as bad.

If you have a large amount of substrate and don't deep clean or change very often, constant conditions allow bacteria and microbes that thrive in that condition to grow unabated. But if you have regular fluctuations, it keeps things in check, so you don't end up with an unbalanced ecosystem in your substrate.

[Guest]

I can't believe how hard it is to acheive this in my tanks. That 40B is just so stubborn.