Importance of daily fluctuations in the crabitat
Posted: Wed Aug 15, 2007 7:07 pm
(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. ^_^
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. ^_^