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Great Moonfaced Gasping Limpets

Limpets, an aquatic snail that I think resembles a flattened volcano, stick so hard to their roosts you have to pry them off with a knife. Notice the researchers returned them to their "scars".
It should come as no surprise to real students of animal behavior that Patella vulgata enjoys the same activities as Helcion pectunculus.
FUNCTIONAL HYPOTHESIS: By manipulating their environment, "We expected the rhythm also to undergo a phase shift and all peaks of activity to be shifted forward by 6 hours.
RESULTS: The percentage of limpets that were active every hour throughout 3 days of continuous observation in constant darkness and exposure to air ranged between 0 and 75%.
Do we need to read any further? YES! Statistical analysis!
JUMPING THE GUN, rewritten for clarity: "The (Limpet) majority's ... activity during (nightly) low tide ... with smaller peaks of activity during (daytime) low tides indicates ... both circatidal (related to tides, i.e. moon phases) and circadian (daily) components of endogenous (internally-stimulated) locomotor (drinking and driving) activity." They want us to believe that because (maybe sixty) limpets showed slight peaks in their hourly activity around low tides (especially at night) during a seventy-two hour observation, that they have internal clocks.
How many hours long is a low tide? Since the moon causes tides, and at full moon/new moon the biggest tides occur twice a day, that leaves each part of a low-high-low-high daily tide cycle about six hours long.
They neglect to consider (mentioned only twice and then related to other animals) lunar influence; "Since the spectral peaks occur at 13.8 and 28.1 h, it would appear that one is not simply a harmonic of another (the harmonic of 13.8 h would be 27.6 h)." WHAT? So 13.8 doubled almost EXACTLY equals 28.1 and they don't see that as harmonic, after mistreating their little charges?!!?? A difference of .5, HALF AN HOUR, over twenty four hours repeated three times and they don't see that as a simple harmonic??? As a matter of concern, the moon advances 1/28th of an orbit every day, .86 of an hour, or 52 minutes. Yeah. Those limpets aren't so dumb.
Maybe limpets can sense the gravitational tug of the moon! Certainly the "shifting tides" have selectively filtered out those individuals that tried to climb above the high tide mark for algae. Ain't much algae up there. High tide waves hit harder, too. SOS! Snails lost at sea! They should repeat the experiment MANY TIMES and calculate for tidal (lunar) cycles. (Their observations suggest Limpets prefer darkness, so what happens on a clear, full moon night?) When the moon shows a quarter face (phase) the tides show a strange pattern around the earth, because of the perpendicular gravitational tugs of both sun and moon at that phase, in contrast to the parallel tugs at full (or new) moon, when the earth sits on the line of light from sun to moon. That's why lunar eclipses always happen on a full moon. Ain't no other way for the earth's shadow to get in between.
I would like to see them study the lunar (tidal) influences over a couple of complete months (which are really Quasi-lunar cycles on our calendar), not just 72 hours.
"It is also apparent that in both species the exogenous entrainment factor of the endogenous free-running rhythm is the time of exposure to air" REWORDED: Apparently, exposure to air (exogenously) trains their free-running biological clock (endogenous rhythm).
They did also prove, over and over, that Limpets lay low (stay inactive) when submerged. Maybe they need air when active, to feed, to avoid waves when in motion, etc.
Comedy Bonus: Does this really describe a limpet gasping for air (oxygen?) like a fish out of water? "In Mytilus edulis, kept continuously immersed in sea water in constant conditions in the laboratory, there are spontaneous changes in shell gape, but these changes are not circatidal and appear largely random, with only a very weak circadian component." Poor babies...