I'm looking a number of papers on abalone larval development and the term °C.days or °C hrs-1 keeps coming up. The numbers before these terms are much larger than they would be if this term actually meant days or hrs. For an example of a publication, see here.

for example one source said larvae are competent to settle at 100 °C.days, however they most likely settle at around 7-10 days

Just wondering if anyone knows what this °C term means in terms of time

  • 4
    $\begingroup$ Welcome Dr Who Fan. :) Could you find a way to link to a source for this seemingly odd notation, to let us see context in case there's some clue? $\endgroup$ Aug 31, 2022 at 22:22

1 Answer 1


From e.g.

Fukazawa, H., Kawamura, T., Takami, H., & Watanabe, Y. (2007). Oogenesis and relevant changes in egg quality of abalone Haliotis discus hannai during a single spawning season. Aquaculture, 270(1-4), 265-275.

Oogenesis of abalone Haliotis discus hannai was examined histologically during a single spawning season using broodstock of various maturation conditions, which were controlled by effective accumulative temperature (EAT)

Once adult abalone have experienced an appropriate EAT, they can release gametes when they are stimulated by environmental spawning cues, such as storm events (Sasaki and Shepherd, 1995)

The units on their figures are given in units of "temperature x time", such as "°C x days". This would be integrated temperature over time. In units of °C x days, you would say that 1 day at 20°C = 2 days at 10°C = 10 °C days.

In this context, we're talking about a mollusc that has a seasonal reproductive pattern where temperature controls reproduction, but not simply via hitting some key temperature one time (which would likely be unreliable and lead to spawning in the wrong season given the possibility for temperature extremes), rather by integrating temperature over time. Once the threshold is reached, other cues trigger the actual spawning behavior.

I presume "°C hrs-1" would be "°C hrs-1" which can also be written "°C/hrs" or read "degrees celsius per hour"; that would be a rate of change of a temperature, but you'd need to provide context to verify.

The authors of the paper I link to write in their methods:

EAT was calculated using the formula defined by Kikuchi and Uki (1974).

...but the paper they refer to is in Japanese. It's not clear to me exactly how EAT is defined, but it's quite possible it involves subtracting a reference temperature that is somewhat above 0°C. Hopefully some of the papers you are reading are more clear about this.

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    $\begingroup$ (+1) Things are a little clearer here, maybe. "EAT (effective accumulative temperature) is expressed in degree days (◦C-days) and calculated by subtracting the BZP from daily water temperature and summing this value over the rearing time (in days). The effect of temperature on gonadal development is cumulative above a certain threshold temperature that varies between species. This threshold temperature is termed as biological zero point (BZP; a theoretical minimum temperature at which gonad growth and development begins)" $\endgroup$
    – user338907
    Sep 1, 2022 at 15:23

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