- Hello, guys and girls.
I'm ReefMan, and today we're going
to talk about temperature.
So, what difference do minor changes
in our reef tank's temperature,
maybe just a few degrees, what does it really mean?
What difference?
Can we change the temperature of our tank
to maybe get more fluorescent colors,
or maybe more healthier corals?
Maybe corals that grow faster.
Maybe. (chuckles)
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So, a quick Google search will tell you
that your reef tank should be somewhere between
about 75 to 78 degrees Fahrenheit,
and that's pretty good advice for most common corals,
although a lot of people, including myself,
run our tanks closer to about 80.
So, right now it's about 78.6 in my tank,
but it goes up and down, 80,
81 maybe, sometimes, when it's warm outside.
So, an interesting paper came out recently
on a preprint server which talks about
the effect of temperature change on corals,
and corals that we commonly keep in our reef tanks.
Anthelia, also known as glove corals.
So, the paper is called:
Effects of increased heat on fluorescence
and dinoflagellate density
in the captive coral, Anthelia species.
And it's by Joleen Santos and Ross Shaw
from MacEwan University in Edmonton, Canada.
Sorry if I mispronounced that.
We are looking, or they are looking specifically
at using fluorescence to measure the health of wild corals
in order to predict bleaching events in the world's reefs.
They also looked at the density
of dinoflagellates in the coral tissues,
because that's directly related to fluorescence.
And they tracked both values over about 6 weeks
as they raised the temperature
from 28 to 34 degrees Celsius.
That's 82.4 to 93 in freedom units.
So, they're looking at the high end
of what anyone might keep our tanks at.
Few folks are gonna maintain their reefs
over about 81, or maybe 82 degrees.
It is important to remember that corals
have a symbiotic relationship
with the zooxanthellae in their tissues.
And that this is not an algae,
although people often call it algae.
They're actually dinoflagellates,
and these tiny creatures are spherical,
about 5 to 10 micrometers in diameter,
and they average about 1.45 times 10 to the 6th cells
per cubic centimeter of coral tissue.
So, a lot of them.
The dinoflagellates use photosynthesis
to produce food and give up about 98%
of the resulting energy to the host coral.
In return, the coral provides protection
and gives nutrients back to the dinoflagellates.
So, it's a symbiotic relationship.
There's 8 general groups of dinoflagellates
that are found in corals,
with differing amounts of heat sensitivity.
So, if anything disrupts that balance,
bleaching or coral disease is the result.
Some other studies go so far as to say
that the most common way this happens, bleaching,
is increased temperature.
As I talked about in a previous video,
corals produce 3 main types of fluorescent protein:
green, cyan, and red.
And all of these are thought as to maybe be
sunscreen for the coral, absorbing light
and then re-emitting it, fluorescing,
with a safer wavelength for the coral
and its dinoflagellates to use in their photosynthesis.
For their research, the authors went to a local fish store
and purchased Anthelia, glove polyps, to study.
They grew them on rubble, and then spread them throughout
a number of tanks for their studies.
They started all of the tanks
at 28 degrees Celsius for one week,
and then they raised the temperature little by little.
They started at 30, then 31 the next week, then 32,
finally ending at 33 degrees Celsius
by the sixth week of the study.
They sampled all the coral in each week as well,
and they found that as temperature increases,
the fluorescence of the coral was steadily decreased,
and it dropped significantly.
It just sort of fell off a cliff
by the time the tanks reached 32 degrees Celsius.
In contrast, up to a limit, as temperature increased,
dinoflagellate density also increased.
This increase started around 31 degrees,
so just a little bit warm, and continued
at about 32 degrees, or 33 degrees
where there was a large drop.
In other words, the coral bleached.
Heat density of dinoflagellates occurred around 32 degrees.
This means in higher temperature water,
your corals are more likely to brown out
as dinoflagellates increase
and then bleach entirely at still higher temperatures.
Dinoflagellates tend to be overall brownish in color,
not something we seek out in our corals.
Fluorescence, on the other hand,
that's something we value highly in captive corals.
It's really interesting to me that
dinoflagellate density increased
even as the overall coral health was decreasing.
And the author's theory about this
was that the dinoflagellates actually
increase their reproduction in anticipation
of a greater need for nutrients from the coral tissue.
And because heat impact the dinoflagellates'
ability to photosynthesize,
a greater number of them are going to be needed
to get the same amount of nutrients to the coral.
This is kind of a double-edged sword,
because growing faster means
the dinoflagellates themselves need more energy.
And one of the final thoughts of the paper
is that as dinoflagellates increase, fluorescence decreases,
and that this all happens before
the coral itself actually bleaches.
So, the idea is, could we use this to measure the health
of wild reefs in order to predict future bleaching events?
They also note that a different species of coral
might react differently.
So, this is really only gonna be
directly useful in Anthelia species,
but I thought it was really interesting
that lower temperatures might lead
to more colorful corals for us.
So, that's it for this week.
I hope you found this interesting.
I really loved it, link's in the description.
We've all had corals bleach out on us,
and it's really interesting
to find a paper that directly studies it,
and studies it in a coral that we commonly in our tanks.
Thanks for watching.
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and subscribe, if you haven't already.
I'll see you next time, bye.