Message from Internet

Julian F. Sprung JSprung at
Tue Jan 20 23:20:53 EST 1998

Hello Everyone,

I wanted to comment on some of the statements in James Cervino's posted
message from January 15. Haven't had time to reply until now. Before I do,
I wanted to explain that my experience with corals is based on observations
in the wild (Caribbean mostly, but also Western Pacific, a little Eastern
Pacific and Red Sea), and also with growing corals in closed system
aquariums. My reason for writing this reply is that my experience
contradicts some of what Mr. Cervino wrote. For example:

>"Localized bleaching might be due to anthropogenic stressors such as
pollution, sewage >runoff, agricultural runoff, storm damage, and

While sudden salinity drops from storm runoff can cause a bleaching event,
in general corals exposed to sewage runoff DARKEN as the zooxanthelae
either develop more pigment or increase in population in response to the
nutrients. When there are sufficient herbivores present, sewage runoff
should encourage the corals to grow more rapidly, unless they are in a
severely enclosed embayment with little tidal flushing.

>"Global Bleaching Events: Present evidence suggests that global scale
>bleaching events are due to elevated sea temperatures and high solar
>irradiance (UV wavelengths) (Glynn, '93,  Coral Reefs 12:1-17; Goreau &
>Hayes, '94, Ambio)."

This statement corresponds with what I've seen too, and not surprisingly we
(aquarists) see exactly the same thing in aquaria. When new lighting
systems are installed that produce high intensities of UV wavelengths, the
corals bleach and produce bright pigments. When organic rich yellow
aquarium water is filtered through activated carbon to remove the tint, the
sudden increase in UV penetration makes the corals bleach. Part of the
cause is apparently superoxide radicals (active oxygen) stimulated by
photosynthesis under UV light. High temperatures also cause bleaching
events in aquaria. High temperature also seems to increase the incidence of
what we call RTN in aquaria, short for rapid tissue necrosis, in Acroporid
and Pocilloporid corals. This rapid loss of tissue is often confused with
bleaching by aquarists, and I wonder if some of the "bleaching" events
reported in nature weren't sudden death due to such coral diseases. Two
types of RTN are common in aquaria. One is caused by bacteria (possibly
Vibrio spp.) and the other is caused by protozoans (possibly Helicostoma
sp.). There is some literature about this in aquarium journals and books.

>"After the expulsion of zooxanthellae (corals photosynthesizes), the
>metabolic activity is weakened, and the coral is basically starving. That
>leads to: a decline in its calcium laying ability, which has stopped
>growth and calcification); impairment of reproduction; and, tissue

I believe that tissue necrosis is a secondary event, an infection of some
origin. I agree that after expulsion of the zoox's the coral is in a
starvation mode... but notice the contradiction here: in aquaria a speedy
recovery can be achieved by feeding the INCREASING the nutrient
availability in the water. This helps the zoox's repopulate the coral
tissue. A bleached coral living in nutrient poor water is on a downward
spiral of health if the temperature does not cool down or the water become
turbid, which would relieve the stress from the light. A cool, turbid,
nutrient rich upwelling is what bleached corals need.

>"Cyanobacterial invasion will disrupt the symbiosis between host and
>increase mucus-secretory production causing a wider surface area on the
>surface of the coral, and cell erosion. Bacterial populations will lead to
>the development of anoxic conditions on the surface of the coral, inviting
>a community of heterotrophic sulfide oxidizing bacteria, and sulfate
>reducers. This will lead to the corals demise (Peters, E. 84)."

I presume the cyanobacteria you refer to is Phormidium/black band and that
you are describing the process occuring at the bands. This relates to the
statement below...

>"According to personal observations since 1980, and photos from the '70s,
>have seen higher indices of coral reef diseases at reefs suffering from
>eutrophication, compared to reefs with less stresses due to excess

That statement is the one I disagree with most. Everywhere I have observed
coral reefs (Caribbean, Australia, Fiji, Solomons, Red Sea) I seem to find
bleaching and coral diseases in the most nutrient poor water and healthy
corals in the most nutrient rich water. (the only exception being extreme
temperature exposure causing bleaching in shallow inshore nutrient rich
areas). It is true that there is more algae on the nutrient rich reefs, but
the corals are generally healthier there. Incidentally black band disease
occurs in aquariums too...only under the most nutrient poor conditions.
Apparently Phormidium does not tolerate high nutrients. I should clarify
here that high nutrients in closed system aquaria are orders of magnitude
higher than anything ever seen in the wild.

I don't know if Marlin Atkinson is a subscriber to this list, but he has
been doing some interesting work with measurements in the aquaria at the
Waikiki Aquarium. A report by him and Bruce Carlson appeared in Coral Reefs
a while back, describing the nitrogen rich CO2 rich seawater used at the
Waikiki aquarium, which seems to produce rapid growth in reef building

So, to answer this statement-

>"Nutrients and Corals: Are Reefs Oligotrophic? The role of nutrient
enrichment as a >concomitant factor enhancing the growth rate and carrying
capacity of the macroalgal >overgrowth on corals needs to be investigated
following bleaching events."

I agree this must be investigated! The most nutrient poor ocean water will
still support lush algal growth on a highly illuminated suface (i.e. a
bared coral skeleton). Perhaps a little extra nutrient availability would
give a bleached coral strength to fight off the growth of algae (via it's
own mucus and antibiotic substances). Given too much nutrients the algae
certainly win, but strong herbivory can give the corals a damn good
fighting chance in the most nutrient rich circumstances. There are multiple
tests to be done!

Well that's my two cents worth. I may be wrong...but not entirely, based on
what I've seen.

Julian Sprung

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