ARTEMIA AND CONTROL OF ALGAL BLOOMS
Sent: December 14, 1999
From: Raúl Coyula <coyula@fbio.oc.uh.cu>
To: <Artemia-l@sparklist.com>
QUESTION:
How does Artemia control the algal blooms in saltworks if they are caused
mainly by cyanobacteria that Artemia ingests but does not use?
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COMMENTS 1:
You make a very good point. If the cyanobacteria are particularly hard to digest such as Coccochloris sp. and the cell density is high, the filter-feeding Artemia will pass the cells undigested and you will accomplish nothing. Maybe a more practical approach is to identify the cyanobacteria and then decide if it can be easily digested by Artemia. If not, I would suggest proceeding to a plan that would introduce key elements to favor a bloom of diatoms...these products are available. However, if your feed water has high organic loading, then it may not be possible.
Howard W. Newman
Artemia task force div.
Inve aquaculture, Inc.
E-mail : BShrimp@aol.com
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COMMENTS 2 :
In a forward flow solar pond system Artemia ingest the diatoms and green
planktonic algae of the preliminary ponds, resulting in clear, nutrient
reduced water by the time the salinity increases to that where the
cyanobacterial mats grow. It is particularly important to remove the
phosphates, as cyanobacteria are phosphate-limited (they fix their
own
nitrogen). The low phosphate water supports only small quantities of
cyanobacteria, and the clear water allows light to penetrate to the
floor,
encouraging the mats to make tight benthic mats. Where the water is
turbid the mats grow loosely, up into the water column. The loose mats are
very mucilaginous and wind mixing allows the mucilage to become
incorporated into the brine. This impacts on the final crystallisation of
salt, causing small, feathery and loose hollow crystals. It can actually
halt production in extreme cases.
Peri Coleman
Delta Environmental Consulting
12 Beach Road
St Kilda SA 5110
Australia
E-mail: delta@adam.com.au
URL: http://www.adam.com.au/delta
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COMMENTS 3:
I would agree that Artemia do not directly reduce cyanobacteria
populations by grazing. Their main mechanism in reducing
cyanobacteria are to tie up nutrients and clear the brine. Reactive
nutrient concentration is the major factor in the growth of essentially
opportunistic cyanobacteria growth, in particular PO4. Brine
clarification means a firmer bottom layer which reduces mixing between the
acid nutrient rich anaerobic sediment and the photo
active zone. Not all cyanobacteria are detrimental to saltworks and
they are not the bacteria directly that are responsible for quality
reduction. The main culprits seem to be the single cell species from the
Synecococcus (sp.?)/Aphanothece group. I have recorded quite high
concentrations of this genus without an increase in brine viscosity, the
major factor in poor quality crystals. In short, ecological balance and
stability is the critical mechanism and of course Artemia is only a part
of the story.
Mark Coleman
E-mail: actis@iinet.net.au
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COMMENTS 4 :
I keep brine shrimp for the purposes of teaching in schools and
Colleges. I have small model ecosystems. They run well when the nutrient
levels are low. I occasionally have cyanobacterial growths on the side of
the tanks.
I know that these are adding atmospheric nitrogen to the ecosystem
(N-fixation). It is my belief that some of these algae are edible.
If
they are not they may be rapidly decayed and the released nitrogen
comes that way into the algal (Chlamydomonads) population that then gives
the shrimps their adequate protein needs.
Blue greens need not be bad news surely.
Stephen P.Tomkins
Director of Studies in Biological Sciences
Homerton College, Cambridge. CB2 2PH. UK
Tel: 01223 507174
E-mail: spt22@cus.cam.ac.uk
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COMMENTS 5:
I agree that blue-greens are not all "bad guys". I have
successfully
raised Artemia on dry Spirulina and Aphanizomenon flos-aquae and they
were active, bright and vibrant animals.
Unfortunately, there are some species such as Microcystis that, when
decaying, release an enzyme (microcystin) that is a pretty potent
liver toxin.
The effluent waters to many shrimp ponds are of low salinity and even
though Artemia can survive at low salinities most often predators of
Artemia are present too, such as fish larvae, crab, corixidae.
Artemia survive and thrive in high salinities without predators and
probably would not be able to multiply before being consumed.
Howard W. Newman
Artemia task force div.
Inve aquaculture, Inc.
E-mail : BShrimp@aol.com
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COMMENTS 6:
Although I am not really a phytoplankton man, I'd like to summarize some
of our findings here in Vietnam.
The systems in Vietnam are small shallow (30 to 50 cm) pond systems
(ponds of 0.5 to 2 ha) run as batch cultures (each pond contains one
Artemia population and is run as a separate unit). Ponds are fed mainly
green water, cultured in separate fertilization ponds (sometimes these are
the intake canals), and organic waste products. Ponds are stocked high (60
to 100 animals/litre) and at this moment cysts are the primary objective.
As Vietnam has a monsoon season, systems are also seasonal. In the wet
season Artemia disappear and ponds are used for fish or shrimp culture.
1) Can Artemia remove blue-green algae from the water column ?
I would say yes, as long as Artemia can ingest them. Artemia is a
non-selective filterfeeder = eats everything which comes his way. What has
been ingested is nicely packed into a faecal pellet, which sinks to the
bottom (I do not really understand the remark of Marc Coleman as would
Artemia act as nutrient captures ? You mean as captures of organic matter
?). But if removing algae from the water is your goal you should not work
with nauplii, as they have a very inefficient feeding system. Juveniles
and adults are much more appropriate. This implies you first have to grow
your animals in a separate pond. Although such a procedure to get rid of
algae might sound a bit complex, it can be done and it has been done. The
only thing you
should take into account are the costs.
Unfortunately, there are some blue-green algae which are ingested,
packed and if the faecal pellet is opened come out and swim away
(Cocochloris). Also if the algae can not be ingested by the brine shrimp,
brine shrimp can not remove them. This is i.e. the case for a number of
blue-green filamentous algae.
2) Are blue-green algae bad news ?
For salt production not necessarily as other people already pointed
out.
They help to seal your bottom and might even enhance heat absorption
(trouble of course starts if you disrupt your pond ecosystem and these
mats start to float ! I think though most salt managers will know how to
keep their pond system stable).
As for Artemia, I tend to believe blue-green are bad news indeed. As
already pointed out by Howard, some are toxic, others can not be ingested,
still others can not be digested. In certain circumstances they even start
clogging the digestive system of the Artemia (very common with the
filamentous ones which start appearing once rains start) after which the
Artemia population collapses. As for the grazing of benthic mats or algae
on glass walls, you indeed often see Artemia "graze" = wave
their thoracopods above such growths. However, did anybody check if the
Artemia are actually ingesting parts of these algae or are the animals
just taking detritus sticking to these mats ? Also, if ingested, is the
stuff digested (you can check this easily in the faecal pellets)? I never
really looked at this (so please comment), but I know for a fact algae
mats are not enough to keep your populations healthy. Furthermore they are
nutrient sinks = take away all the nutrients needed by the good micro
algae. Finally they are really difficult to clean out your cysts.
In this respect it is important to manage your algae populations
properly to maintain high concentrations of green algae (Dunaliella,
Chlamydomonas, Tetraselmis) and small diatoms (Chaetoceros). This can be
done via manipulation of the N:P balance with inorganic fertilizers (as
many people already pointed out, high P-levels tend to stimulate the
blue-greens as they can fix nitrogen from the air). But other factors such
as turn-over rate of water in your fertilization ponds, intake water,
solubility of phosphor/nitrogen, water circulation, salinity (blue-greens
tend to become a problem rather at lower than at higher salinities),
shading, temperature, pond bottom (as a nutrient sink and nutrient source)
all do interfere with this process.
Also, putting high N concentrations is nice, but if you start
stimulating
the large diatoms (often the case once the blooms become dense; at
that time the green algae are replaced by diatoms) you also are in trouble
as Artemia can not ingest these (ie Navicula, Nitzchia, Pleurosigma etc.)
and you basically starve your population.
In short you should manage your pond in such a way that you get a lot
of green algae (but not too much, as you will start running in other types
of problems if you do that) some small diatoms (to get the HUFA levels
high in your cysts) and as little blue-green as possible. The way to do
this requires that you understand your pond ecosystem (cf. bottom-water
interactions and biological community) as working with one set of rules,
might prove excellent in pond "A" but near disaster in pond "B",
although in both ponds the same principles apply.
For us to know which is the best strategy in your pond requires a
basic
amount of back-ground information about your ponds. This type of
information always seems to be lacking on discussion lists. So, may I
invite the people who post a question to include a short description of
their pond or tank system as there is no such thing as "a
standardized Artemia" or "a universal pond" or "a
good-for all-purposes tank" ?
Peter Baert
E-mail: bpeter@hcm.vnn.vn
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COMMENTS 7 :
More on Artemia and their benthic grazing habits: a recent International
Journal of Salt Lake Research paper (1998, Vol. 7(1)) (online at Kluwer
Academic publishers) examined benthic grazing by Artemia as a behavioural
modification, at Lake Hayward in Western Australia. The researchers
discovered (by observation in glass aquaria) that the Artemia were
brushing diatoms free from the surface of the mat and then ingesting them.
This behaviour can be observed at Pink Lake in SA, where the intake
water is phosphate-rich and nitrate-deficient. There are few planktonic
algal species, but a dense mat of cyanobacteria coating the entire benthic
surface of the lake. Growing on the surface of this mat, partially
embedded in the mucilage, are diatoms. They give the mat a lovely golden
colour. The Artemia actually "latch on" to the mat with their
reproductive claspers and brush the surface to release the diatoms. Where
rocks are present in the lake the Artemia look like a fuzzy hairdo all
over the rock. An interesting observation is the amount of fine mud that
must also be embedded in the algal mats - where the Artemia are attached
to the rocks there is a halo of fecal pellets, which are coloured
distinctively with the local mud. This is very obvious against the uniform
gold of the benthic mat surface.
Peri Coleman
Delta Environmental Consulting
12 Beach Road
St Kilda SA 5110
Australia
E-mail: delta@adam.com.au
URL: http://www.adam.com.au/delta
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COMMENTS 8:
I repeat that we are aiming at maximizing cyst production here in
Vietnam. Trying to maintain your populations with benthic algae is in that
respect not to be recommended. But no doubt, you can maintain natural
populations that way (often is the case in large permanent salt works
too), be it I suspect your cyst yields will not be extra-ordinary (low
number of females and often lot of ovoviviparity).
PS : I also saw the message of Howard concerning reduced feeding rates and slower growth of Artemia in higher salinity. Probably the fact that more energy has to be redirected to maintain a proper osmotic balance also explains the smaller size of your animals. If temperatures are high and your animals very red, you can add respiration problems to the list.
Peter Baert
E-mail: BPETER@HCM.VNN.VN