We have decided to begin a short column
that reviews scientific articles of both recent developments
and those that have been written that may be of interest to
aquarists. We feel that one of the shortcomings of our hobby
is the continued presence of anecdote for which information
might be available to support one idea or another. Furthermore,
for many well-meaning aquarists, access or even the ability
to read such information may be very limited and may pose
a distinct disadvantage to those desiring such information.
We would greatly appreciate suggestions for topics any of
you might want to know more about, and the submission of potentially
interesting article citations that any of you may have read
and would like to see mentioned in a future column. Please
use the relevant reviewer's author forum to present such topics.
Reef Science: Development Highlights
This month I cover a few articles on herbivory
Miller MW, Hay ME, Miller SL, Malone
D, Sotka EE, Szmant AM. 1999. Effects of nutrients versus
herbivores on reef algae: a new method for manipulating nutrients
on coral reefs. Limnology and Oceanography 44(8): 1847-1861.
This article set a new standard for investigating
the roles of nutrients and herbivores on algae growth on coral
reefs. In the method, cinder blocks were used to create diffusible
compartments filled with fertilizer. A carbonate substrate
was placed on top of the cinder blocks and then the blocks
were either totally or partly enclosed in chicken wire to
allow large and small herbivores, or only small herbivores,
access to the blocks which were either nutrient enriched (by
addition of fertilizer) or not enriched (control).
Water drawn from the surface of the enriched
blocks showed elevated levels of dissolved inorganic nitrogen
and soluble reactive phosphorus compared to controls (1.1-3.1
v. 0.3-0.9 TIN, and 0.11-0.14 v. 0.01-0.03 SRP, in mmoles/liter).
Thus, it effectively produced levels comparable to naturally
Algal response to elevated nutrients with
exclusion of large herbivores showed that only one type of
cyanobacteria increased in response to enriched nutrients.
However, herbivore exclusion treatments had large effects.
Turf algae and frondose macroalgae both increased when herbivores
were excluded, and coralline algae decreased. It was found
that increasing nutrients did not cause more algae to grow,
but resulted in more nutrient rich algae that were, incidentally,
grazed at a faster rate (thought to be a result of them being
more nutritious to herbivores preferentially seeking and requiring
nitrogen rich material). It appeared, from this article, that
algae are not nutrient limited on coral reefs and the primary
control of algae on reefs is herbivory, not nutrients.
Note: the results of this study have been
supported many times since it was published, and it is becoming
widely accepted that the primary control of algae is the rate
of herbivory and not nutrient enrichment (termed "top-down"
control rather than "bottom-up").
Belliveau Stephanie A., Paul Valerie
J. 2002. Effects of herbivory and nutrients on the early colonization
of crustose coralline algae and fleshy algae. Marine Ecology
Progress Series 232: 105-114.
This study is one of many that support
the findings of the preceding findings by Miller et al. (1999).
Once again, fertilizer was used to enrich tiles either exposed
to or excluded from herbivores. The tiles were examined after
a period of time for percentage cover of coralline algae,
fleshy algae, sediment load and coral recruitment. Results
showed that fleshy algae biomass and sediments (correlated
with the presence of sediment trapping turf algae) were highest
on tiles excluded from herbivores. Nutrients did not have
a significant effect on macroalgae, and had a slight positive
effect on coralline algae. Coral settlement rates were too
low to measure during the experimental study (although other
studies have shown coral recruitment to be correlated to the
amount of coralline algae covered substrate available). Herbivory
was found to exert primary control on algal cover, even in
the presence of increased nutrients.
Taylor Richard B., Sotka Erik, Hay
Mark E. 2002. Tissue-specific induction of herbivore resistance:
seaweed response to amphipod grazing. Oecologia 132: 68-76.
This paper examines the role of defensive
metabolite composition in algae. Plant tissues vary greatly
in the amount of permanent and inducible defenses, with it
being thought that defenses occur mainly in areas of the plant
most at risk of being grazed. This study used the brown algae,
Sargassum filipendula and the amphipod herbivore, Ampithoe
longimana to examine plant-induced defenses that occur
from grazing. The most important parts of the plant, the bases
that attach the plant to the seafloor, were defended from
grazing primarily by their toughness and permanent resistance
to grazing. However, the areas of new growth that are the
preferred tissues of amphipod grazing, were stimulated by
grazing to produce defensive chemicals that deterred grazing
by making the tissues more unpalatable. This study confirmed
that some algae are able to locally ramp up production of
feeding deterrent chemical metabolites in response to grazing
and this has also been found for Dictyota and Padina
species in the tropics. It has also been suggested that primary
chemical defenses, at least in algae, are a response to smaller
grazers (mesograzers) and not macrograzers (fish, urchins).
L. Shimek, Ph. D.
It's A Snap,
This month, I will discuss some interesting
articles on snapping shrimp that have appeared over the last
couple of years.
von-der-Heydt-Anna; Lohse-Detlef , 2000, How snapping shrimp
snap: Through cavitating bubbles. Science: 289 (5487): 2114-2117.
We all know that snapping shrimp snap.
It has been assumed that the snap was caused by a mechanical
snap of one part of the shrimp's exoskeleton against another
or by a release of a mechanically loaded skeletal string.
The authors found the actual reason for the snap to be quite
different. Looking at the snapping shrimp, Alpheus heterochaelis,
they found the loud snapping sound was caused by an extremely
rapid closure of its snapper claw. During the rapid snapper
claw closure, a high-velocity water jet is emitted from the
claw with a speed exceeding cavitation conditions. Hydrophone
measurements in conjunction with time-controlled high-speed
imaging of the claw closure demonstrate that the sound is
emitted at the cavitation bubble collapse and not on claw
closure. One of the effects of the snapping is to produce
sound loud enough to stun or kill prey animals. The claw closure
itself is silent.
And that ain't all
bubbles flash like flashbulbs!
Lohse, Delef, Barbara Schmitz and
Michel Versluis. 2001. Snapping shrimp make flashing bubbles,
Nature 413, 477 - 478
The authors found that the cavitation bubbles
created by shrimp in stunning their prey have some surprising
properties. As the paper above indicated, the sound created
by snapping shrimp originates from the rapid and violent collapse
of a large cavitation bubble generated under the tensile forces
of a high-velocity water jet formed when the shrimp's snapper-claw
snaps shut. As this bubble collapses, a short, intense flash
of light is emitted. This means that inside the collapsing
bubble there are extremely high pressures and temperatures
of at least 5,000° K (about 8,000 °F).
The authors were the first people to observe
the flashing and they named it "shrimpoluminescence."'
This is also the first observation of this mode of light production
by any animal. It is similar to sonoluminescence, the light
emission from a bubble created by ultrasound. During their
investigations they positioned a snapping shrimp (Alpheus
heterochaelis) in a seawater aquarium maintained at 20
°C and evoked a snap by gently stroking its snapper claw
with a paintbrush. The sound pressure was recorded using a
hydrophone in close proximity (1-3 cm) to the imploding bubble.
The light emitted during the collapse was detected using a
calibrated photodetector, and all experiments were carried
out in complete darkness. The flash duration is extremely
short, less than 10 billionths of a second. Only about 50,000
photons are produced by the hot bubble interior, and consequently
the light is too dim to be seen with the unaided eye. Through
the examination of two different shrimp, they found no correlation
between sound and light intensity, so loud and soft pops both
produced light flashes. There doesn't appear to be any biological
significance to the flashes, rather they seem to be simple
byproducts of the snapping noise. However, the light emission
certainly indicates the extreme conditions inside the bubble
at collapse and, therefore, demonstrates the violence of the
And finally, one last snap and flash
Duffy, J. Emmett and Kenneth S. Macdonald.
1999. Colony structure of the social snapping shrimp Synalpheus
filidigitus in Belize. Journal of Crustacean Biology. 19:
In an investigation of some snapping shrimp
living in a sponge, these researchers found evidence of a
second case of a true social hierarchy, similar to that found
in social insects. The social insects, such as ants and bees,
have highly organized colonies based around a single reproductive
female, and a "caste system" for the partitioning
of labor within the nest. These snapping shrimp, Synalpheus
filidigitus, live as colonies of 30 to about 120 individuals
within large sponges in the Caribbean. The colonies were produced
and dominated by a single large reproductive female who was
over twice the size of other females in the colony. Such a
colony structure had previously been demonstrated for another
snapping shrimp, Synalpheus regalis.
In addition to the interesting symbiotic
behavior shown by some snapping or pistol shrimps, we now
have the opportunity to observe, and possibly maintain true
social crustaceans. Presently, it is unlikely we could maintain
these in hobbyist sized tanks; the sponges are too large and
require specific conditions we can't provide. Nonetheless,
such maintenance may be a possibility in the near future.