Reef Science: Development Highlights
Phylogeny of the order Zoantharia (Anthozoa,
Hexacorallia) based on the mitochondrial ribosomal genes.
Sinniger, F., Montoya-Burgos, J. I., Chevaldonné, P.
and Pawlowski, J. 2005, Marine Biology 147: 1121 - 1128.
Zoantharia (or Zoanthidea) is the third
largest order of Hexacorallia, characterized by two rows of
tentacles, one siphonoglyph and a colonial way of life. Current
systematics of Zoantharia is based exclusively on morphology
and follows the traditional division of the group into the
two suborders Brachycnemina and Macrocnemina, each comprising
several poorly defined genera and species. To resolve the
phylogenetic relationships among Zoantharia, we have analyzed
the sequences of mitochondrial 16S and 12S rRNA genes obtained
from 24 specimens, representing two suborders and eight genera.
In view of our data, Brachycnemina appears as a monophyletic
group diverging within the paraphyletic Macrocnemina. The
macrocnemic genus Epizoanthus branches as the sister
group to all other Zoantharia that are sampled. All examined
genera are monophyletic, except Parazoanthus, which
comprises several independently branching clades and individual
sequences. Among Parazoanthus, some groups of species
can be defined by particular insertion/deletion patterns in
the DNA sequences. All these clades show specificity to a
particular type of substrate such as sponges or hydrozoans.
Substrate specificity is also observed in zoantharians living
on gorgonians or anthipatharians, as in the genus Savalia
(Gerardia). If confirmed by further studies, the substrate
specificity could be used as reliable character for taxonomic
identification of some Macrocnemina.
Molecular evidence suggesting species
in the zoanthid genera Palythoa and Protopalythoa
(AnthozoaL Hexacorallia) are congeneric. Reimer, J.D., Ono,
S., Takashita, K., Tsukahara, J., and Maruyama, T. 2006. Zool
Sci 23: 87-94.
Taxonomic status of the zoanthid genera Palythoa and
Protopalythoa has been in question for almost a century.
Separation of the two genera has been based on traditional
morphological methods (colony and polyp form, nematocyst size
and form, and number of septa), with Palythoa polyps
embedded in a well developed coenenchyme and Protopalythoa
polyps standing free and clear of the coenenchyme. Here we
sequenced two mitochondrial regions, the cytochrome oxidase
I (COI) gene and 16S ribosomal DNA (16SrDNA) genes from Palythoa
and Protopalythoa samples from various parts of the
world and performed phylogenetic analyses of the sequence
data. The phylogenetic trees for both COI and 16SrDNA from
Palythoa and Protopalythoa show four monophyletic
groups (designated Palythoa tuberculosa, Palythoa
heliodiscus, Palythoa mutuki 1 and Palythoa
mutuki 2), with levels of sequence divergence (COI and
16SrDNA divergence approximately 0.0-1.1%) similar to or lower
than previously found among congeneric species within the
closely related genus Zoanthus. Surprisingly, sequence
differences among Palythoa tuberculosa, Palythoa
mutuki 1 and Palythoa mutuki 2 were negligible
(0.0-0.2% for both COI and 16SrDNA), potentially indicating
relationships below the species level. Our sequences align
well with the few Palythoa and Protopalythoa
sequences reported to date. These findings strongly indicate
that our samples represent a minimum of two and possibly up
to four species (the Palythoa tuberculosa-P. mutuki
1-P. mutuki 2 group, and P. heliodiscus) within
the genus Palythoa and that the genus Protopalythoa
is erroneous nomenclature.
The state of zoanthid taxonomy has long been questionable
and in need of revision. These two papers bring some new information
to the systematics of these popular aquarium inhabitants.
The findings of Palythoa and Protopalythoa being
congeneric and nearly conspecific, especially given the samples'
geographic range, is surprising. I would like to see a larger
number of types and samples and a replication of this study,
for it almost seems implausible. It might be possible that
the primers used were too conservative and did not allow for
the determination of enough genomic variation of key alleles
in this phylogenetic group.
The effects of waves and morphology on mass transfer within
branched reef corals. Reidenbach, M. A., Koseff, J.R., Monismith,
S.G., Steinbuck, J.V. and Genin, A. Limnol. Oceanogr., 51(2),
Rates of mass transfer in coral reefs are governed both by
the physical flow environment and the morphology of the coral.
Laboratory experiments were conducted to estimate mass transfer
in unidirectional and oscillatory flows by measuring the rate
of dissolution of gypsum cylinders (clods) placed within the
branching structure of three morphologically distinct coral
species. Unidirectional flows were varied between 2.9 and
14.1 cm s-1 and, as expected, mass transfer rates increased
with increasing flow and a more open branch spacing. Depending
on morphology and flow, mass transfer rates within the interior
of the branching structure were 50 to 75% of that measured
outside the coral in free-stream conditions. Oscillatory conditions
showed relative mass transfer rates 1.6 to 2.9 times greater
than equivalent unidirectional currents. This ratio increased
with increasing wave frequency, likely due to the corresponding
decrease in the diffusive boundary layer thickness. The ratio
also increased with a greater compactness in branch spacing,
with mass transfer rates within the coral structure up to
130% of free-stream conditions. We used planar laser-induced
fluorescence imaging to study the instantaneous structure
of mass advection through the coral. Oscillatory flow acts
as a dominant forcing mechanism to generate water motion within
the coral structure at levels not attainable with comparable
Uptake and release rates (mass transfer rates) of nutrients
and waste products, for example, is determined to a large
extent by the boundary layer's thickness. This is a thin,
stagnant layer of water touching the coral. The thinner this
layer is, the faster the exchange rates will be. Usually,
a higher water flow rate reduces the boundary layer's thickness;
thus a flow is required that's strong enough to keep a coral
alive. Within the coral's branches the flow is far lower than
on the outside of the colony, and that flow is further reduced
with increasing branch density. In the above study, the researchers
found that an oscillating flow increased mass transfer rates,
likely by reducing the boundary layer's thickness. The increase
in mass transfer rates was sometimes severalfold and increased
with increasing oscillation frequency. The authors suggest
that oscillatory flow acts as the dominant mechanism forcing
water motion within the coral colony at a level higher than
would be attainable using a comparable unidirectional flow.
Alkaline phosphatase activity in the phytoplankton communities
of Monterey Bay and San Francisco Bay. Nicholson, D., Dyhrman,
S., Chavez, F. and Paytan, A. Limnol. Oceanogr., 51(2), 2006,
Enzyme-labeled fluorescence (ELF) and bulk alkaline phosphatase
(AP) activity enzyme assays were used to evaluate the phosphorus
(P) status of phytoplankton communities in San Francisco and
Monterey bays. Both regions exhibit spatial and temporal variability
in bulk AP activity with maximum activities during the early
spring and summer periods of high biological productivity.
ELF analysis revealed pronounced differences in the makeup
of organisms responsible for AP activity in these two environments.
In Monterey Bay dinoflagellates are responsible for the bulk
of the AP activity. Diatoms infrequently exhibited AP activity.
Dinoflagellates that comprised only 14% of all cells counted
in Monterey Bay accounted for 78% of AP-producing cells examined.
The presence of AP activity in this group suggests that changes
in P sources, concentrations, and bioavailability could disproportionably
influence this group relative to diatoms in Monterey Bay.
In San Francisco Bay, AP production, indicated by ELF, was
associated primarily with bacteria attached to suspended particles,
potentially used to hydrolyze organic compounds for carbon,
rather than to satisfy P requirements. Our results highlight
the importance of organic P as a bioavailable nutrient source
in marine ecosystems and as a component of the marine P cycle.
From the above abstract the following part is, in my opinion,
the most interesting for aquarists:
"In San Francisco Bay, AP production, indicated
by ELF, was associated primarily with bacteria attached
to suspended particles, potentially used to hydrolyze organic
compounds for carbon, rather than to satisfy P requirements.
Our results highlight the importance of organic P as a bioavailable
nutrient source in marine ecosystems
Phosphate, if chemically bound to organics, usually can't
be taken up by bacteria. Bacteria excrete an enzyme called
alkaline phosphatase for that purpose, which splits the phosphate
from the rest of the organic molecule. This allows the phosphate
to be taken up by bacteria as a source of phosphor. Bacteria
usually do this (excrete the enzyme) if the free inorganic
phosphate concentration is very low. The most striking part
of the study is that bacteria used the enzyme not to make
the phosphate part, but to make the organic part bioavailable.
The bacteria (in that particular environment) were apparently
not phosphor-limited but organic carbon-limited. That is,
it appears as if enough inorganic phosphate (the type of phosphate
measurable by hobby test kits) was present in the water, but
simple organic carbon compounds were not.
If something like that occurred in an aquarium not limited
in inorganic phosphate but limited in simple bioavailable
organics, then it would have implications. The organic phosphate
compounds would be split by bacteria to obtain the carbon
part before most of them could be skimmed out. This would
result in an increase in phosphate's concentration because
the bacteria would not care about the extra phosphate released.
That is, the bacteria would not take the phosphate up and
would leave it in the water.
This could be prevented if sufficient simple, non-phosphate
containing, organic carbon compounds were present so that
bacteria would not be limited by them, reducing their need
to split the phosphate-containing organic compounds just to
use the organic part and not the released phosphate part.
I would speculate that this might be one of the mechanisms
for reducing, at least partly, the phosphate concentration
by the addition of certain simple organic carbon compounds,
A different mechanism proposed elsewhere is that organic
carbon fuels bacteria's growth and multiplication. This growth
and multiplication requires phosphor and nitrogen, thus reducing
the phosphate and nitrate/nitrite/ammonia concentration.
The mechanism which I proposed (based on the above abstract)
is, therefore, different. If organic carbon (but not phosphate),
is limited, and if it is dosed, it may reduce the bacteria-driven
breakdown of organic phosphate compounds. This would keep
them intact for longer periods and might increase the likelihood
of their removal by skimming.
Results for phosphate and nitrate concentrations over time
during an ethanol (Vodka) dosing experiment, published by
Michael Mrutzek and Jörg Kokott in 2004, if measured
accurately, support the mechanism I suggested by the initial
decrease in phosphate concentration only, and not by the nitrate
concentration. This mechanism is probably followed (after
a few weeks of dosing) by the bacteria growth/multiplication
fueling mechanism. This "fueling mechanism" results
in a decrease in both phosphate and nitrate concentrations
as opposed to a reduction of only phosphate in the initial
part. Note the initial drop in phosphate only, followed by
a "steady-state" period and then a drop in both
nitrate and phosphate, from a graph of their results: