To the reef aquarium
hobbyist, one of the rudest of surprises is to be confronted
with an aggressive outbreak of 'bubble algae' in the tank.
In the right conditions, they multiply and spread rapidly,
offering good resistance to many herbivores, while threatening
to smother many sessile ornamental organisms in the tank.
When we hear of 'bubble algae', one
reflex is to think of the infamous "Valonia ventricosa",
without even considering the many other algae that form bubble-like
structures. Premature judgment can be regrettable, but there
is this added twist: the much-cited 'Valonia' of our
nightmares is no longer Valonia, but, thanks to Olsen
& West (1988) now has its own Genus, Ventricaria.
That deft taxonomic adjustment aside, there
still should be no bar to our tentatively identifying
the bubbles of our troubles. Proper identification can lead
to a more accurate perception in the hobby of which algae
are common problems, rare nuisances, or even benevolent guests.
In some cases proper identification can tell us how to best
combat a problem alga. With some bias towards species found
in my corner of the world (the Philippine Islands) I have
selected some 'bubble algae' for description, and hopefully,
is the most infamous of the bunch. It bears a single,
fluid-filled, and nearly spherical bladder of a thallus
(or 'body'). To say that the bladder or vesicle is 'single'
simply means it does not branch off 'daughter' bladders;
each and every bladder has its own anchorage on the substrate.
The bladders, which are single cells each, can grow to
nearly 2 inches in diameter, and can appear to have a
curious sheen, especially when underwater, that can almost
conceal its dark green color. The optical effect derives
from the parallel arrangement of cellulose micro-fibrils
in the vesicle's wall, and the near-crystalline state
of the cellulose, similar to the same way that 'star'
and 'cat's-eye' gemstones create their chatoyant sheen.
The cell wall's toughness, smoothness, and the sheer size
of the bladder, discourage many grazing herbivores from
obtaining suitable purchase. Its anchorage to substrate
can be surprisingly strong. The species is found around
the Indian Ocean into the Pacific, as far east as the
Samoas and as far south as Australia, as well as throughout
the Caribbean. It is notorious for its tolerance of very
low light levels.
is often found as large single bladders that at full size
can look almost like shiny, bite-size, clear-green hotdogs.
These vesicles grow to around 2 inches length and up to
nearly an inch in width. This alga does not restrict itself
to rocky substrate, and is easily found epiphytic -that
is to say, living on other plants like sea-grass or sturdy
algae. It seems to have a less sturdy vesicle wall than
fellow giant, V. ventricosa. The image to the left
shows young vesicles, only half an inch long; the brown
lump in the foreground is the remains of a larger, spent
vesicle, which peaked at about an inch-and-a-fourth in
length. Interestingly, Trono (1997) singles out the species
as a good bio-indicator for marine radioactive pollution,
but does not elaborate if it is merely superior at assimilating
radionuclides that can be revealed by assay of samples,
or if (less likely) the alga actually exhibits geographic
affinity with radioactive concentrations.
forms small, densely packed, single-cell bladders with
a tendency towards a long, distorted, curved-sausage shape.
The dark- to olive green, clear vesicles, grow to about
½ inch length and maybe 1/6 inch width. The vesicles
are NOT singular, branching off into successive tiers
of bladders, up to five sprouting from the top of each.
This branching can be difficult to detect visually, given
the often very tight clustering of the vesicles. This
alga is found widespread in the Western Pacific from Australia
up to Japan, throughout the Indian Ocean and the Caribbean,
about the Canary Islands in the Atlantic and into the
Mediterranean The dense packing of vesicles can make careful
manual removal of them difficult, though the anchorage
to substrate is only moderate on strength.
|Valonia fastigiata also
features small, 'branching' unicellular vesicles, with
a lesser tendency towards curving or distortion of shape,
which ranges from clavate (club-like) to oblong, to nearly
spherical. Reaching about 1/3 inch in length, the vesicle's
more regular shape allows for very dense clustering. The
species is found around the Indian Ocean, out to the Western
Pacific, and still further eastwards to Fiji.
|| Valonia macrophysa
forms dark green, branching, unicellular vesicles under
½ inch thick and up to an inch or so in length.
The vesicles are roughly clavate (club-shaped), with much
distortion, swelling towards a usually very-rounded top
end. Given the dense packing of the vesicles, only these
tops are visible, and the mistaken impression of spherical
vesicles is easily obtained. The species enjoys a global
distribution, from the Indian Ocean through the Western
Pacific into Tahiti, throughout the Caribbean, throughout
the Mediterranean out to the Canary Islands in the eastern
Atlantic. Relatively weak anchorage to hard substrates
allows for the often-easy manual removal of several vesicles
at a time.
bears somewhat-curving, clavate, branching vesicles sometimes
reaching 2 inches in length but usually only ¼
inch thick. These vesicles tend to be clustered loosely,
many vesicles lying nearly prone and thence sending out
upright vesicles, thus their elongated shape is easier
to perceive. This alga shares geographical distribution
with V. macrophysa, and indeed, there are suggestions
that the two are actually manifestations of a single,
polymorphic species. Anchorage is relatively weak (except
on highly convoluted, hard substrate), but the prone position
of vesicles increases the chance of rupture when attempting
the removal of whole clumps of vesicles.
||Dictyosphaeria cavernosa forms
a bladder-like, grainy-textured, multi-cellular thallus
easily an inch across, which can be sub-spherical but
more often irregular in shape. When the large bladder
inevitably ruptures on maturity, the small (3 mm) cells
that comprised its wall can themselves be mistaken for
a nascent vesicles of other bubble algae species. A tough
skin on every one of those small cells, and very strong
anchorage somewhat makes up for cell sizes that can allow
many herbivores an easy grip. The image shows several
ruptured thalli, and the many small 'bubbles' seen are
the cells that made up the thallus walls. A young bladder
is forming in the topmost center of the photo. This alga
is susceptible to overgrowth by sponges and by other algae.
Its geographic distribution ranges from around the Indian
Ocean to the Western Pacific up to Polynesia, as well
as throughout the Caribbean. A similar-looking species
with similar distribution, Dictyosphaeria versluysii
forms grainy, somewhat flattened, multi-cellular bladders
forms single, grape-like, multicellular bladders sporting
a hexagonal array of lighter blotches across the sturdy
surface. These markings correspond to the ends of interior
filaments radiating from a vertical spine-like axis within
the vesicle. The vesicle itself grows to just over 1/3
of an inch in diameter. The internal framework of filaments,
which lends the alga a surprising resilience, forms as
the vesicle approaches sexual maturity -not surprising
since the filaments bear spore-bearing structures. The
species is found in the Western Pacific, from Japan down
south to the Philippines, and eastward to Hawaii and Fiji.
Two other species of Bornetella, B. nitida
and B. oligospora, form singular, elongated vesicles
up to two inches long and 1/5 inch thick. Mature bladders
again feature the internal axis that radiates filaments
out to a lightly calcified bladder wall. These two algae
are chiefly distinguished from one another by an internal
characteristic: the number of sexual structures on the
tiny internal filaments. They can be confused at first
glance with Merman's Finger algae (Neomeris spp.)
and are found in the Western Pacific, from Japan to as
far south as Australia, and as far East as Fiji.
forms large multi-cellular thalli that are first solid
and then become hollow and often rather contorted, easily
up to two inches in diameter, with some specimens reaching
8 inches. The yellow to yellow-brown thalli have broad
but weakly moderate anchorage to hard substrate, and a
very thick wall. The reproductive structures are found
in tiny pits scattered across the thallus exterior. This
species boasts of a remarkable global distribution, even
into the Antarctic, with a notable absence from the northeastern
U.S. seaboard and the Arctic.
is normally found in the cold Northern Pacific from Japan
and China to Alaska, but there is at least one tropical
record (in Vietnam). The species produces bunches of eventually-hollow,
upright structures somewhat resembling distorted, dirty-yellow
chili peppers, sprouting from a shared holdfast complex.
||Codium ovale forms
roughly egg-shaped bladders reaching 2 inches diameter.
These bladders do not branch, but may share a single holdfast
structure. Tiny structures called utricles, bearing reproductive
structures, are distributed on the outside of the bladder,
giving the whole structure a fuzzy or scruffy dark green
surface. This alga is found in good current, quite often
epiphytic on sea grasses and sturdy algae. It is not too
commonly found in home aquaria, and in any case are found
in very small, isolated clusters of up to eight, sharing
a holdfast complex. This alga is found throughout the
Indian Ocean into the Western Pacific between Japan and
the Philippines, and is also found throughout the Caribbean.
Some Rhodophytes have also qualified in
the hobby for the colloquial term 'Bubble algae':
has been dubbed by some as 'Red Valonia', though
the implied comparison is apt only when a specimen is
very young, and the grapelike bladders appear to be directly
attached to the substrate as in the photo. As this red
alga grows, the rust-colored, branching stipe becomes
obvious, though the entire thallus rarely grows to protrude
more than an inch off the substrate. The bladders themselves
are small, rarely growing little larger than 1/3 inch
in diameter, and appear a smooth, transparent red-brown
to reddish purple. Tiny dark spots (called cystocarps)
visible on the inside of the vesicle wall herald sexual
reproduction. The species is found around the Indian Ocean,
into the Western Pacific, south to Australia and eastwards
to Hawaii. Botryocladia uvarioides forms smaller,
more numerous vesicles, on a highly branching stipe that
can give specimens heights of nearly a foot from the substrate,
looking very much like a bunch of grapes. The species
has a curious distribution, with records thus far only
in the Philippines and in Baja California. Botryocladia
botryoides also forms tall thalli, but there is less
incidence of branching, and so the 'stems' are longer,
and adorned with bladders. It is found throughout Indian
Ocean and the Mediterranean, as well as locations along
the Eastern Atlantic. Only record in the Western Pacific
is in the Philippines. Other species include: Botryocladia
leptopoda from Arabia to the eastern shores of continental
Asia and down to Australia; Botryocladia microphysa,
a primarily Mediterranean alga with records in the Canary
Islands and Indonesia; and Botryocladia pyriformis
from the Canary Islands, the Seychelles in the Indian
Ocean, and the waters from China to the Philippines. Botryocladia
vesicles usually float when severed, because the mucilaginate
fluid inside is less dense than water.
Certainly there are many other algae that
might qualify for inclusion based on possession of some sort
of vesicular structure, but I feel the preceding list fairly
covers some of those most commonly encountered in reef aquaria
and perceived as 'bubble algae', and the ones that most commonly
give us trouble.
Given available nutrients, available substrate
for colonization, and a lack of controlling agencies, many
of the above listed algae can reproduce spectacularly and
dominate a reef tank.
Since impact on tank neighbors derives
from the alga's physical presence, we can try to manually
reduce said presence to provide relief, and include in the
affected tank a set of agencies that exert pressure against
the problem alga. Since availability of usable nutrients fuels
the alga's aggressive growth and reproduction, we attempt
to restrict such availability. That is pretty much the standard
threefold approach to most algal outbreaks:
1. Manual removal of the problem alga
2. Suppression via appropriate herbivores
3. Denial of resources
Normally, there would be a fourth aspect,
of fiddling with temperature, pH, or some other physical-environmental
parameter to suppress the problem alga. However, the environmental
tolerances of most bubble algae exceed those of most ornamentals
put into reef tanks.
Manual removal, properly done, effects
an immediate reduction of the problem's ability to spread
and affect other tank inhabitants. This sort of intervention
is particularly important against bubble algae, some of which
can defy almost any herbivores found in a hobbyist tank..
My weapon of choice ought to be a small
stainless-steel flathead screwdriver, sharpened to wicked
excess, and used to gouge out the offenders at the anchorage,
even including a thin veneer of rock. Bare fingernails can
be unreliable for removing certain 'bubble algae', and can
invite injury and infection. I have seen small manicuring
scissors, carefully bent in a curve, used to snip off vesicles
'at the root' -but this almost surely leaves the anchorage
structure intact, and likely ruptures the vesicle.
Much has been said about the danger of
liberating spores when popping the vesicles of bubble algae.
This is particularly true for members of Order Valoniaceae,
but even then, the vesicles are said to be a sporulant risk
only when having reached at least a third of their full size.
Even if spores escape when you botch the job of vesicle-removal
('vesectomy', anyone?), those escapee spores have to run the
gauntlet of herbivorous filter feeders, filtration equipment,
and the wild lottery of hitting a good, unoccupied spot to
settle and grow. Those spores will eventually be released
anyway if you don't remove the vesicles.
In any case, it is prudent to remove the
whole alga, from the vesicle down to the holdfast. During
'uprooting' of a problem alga, a siphon hose can be positioned
at close hand to draw off any spores or tissue. One can also
use the siphon to hold onto a removed plant by suction -most
of the vesicles described above will sink rather than float,
and can be very hard to hold onto. This siphon hose can held
in a looped manner that allows you to bend it with the same
hand, pinching the siphon off at will. Philips proposes rigid
plastic tubing, sharpened at one end, and affixed to the siphon
hose, for use as a combination vesicle-piercing and draining
apparatus, followed by removal of the deflated vesicle with
tweezers. In any of the above methods, if one can temporarily
move the infested rock to a clean plastic basin of proper
saltwater, vesicle removal is made so much easier. For those
with a paranoia against spores, the basin water can be discarded
after vesicle removal, the rock flushed with tank-water and
returned to the tank.
Whatever remnant algal material, regenerating
algal structures, or newly-settling spores might then manifest
themselves, an in-tank population of appropriate herbivores
is supposed to help with 'mopping them up'.
'Appropriate herbivores' must be a literally-plural
concept, as a varied team of herbivores are required to keep
algal problems in check. In the case of bubble algae, once
the visible vesicles have been manually removed, grazers are
needed to limit any tender new growth.
The performance of commonly-available herbivorous
snails (Turbo spp., Trochus spp., and Astraea
spp.) seems abysmal against most bubble algae, their rasps
typically insufficient for tearing into the vesicles of all
but the youngest bubble algae vesicles. Such gastropods DO
have the advantage of a fairly wide patrol area for their
size, and against widely-scattered, newly-settled spores and
young growth, they likely exert valuable pressure. Certain
sacoglossan slugs have been reported as occasionally feeding
on bubble algae, including the popular Tridachia crispata.
A recently described species, Ercolania endophytophaga
(Jensen 1999) seems to target Valonia algae particularly,
somehow entering a vesicle without rupturing it, and then
consuming tissue and spores from the inside(!).
Success against bubble algae has long been
reported through the crab Mithrax sculptus (Siegel,
1997, etc.). These crabs (like others less colorful) can pinch
and tear a bubble alga's vesicular wall, enabling subsequent
consumption of algal tissue. Occasionally the crab's pincers
can only grasp and sever the narrow anchorage, and the unmoored
vesicle falls away uneaten. While these crabs may have a taste
for algae, virtually all crabs are omnivores, and thus have
the potential to sample valuable ornamentals, such as 'polyps',
corals and mollusks. While many other 'herbivores' are also
opportunistic omnivores, they are much easier to capture and
remove when/if they make a nuisance of themselves.
Herbivorous fish like certain Acanthurids
and Siganids are touted as controls on bubble algae. Some
surgeonfishes of Genus Zebrasoma are particularly promoted,
for they do tuck into the little green marbles (especially
if there is little other fodder), and do not grow especially
large. However, surgeonfishes are often too delicate for the
beginner -often the very sort of hobbyist with serious algae
problems in hand. The rabbitfishes are not quite as disease-prone
as their close kin, but make up for it with handling risks
(weakly-venomous dorsal spines). Then there is THE issue of
appropriate tank-size. The vast majority of 'surgeons' and
'rabbits' tend to be semi-pelagic schoolers, used to vast
patrol-areas, and are noted for territorial meanness and stress
in the confines of a small glass box with others of their
kind. One authority, holding forth in cyberspace on the subject
of reef tank herbivores, suggested a rough stocking guide
of 150 liters (40 US gallons) aquarium volume to a surgeonfish,
and at least 300 liters (80 US gallons) to a rabbitfish. These
estimates must have been made with a small solitary fish in
mind, rather than meant as a tank-size estimator for housing
several, else the issue of territoriality was disregarded.
Urchins are sometimes
recommended, and they do make serious progress against the
smaller vesicles of bubble algae. When food is short, even
the largest and toughest vesicles cannot withstand them. The
main complaint against urchins is that they can be too thorough,
with serious impact on the crustose coralline algae so desired
in the hobby. The photo below may give an idea.
The image shows one
situation: this 4-year old tank's chief herbivorous
resident for the past 11 months is the rock-boring urchin
Echinometra oblonga. While not as wide-ranging
as the popular Diadema setosum, it is more easily
handled and arguably more thorough, as the rock surface
in the photo might attest to. Isolated thalli of Bornetella
sphaerica can yet be seen within the urchin's patrol
area. It seems that if a particular spot of rock surface
is not grazed often enough, a settled spore there can
get a serious head-start towards reproductive maturity:
none of the algal vesicles in the image are larger than
½ inch in diameter, and all of them are survivors
of the urchin's attentions from their earliest beginnings.
Nevertheless, the 'bubble' alga presence in the system
is minimal. The few settled spores that make it to reproductive
size will release their own progeny, and only a small
fraction of those that colonize suitably will survive
the urchin and motley herbivorous gastropods, long enough
to reach spore-bearing size.
Whatever combination of herbivores
is deployed, knowing and preparing for their requirements
and will allow them to do the job you want them to perform.
To reverse that principle, knowing the requirements of bubble
algae, we can try to deny them what they need.
Denial of resources, for present convenience,
here falls into two categories
a. Nutrient suppression
b. Denial of living space and light
'Nutrient suppression' is a concept that
has to be qualified. It is not, as some may think, about limiting
the amount of food imported to the system.
Rather, it is about reducing the availability
of the food to problem algae. A system with robust biodiversity
minimizes the chance of leftovers releasing nutrients straight
to the water, because you will tend to have organisms of every
size and dietary preference scavenging 'stray food' and recycling
the waste of others. Many algal outbreaks stem from the death
of a snail, or some other animal in the tank, the decomposing
body releasing nutrient. Certainly the corpse will have to
be removed, though in a tank brimming with scavengers of all
sizes and shape, most any-size carcass is quickly dispatched
before it can rot.
When mature sand-beds and/or remote refugia
are present, they not only enable efficient assimilation of
potential nutrient, but can reduce the need for 'dead' food
imports by contributing edible plankton and nekton -such live
'food' avoiding spoilage if left uneaten.
While the lion's share of imported food
can be assimilated by ornamentals and scavengers, all the
way down to bacteria, that vast conglomerate of creaures nevertheless
still produces net metabolites for algae to exploit. This
is on top of a background quantity of nutrients 'in transit'
from one utilizer to the next. That net amount of nutrient
is still surely less than in a scenario where a lack of biodiversity
results a greater share of food imports decomposing.
In nature, myriad algae are there to utilize
this resource. The trick then, is to carefully select competitor
algae to scrub such nutrient from the tank water, all to the
disadvantage of any problematic bubble algae. The best in-tank
candidates seem to be the calcareous greens and reds which
grow at a moderate rate and can withstand much herbivore attention,
such as Halimeda spp., and the various crustose corallines.
A key distinction between scrubber and unwanted algae is that
there will be a large, air-breathing 'herbivore-surrogate'
that obliterates only the bubble algae, with siphon hose and
gouging implement in hand.
Algae like the various Caulerpa
species are prodigious, fast-growing assimilators. They would
be ideal for scrubbing certain nutrients, except their very
growth rate can make them a problem in the display tank. Locating
the scrubber alga in a remote location can reduce such a risk,
and stack the deck in favor of said scrubber alga (brighter
light, longer photoperiod, and water flow). For Caulerpa
in particular, though, there is the constant leaching of substances
(terpenoids, sugars etc.) that can affect the display inhabitants
A case can be made for increasing the amount
of food in order to control bubble algae, albeit food of the
right kind. Many of the organisms that hobbyists value --corals,
sponges, polyps and coralline algae--have a natural ability
to put up a fight against encroaching bubble algae, otherwise
wild reefs would look very different. Putting up this kind
of fight requires a lot of energy, and increased amounts of
live plankton and nekton will give them the energy to attack,
overtop and generally outgrow bubble algae; while avoiding
the largely 'dead' soup of nutrients that can attend heavy
import of 'dead' food and lead to algal blooms.
One can observe certain patches of coastal
reef in the Philippines seasonally declining due to terrestrial
runoff, the latter producing both a pollutant/nutrient spike
and a macrobenthic algal bloom. But after the rain-driven
flood of nutrients has passed, those affected portions of
reef can start reclaiming coverage. I have observed V.
ventricosa thalli big as eyeballs, being overgrown
by coralline algae, compound tunicates, sponges, and in some
rather tenuous cases of colonization by newly settled stony
coral growth, mere weeks after the rains have passed.
If you were to take the case pictured in
Fig 1.1 earlier and imagine there were corals sexually reproducing
upstream in the system, the rock's urchin-scoured bareness
might then be showered with stony-coral larvae. Some would
be mindlessly eaten by the urchin, but some would survive
and grow, and the whole rock surface might, over time, be
rendered increasingly inutile to bubble algae.
Indeed, among competitors against bubble
algae for the resources of living space and light, stony corals
are among the most attractive options, particularly encrusting-massive
species. In hobbyist reef tanks, there's supposed to be a
prevailing environmental bias in the corals' favor anyway,
so there's no added imposition of adjusting the tank to support
them. Stony corals can hog settlement surfaces and/or block
off light. The zooxanthellate corals hand a share of their
metabolites to tenant photosynthesizers within their bodies,
rather than dump all the stuff into the water where bubble
algae can exploit it.
Sponges and 'mat' colonial polyps are nearly
as useful for pre-claiming settlement space. Corallimorpharians
(a.k.a. mushroom anemones) on the other hand, can be inadequate
against bubble algae, as their bodies are too soft and translucent
to effect a decent barricade.
Certainly one must look hard at food imports,
and at potential competitors for living space and nutrients.
But there is yet one more factor to consider for restricting
algal resources. Given how nitrogenous nutrient is a prime
resource, it is worth considering how hobbyist tanks are stocked,
and how nutrient levels are affected. After all, the more
animals you have, the more ammonia and CO2
is dumped into the system. Herbivores, scavengers and corals
'pay their rent' by exerting pressure on, or keeping/stealing
resources from, problem algae. But what about showcase animals
that don't 'pay the rent'?
Most reef tanks are really stocked top-down,
which is to say, after lip service is paid to bottom-up preparation
of a mostly-bacterial safety net, large ornamental animals
are selected, bought and introduced. A mad scramble usually
ensues trying to fill in all the niches in the pyramid of
diversity that might address the metabolites and demands of
the large livestock purchases. Often the thing that can really
address these large-animal consequences is greater tank volume,
which in turn can provide license to add even more large ornamentals.
When it comes to large ornamental animals: stock wisely, stock
ending many an article presents rich opportunities for philosophical
pontification. As I seem to have already sneaked a fair bit
of that stuff into the preceding paragraphs, we are now freer
to hew more closely to a simple, brief recapitulation.
Proper identification of bubble algae species
can dictate adjustments in a basic template of responses to
an algal infestation problem. That template can be described
Physical removal of aggressively-spreading
bubble algae is recommended, taking care not to rupture any
spore-bearing vesicles, nor leave algal debris behind. Whatever
present complement of mild herbivores there is should be boosted,
and notes have been provided on the pros and cons to many
popular and commercially available herbivores. Lastly, resource
availability to the algae must be severely reduced, both at
the source and by providing rival consumers of said resources,
including nutrients, living space and light.