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Aquarium.Net Nov 96 Sponges

Rob Toonen brings his teaching skills to the web via Aquarium Net with his first in a series on Invertebrate Zoology, November 1996 Index for Aquarium Net, Aquarium Net has numerous articles written by the leading authors for the advanced aquarist

A Reefkeeper's Guide to Introductory Invertebrate Zoology: Part 1: Sponges.

By Rob Toonen

I have discovered that I spend most of my free time on the rec.aquaria.marine.* newsgroups, answering questions like "Why does animal X do Y?" or "I have something on my live rock that looks like Z, what is it?" I have come to the conclusion that 1) I may save myself time by writing a series of articles dealing with the behavior and/or biology of marine invertebrates commonly found in marine aquaria, and 2) reefkeepers in general seem to be sophisticated enough to appreciate a series of articles on collegiate-level invertebrate zoology. I will try to cover groups in as generic a form as possible in these articles (Phylum when possible, Class or Order when necessary), starting with sponges (Phylum Porifera) and ending with tunicates (Subphylum Urochordata).

Over the past year, I have had many questions dealing with keeping sponges in reef aquaria, and thus far, my general impression is that few aquarists have success with these odd animals. I think that there are two primary reasons for this unfortunate circumstance. First, most collectors and hobbyists are ignorant of sponge biology, and do not realize that removing most reef sponges from the water, even for several seconds, will kill them (I will explain this in more detail below). Second, very little is known about sponges even within the scientific community, and their tolerances and requirements are as much a mystery to most marine biologists as they are to reefkeepers. Related to this second point is the current debate among sponge biologists (primarily between the laboratories of Joe Pawlik and Janie Wolfe) concerning the factors controlling sponge distribution in the wild. Wolfe and colleagues contend that the many sponge species found primarily or exclusively in mangrove areas are excluded from reef habitats by physical tolerances. Pawlik and coworkers, on the other hand, have shown that transplanted sponges from the mangrove habitat are consumed by predatory fishes on the reef within hours of being moved, and suggest that predation pressure limits the range of sponges to the mangroves (because sponges moved in cages seem to survive perfectly well). Conversely, in the mangroves, there are poor water conditions relative to the reef (elevated ammonia levels coupled with reduced oxygen), and sponges often survive only on the suspended roots of mangroves. Some researchers assert that these sponges find refuge from predation on the reef by living in the marginal habitat of the mangroves and that they grow on suspended roots of mangroves because roots that extend far enough to touch the substrate allow predatory starfishes to climb the roots and eradicate the sponge. However, sedimentation rates are reduced and flow rates increased on mangrove roots, so survival may instead be linked to sponges which avoid clogging of their water canal.

Given that marine biologists studying these animals cannot currently arrive at an unambiguous answer to explain how and why these animals live where they do, it is not surprising that reefkeepers in general have variable results keeping sponges in captivity. In fact, given our ignorance of sponge biology, it is surprising how successful many people are keeping these animals! They are remarkably hardy and adaptive, if healthy, and many not only survive in reef tanks, but grow well and reproduce. Of course, some species are substantially easier to keep than others, but many species are likely to survive in a well established and maintained reef aquarium if a few simple rules are followed for the introduction. I do not plan to give these sort of details for many taxa in this series, but because I have answered this particular question a number of times, I will explain how I select and introduce sponges into my reef tanks. First, always select a sponge that has a uniform consistency. By consistency,I mean that there are no dead, dying or discolored sections of the body. You should not see any `fuzzy' regions or clear spots anywhere on the sponge. I did not say select a sponge with uniform color because some healthy sponges may display different color patterns on different body regions; if you are unfamiliar with selecting sponges, however, it is best to avoid ones that have variable colors, because you may not be able to differentiate an unhealthy sponge from one that is mottled. Second, make sure that the sponge goes into a tank with the same relative environment as the one from which it is collected. For an extreme example, if you see that a sponge is growing well in a protected and darkened corner of your dealers tank behind the live rock, do not stick it into the middle of your reef tank and expect it to do as well. If neither you nor your retailer have any idea of the habitat from which the sponge was collected, you are better off not buying the animal, because chances are low that it will survive long in your tank. Especially if you cannot even identify whether it is a mangrove or a reef species, because placing these animals into the wrong environment type is almost certain to doom them. Finally, make sure that the sponge never leaves the water when you are moving it. Although there are many species of intertidal sponges which are stranded in the air each time the tide goes out, reef sponges are not among them. Personally, after floating my sponges in my tank, as usual, I move them to a large bucket of water siphoned from my tank, where I submerge the bag before liberating the animal. I let the sponge sit in the bucket for about 15-20 minutes. Then using a Ziplock bag, I seal the animal with a small volume of water (done completely underwater without any air in the bag at all), transfer it to a new bucketful of seawater from my tank, and let it sit for another 15-20 minutes after letting it out. I then seal it into a Ziplock bag one last time (again underwater to avoid any air) and then transfer the animal along with a minimal amount of seawater into my tank, making sure the bag is completely underwater before releasing the animal and placing it where I think it will do best. Particularly hardy reef sponges which are well suited for the novice and nervous include Callyspongia vaginalis (Lavender tube sponge, typically with Parazoanthus throughout the body wall), Chondrilla nucula (Chicken-liver sponge), Cliona delitrix (Red boring sponge), and Cinachyra kuekenthali (Orange ball sponge).

There are three classes of sponges defined on the basis of the skeletal elements. The first, Class Calcarea, is entirely marine, and produces spicules of calcium carbonate which are laid down entirely as calcite. Although these sponges are not particularly common or obvious in the wild, they are interesting to reefkeepers because they are commonly found between pieces of live rock and in sumps or overflows in our tanks. There are several common species, all small (about the size of a rice grain) and usually with a very fine, funnel-like extension on one end (e.g., Leucilla, Leucandra, Scypha = Sycon, Clathrina , etc.). The second class, Hexactinellida -- better known as the glass sponges -- is also entirely marine. These sponges produce spicules made of silica, and although beautiful, are almost entirely deep-water species unsuitable for aquaria. The only specimen of this class anyone is likely to have seen is Euplectella aspergillum , the Venus's flower basket. This sponge has become popular as a collectors item, but was traditionally given as a wedding gift in some Asian cultures because there are symbiotic shrimp which colonize the sponge as larvae, and then become trapped within as they grow. These shrimp ( Spongicola ) form mated male-female pairs, and the `lovers encased within the sponge,' I am told, is considered a good luck gift for the betrothed as a symbol of the lifetime bond between the two partners. The final class is the Demospongiae (for readers following the incorrect taxonomy presented in texts, such as Barnes 1987, Moe 1993 or Haywood & Wells 1989, this is the class which largely absorbed the Sclerospongiae, although some were discovered to be Calcarea, as well – see Brusca & Brusca 1990). Demosponges are the animals everyone thinks of when you hear the word "sponge." They typically have siliceous spicules, and often supplement or replace the silica-based skeleton with a collagenous network referred to as `spongin' (this is the material of which your authentic bath sponge is composed). The Demosponges are found in marine, brackish and freshwater, and at all depths. This classification becomes more complicated and confusing, however, by the adherence of some to an archaic system of classification by `body type.' There are three basic body types among the sponges: asconoid, synconoid and leuconoid (in that order) levels of organizational complexity. Rather than getting into all sorts of technical details about these definitions, let me just say that they have no basis for classification (they simply refer to how the body is designed and how water travels through the sponge), and all three classes have sponges with all three levels of complexity. If you really care what the differences are, go to the library and take out a good invertebrate zoology textbook like Barnes (1987) or Brusca & Brusca (1990).

There are two basic attributes that are shared by all sponges: their water current channels ( aquiferous system ) and the totipotent nature of sponge cells (ability to revert to an immature state and become a new cell type - for an extreme example, if we had totipotent cells, a cell from our tongue could become an undifferentiated cell and travel through our bloodstream to replace a damaged eye or brain cell). Some sponges are so good at this that they can reform after being mashed up, squeezed through a cheesecloth mesh, and poured into a beaker of seawater. You can even do this experiment with two different kinds of sponges, and have them sort themselves out of the mix. The aquiferous system is just as amazing: an individual Leucandria 10 cm long and about the diameter of a pencil pumps 22.5 liters (about 5.5 gallons) of water through it's body every day. That fact is even more amazing when you realize that the cells responsible for pumping this water ( choanocytes ) are about the size of our white blood cells. Aggregations of several hundred of these cells form chambers, and these choanocyte chambers may be as dense as 18,000 per cubic millimeter in complex sponges. Each cell has a tiny hair ( flagellum ) surrounded by a collar made of other even smaller hairs ( microvilli ). The flagellum waves back and forth from base to tip, pushing water ahead of them as they do. Each cell beats at it's own pace, and pulls water from very tiny openings ( ostia ) all over the surface of the sponge (the largest of which are about 1/10th of a millimeter) into the sponge, along the cell body, through the collar which captures food particles from 0.1-1.5 microns (that's less than 1/600th of a millimeter -- about the size of a bacterium), and pushes the water away from itself towards a common exhaust system (the oscula ). As water moves along the cell body, oxygen diffuses into the cell, while carbon dioxide and other wastes diffuse out of the cell into the `exhaled' water. Some free cells ( ameobocytes ) cruise around through these water channels and ingest small algal cells, protozoans, detritus and other organic particles in the range of 2-5 microns. Other freely moving cells ( archeocytes ) take these captured particles and complete the digestion of them before passing nutrients along to the rest of the body. Dissolved organic matter (DOM) is extremely important to the nutrition of sponges; studies on three species of Jamaican sponges showed that 80% of organic matter taken up by sponges was below the resolvability of microscopy, while the other 20% was comparised primarily of bacteria and dinoflagellates (H.M. Reiswig, unpublished data, also see Reiswig 1975).

The sponges get a hand in transporting water through their bodies by oceanic water currents around them and something called the Bernoulli Principle. Basically, when water or air flows over a smooth surface, and then hits something that is raised, it creates suction at the raised area. If you look closely at a living sponge, typically you see a more-or-less flat surface with a few raised holes in it -- these are the oscula (exhaust system). As water flows across the surface of the sponge, the lift generated by flowing over the raised holes leads to suction pulling water through the aquiferous system and giving the choanocytes a helping hand. However, the sponge builds these bumps to specific sizes and diameters under certain flow regimes, and changing the amount or direction of flow over those bumps can lead to water being forced back into the holes, or being pulled through so fast that wastes and oxygen cannot be efficiently exchanged. A study on the transplantation of marine sponges to different conditions of light and current on natural reefs, showed that growth of species with obligate (always present) symbionts (e.g., Verongia aerophoba ) was enhanced by high light levels, whereas growth of species without symbionts (e.g., Chondrosia reniformis ) was inhibited by strong lighting (Wilkinson & Vacelet 1979). Species which had facultative symbionts (may or may not have symbionts present), such as Chondrilla nucula and Petrosia ficiformis did not appear to be affected by the light regime (Wilkinson & Vacelet 1979). Growth was greatly reduced in sponges grown in low flow relative to high flow areas, and sponge morphology differed dramatically within each species between the individuals grown under different light and flow regimes (Wilkinson & Vacelet 1979). This morphological specialization to specific environmental conditions may be part of the reason that few hobbyists have a lot of success with sponges. But, contrary to popular belief, sponges are capable of moving, and if they are unhappy, they can slowly (on the order of 0.5 cm per day) slide across the surface to find a place they prefer or change the shape and size of their oscula or even body to match changed flow conditions. This assumes, of course, that they are completely healthy and water conditions are otherwise ideal for them (which is often not the case when the animals are imported for the hobby).

All sponges appear to be capable of sexual reproduction and typically also exhibit one or more forms of asexual reproduction. Sponges are hermaphroditic, but typically produce eggs and sperm at different times. In terms of methods of reproduction, "sponges probably win the prize for variety" (Brusca & Brusca 1990). Common methods of asexual reproduction include regeneration from fragments, budding, and possibly asexual production of larvae (although this last method remains contentious). Once larvae are formed (whether by sexual or asexual production), they may be released through the excurrent water flow, or may rupture out of the body wall. These larvae are typically free swimming, all are non-feeding, and after a short period of swimming or grubbing about on the sea floor, these larvae attach to the substrate and metamorphose into tiny sponges. Growth rates are highly variable among the sponges, but in general, tropical and polar Demosponges tend to live on average from 20 to 100 years. Some sponges, like Callispongia vaginalis (lavender tube sponge) grow so quickly one can notice differences within a week. One sponge, Terpios from Guam, grows an average of 2.3 cm per month! Others, like Xestospongia muta (tub or barrel sponge) grow so slowly that no difference can be seen in the sponge from one year to the next; these sponges obviously grow, however, since some of them are large enough for an adult SCUBA diver to climb into and hide.

Sponges are highly variable in color, ranging from white to black, with many brilliant shades of red, orange, yellow and even blue in between. The pigments responsible for the color of the sponges appear to be derived from a number of sources, including de novo synthesis, translocation of pigments from food particles and symbiotic bacteria and/or algae. Some texts (e.g., Haywood & Wells, 1989) have attributed these bright colors to a warning to potential predators, and go so far as to suggest color may provide an indicator of preferred depth, with dull sponges collected from deep sites and colorful sponges collected from shallow ones. I believe both claims are incorrect. The second claim is most certainly wrong, because many species of sponges from deep sites are brilliantly colored (e.g., I have collected the beautiful scarlet sponge Cliona delitrix and the more variable Aplysina lacunosa -- ranging from bright yellow to pink to lavender to rust – from 180 ft, at which depth everything looked black). The reason I disagree with the first claim is that many colorful sponges are undefended by antipredatory chemicals (e.g., Callispongia vaginalis ), while many dull species are heavily defended (e.g., Neofibularia nolitangere – the "touch-me-not" sponge, which causes severe contact dermatitis in most humans), and vice-versa. These chemical defenses may prove effective against many scavengers, and perhaps even other invertebrates seeking to settle and grow on the sponge, but some sea slugs, polychaete worms, sea turtles and fishes have managed to find a way around the nasty toxins produced by many of the tropical sponges, and not only eat them, but specialize on sponge diets.

This raises another interesting point: many chemically protected sponges are entirely unsuitable for reef tanks because their antipredatory chemistry adversely affects not only potential predators, but tankmates and reefkeepers as well. For example, the fire sponge, Tedania ignis has such potent defensive chemicals that after simply putting my arm into the tank in which this sponge was kept, my arm turned red and appeared (and felt) badly sun burned wherever it touched the tank water -- even though this was a flow-through system (i.e., we pump water in from the ocean on one side of the tank, and out back into the ocean on the other)! Few sponges have this potent an effect, but it is worth noting that some (e.g., T. ignis and N. nolitangere ) can elicit painful reactions if handled. Other potentially undesirable sponges include species like Siphonodictyon which use a type of `chemical warfare' to prevent crowding from scleractinians by exuding a toxic mucus from their oscula which kills the coral polyps on contact. Cliona , although not often attacking live corals, do often hollow entire pieces of live rock as they grow, eventually leading to the rock becoming a thin crust surrounding the sponge which is prone to collapse. Terpios , mentioned for it's extremely fast growth above, produces some toxin which appears to kill algae, clams, hydrocorals, and even molluscs prior to contact, allowing the sponge to overgrow their competitors. Sponges are, in fact, the most chemically rich group of animals discovered to date, and some predict that the majority of new pharmaceuticals discovered over the next decade or so will be isolated from marine sponges. Halichondria moorei , for example has long been used by New Zealand natives to aid healing. Recent chemical analysis of the sponge discovered that nearly 10% of the sponge weight is composed of the potent anti-inflammatory drug potassium fluorosilicate. Pawlik et al. (1996) provide a survey of the chemical defenses of common Caribbean sponges, if you want to find more information regarding this subject.

The final point I want to discuss is the remarkable symbioses common among the sponges. Reefkeepers in general are all familiar with the association of zooxanthellae and corals, but the same is true of sponges. Most marine sponges have symbiotic bacteria (primarily Pseudomonas and Aeromonas ), and in some Verongid sponges, bacteria account for about 40% of the body weight on average. Sponges are also the only animals known to maintain symbioses with cyanobacteria, and recent work suggests that both bacteria and cyanobacteria are common in most sponges, the former being located deep within the sponge and the latter living close to the surface where light is readily available. Some sponges also have symbiotic dinoflagellates , and others maintain symbioses with red algae, filamentous green algae and diatoms. On many healthy reefs, sponges are second only to corals in overall biomass (Brusca & Brusca 1990). Wilkinson (1983) showed that six of the ten most common sponges species on the Great Barrier Reef (GBR) are primary producers rather than consumers, and that these animals actually produce three times more oxygen through photosynthesis than they use in respiration. Many sponges also have numerous small commensals living within their bodies. For example, a single specimen of Spheciospongia vesparium in Florida was found to contain over 16,000 pistol shrimps (Alpheiidae). Another study counted over 100 different species in a 15x15 cm piece of Geodia mesotriaena from the Gulf of California.

Given the complexity of the associations among sponges and their symbionts and the general lack of concern for or knowledge about their biology, it is not surprising that results have been highly mixed in keeping these animals in reef aquaria. Hopefully, with a bit more fore-thought and knowledge about these amazing animals our success rate will increase.

Literature Cited:

Barnes, R.D. 1987. Invertebrate Zoology, 5th Edition. Suanders College Publishing. New York, NY. 983 pp. Brusca, R.C. & G.J. Brusca. 1990. Invertebrates. Sinauer Associates, Inc. Publishers. Sunderland, Mass. 922 pp. Haywood, M. & S. Wells. 1989. The Manual of Marine Invertebrates. Tetra Press, Salamander Books Ltd. Blacksburg, VA. 208 pp. Moe, M.A., Jr. 1993. The Marine Aquarium Reference: Systems and Invertebrates, 5th Printing. Green Turtle Publications. Plantation, FL. 512 pp. Pawlik, J.R., B. Chanas, R.J. Toonen & W. Fenical. 1995. Defenses of Caribbean sponges against predatory reef fish. 1. Chemical deterrency. Marine Ecology Progress Series 127:183-194. Reiswig, H.M. 1975. Bacteria as food for temperate-water sponges. Canadian Journal of Zoology. 53: 582-589. Wilkinson, C.R. 1983. Net primary productivity in coral reef sponges. Science 219:410-412. Wilkinson, C.R. & J. Vacelet. 1979. Transplantation of marine sponges to different conditions of light and current. Journal of Experimental Marine Biology and Ecology 37:91-104.

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