Everybody’s favourite: Nemo

In the last blog I described the importance of microscopic symbiotic algae as the primary producers of energy, and hence the engine that drives reef ecology. But there are a multitude of fascinating symbioses among reef organisms, and in the next few blogs, I will try to describe some of these.
Children from the UNBC Daycare Centre often come by to have a look at the UNBC reef tank. One of the primary attractions is of course “Nemo”, represented in the tank by three Clown Anemonefish, Amphriprion ocellaris, also known as Common Clownfish, Ocellaris Clownfish, or False Percula Clownfish. The kids obviously know this fish from the popular animated Disney movie “Finding Nemo”, first released in 2003, but equally popular now leading to the re-release of a 3D version in 2012. The movie made these fish so sought after that wild populations were actually threatened, and a substantial captive breeding program has now been established that can cover much of the demand, at least for this species. The story has been documented in the excellent documentary “Filmstar fish – struggle for survival” http://www.oasishd.ca/index.php?option=com_content&view=article&id=378&Itemid=2 .
Before I describe the role of symbiosis for this type of fish, I will describe some other fascinating aspects. Anemonefish belong to the large family of damselfish, Pomacentridae, which include many different types of fish. The family is further subdivided into four subfamilies, three of which are represented in the UNBC reef tank. These are the green chromis (Chrominae), yellowtailed damsels (Pomacentrinae), and of course the anemonefish (Amphiprioninae). In “Finding Nemo”, the young Nemo lived in an anemone with his father Marlin as the only two survivors of a barracuda attack. Making the only surviving young a male was correct, but that is pretty much where accuracy ends. In reality, Anemonefish tend to live in small groups (a breeding pair and up to 4 additional non-breeding fish) hosted by a sea anemone (see below), and within each group there is a strict hierarchy of dominance, reflected by a fairly predictable size distribution (Buston 2003; http://www.nature.com/nature/journal/v424/n6945/fig_tab/424145a_F2.html). The largest fish is the only female, and the next largest fish is her reproductive partner. The other members are non-reproductive males that help in defending the anemone. The fascinating part is that if the female is removed, the reproductive male will change to become female, and the largest non-reproductive fish will become the breeding male. This process takes about 4 months (Madhu et al. 2010). This is called protandrous (=first male) sequential hermaphroditism.
Also unlike “Finding Nemo”, the eggs of Anemonefish are protected until they hatch, but the fry then spend time as pelagic plankton, drifting in the water column until they are large enough to find their way to a suitable reef, which they do in part by smell (Dixson et al. 2008). In fact, the Anemonefish in the UNBC reef tank have spawned regularly, but because of the pelagic stage, none of the fry survive without special rearing facilities, which include feeding them tiny animals called rotifers (Phylum Rotifera).

The current female nestles in among the protective tentacles of her host anemone.

What about symbiosis then? The name “anemonefish” immediately gives away that these fish live with sea anemones. In nature, each species of anemonefish will live only in specific anemones, but in captivity, they will pretty much occupy whatever is available to them, including some soft corals. Sea anemones have stinging cells, however, so how can these fish live among tentacles that can capture and kill some other fish? The fish are protected by special mucous, but in addition the acquire compounds from their host anemone by constantly rubbing against the antennae. Consequently, the stinging cells of the anemone do not fire as they would in response to most other stimuli. Why do they live in anemones? Well, in nature they depend on the anemones to protect them from predation. The anemone in turn gets protection from its predators by the aggressive defense of their host by the anemonefish. When cleaning in the UNBC reef tank, it is not unusual to get bitten, often by the smallest member. In fact, when anemonefish are removed from its host, angelfish move in and attack the anemone within hours, and anemones lacking anemonefish experience negative growth and eventually disappear (Porat and Chadwick-Furman 2004). Thus, this type of symbiosis is a good example of mutualism.
In captivity anemonefish may live for up to 18 years if conditions are excellent, and because of the lack of predators, they don’t need anemones as they do in the wild. Nevertheless, they lay their eggs on a cleaned section of rock under the anemone as they would in nature. In breeding programs, they are deprived of this, and may use any suitable substrate for breeding. The fish in the UNBC reef tank are now 12-13 years old, and have survived a number of trauma that killed a lot of other fish. The original female died in 2012, and based on her behavior recently, the current female may not last long. There is no question, that once the last of these wonderful fish have passed, I will repopulate the tank with a new group.
References
Buston, P. 2003. Social hierarchies: Size and growth modification in clownfish. Nature 424: 145-146
Dixson, DL, GP Jones, PL Munday, S Planes, MS Pratchett, M Srinivasan, C Syms, and SR Thorrold. 2008. Coral reef fish smell leaves to find island homes. Proc Biol Sci. 275: 2831–2839.
Elliott, JK, RN Mariscal, and KH Roux. 1994. Do anemonefishes use molecular mimicry to avoid being stung by host anemones? J.Exp. Marine Biol. Ecol. 179: 99–113
Madhu,R, K Madhu and KM Venugopalan. 2010. Sex change of hatchery produced Amphiprion ocellaris: Influence of mating system removal on gonad maturation and nesting success. J. Mar. Biol. Ass. India, 52: 62 – 69.
Porat, D, and NE Chadwick-Furman. 2004. Effects of anemonefish on giant sea anemones: expansion behavior, growth, and survival. Hydrobiologia 530-531: 513-520.

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The coral reef – a solar powered ecosystem

Coral reefs, as most of us think of them, occur primarily in relatively shallow, warm, crystal clear waters. The clarity of the water is a good sign that there are few nutrients in the water column. Yet, the richness of life in these ecosystems is unparalleled. How is that possible?
In terrestrial ecosystem, energy is captured through photosynthesis by plants, and incorporated in sugars by combining the carbon available in carbon dioxide with the hydrogen in water, producing oxygen in the process. But on a healthy coral reef, there are no plants, and generally only a few macro-algae that can do the same thing. There are, however, small single-celled organisms that take the place of plants. These have variously been placed among the plants, because they can photosynthesize, but are now treated as protozoans (≈first animals). They do not live in the water column, but in the tissues of the corals. In fact, they are the organisms that give corals their colour – generally green or brown. They are special mutualistic dinoflagellates (Phylum Dinozoa) called zooxanthellae. These tiny organisms capture light, and provide the anemone or coral with carbohydrates (sugars) that can be used for growth and reproduction. In fact, most corals kept in a reef tank do not require feeding, but can survive solely on the photosynthetic products provided by their tiny helpers. Some corals do require feeding, but for the most part they survive on photosynthesis alone.

The right portion of the UNBC reef tank, showing numerous corals and polyps, most of which survive largely on carbohydrates (sugars) provided by their photosynthesizing dinoflagellate (zooxanthellae) symbionts.

Which corals are “solar powered”, and which ones are not? In general, corals that are green or brown tend to be dependent on their symbiotic zooxanthellae, whereas yellow and red corals may depend more heavily on capturing organic food. In reality, most corals can subsidize their nutrient requirements by capturing food particles and plankton. But without a strong light source, it is very difficult to maintain healthy corals in a reef tank. Depending on the type of coral kept, sufficient light may be provided by fluorescent lights, but a stronger light source is required for most of the reef-building species. Until recently, the main option to fluorescent lighting was metal halide lights, which provide excellent light, but are expensive and produce a lot of heat. Recently, LED technology has emerged which provides good lighting, produce little heat, are long lasting, and can be programmed to provide more natural transitions between night and day (http://www.pacificeastaquaculture.com/lighting.asp).
One of the main threats to coral reefs is increasing water temperature. When water temperatures increase by even a few degrees, the result may be “coral bleaching”. Thermal coral bleaching is the result of the corals expelling their symbionts, thereby losing their colour and appearing white. A recent study indicated that this may be due to changes in the interactions of the coral and the zooxanthellae (http://www.biomedcentral.com/content/pdf/1472-6793-9-14.pdf). In fact, a coral bleaching event occurred in the UNBC reef tank a few years ago, when the installation of a new and more powerful sump return pump caused a sudden increase in water temperature. In addition, bacterial infections and other external factors may cause coral bleaching.
In summary, even at the most basic level of coral reef functioning, the symbiosis between two different types of organisms. Many more obvious symbiotic interactions occur as well, and some of those will be the subject of future blog posts.

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Inhabitants of a coral reef tank

Everybody has a pretty good feeling for what a coral reef is. It is a reef where lots of corals grow, right! And there are lots of fish there as well. But what are corals, and what else lives on coral reefs? The fact is that coral reefs are among the richest ecosystems on planet earth. Seventy percent of the planets surface is occupied by oceans, but only 0.1 percent of the ocean floor is occupied by coral reefs. Yet, these amazing ecosystems account for about a quarter of all known marine life forms, providing homes for a majority of the Phyla (major groups) of animals. A coral reef tank aims to emulate a real tropical reef, albeit at such a miniscule scale that only some of the organisms can successfully be kept there.

Even so, the diversity of animals in a coral reef tank can be astounding. When you look at the UNBC coral reef tank , you see the many corals (Phylum Cnidaria), a fair number of fish (Phylum Chordata), some shrimp and hermit crabs (Phylum Arthropoda), brittle stars, sea urchins and if you look carefully a sea cucumber (Phylum Echinodermata) and some snails (Phylum Mollusca). That is five of the 30+ Phyla of multicellular animals that you can see without making any effort whatsoever. If you look a little closer, you will also see sponges (Phylum Porifera), and several types of worms (Phylum Annelida), e.g., a Hawaiian feather duster fan worm and cryptic bristleworms that may come out at night, and on some of the corals you will see small acoel flatworms (Phylum Acoelomorpha), distant relatives of the true flatworms which include flukes and tapeworms. Take some samples and look under a microscope, and now you will find roundworms (Phylum Nematoda) and rotifers (Phylum Rotifera). That takes us to ten Phyla, or 1/3 of all existing types of animals living in that tiny space. If we add the various protozoans and more cryptic organisms that lurk in various crevices, the diversity becomes even more impressive of course. And within each Phylum there are many different sub-groups (Classes) of animals, e.g., sea urchins, sea stars and sea cucumbers represent different Classes of this Phylum. Finally, there are organisms that are not animals, e.g., diatoms, as well as green and red algae, and various bacteria that are all critical for the well-being of a reef aquarium. Keeping this system in balance is the trick in maintaining a healthy system. Because of the small volume of water, this can be difficult at times, with even relatively minor perturbations causing chain reaction leading to a more or less complete crash. Usually such events are caused by a drastic water quality change.

In this photo, you can see representatives of four Phyla. Center bottom is an orangespotted shrimp goby (Phylum Chordata) with its companion pistol shrimp (Phylum Arthropoda). To the left are corals (Phylum Cnidaria) and in the upper right corner is a Hawaiian feather duster worm (Phylum Annelida). Photo: Doug Parkes

In order to establish such a rich environment in  a reef tank, a key component  is the use live rock. This is coral rock that has been harvested from, or placed in a natural environment to allow organisms to occupy them. The organisms that are deliberately introduced into a reef tank generally come from the frist five Phyla mentioned above. All the rest come in with live rock. Live rock is critical for establishing the proper balance in a reef tank, but on occasion undesirable hitch-kikers may be introduced. That is a risk one has to accept, however.

One of the key features of a coral reef is the close interaction between different types of animals. The term for this is symbiosis, which essentially means “living together”. Parasitism is one type of symbiosis, where the host is harmed by the parasite, which gets some kind of benefit from the association. The acoel flatworms may be parasites on mushroom corals, but it is unclear if they actually harm them or simply live on them, in which case they would be called commensal symbionts. Most of us associate the type of relationship that exists between clownfish, or anemone fish as the are also called, and the sea anemone as an example of symbiosis, and this is called mutualism, because both the host and the symbiont derives a benefit from the association. But there are a number of fascinating relationships that may not be that obvious unless you know what to look for, and I will describe some of these in upcoming blogs.

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The reef tank blog

Welcome to the UNBC reef tank blog. On this site I hope to publish occasional muusings about the life in the UNBC reef tank, including species profiles, news about what is happening, notifications about new inhabitants et. The binder hanging by the tank has essentially been out of date for 10 years, so this blog will give me the opportunity to post up-to-date information that can be accessed on the internet. I will also post information on reef keeping as I know it, as well as things happening around Prince George like the Annual Reef tank tour. For the past few years this has been organized by Russell vanderEnde, and we just finished our 7th year. It provides an opportunity to view reef tanks at different stages of development and to connect with other reef tank keepers.

Today I added some new fish to the tank as there has been some losses in the past few months. Four yellowtail damselfish, one Lubbock’s fairy wrasse, one eibli dwarf angel, one scooter blenny dragonet, and one purple porcelain crab were added without incident. Some of these have some personality issues that can be troublesome, so I will follow them and provide updates on how they fare.

UNBC reef tank in the early days

The photo above shows the reef tank when most of the corals were so called soft corals, which require less light and therefore tend to be easier to keep. Some of the fish you see in the photo (e.g., the clownfish and the green chromis) are still there, however, as many can live for 10 years or more. The tank looks very different now, because corals grow and multiply. In fact, the header picture was taken 3 years ago, and there is little resemblance between that photo and the tank today. I will describe some of the changes in the tank as they occur, including natural and human imposed ones.

I hope you will find this blog site informative and helpful. Many of the animals in the tank, and yes corals are animals, have fascinating little secrets that you may find interesting.

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