Friend or Foe Friend or Foe TRISTAN LOUGHER B.SC. Part 3 DIGITAL IMAGES BY THE AUTHOR his instalment in the series Fig 2 will centre on the the Fig 1 TCnidaria, that is the anemones, corals and their allies, the vast majority of which the reefkeeper can view as a bonus when they arrive in association with live rock or specimen pieces of coral. We will also have a quick look at a closely related group that is represented by a common species that has caused great consternation to aquarists due to its bizarre feeding apparatus! The Phylum Cnidaria contains over 5000 species – the classes is the little recognised Hydrozoa. majority of which are marine. Their name is Hydrozoans show a wide variety of derived from the unique cells that they can structures and range in size from extremely the U.K. Recently some specimens of possess called cnidocytes. These are home small – (< 2mm) to extremely large (several Distichophora (Figure 3), a purple to the stinging organs that are so obvious in metres across). They range in form from branching variety, have been imported from anemones and jellyfish but hard and soft simple “button polyp” – like animals to the Indonesian waters and sometimes Millepora corals can possess them too. complex Portuguese Man o’ War (Physalia (Figure 4) can be found for sale as a We can further divide the Cnidaria into sp.). specimen piece. But it is the arrival and separate Classes of interest to aquarists, The life cycle of many hydrozoans identification of hydrozoans as hitch-hikers namely: incorporates a medusa stage. The medusoid on live rock and associated with hard and Scyphozoa Jellyfish stage can be a means for hydrozoans to soft coral specimen pieces that we are most Anthozoa Anemones facilitate sexual reproduction – there are interested in here. Hydrozoa Hydroids / Fire corals separate egg and sperm carriers, or In my experience, Millepora is a very (Millepora sp.) dispersal – the medusoid stage is free common import, particularly with swimming and enables the animal to Clavularia and Anthelia specimens (so- Hydrozoa distribute its genetic material over a wider called star polyps). It can be very desirable The class which seems to demonstrate range. The medusae are often mistaken for as large specimens can resemble branching characteristics of all of the above named jellyfish and understandably so since they or leafed true hard corals. Figures 5 and 6 have a bell shaped show some Millepora a day after upper body usually importation when the hair-like polyps have with dangling not extended but the colouration and shape tentacles. See the of the colony are typical. Figures of Care must be taken with Millepora as Cassiopea the common name for the genus suggests. (Figures 1 & 2), a Fire corals can be dangerous for humans true jellyfish, for a producing a nasty rash when coming into better idea of the contact with soft skin. They can also cause overall shape of a problems to fish if placed in flow that is too medusa. strong or direct. Polyps can be ripped free Hydrozoans of the coral in this situation and as they are only float they continue to be capable of stinging infrequently anything they come into contact with – Fig 4 offered for sale in including fish! 28 • MARINE WORLD – FEBRUARY/MARCH 2002 Friend or Foe Despite this, will become reacquainted in a Millepora can make an week or so! excellent freebie in the reef aquarium and give Scyphozoa- the vital clues as to the correct positioning of the jellyfish specimen piece on which I know that many of you it arrived. All species of reading this will be thinking “I Millepora from the Indo- have never seen a jellyfish in Pacific, where the my aquarium!” and if every majority of U.K. imports jellyfish resembled Cassiopea come from, are found in (Figures 1& 2) then you could relatively shallow water be right but, like the hydrozoa, (<10m) and in areas of some jellyfish have different moderate to powerful life-cycle stages that can flow. demonstrate a sessile stage Specimens of resembling small polyps or Millepora and tubeworms. The commonest Distichophora are Fig 3 form belongs to the genus unlikely to go unnoticed Nausithoe in which the sessile for long in the reef polyp stage lives in leathery aquarium due to their size and the fact that the area they were collected. tubes up to 20mm tall on the surface of live they have a calcareous skeleton. However The Hydrozoan Class also contains a rock (Fig 9). One reason they thrive in the majority of hydrozoans are very small free-living form of hydroid which is marine reef aquaria is due to the presence and often overlooked. Investment in some capable of reaching plague proportions in of zooxanthellae in their tissues although sort of magnifier or hand lens can reveal a specialised breeding systems where there is they will filter feed and can be found in beautifully delicate new world. abundant food (Figures 8a, b and c). I association with photosynthetic corals that Like Distichophora, the majority of have experienced them particularly in require a lot of supplementary feeding. hydrozoans likely to be encountered are association with seahorse grow-out aquaria I believe most sightings of jellyfish in filter feeders and therefore common around which are kept saturated with food at all the aquarium are due to sessile hydroids the bases of soft corals such as times. This species forms an orange furry producing medusoid stages, Nausithoe Dendronephthyea, Gorgonians and sponges mat where they are abundant although the being one of the most likely origins. It is but also many corals that photosynthesise – colour may be due to their food source possible that if they avoided being sucked suggesting a need for supplementary which is primarily freshly hatched brine into filters that they could grow (they reach feeding of the latter in the aquarium. shrimp nauplii and may differ where other a maximum size of 25-30mm) as the Such colonies often resemble long foods are presented. They also seem to be medusa has photosynthetic pigments too. strands of filamentous algae but closer copper tolerant and their origin is a The polyp stage can reproduce scrutiny reveals very small polyps mystery. They could come with the brine asexually which explains the large scale sometimes less than 1mm tall. Often these shrimp eggs or in the artificial salt mix; in coverage experienced by some aquarists. hydrozoans are brightly coloured – yellow, either case they have to be capable of The only jellyfish that is regularly kept red and orange forms are common. surviving complete desiccation! by aquarists is Cassiopea (Fig. 1). This Of little practical use but of general The only way to eradicate these pests fascinating creature is available for sale but interest is the presence of hydrozoans on is by thorough cleaning, which is is not suited to the typical reef aquarium as animals such as decorator crabs or spider something that most breeding and grow-out there is usually too much flow present. crabs suggesting the type of environment in systems demand anyway. You just have to These animals are found in shallow lagoons accept the fact that you and the hydroids Fig 5 Fig 6 MARINE WORLD – FEBRUARY/MARCH 2002 • 29 opinions here Fig 8a Fig 8b but they are based on good solid experiences – both mine and those of my customers. Firstly, I would like to state my opposition to the control of Aiptasia using fish. Two Actinaria – the butterflyfish species have been regularly cited in the anemones literature as capable of controlling glass anemones: The Copperband (Chelmon on sandy or mud substrates and Fig 8c rostratus) and Sunburst (Chaetodon kleinii). mangrove areas. They have My experience of these fish is that while abandoned the stinging cells that giving the appearance of consuming the jellyfish are renowned for and anemones all they succeed in doing is now their tentacles are full of causing them to remain withdrawn in zooxanthellae. To enhance the crevices. The fish can remove tentacles performance of these symbiotic adroitly and repeated attacks on the algae Cassiopea has evolved to anemones "train" them to stay hidden. rest "upside-down" on the However, remove the fish and almost substrate. miraculously within a couple of days your reef will be overrun with anemones again! Anthozoa Copperband and sunburst butterfly are not really suitable subjects for the reef This class contains the objects of desire for There are two main species that compete aquarium either with their tastes stretching most reef aquarists – the hard and soft for attention within this order. The first is to hydrozoans, colonial anemones such as corals and anemones. We can further the all too common Aiptasia sp (Figures zoanthids and also tubeworms. They will subdivide this class into the orders and sub- 10a and b). This has several common orders which we are most likely to names such as triffid anemone, glass encounter: anemone, glass rose anemone etc. Fossa Fig 10a and Nilsen 1998 state that Aiptasia sp. are Acinaria Sea anemones the most troublesome pests in reef aquaria! Zoanthinaria Colonial anemones Whether you agree with this statement may Corallimorpharia Mushroom anemones depend upon whether your reef is home to Scleractinia Stony corals these persistent creatures or not! Stolonifera Star polyps The main reasons for the proliferation Alcyoniinae Soft corals of these anemones in reef aquaria are firstly that they possess zooxanthellae. This means that the conditions in a reef aquarium with high light intensity provide much of the food they need. However, they are also capable of feeding upon almost any kind of Fig 9 food that is offered to your reef inhabitants NOTE: Tentacles finer – thus supplementing the energy provided than small tubeworms by light.