Frequently asked questions on low light invertebrates

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Not all inverts need expensive metal halide lighting. Many species thrive under fluorescent tubes, as Matt Clarke explains.

> Why is lighting important to some invertebrates?

Many corals have symbiotic algae called zooxanthellae in their tissues. The corals provide the zooxanthellae with access to light, and in return, the zooxanthellae remove the wastes of the coral and provide important nutrients, such as carbon, that arise from photosynthesis.

Not so long ago, all inverts were thought to hold a single species of zooxanthellae called Symbiodinium microadriaticum. But recent research has suggested that there could be over 200 different species. And, oddly, closely related corals don't always contain the same types of zooxanthellae.

Those species living towards the top of a reef slope are exposed to brighter light than those in deeper or murkier water, and may contain different zooxanthellae. It's those species from murkier waters that thrive under the lower light levels provided by fluorescent tubes.

Some invertebrates are azooxanthellate - they don't contain any zooxanthellae at all. Instead, they rely on different methods, like filter feeding, to get their nutrients.

> Are low light inverts easier to keep?

While some inverts from low light regions are fairly easy, some can be very difficult and extremely challenging to cater for - especially the

azooxanthellate forms. You'll still need to ensure that ammonia and nitrite levels stay at zero, and that nitrates and phosphates are kept very low.

> How much light do I need?

For certain species from lower light regions, a few decent fluorescent tubes fitted with reflectors can often be adequate. If you've got a deeper tank, or more light-demanding species, you'll need to add much more lighting. Hard corals and many other inverts need higher light levels, and generally do better under metal halides.

> What low light inverts should I avoid?

Some low light inverts seen in the trade need very specialised conditions and won't usually fare well in the average reeftank.

Sun corals, such as Tubastrea faulkerni, are azooxanthellate, and prefer very low lighting or complete darkness. They'll generally do best kept inside a cave in the aquarium. The tentacles extend at night, and they need frequent feeding.

Some Dendronephthya are among the most difficult corals to keep in captivity. Unless you're going to set up a special tank for them, don't bother trying...

Sponges may get smothered by micro-algae, and benefit from quite specialised conditions.

> I've only got fluorescents. What species should I go for?

Inverts that live in deeper or more turbid water away from the reef generally do better in tanks with less intense lighting. The three main groups worth looking at are: corallimorphs (mushroom anemones), zoanthids (button polyps) and leather corals.

Although there are a few exceptions, most of the inverts in these groups are easy to keep, and will do well in tanks lit by a small bank of good tubes.

They are also among the most widely available inverts in the shops - so they're a bit cheaper to buy - and they'll all reproduce readily in the aquarium.

Metal halides not required

> Corallimorphs

Corallimorphs (mushroom anemones) are disc-shaped colonial anemones, which come attached to pieces of live rock. They are available in a huge range of colours, shapes and sizes. Most of the common varieties have a disc size of about 6cm/2", but some can reach over 30cm/12" in diameter. They're generally undemanding to keep. Some can lose their bright colours when kept under intense lighting. It's possible that they may harm other invertebrates if they come too close, but other corallimorphs will usually mingle together.

Prices range from about 10-30 depending on the species and the size of the rock. Blue or spotted specimens tend to fetch a fraction more.

> Leather corals

Dozens of different leather, soft and toadstool corals are available including Sarcophyton, Lobophytum and Sinularia species, most of which are very simple to keep. They are generally found in lagoonal systems where the nutrient level of the waterm is often higher. This means that they're slightly tougher than some other inverts. They can tolerate lower light levels, as well as brighter metal halides, but will usually be paler under dimmer lights.

Leather corals regularly shrink, retract their polyps and shed mucus to clean off microalgae.

Prices range from around 5-50 depending on the size and species.

> Zoanthids

Zoanthids, like Star, Button and Yellow polyps, are individual polyps that congregate together as a colony of the same species. Many species are joined together by a rubbery basal mat. Most are easy to keep and don't need particularly intense lighting or special care, apart from good quality, pollution-free water. But some will lose their bright colour under very low light conditions.

Button polyps, such as Zooanthus sociatus, are fairly large, with a stalk length of about 5cm/2" and a polyp about the size of a five pence coin. They form quite dense colonies and are attached to each other, but don't grow from a basal mat.

Star polyps, like Pachyclavularia violacea, are very easy to keep and propagate. They form a dense rubbery mat and can quickly spread onto surrounding rocks, and the glass.

To propagate Star polyps, simply chop off a section of the mat with attached polyps and anchor it to a piece of rock with a rubber band.