Reef Safe Critters Explained

8 Reef Safe Critters Explained

Critters For The Reef Aquarium

Reef safe critters are those that will not under normal circumstances eat, injure or in other ways harm delicate coral found in your aquarium. Many of the species listed here are very beneficial to the home aquarium and some are even required to maintain the health of your reef ecosystem. Please follow the links below to find out more about each type of reef safe critter and to learn more about the different species within each category.

Starfish For The Reef Aquarium

Starfish

There are many types of Starfish that can be used in marine aquariums; however there are only a few which are useful in a reef aquarium. The starfish not listed here are left out do to their natural tendency to eat corals, coralline algae, snails, crabs and other beneficial reef inhabitants. I can tell you personally when I bought a Green Serpent Starfish for my 65 gallon reef aquarium I never expected to see a large mass in the center of its body and to be missing a Diamond Head Goby!! This variation of the Serpent Star cruises around at night and sneaks up on sleeping Gobies (and other fish) and eats them!! Can you believe it?

We have listed below the Starfish that are well suited to the reef aquarium (including non-green variations of the Serpent Star).

San Sifting Star:

The Sand Sifting Starfish is a welcome addition to any reef aquarium with an active sand bed. These guys cruise around at night, sifting through the sand cleaning up un-wanted detritus and left over food that would otherwise decay and cause Phosphate, Nitrate and Nitrite problems. They should be feed small pieces of food in the sand bed if there are not sufficient supplies of leftovers, and they should not be housed with invertebrate aggressive fish like Puffers and Triggers because they will inevitably flip them over and eat them alive, not good.

Serpent Star:

The Serpent Star is on my list titled “maybe I shouldn’t keep this thing with my expensive fish” due to my past experiences. With this said I have had many friends with Serpent Stars in their reef aquariums with no problems so I thought I would list them here.

First, I had a Green Serpent Star that ate my Diamond Head Goby, period!! For whatever reason this color morph, in my experience is not the best choice for a reef aquarium with calm fish that sleep stationary in a small hole. Once I removed the Green Serpent Star, replaced it with a Brown Serpent Star and replaced the Diamond Head Goby with a Yellow Watchman Goby everything was just fine. It could have been that this one Starfish liked Gobies, I don’t know. What I do know is that with the Brown Serpent Star, under the exact same conditions (feeding, light, filtration, etc….) I’ve had no problems.

The Serpent Star has five arms and a central disc that houses its mouth and digestive organs. They are nocturnal, using the cover of darkness to sneak up unsuspecting Gobies!! Sorry, I got off track again. They rest under rocks during the day and feed at night under the cover of darkness. If one of their limbs is lost they will regenerate a new one very rapidly. They are very sensitive to water quality fluctuations so they should be acclimated thoroughly before introducing them to your tank.

Brittle Star:

The Brittle Star is another beneficial starfish for the reef aquarium that both helps keep the tank clean and adds an interesting visual touch. These starfish are very delicate, as the name implies, and feed on detritus and other organic matter found in your reef aquarium. They are nocturnal like most other starfish and will hide amongst the rocks during the day only to come out at night to feed under the cover of darkness. They can usually find a sufficient amount of food in your tank but may need to be feed small pieces of shrimp or fish if your aquarium is extremely clean.

These guys come in a variety of colors, and are commercially available in the range of 3in to 10in, from tip to tip.

Crabs For The Reef Aquarium

Crabs For The Reef Aquarium

Crabs are an essential part of any healthy reef aquarium and careful consideration must be taken when figuring out which type, and how many of these critters you will have. Below you will find a list of reef aquarium crabs that are available for placement in your tank with a description, and photo of each.

Blue Legged Hermits (Phimochirus operculatus):

The tiny Blue Legged Hermit Crab is one of the favorite scavengers and aquarium cleaners on the market today. Their beautiful coloration, small size, aquarium hardiness and excellent reef compatibility make them perfect additions to your reef aquarium. They are small enough to get into tight holes in the rock to scavenge on detritus, algae and other organic matter that larger invertebrates can’t reach. The common blue legged hermit crab, as its name states, has bright blue legs and reaches sizes up to about ?” in length. In a reef aquarium, it is advised to have at least one blue legged hermit crab for ever two gallons of aquarium water. This quantity is a suggested minimum; however, if you plan to have only this species of crab as your cleaner crew, you might require more.

Important note: If you have a large amount of any shell dwelling crab in your aquarium, it is necessary to provide them a large assortment of shells that they can move into as they grow. If you have no extra shells in your tank, they will fight over the shells you do have and they will kill each other in the search for new homes.

Scarlet Hermit Crabs (Paguristes cadenati):

By far, my favorite reef aquarium scavenger is the Scarlet Hermit Crab. The coloration of these little crabs is amazing, and their ability to clean a tank is just as spectacular. Like most other reef aquarium crabs, these little guys feed on algae, detritus and other organic waste present in the aquarium. They are great at cleaning hair algae off of rocks and substrate, but they will also feed on left over fish food, cyanobacteria and will actively scavenge on dead aquarium inhabitants. They require minimal maintenance in an established reef aquarium, but they might need to be provided additional food such as seaweed or extra fish food if your tank is extremely clean. Scarlet Hermit Crabs eat voraciously but only reach maximum lengths of about 1.5” in.

Some refer to these crabs as being very docile and nonaggressive, but I have personally seen them attack each other to steal new homes (shells); being so, I would classify the scarlet hermit crab as moderately aggressive. With this said, I have added a large amount of empty shells to my reef tank and have had ended the battles for new homes.

Green Emerald Crab (Mithrax Sculptus):

Green Emerald Crabs are a great addition to any reef aquarium cleaner crew. They feed on nuisance algae like hair and bubble algae as well as on meaty foods and organic material. They are very attractive crabs with shiny green bodies and hairy legs. They have flat tipped pinchers that they use to grasp algae and other foods with, and, when startled, they use their pinchers to put on quite a ferocious display.

Although they eat algae and detritus as the main part of their diet, I have, on occasion, caught mine picking polyps off SPS corals and even off of Purple Gorgonians. They hide by day in rock crevasses and come out to graze on algae at night in the relative safety of darkness. It is recommended to keep one Emerald Green Crab per 20 Gallons of aquarium water and to feed them regularly if they are not in an established reef aquarium.

Sponges For The Reef Aquarium

Sponges

Sponges are one of the simplest creatures on the earth and have been around since there was life on this planet. They are animals, but their cells are not specialized like most flora and fauna. They act like a collection of separate organisms working together for a common goal: to filter our particulate matter from the water to use as food. They use their porous bodies to passively filter out phytoplankton and other food from the water. Passive filtering means that they do not expend any energy in the search for food; they just use the water’s natural currents to bring food to them.

Sponges can help in cleaning the water of your reef aquarium by removing particulate matter and even some chemicals as the water flows through their bodies. It is important to note some things that apply to all sponges, especially if you plan on placing them in your aquarium:

1) Sponges have no life span and can last indefinitely in the wild as well as in captivity if given the proper care.

2) Sponges must NEVER be exposed to air!! Let me repeat… Sponges must NEVER be exposed to air!! A sponge’s body is made of millions of small holes and water passageways that are used to filter food from the water. If the sponge is exposed to air, its channels could become clogged with an air bubble and then not function properly. Think of it like this: if you dam a river completely, everything that was growing downstream will die; the same rule applies to sponges. If a sponge’s passageway is clogged, everything downstream of that passageway will die. Thus, it is very important that when you bring a sponge home from the store, take the sponge in the bag it was given to you in and open the bag underwater so that you don’t expose the sponge to air.

3) Some sponges can kill coral by smothering them or excreting chemicals that the coral cannot survive. We have listed the sponges that have never been knowing to kill corals and HIGHLY recommend that you do not risk putting one that is not on our list into your tank; it’s just not worth the risk.

Orange Fan Sponge:

The Orange Fan Sponge is shaped like a fan!! You didn’t see that coming did you? Anyway, it resembles one of those Japanese fans the Geisha girls use to use to mask their faces. Like all other sponges, the Orange Fan Sponge is a filter feeder and will require medium flow and lighting. This sponge is reef safe and is a very attractive addition to any tank.

Red or Orange Tree Sponge:

The Red and Orange Tree sponges grow branches like trees and are a very attractive addition to a reef aquarium. It is a filter feeder like all other sponges and requires medium flow and lighting to be healthy and flourish.

Yellow and Red Ball Sponge (Cinachyra allocladia):

The Yellow and Red Ball Sponges are as their names imply: ball-shaped. These sponges can be found in sand beds or gripping to rocks. They are an attractive addition to any reef aquarium. Although they are called Ball Sponges, they can vary in shape depending upon water conditions; however, the shape remains generally spherical.

Like all sponges, they are filter feeders and require medium flow and lighting to be healthy in a reef aquarium.

Clams and Scallops For The Reef Aquarium

Clams and Scallops

Clams and scallops are some of the most beautiful and interesting reef aquarium inhabitants you can keep in your tank. In addition to their visual appeal, clams and scallops provide the practical benefit of filtering food and organics from the water that would otherwise increase the levels of Nitrate, Nitrite and Ammonia in your tank.

A few basic points regarding clams and scallops are listed below for easy reference:

1) Clams and scallops require medium to high water flow. They need this level of water flow so that they can remain healthy by filtering sufficient amounts of food.

2) Lighting:

a. All clams require high lighting (i.e. T5 or Metal Halides) to grow and be healthy as the majority of their food is created within their own fleshy tissue through photosynthesis. Although the majority of a clam’s diet comes from photosynthesis, a portion of its diet comes from supplemental filter feeding.

b. The scallops listed on this site require constant feeding as they do not receive any of their energy/food from photosynthesis. Be aware, though, that some scallops do gain some energy/food from photosynthesis.

3) The Calcium and Alkalinity levels for both clams and scallops must be maintained so that they can grow a thick, healthy shell that will benefit their well being and rapid growth.

4) Clams and scallops are very friendly and will not harm other reef inhabitants. I have seen clams growing in beds of Ricordia and it is truly a beautiful sight.

5) All clams and scallops are very sensitive to medications (especially copper- based ones) and should be removed from the tank if treatment is necessary.

Maxima Clams:

Maxima Clams are the most prolific clams on the market today. Their intense coloration and hardy nature have made them extremely desirable for the most picky of reef hobbyist. They have many color morphs from “Electric Blue” to “Neon Green,” but they all require high lighting, moderate water flow and sufficient nutrient levels.

Maxima Clams are best placed either in the sand bed (for tanks with strong lighting) or on the rockwork closer to the lights if you are not using MH’s or T5’s.

Gigas Clam:

The Gigas Clam is the largest Clam species found in the trade and is also one of the largest clams in the wild. With maximum lengths of over 3 feet the guys are truly huge. These Clams are naturally medium to deep water clams (30-45ft) and do best under moderate lighting (power compacts, NO or VHO lighting). When placing them in a tank with MH or T5 lighting it is very important to acclimate them to the bright light so they do not get stressed and die from shock. This is best accomplished using pieces of screen that are placed between the Clam and the lights that are removed one by one over the course of a few weeks gradually increasing the amount of lumens reaching the animal.

In the right conditions these clams have been know to outgrow there tanks so choose carefully if you plan to keep this guy in your reef aquarium.

Deresa Clam:

The Deresa Clam has much the same requirements as the Maxima Clam although it looks slightly different. The Deresa has a fleshier mantle than the Maxima, but the coloration can be just as beautiful. These guys are very hardy in the reef aquarium and require either moderate to high lighting and water flow. They are a shallow water species and do best under lighting in the 5K to 12K range.

Crocea Clam:

The Crocea Clam has the same requirements as the Maxima and Deresa Clam and is often mistaken for the Maxima. The mantle is more fluted on this clam which is really the only giveaway that it is not a Maxima. They require strong lighting (being a shallow water species) and good water quality to thrive in the reef aquarium.

They should be placed on the substrate or on the rocks near the top half of the aquarium so they receive sufficient lighting.

Tridacna Clams:

Tridacna Clams come in many varieties, but the ones most often found at the local fish store are Hippopus and Squamosa. Both of these clams can grow to approximately 16” in mantle length with very thick, patterned shells. The Hippopus is a variety of Tridacna that is the less decorative, having either a brown or green mantle with, depending on the individual, lighter colored spots or stripes. The Squamosa is a variety that, on the other hand, can come in a variety of colors, including bright blues and greens. This bright coloration is mainly located in the many spots covering its mantle.

The Tridacna Clams are very hardy and are tolerant of varying lighting conditions; however, they tend to do best under medium to high lighting since the majority of their food (about 80-90%) comes from photosynthesis.

Flame Scallops:

The Flame Scallop is named so for its bright red, fleshy mantle that is covered by many long, thin tentacles. These guys are 100% filter feeders that, unlike the previously discussed clams, get no food from the sun. Because of their non-photosynthetic lifestyle, they require supplemental feeding to stay alive in the marine aquarium (e.g. phytoplankton, baby Mysis shrimp or crumbled fish food). They are un-intrusive and will not harm any other creature in the marine aquarium, although they will fly away from predators if threatened; they might strike a nearby coral in their flight.

The sub-species of the Flame Scallop is called the Electric Flame Scallop. It has the same bright red mantle as the flame scallop, but it also has a strip of bio-luminescent tissue on its mantle that sends a flash of color back and forth over the mantle. This bio-luminescent tissue is bright enough to be seen at night and is what gives the scallop its name. This guy is also a filter feeder and will require the same supplemental feeding as the Flame Scallop.

Anemones For The Reef Aquarium

Anemones

Bubble-Tip Anemone (Entacmaea Quadricolor):

The Bubble-Tip Anemone is one the most sought after and easiest to keep anemones you can have in the reef aquarium. They come in a variety of colors including white, brown, green, and red. Red, being the most desirable, has been given a special name, “Rose Anemone,” and can run upwards of $100.00/pc. The Bubble-Tip Anemone requires medium to high lighting and good water flow. It is really a waste of time trying to specifically place one of these, or really any anemone, in your tank because they will all move to find a spot that is suitable for them.

The best thing to do is to place the anemone on a rock, making sure that it has attached. Then, just stand back to monitor in which direction it moves because all of the coral that’s in the way of the anemone needs to be moved so it doesn’t get stung. Hopefully, the anemone will find a home and not start rolling around in the current. If this happens, everything is in danger! It is very important to get the rolling anemone stuck to a rock as soon as possible.

The anemone should be fed small pieces of fish, shrimp or worms on a regular basis to ensure it is getting the nutrition it needs. The Bubble-Tip is best kept in an aquarium with Clownfish as they will help feed, clean and shelter the anemone. This particular species of anemone will host Maroon, Clarki, Tomato, Percula and Ocellaris Clownfish.

Long Tentacle Anemone (Macrodactyla doreensis):

The Long Tentacle Anemone, as the name implies, has long cylindrical tentacles that are often white with some form of striping. The tentacles originate from a round disk and the anemone’s foot is either yellow or orange. These guys grow to about 10” in diameter and require medium to strong lighting and water flow. The Long Tentacle Anemone hosts most Clownfish and will be more settled and happy if provided with a fish to clean, feed and protect it.

Sebae Anemone:

The Sebae Anemone is a favorite amongst experienced hobbyist due to its bright coloration and unique shape. This anemone will host most, if not all, Clownfish species and, in fact, will benefit from the diligent care of the Clownfish. These anemones are typically yellow with purple or magenta tentacle tips, but they sometimes appear bright white when seen in local retail stores. Note: The Sebae Anemones that are bright white have lost the majority of their zooxanthellae and should be avoided at all costs! Without zooxanthellae, the anemone cannot make food from sunlight and, thus, will starve in a short period of time. The rule is this: if the Sebae is yellow, green or even a shade of brown, then the zooxanthellae is healthy and you have a much better chance of keeping it alive. If the Sebae is white, avoid it at all costs no matter what the salesman tells you! After all, they are SALESmen!

The Sebae Anemone is an advanced aquarist’s specie and should only be kept by reef hobbyists with an established aquarium providing perfect water quality and bright lighting. Acclimation of this species is easier if there is a Clownfish in the tank, but care must always be given when trying to place one of these anemones in your aquarium.

Tube Anemone:

The Tube Anemone makes its home in the substrate of the reef aquarium and is particularly suited for sand beds greater than 5” deep. This anemone creates a tube from the tentacles is throws away and makes a home in the sand or rockwork of you aquarium. The Tube Anemone comes in a variety of colors with the most desirable being the red, yellow and purple varieties. Being a nocturnal animal, it will take some time for the Tube Anemone to come out during the day, but after acclimation, it will come out on a regular basis.

This anemone is non-photosynthetic and, thus, must be fed often to maintain its health. A refugium provides a good source of food in the form of microalgae, but small pieces of fish, mysis shrimp or brine will also need to be introduced to meet the anemone’s dietary needs.

Carpet Anemone (Stichodactylia sp.):

The Carpet Anemone is one of the most prevalent anemones in the reef aquarium hobby. Its natural ability to host all species of Clownfish coupled with the different colorations available and its hardiness in the reef aquarium make it very well suited for most enthusiasts. The tentacles of the Carpet Anemone are short and originate from a large disk that makes up the majority of its body. These anemones come in variety of colorations including brown, green, white, red, blue and purple. The brighter the coloration, the higher price you can expect to pay. You may be expected to pay over $300 for a purple or blue Carpet Anemone.

These anemones require high lighting and good water quality to stay alive and flourish in the reef aquarium

Shrimp For The Reef Aquarium

Shrimp

Peppermint Shrimp:

The Peppermint Shrimp is the most common shrimp in the reef aquarium. It’s low price and high availability make it one of the first critters most people place in their marine aquarium. The bodies of these little guys are mostly transparent with varying amounts of red striping covering their entire body. Growing to about 2in in total length the Peppermint Shrimp is a great addition to any reef aquarium.

Peppermint Shrimp will feed on all kinds of tank food such as left over fish food, some types of algae and other organic materials. They are also known for there propensity to devour Aptasia anemones which are a well known nuisance in the reef aquarium, multiplying until every corner of the tank is covered.

I have one in my reef aquarium that has made it’s home under one of my Favia corals. He/She hangs out on the bottom side and whenever I feed the tank it runs out to feed on any leftovers. They are very hardy in an established reef aquarium and are highly recommended as a part of your clean-up crew.

Pistol Shrimp:

The Pistol Shrimp gets its name from the snapping sound it makes with it’s oversized claw as a warning to potential predators or intruders. Other names for this guy include “Snapping Shrimp” and “Symbiosis Shrimp”. It gets the name Symbiosis Shrimp from its symbiotic relationship with some species of Goby Fish. In this relationship the Goby, with its superior eyesight warns the shrimp when predators are near and the shrimp awards the gobies effort by giving up some of its food.

They often will share a burrow and are quite interesting to observe as the shrimp collects food to bring back to the Goby as the Goby stands vidjule over the safety of both.
There are many varieties of Pistol Shrimp and when trying to pair one with a Goby it is very important to select a Shrimp and Goby that are know to live together. Otherwise you will just have a Shrimp and a Goby living in the same tank with no interest in each other, and that’s no fun for anyone.

Other than the naturally interesting nature of the Pistol Shrimp they also scavenge and clean the reef tank by removing leftover food and organics and sift the sand as they make burrows.

Scarlet Skunk Shrimp:

The Scarlet Skunk Shrimp gets its name from the fact that it has a dark crimson red and white stripe down its back, stupid I know but what are you going to do?? This little guy is great for both reef and fish-only tanks because its main goal in life is to clean things!! In its natural habitat these little shrimp set up cleaning stations where large fish will stop by to let the cleaner shrimp crawl all over its body to pick off parasites, dead scales, ich and whatever else the fish might have. These huge fish will even let the little shrimp into their mouths to pick out pieces of food that are stuck and will not naturally come out.

In the reef aquarium they will act more natural if placed in groups of 2 or more and will set up their own cleaning station on top of a rock somewhere and open up shop. It’s very interesting to watch them as they wait for a fish to “pull up” and “pop the hood” for a good cleaning. In addition to eating parasites off fish they will feed on other food in the aquarium including pieces of fish, shrimp or leftover fish food.
They will grow to about 1.5in in length and should be kept in an aquarium of at least 30 gallons. They are very hardy in an establish reef aquarium.

Fire Shrimp:

The Fire Shrimp A.K.A the “Blood Red Shrimp”, A.K.A. the “Scarlet Cleaner Shrimp” are dark red with bright white spots and antennae. They are a very colorful addition to the reef aquarium and are beneficial in much the same way as the other shrimp on this page. They scavenge food and other organic material from the tank keeping it clean and will sometimes clean fish of parasites and other necrotic material.
These shrimp should be given many rocks and places to hide as they don’t like being in bright lights, especially high intensity light like Metal Halides and T5 fluorescents.
These are very hardy shrimp in an established reef aquarium and should be kept in a tank at least 20 gallons to provide the space it needs to scavenge.

Coral Banded Shrimp:

The Coral Banded Shrimp has to be one of the most interesting-looking creatures for the reef aquarium. They have two large claws with three sets of little pinchers that they use to scavenge with. They are active predators of Bristle Worms and will catch and kill them if they can.

These shrimp are very hardy in the established reef aquarium and should be kept in an aquarium of at least 20 gallons.

Snails For The Reef Aquarium

Snails

Snails are an essential part of any healthy reef aquarium and careful consideration must be taken when figuring out which type, and how many of these critters you will have. Below you will find a list of reef aquarium snails that are available for placement in your tank with a description, and photo of each.

Turbo Snail (Astrea):

Turbo Snails are the basis of any successful reef aquarium cleaner crew. They move around removing algae and diatoms from your tank and will polish your live rock to pristine condition. If a turbo snail flips over in the aquarium, it will often be unable to turn itself back over and will die unless the aquarium owner assists it in righting itself. These little guys are one of the first inhabitants you should add to a new reef aquarium as they will control the growth of algae as the aquariums Nitrate, Nitrite and Ammonia levels stabilize.

It is recommended to have one turbo snail per three gallons of aquarium water in an established reef aquarium.

Mexican Turbo Snail:

If turbo snails are the Dodge Ram of the reef aquarium, the Mexican Turbo Snail is the Mack Truck. Pound for pound, or gram for gram, these snails remove more algae, detritus and organic matter than any other reef inhabitant. Being that they are about two to three times larger than the regular turbo snail, they can eat two to three times as much algae and other food.
The problem with these bulldozers is that they do what bulldozers do, namely move stuff around. If you have corals or rocks that are not glued down, these little guys will get behind them and knock them over. They are extremely strong for their size, so care must be given in securing prized pieces of corals.

It is recommended to have one Mexican Turbo Snail per 10 gallons of aquarium water. If you are using other snails to maintain your tank in addition to the Mexican Turbo, you might only need one or two to do the heavy work the others can’t do.

Nerite Snails:

Nerite Snails are about the same size as turbo snails and they do pretty much the same thing, eat algae. The main difference between the common turbo snail and the Nerite snail is the ability of the Nerite to turn itself back over when it gets flipped on its back. This is a huge advantage over the common Turbo Snail; however, there is a down side to the Nerite snail: some of the sellers of Nerite snails get them from suppliers that collect them from tidal areas. These tidal Nerite snails look the same as other Nerites, but they will almost certainly climb out of your tank and die on your floor! I assume that these snails in nature leave the water to scavenge, and, unfortunately, the same tendencies persist when placed in an aquarium.

It is recommended to use one Nerite Snail per three gallons of water in an established reef aquarium.

Nassarius Snails:

The Nassarius Snail has a very different lifestyle in the reef aquarium than the Turbo or Nerite Snail. These little guys lay in the substrate of the aquarium and emerge when they smell food — feeding frenzy! They are very fast movers and are very hardy in the reef aquarium. Sifting and cleaning the substrate is their main goal, but they will feed on other organic materials when introduced to the aquarium. Growing to about 1” in length, it is recommended to have one Nassarius Snail per one gallon of aquarium water. It is also recommended to place them in an established aquarium with a live sand bed.

Sea Urchins For The Reef Aquarium

Sea Urchins

Urchins can be a welcomed addition to your reef aquarium but care must be given to the type and quantity of these creatures you add to your tank. Some sea urchins will eat coralline algae when placed in an aquarium with ample supplies, which means only one or two should be placed together. We’ve included a list of some of the more popular sea urchins below with a description and photo of each so you can decide which one(s) will be right for your tank.

Pin Cushion/Tuxedo Urchin (Mespilia globules):

Pin Cushion/Tuxedo Urchins are generally small (about 2-3in in diameter) and they’re covered in short, sharp spines. They have five to ten broad-colored bands around their body which gives them a strikingly formal appearance and thus the second name “Tuxedo Urchin”. They can have black or blue bands and red, brown or black spines in any combination possible.

One of the unique characteristics of these urchins is there tendency to collect shells, coral or substrate on there bodies as they try to disguise themselves to avoid predators. This tendency sometimes gets them the additional name “Decorator Urchin” but they are all the same species.
These little guys are great for eating algae and detritus and will move about the aquarium scraping algae off glass, rocks and substrate alike. They are nocturnal creatures that do their grazing under the cover of darkness, and during the day they mostly hide in crevasses or in other dark, safe places.

These urchins have not been found to eat coralline algae and are considered safe for reef aquariums. It is important to note however that if there is insufficient alga or other organic food sources that these, and any, urchins will turn to coralline algae as their main food source.

Long Spine Urchin (Diadema antillarum):

The Long Spine Sea Urchin is an active algae eater and a very attractive addition to the reef aquarium. The long, thin spines of these urchins are perfect for deterring fish and other animals from feeding on them. It is this attribute that makes them well suited for algae control in aquariums with Trigger or Puffer Fish, which have been known to eat urchins after picking their spines off.

Like other urchins they are nocturnal, choosing to graze on algae under the cover of darkness. Their bodies are predominately black, although I’ve personally seen some that were a light brown color. One feature common to all of the Long Spine Sea Urchins is the eyespot located in the center of the body, which is usually a red or dark orange color.

Pencil Urchin (Eucidaris tribuloides):

The Pencil Urchin is one of my favorite urchins because of its thick rod-like spines that eventually get covered in coralline algae. This unique feature makes them very beautiful for a reef aquarium and thus I highly recommend this species for you mini reef.
This urchin is nocturnal as are the rest of the urchin families and will come out at dark to graze on unwanted algae.