X. Non-Sessile Invertebrates - Reef Cleaners

This article discusses invertebrates with jobs like Hermit Crabs, Snails & Echinoderms

 

     Invertebrates account for a vast population of ocean life. Simply speaking an invertebrate is an animal that lacks a spinal cord, many like their terrestrial ecological equivalents insects possess a durable exoskeleton or shell to protect themselves from predators. Other invertebrates have developed more elaborate forms of camouflage or in some cases becoming noxious to ingestion or outright deterring predators with elaborate warning colors.

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Hermit Crabs

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    Terrestrial hermit crabs are something we are often familiar with to some extent and while these are not the type of hermit crab that you would find in a reef tank, they are a larger scale version of them. Saltwater hermit crabs will happily collect stray food and can be seen at times taking food from coral, but, they primarily spend their days scuttling around the rocks and sand scraping algae and detritus from the surface.

 

     Due to their helpful nature in keeping a tidy tank, hermit crabs are desirable in large quantities. Coming in a wide variety of color patterns and sizes the most common hermit crabs are the zebra, blue legged and scarlet hermit crabs. Territorial disputes are possible between passing hermit crabs but this rarely results in death unless the victim has recently molted. When hermit crabs molt they shed their hard exoskeleton and for a period of time after they are much more vulnerable to injury until their new exoskeletal layer hardens. As hermit crab exoskeletons get outgrown, so too do the shells carried on their backs.

   

     Unlike some invertebrates, hermit crabs are not capable of creating their own shell and thus rely on the shells left behind by other animals. They are known to be quite ingenuitive as well, having been recorded sporting some odd homes. As shells are seen as a commodity in these tiny crustacean circles, competition for a new home can be fierce. To prevent the possibility of cannibalization by other hermit crabs for their shell, empty shells of assorted shapes and sizes should be scattered throughout the tank to provide selection as shells become too small. It should be noted that despite our best efforts losses will occur and hermit crabs may need replenishing once in a while.

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Snails

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     Comprising the majority of gastropods available, snails are the obligate herbivores spending their days clinging to rock work and their nights scrounging for algae along the tank surfaces. As they are very good climbers capable of scaling glass they tend to fill that niche in our aquarium cleaning crews. There are several varieties of snails available and some are preferred over others for varying degrees of aesthetic or opinions of efficiency however the most common are the Astrea and Turbo snails.

   

     Both are arguably amazing algae eaters that will make quick work of an algae problem however snails like any addition are not without drawback. Snails may knock over coral that is not properly secured, they may get stuck on filter and pump intakes or, they may fall into the sand bed onto their backs. If left stranded stuck to a pump or upside down, many snails will be unable to right themselves and carry-on. Care should be taken to assist snails when possible to right themselves in sand beds and free them from pumps. However, as with hermit crabs, despite our best effort we tend to need to replenish the snail population from time to time.

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Echinoderms

   

     Meaning Spiny Skin, echinoderms are a unique classification of animals that comprises sea cucumbers, sea stars, and urchin. Most echinoderms are diverse scavengers that consume a variety of meat fare, detritus, sponges, algae and microcrustaceans. While they are more interesting than snails and hermit crabs, by and large, most echinoderms come with careful consideration. Some Sea stars such as the Chocolate Chip or Red General sea stars will eat coral and are not to be considered in a reef tank. The Pencil Urchin has been known to graze on coral while other urchins may pose an unintentional threat to coral while they are obligate herbivores. The sharp spines of the long-spined urchin may puncture coral and cause injury. Lastly, many sea cucumbers can pose a threat in the form of noxious chemical emitted when threatened. In a closed environment, these chemicals can foul a tank and lead to losses.

 

     While I do not intend to discourage those interested in echinoderms from keeping them in their tanks I do urge that individual echinoderm be thoroughly researched before deciding if it would be a good fit for your aquarium. Many an aquarist have starred in awe of an Australian Sea Apple, purchased, acclimated it and enjoyed its beauty. Perhaps over time, they notice it being nipped by their Flame Angelfish which is usually well behaved, or perhaps they are not lucky enough to see the attacks. As time passes it becomes less a matter of if and more of a matter of when your tank will have a crash. Each time the sea apple gets nipped it is under attack if it feels attacked it may defend itself. Its defense mechanism is a noxious ink that is spewed forth from its intestines. At some point, the once happy Sea Apple owner looks over the tank to see a like pinkish purple hue in the water and many dead or dying fish.

 

     Once chemical warfare has begun it is very hard to neutralize. It is stressed that those choosing sea cucumbers like the sea apple diligently monitor the specimens and rehome immediately if signs of stress become apparent. Similarly, there is not a lot known about the complexity of many starfish diets, lethargic sea stars that do not appear to be moving around the tank at all even over long periods of time may be in-fact starving due to an inadequate food supply. Efforts should be made to of the sea star food by placing it on top of the desired food item. If the starfish cannot be coaxed into eating when food is presented and it is given time to consume it, we should assume that the starfish will be too particular with feeding in our tank and may not be a suitable fit due to unspecified dietary needs that can not be met.

   

     Most of the non-sessile invertebrates discussed above are components of a cleaning crew. A dedicated team of invertebrates with specialized diets that benefit our needs as aquarists. Consuming algae, uneaten food and detritus to help reduce waste and maintain a clean tank is the primary motivation for keeping these critters that often get overlooked while staring at a tank. Usually when first looking at a tank someone's response is to the fish and bright colored corals, but after close inspection they will realize “a rock just moved, wait is that alive!?”. While a small detail, they are quite fascinating and facilitate a job within the tank, overall many invertebrates are understated additions that are quietly doing a thankless job by cleaning our tanks while we enjoy them.