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Horseshoe Crabs

It has always been the Museum’s intention to develop displays of “living fossils” – animals that are both seen in the fossil record and still alive today – and 2013 saw the building of a marine tank to provide a habitat for one of our favourites, the Atlantic Horseshoe Crab, Limulus polyphemus.

Our intention was to build a biotope - a piece of Western Atlantic seafloor recreated in miniature. All of the materials used and co-existent livestock had therefore to match what our horseshoe crabs would encounter in the wild and so provide as natural a habitat as possible for them.

The range of the Atlantic Horseshoe Crab is along the eastern seaboard of the United States from Virginia to Florida and extending into the Gulf of Mexico. Water temperatures across this range of latitudes varies from an average of 15.8° Celsius off Virginia/Maryland to 23.8° Celsius off the coast of Texas. We decided to maintain our water temperature at a mid point range of between 20 - 21° Celsius, the mean ocean temperature off the state of North Carolina and acceptable to all the intended inhabitants of our tank.

Marine Aquarium
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The aquarium was started in June with 100 litres of artificial seawater and 25kg of fine grained oolitic “live sand” from the Bahamas. “Live sand” is sand that contains natural bacteria to help start the nitrogen cycle in the tank. This is essential for the maintenance of healthy water in that the bacteria break down ammonia (from the waste products of living organisms) into nitrites and then into nitrates. In too high proportions, all of these substances can prove toxic to marine life.

All of the life support systems that the eventual occupants would need were also added at this stage, i.e. protein skimmer to help clean and oxygenate the water, 100 watt heater, canister filter, pump (to send water through the filter), powerhead (to provide water flow around the tank), temperature gauge, white (daylight) and blue (moonlight) LED lighting and a ˝ horsepower water chiller.

The tank was left to cycle for six weeks with regular water quality tests undertaken for Salinity, Specific Gravity, Ph, Ammonia, Nitrites, Nitrates, Phosphates, Calcium and Iron.

During this time, the top of the sand turned from pristine white to a dark reddish-brown in places as diatomaceous algae started to develop. This is perfectly normal for a new marine tank during its start up cycle. Beneath the sand, patches of bright green and black started to form from the action of the bacteria and from algal growth. Again, this is normal although excessive patches may indicate a build up of anaerobic bacteria that produce hydrogen sulphide gas which is toxic to marine organisms.

At the beginning of August we planted a bed of seaweeds comprising Caulerpa prolifera and Caulerpa sertulariodes.

One week later we added 5 Nassarius snails (to help aerate the sand bed and to control the diatomaceous algae), a Caribbean Feather Duster Sabellastarte and a large piece of aquacultured “live rock” from Florida.

Similar to “live sand”, “live rock” is rock that has been kept underwater for up to 30 years in the ocean to that organisms can colonise it. When newly acquired the rock appears to be quite bare but life develops from it as it matures given stable and optimum conditions in a marine tank.

Six weeks later, the reddish-brown diatomaceous algae had all disappeared and so we introduced our main exhibits - two juvenile horseshoe crabs. One week later we added 2 Caribbean Blue Bass Serranus torugarum (also known as the Caribbean Chalk Basslet) and 2 Blue Neon Gobies Elacatinus oceanops.

Horshoe Crab
CopyrightStone Museum of Geology
  Close-Up
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Blue Bass
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  Blue Neon Gobies
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Eight months on the tank is maturing nicely with stable water conditions, healthy livestock, good seaweed growth and organisms such as pink and purple coralline algae developing on the live rock and tiny flatworms and polychaete spaghetti worms Terebellidae sp. appearing on the glass.

The water quality is tested each week and show ammonia levels about 0.1 to 0.3 mg/l and nitrite about 0.1 mg/l and nitrates 5-10 mg/l. Ph is rarely anything other than 8.1. SG can vary between 1.022 – 1.025 (depending on evaporation rates through the year).

Whilst nitrites and ammonia have to be held as close to zero as possible, nitrates are necessary for macro algae growth and so are held between 5 -10 mg/l. Iron (to aid photosynthesis of the macro algae) is maintained between 0.1 and 0.2 – sufficient to keep it the plants healthy without encouraging them to grow too fast.

Weekly top-ups/water replacement are made of up to 2 litres each of salt water and reverse osmosis water to maintain these levels.

5ml of liquid marine supplement is added weekly to ensure that the water contains the trace elements necessary for healthy development of the occupants. 10ml of marine buffer liquid is added to ensure the Ph level is maintained between 8.1 and 8.3 along with 2-3 ml of chelated iron supplement.

Feeding takes place morning and evening with Hikari Crab Cuisine sinking sticks for the Horseshoe Crabs and Ocean Nutrition Prime Reef Flakes for the Gobies and Bass, although the Bass and Gobies have been seen to take the occasional crab stick and the crabs clean up those flakes that sink to the bottom. Live food supplements are occasionally provided, blood worms for the crabs and both marine copepods and brine shrimp for the fish. Reef Nutrition Phytofeast live is given daily for the microscopic animal occupants of the tank.

The Crabs are most active in the early hours before dawn up to late morning. The Gobies are most active during the day, particularly if it is a sunny day. The Bass are most active from late afternoon until mid evening.

The Crabs bury themselves completely in the sand to sleep while the Gobies hide in holes in the live rock. Interestingly, the female Bass uses her tail to make a depression in the sand most evenings and sleeps within this depression.

Having exo-skeletons, several times a year the Crabs disappear from view for 2-3 days at a time while they moult their shells. This is something they will do every year until they reach adulthood (about 7 years) when they will then moult once annually.

Moulted Carapace
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It has not however been all plain sailing. We have made mistakes. The Nassarius snails and Feather Duster all died within 4-6 weeks of being introduced due to fluctuating water quality. We knew that Bass were notorious for jumping and so covered the tank with metal mesh. However, we had to leave small spaces in this mesh to allow pipework into and out of the tank and unfortunately the larger of our two Bass jumped out of the tank through one of these. As Bass really need to be either kept singly or in shoals (and we do not have the space for a “shoal”) we will not be replacing this loss.

The job of the snails, cleaning up detritus and aerating the sandbed, has been taken up by the Horseshoe Crabs so we do not intend to replace these. We will replace the Caribbean Feather Duster once we are confident that the water quality is sufficient and stable. This may be reached once the tank is a year old.

Two new “arrivals” from the live rock will bear close scrutiny over the next few weeks. One is a small brown anemone that could be a harmless beadlet anemone but could also be the Glass Anemone Aiptasia sp. The other is a cluster of small shiny round balls that could be Bubble Algae.

Both Bubble Algae and the Glass Anemone are considered unwanted and invasive species that could, if allowed to spread uncontrolled, take over the entire biotope. The photo below shows the 8 bubble algae that have appeared - middle top of picture. Note the tracks that the horseshoe crab has left in the sand at the left side of the picture as it searches for food.

Bubble Algae
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Despite weekly cleaning of the glass and the canister filter the water has had a slight cloudiness to it from disturbed sand and suspended particles ever since the tank was started. Around the middle of February however, almost overnight it became crystal clear and has remained so ever since although we have changed absolutely nothing in the way the tank is managed. It may be an indicator that the nitrogen cycle has now fully matured or it may just be a seasonal change. We will know more as the year progresses and we collect more data.

March 2014 has been a bad month. The cloudiness of the water is back, the anenome has turned out to be the dreaded Aiptasia (and has spawned 4 small offspring) and the second Bass also managed to jump out of the tank. The first issue may be down to over feeding as the horseshoe crabs have been very active over the past few weeks and search for food constantly. The second issue has two solutions. The first is to treat the anenomes with special poison to kill them off (this seems to be the favoured option by most local fish societies) or to introduce a predator of Aiptasia. We have chosen this second option as being the most natural and have acquired a Peppermint Shrimp (Lysmata wurdemanni) - see below.

Peppermint Shrimp

These are found around the Western Atlantic and Gulf of Mexico and so will be a natural tank mate for the other specimens. The third issue is a disappointing one but the absence of the Bass has changed the behaviour of the resident Neon Gobies markedly in that they are now much more active and visible. They presumably saw the Bass as a threat. As the old adage goes "every cloud has a silver lining" and so, to keep the Gobies happy, we shall not be introducing new Bass. (Postscript: reduced the amount/frequency of feeding and the water is once again crystal clear).

With three invertebrates in the tank we are now dosing the water with 5ml of iodide solution each week. The addition of this trace element will help them all moult when they outgrow their shells. We have also started feeding New Era Marine Pellets as, unlike the Hikari Crab sticks which need to soften before they can be eaten, these can be consumed immediately.

The Neon Gobies habitually sit on the glass of the aquarium heating tube. On the grounds that this is a hint, we've turned up the thermostat to 22 degress Celsius - representative of the coastal waters of South Carolina - and will continue to monitor the behaviour of all the aquariums occupants.

May 2014 proved a worrying month as both crabs "disappeared" from view for over a three week period. This, we understand from aquarists in the United States, is normal behaviour in older crabs as they prepare to moult their shells. This is in marked contrast to their last shedding in February 2014 which only lasted 2-3 days. The size variation before and after is encouraging and an indication of ample food supply, general good health and acceptable water quality.

Growth Rate
CopyrightStone Museum of Geology

June 2014. Both have now re-surfaced and are catching up with three weeks worth of missed meals! From inspecting the shed carapaces both crabs appear to be female.

More micro-life that has appeared recently include small hydrozoa animals in their free-swimming "medusa" stage.

Medusa

End June 2014 and the crabs have disappeared again - presumably to shed once more? If they continue to grow at this rate, the Museum will soon need a much larger tank!

Two weeks later both have reappeared and yes, they have shed once more and are now about 5cm in diameter. Both are now large enough that they are disturbing the sand bed significantly and making the water cloudy. To counter this we have added another external canister filter with bio-balls to supplement the bacteria in the live rockl/live sand to maintain the nitrogen cycle and additional filtration and polishing with foam inserts and activaed charcoal. This has proved successful in improving the water clarity. The original pump and filter have been retained but now purely to protect the internal pipework of the water chiller. The new filter has an integral pump and returns the water to the tank via a spraybar. This has been fixed slightly below the water level to provide water flow around the tank and has meant that we no longer need a powerhead. One unforeseen benefit of this appears to be that by reversing the way the water circulates around the rockwork (the spray bar had to be fitted to the opposite side of the tank to where the powerhead had been) the aiptasia anemones have reduced in both number and size. It will be interesting to see whether this is a permanent change or whether they simply move to another location.

Mid September 2014 and after a further absence, both crabs have moulted again and the aiptasia don't seem to have been affected by the water flow changes at all, they have just moved to different locations.

Growth Rate
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October 2014. The Peppermint Shrimp is now in it's fifth moult and appears to be thriving. It is not, however, taking any interest whatsoever in eating the Aiptasia anenomes, preferring to feast on the food we have been adding for the Neon Gobies. Time to try something different so we have introduced three nudibranch sea slugs, the young of which only eat Aiptasia - Aeolidiella stephanieae. These are also found in the Caribbean and so should find themselves at home. It will take several weeks for them to settle down and start breeding and we will keep an eye open for their eggs laid in a distinctive spiral as an indicator that they have settled in successfully.

Nudibranch

More hydrozoa medusa have appeared in the filter bed. Normally only 1 or 2 are found but this week 8 were counted.

Medusas

18 October 2014. Disaster! Turned off the circulation systems last night to feed the crabs and forgot to turn them on again. This morning, the Peppermint Shrimp was dead, as was one of the Neon Gobies (and attracting the attention of a Caribbean polychaete bristle worm called Eurythoe complanata). The other Goby, along with both horseshoe crabs, seemed very lethargic. On testing the water, ammonia, nitrites and nitrates had gone through the roof and so the survivors were extracted and put in a large plastic container of fresh saltwater. Several hours followed cleaning out the tank, filters and sieving detritus out of the sand. According to my LFS, live rock dies in about 5 hours if the water flow stops and this is what has probably happened. It will probably take about 6 weeks to recover. Even after a 50% water change the nitrite levels at 5ppm and the nitrates at 60ppm are still very high although the ammonia has come down considerably. A 25% water change daily until conditions stabilise will be necessary. The remaining Neon and both crabs have been re-introduced (they couldn't stay in a plastic kitchen container for too long!) and appear lively and reasonably comfortable. The fate of the Nudibranch slugs is as yet unknown.

24 hours later and a further 25% water change and the water quality is now almost back to normal. The Neon Goby, which was regularly chased by the other whenever it came out to feed, is happy having the tank to himself and both horseshoe crabs have settled back to their normal routine, i.e. constantly looking for food!

It is said that clouds can have a silver lining and in almost emptying the tank of water, we disturbed a small crab we didn't know was there. It almost immediately scuttled back under the live rock but we will keep an eye open for it to try and take a photograph for identification.

November 2014. No sign of the nudibranch slugs so have written these off. The Neon Goby however is lively, active and all of its' colour has returned. Both horseshoe crabs have also recovered fully from the ordeal and, after ravenously demolishing a number of bags of blood worms, have buried themselves to moult once again.

End November 2014. The new external filter began to play up. Refusing to prime the pump, leaking seals and, for a while, even reversing the water flow - something that should not be possible given that the inlet tubes are keyed and can only be inserted one way round! This filter has now been disconnected from the system and the spraybar attached to the outflow of our original pump. The powerhead has also been reinstated. A disappointing waste of some £60 but one lives and learns.

6th December 2014. One rather large moulted crab shell has appeared leaning aginst the live rock and looking like a crashed spacecraft! The crab itself is still buried as it's new shell hardens. The other crab will probably not be far behind.

The crab that had moulted did not appear again until January 1st. The moulted shell from the second crab appeared 10 days later and it too is now buried while the new shell hardens. There has been no sign of the Neon Goby now for three days and so we suspect the worst.

Now that the crabs are so much larger, they kick up a dust storm burrowing through the oolitic Bahamas sand to the point that the water is perpetually cloudy. We are therefore thinking of replacing this sand with a larger grain size substrate, possibly West Caribbean Reef Sand.

17th January 2015. Both crabs have now buried themselves again (so soon?) and the Neon Goby has surfaced once more. Perhaps it has been hiding now that the crabs are so very much bigger. With no crab activity, the tank should have started to clear but seemed slow to do so. Investigating the water flow, we determined that having moved the live rock (albeit only by a couple of inches) to make more open space for the crabs, we had disturbed the flow over the rock and reduced its' effectiveness as a bio-filter. Testing the water quality we found that Ph levels had dropped and ammonia risen slightly. Nitrites were still at zero and nitrates were steady at about 10 ppm. We moved the pump and powerhead to increase water flow across the rock and conditions have improved considerably overnight. Two key lessons from this, a) that small changes can have significant implications and b) trying to artificially reproduce a biosphere - something that nature does easily - is no easy task.

15th February 2015. The crabs are still buried in the sand and so did some additional research to see whether this is normal or whether we should be worried. There are quite a few websites around the world that cover the life cycle of the horseshoe crab but only one mentioned then spending considerable periods of time inactive. This was the Encyclopaedia Americana (presumably the US version of the Encyclopaedia Britannica). This said that they tend to bury themselves in soft sand or mud around November and do not reappear until Spring. Two possible reasons for this is that in the US, oyster fishing is common at this time of year and the crabs are staying out of the way of the dredges and to shelter from the effects of winter storms. This knowledge is a comfort. The crabs were active all last winter but then they were still small and needed the extra time to grow. Another trigger for their behaviour this year may be that unlike last winter, we have kept the LED lights switched off and as horseshoe crabs have ten eyes they are experiencing the short winter daylight hours and long nights for the first time.

The horseshoe crabs reappeared at the end of February and are both active and hungry.

1st March 2015. There has been no sign of the small crab we discovered back in October but in cleaning the tank today, a moulted claw was found in the sand. Not much to go on admittedly but a cursory examination of the colour and patterning suggests that it might be a Batwing Coral Crab Carpilius corallinus. These are one of the most beautiful and largest crab to be found in the Caribbean. "Large" is a relative term - 15 cm (about 6") in width - when compared with the potential adult size of the horseshoe crabs - 30cm x 60cm (12" x 24")!

14th February 2016. Not a great deal to report. Crabs are healthy and still growing fine. Given their size now, we moved onto feeding them a much larger sinking pellet. Unfortunately, these caused the aquarium water to go so cloudy that everything within it was completely obscured despite regular water changes. The answer was to add an ozone generator to our systems. Adding ozone to the water improves the efficiency of the tank's protein skimmer so that more waste is removed and completely eliminates cloudiness. Adding 50mg of ozone daily for one hour has completely transformed the tank and the water is now crystal clear and cleaner than it has ever been. An unexpected but well worthwhile investment. We have however, abandoned the large pellets we were using in favour of a similar product that says that it does not turn the water cloudy. So far, so good!

Easter 2016. The crabs have now reached a size where they need an upgrade to their accommodation. We have therefore upgraded them to larger quarters - at almost 4 foot long (1.2 metres), twice the size of the original - this should be sufficient for them for the next five years. The larger water capacity (about 200 litres) should enable us to better control water quality as the same amount of food (and crab poo!) will be diluted proportionately.
New Tank

July 2016. Both crabs have disappeared into the sand bed and have not moved much for several weeks now. This is usually an indication that they are resting while growing their new shells and may therefore be ready to moult by late mid August/early September.

We have found in the past - to our cost - that if the water flow around the tank ceases for more than a couple of hours that the bacteria in both the live rock and live sand tend to die off, providing dangerous spikes in ammonia, nitrite and nitrate levels and turning the pH of the water acidic. Mindful of the potential harm that power outages would have on the tank, we have invested in an uninterruptible power supply unit (UPS). Although more usually associated with the iT sector where they are used to protect computer equipment while it can be shut down safely, the power used by the tank circulation systems are so low - less than 20 watts - that we will be able to maintain water flow for perhaps as long as 6-8 hours in the event of a failure of the mains electricity supply. As an additional emergency measure, we have also installed a car battery and inverter system that can be used after the UPS is fully discharged to maintain tank circulation for a further 4-6 hours. If we lose power for longer than this then yours truly will be sitting next to the tank and stirring it by hand until normal service resumes!

It was only a matter of time! One of the banes of the marine aquarist is take-over of the tank by the dreaded Aiptasia - the Glass Anenome. We always had one or two, they hitched a ride on the Caribbean live rock we bought, and so long as there was only one or two, then as a natural occurring part of sealife, we were content for them to stay. After all, the crabs took no notice of them whatsoever, or harm. But today (July 6th) we found two small anenome growing out of the sand bed! This prompted us to take a long hard look in detail in all the nooks and crannies of the rock and sure enough, dozens of the darn things were hiding - and growing - under the seaweed.

Fortunately, there are a number of preparations available for killing off Glass Anenomes without affecting any other marine creatures or adversely affecting water quality. One of these we have now procured (one of the lesser known but reportedly effective treatment - Aiptasidol, from The Netherlands) and deployed this against all the anenomes we could see. The treatment is ingested by the anenomes and - because it contains caustic Sodium hydroxide - both kills and dissolves them. Watch this space for updates on how effective it proves to be.

September 2016. The larger of the two crabs has now moulted and is currently buried under the sand while her new shell hardens. She is now 11cm wide and about 23cm long (including her tail). The smaller of the two is now two moults behind her sister and is still asleep under the sand.

The Aiptasidol seems to be working with most of the aiptasia now gone, although we are still finding one or two on a daily basis. If they persist, we'll reintroduce some Berghia to the tank to finish them off.

November 2016. All of the aiptasia have now disappeared and the smaller crab has also moulted and is now only one moult behind her larger tankmate. Unusually she is taking longer than normal to recover from this ordeal and has not yet starting eating again. We will have to monitor this closely over the next few weeks. Horseshoe crabs go months between feeds when they are preparing to moult so this is only a slight concern at this stage.

As larger crabs = more waste & debris around the tank we have upgraded our filter pump from a Hailea 1500 to a Hailea 2000 version to maintain a high level of water quality.

December 2016. Crabs both eating normally (like horses!) but the additional food seems to have fostered a bloom of brick-red algae that is settling over every flat surface like a fine dust. There do seem to be some pros as well as cons though in that the crabs do seem to like eating the stuff! They cannot keep place with the bloom however and so our cleaning regime has had to be increased from weekly to once every 2-3 days. Cutting down on the food should reduce nitrate levels and the bloom should eventually disappear.

March 2017. The red algal bloom has been very persistent so we added a small UV steriliser unit to the tank which has helped considerably. We have also moved the live rock from the end of the tank to the centre as the crabs do seem to like the corners of the aquarium and the larger of the two was geting her tail stuck under the rock!

August 2017. The good news is that the red bloom has now completely gone. The bad news is that the Aiptasia Glass Anenomes love the rock in its' new position and are thriving behind it - just where it is most difficult to kill them off with the Aiptasidol solution!

Aiptasia

As the crabs are quiet at present, probably gearing up to their annual moult, time to try again with the anenome's natural predator, the nudibranch sea slug Berghia stephanieae. These live in western atlantic waters from North Carolina to the Gulf of Mexico and are only 1-2cm long. They do however, have the reputation of being prolific breeders and they eat only Glass Anenomes.

One unexpected addition to the tank, either introduced from the live rock or the new Bahamas sand we added when we upgraded last year, are limpets! There are about ten of these visible at present.

Limpet

Completely harmless to the crabs, sea slugs and macro algae, they graze on the diatoms that cling to the glass of the tank, thus helping to keep it clean.

October 2017. The larger of the two crabs has completed its annual moult and is now a magnificent 15cm x 30cm. Her smaller sister, however, shows no sign of following suit and so is now two moults behind. Why, is a mystery as she appears active, healthy and well fed.

Horseshoe Crab

Two species have thrived over the past three months - and I am happy to report that the Aiptasia is not one of them! The Berghia have done a fantastic job in completely clearing the tank of all of the Aitptasia and given the number that were present this was surprising. A few days ago, however, the Berghia - who only feed at night - started to appear during the daytime. This was a sign that they were short on food and were actively hunting. Three Bergia were added back in August and, beyond all expectations, had successfully bred. Over the next few days, the three became thirty as more and more Berghia vacated all the crevices in the live rock to look for food!

Berghia only eat Aiptasia and with these all gone, they would starve to death within 5-7 days. Desperate measures were needed and so the search began for a "host" who had an Aiptasia problem and who was prepared to give these fascinating little critters a home. On Friday, 20 Berghia, ranging from babies to fully grown adults, were donated to our main zoological supplier, Maidenhead Aquatics of Hawley, Kent. Hopefully, the remaining Berghia will be sustainable with what Aiptasia cells remain in the tank stuck to the glass and in the live sand. If this proves not to be the case - the indicator of having insufficient food being not just daytime hunting but also a loss of colour in their cerata - then I am sure that Maidenhead Aquatics will welcome an additional donation.

The other species to have done well are the Limpets. Again, the original 10 have bloomed into more like 50 but unlike the Berghia they are not fussy eaters and will be able to filter any uneaten food the crabs leave behind and help keep the tank clean by eating the diatoms. The water clarity in the tank is now crystal clear. Something that previously was only seen when the crabs were dormant and no food was being regularly added.

December 2017. The crabs are active and eating well. They also seem to be cleaning the inside of the aquarium glass by eating the brown diatoms that appear and are perhaps also "hunting" the limpets that stray too close to the bottom of the tank!

March 2018. Update: Not many limpets left now. Given that Horseshoe Crabs do eat clams, it is not unreasonable that they would like limpets too and as they cannot attach themselves to the aquarium glass as strongly as they can to rock they will be easy prey for the crabs. Horseshoe crabs reach sexual maturity when they are between nine and eleven years old. Ours were about 18 months old when we bought them. We have therefore until Summer 2022 to design and build a marine aquarium that includes a shallow end that terminates in a beach for them to be able to lay their and fertilise their eggs. If successfully fertilised - and without natural pedators to reduce the numbers of offspring - I could be the proud Uncle of up to 10,000 babies!

August 2018. The crabs have become sluggish again as they prepare for their annual moult becoming active only twice a week for a few hours while they look for food and then going back to sleep again for a few days.

The ozone generator we added a couple of years ago packed up in May and as we had difficulty sourcing an exact replacement left it for a couple of months. Big mistake! The water clarity (although thankfully not the quality) suffered, taking on a yellowish tinge because of the presence of dissolved organics from uneaten food. We have now acquired a new ozone generator similar to the original and after only two weeks the water clarity is now crystal clear once again.

With the long hot summer we have had so far, the chiller has been essential to control the water temperature as warm water cannot hold oxygen as well as cold water. The room temperature has been 30 degrees Celsius and over, but the water temperature in the tank has been successfully maintained between 20 and 22 degrees. Just to be on the safe side however, we have been running an air pump/bubbler to ensure the crabs do have a healthy supply of oxygenated water.

Whether it is the time of year, the water temperature, the lack of ozone or something completely unrelated, the dreaded Aiptasia are back! Only a few but two were found hiding behind the live rock and have become quite large. Will try and kill them off with Aiptasidol solution and if this proves ineffective consider obtaining some more Berghia.

December 2018. This page will no longer be updated. Click here for further information.

For additional information on the horseshoe crab click here

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