Refurbishment of our Large Marine Aquarium

Our newly refurbished aquarium

In aquariology, there is a “Fish only” [FO] aquarium and “Reef” aquarium [R] whereas we were developing the more complex “Fish-only with live rocks” aquarium [FOWLR]. This latter type is designed to showcase fish along with living corals naturally colonised by a variety of marine life (sponges, invertebrates, beneficial nitrifying bacteria). This creates a natural-looking environment and provides excellent supplemental filtration to help maintain a stable eco-system. Usually, a FOWLR aquarium does not contain living corals or invertebrates as these may get eaten by the fish, so to prevent this we will be feeding the occupants daily with a variety of foods.

Our old aquarium – a very popular feature with visitors (click)

• Create a safe environment for marine life, staff and visitors;
• avoid stagnant water and sedimentation areas; easy to clean and to keep clean; hide pipes and pumps;
• representative of Maldivian waters.

Options – materials for the aquarium background

• Expanded polystyrene (inexpensive, but artificial in appearance and not durable);
• prompt natural cement [PNC] (porous, lightweight and easy to model, but not available in Maldives);
• grid with stones (natural elements, but heavy and bulky installation with sedimentation areas);
• polyurethane foam (natural in appearance, durable and lightweight, but expensive and potentially toxic).

From these potentials materials, we choose to make the background with “polyurethane foam”, which is commonly used in public aquaria (as well as in home furniture). This foam is made from two separate ingredients that harden when mixed together and allowed to dry. Before drying, the foam can be modelled and shaped to cover the walls, hide technical equipment and give a natural appearance. Whilst modelling, we were careful to keep the thickness of the foam to a minimum (<10cm) to allow the maximum space for the fish to swim around. Finally, to neutralise any potential toxicity of the foam, we applied four coats of “Epoxy resin”, commonly used in marine aquaria for waterproofing.

300kg of sand was taken directly from the sea to keep its biological benefits. We then added soft and hard varieties of living corals, along with anemones and other marine life beneficial to the ecosystem. We chose different species of corals, sponges and ascidians, to represent Maldivian biodiversity. Crustaceans, echinoderms and molluscs were also added, to facilitate in the tank cleaning process and help to create a balanced and stable ecosystem.

The fish population was carefully selected according to temperament, ability to live together and biological function in the food chain. We avoided carnivorous predators and chose smaller sized fish – a mixture of filter-feeders, detritivores, herbivores and omnivores. Once the fish were caught, we acclimatised them in our turtle pool to become accustomed to dry foods and a closed environment. Aggressive fish and those which did not acclimatise well were returned back to the sea. (As a bonus, having fish in the turtle pools was also beneficial for our rehabilitation turtle residents, as they keep algal growth under control and remove parasites from the turtles).

Sample of fish caught (left, click to enlarge)
Maori wrasse (* top), Picasso triggerfish (left),
Brown butterflyfish (middle), cleaner wrasse (left-middle),
Regal angelfish (right), Emperor angelfish (bottom),
Honeycomb grouper (* bottom right).
(*) The grouper and the Maori wrasse were released due to their size and predator function.

SOFT CORALS
– Bubble coral pearl (Physogyra species), Blue coral (Heliopora coerulea), Mushroom leather coral (Sacrophyton species), Long-lobed cladiella (Cladiella species).

INVERTEBRATES
– Sea anemone (Heteractis magnifica), Sponge (Acabthella klethra), Red pencil urchin (Phyllacanthus imperialis), Mathae’s sea urchin (Echinometra mathae).
– Sea star (Choriaster granulatus), Giant clam (Tridacna squamosa), Sea cucumber (Isostichopus badionotus), hermit crab (Dardanus lagapodes).

VERTEBRATES (FISH)
– Picasso triggerfish (Rhinecanthus aculeatus), Blotched porcupinefish (Diodon liturosus), Crescent perch (Terapon jarbua), Emperor angelfish (Pomacanthus imperator).
– Blue-streak cleaner wrasse (Labroides dimidiatus), Maldivian cardinal fish (Apogon maldivienses), Saddled pufferfish (Canthigaster valentini), Brown tang (Zebrasoma scopas).

Updates February 2017

On 12 February, we upgraded our pumps to more powerful models, so now the tank volume is renewed every 1.5 hours, giving us a better supply of oxygenated water. We also introduced some new inhabitants this month:

• White-spotted pufferfish (Canthigaster janthinoptera)
• Adorned wrasse (Biochoeres cosmetus)
• Six-spots sleeper-goby (Valencienna sexguttata)
• Bird wrasse (Gomphosus caeruleus)
• Imposter blenny (Plagiotremus phenax)
• Monocle bream (Scolopsis bilineata)
• Eye-line surgeonfish (Acanthurus nigricauda)
• Crested sabretooth blenny (Petroscirtes mitratus)

Updates March 2017

Throughout March, the coral life in our aquarium remained stable, except for Acropora and Pocillopora species which showed some bleaching. Using a stronger light to increase the activity of their zooxanthellae (which provide 90% of their energy) did not help, so we chose to transplant them onto our coral frames out in the lagoon. The soft corals which were the most affected in January and February have now recovered.

In aquariology there are 3 different filtering methods:

• Mechanical Filtration (foam, sand, bag): the first step, trapping organic matter particles suspended in the water avoids sedimentation in the tank [we use: 4 sand filters (10μm) followed by 4 ultrafiltration filter bags (5 μm)].
• Biological Filtration (ceramic, bio-balls, living stones): bacterial action transforms dissolved organic matter to cycle Nitrogen [we use: living stones inside the tank].
• Chemical Filtration (charcoal, zeolite, ultraviolet): to modify the chemical parameters of water. Activated charcoal removes organic dyes; ‘green’ water is sterilised with UV [we use: a UV filter].

In order to maintain good water quality in the aquarium, we perform regular cleaning tasks ranging from daily backwashing to annual sand filter cleaning. During March, we cleaned 2 of the 4 sand filters. Each filter contains 450kg of sand, and it took 2 full days of hard work to clean all of the sand from just one filter. We also discovered that some fish had made a home in the filters! (The two puffer fish were moved to our aquarium).

Aquarium – new arrivals

• Long-nose filefish (Oxymonacanthus longirostris)
• Yellow-tail basslet (Pseudanthias evansi)
• Two-colour cleaner wrasse (Labroides bicolor)
• Turn-worm blenny (Plagiotremus rhinorhynchos)
• Two-colour combtooth blenny (Ecsenius bicolor)
• Lined soapfish (Grammistes sexlineatus)
• Red fire-goby (Nemateleotris magnifica)
• Yellow-head butterflyfish (Chaetodon xanthocephalus)

Updates April 2017

Throughout April, we recorded an increase in water temperature of our large marine aquarium. Water is pumped directly from the sea, and as the seasonal ocean temperatures have risen, so too has the temperature of our tank. The average sea temperature for April is 1.4°C higher than last month, with a maximum value of 30°C recorded on 19-20^th April. Thankfully, in the controlled conditions of our aquarium, it is relatively straightforward for us to lower the water temperature with a water chiller or simple ice bucket, and the coral life remains healthy and stable. However, the corals and marine creatures out in the lagoon must cope with and adapt to the increased water temperatures on their own…

We recently caught and released our small Honeycomb grouper (Epinephelus merra) after 4 months, as we think this predator was responsible for the disappearance of some of our aquarium’s smaller occupants! In addition, our Porcupine fish (Diodon liturosus) sadly died after 89 days, maybe due to lack of food (we manually feed during the daytime, and this fish is nocturnal). We also noticed our six-spot sleeper gobies were looking skinny, maybe through a lack of nutrients; these limnivorous (mud-eating) fish need a rich soil substrate, so we decided to put more food at the bottom of the tank.

Some of our new inhabitants this month include:

• Green puller (Chromis viridis)
• Arrow goby (Ptereleotris evides)
• Wrolik’s wrasse (Platyglossus chrysotaenia)
• Moon wrasse (Thalassoma lunare)

Updates May-June 2017

In response to the rise of ocean seawater temperatures observed in April-May, the coral life in our main aquarium was affected –

• Favidae has some necrosis but is globally recovering its green colouration;
• Halomitra and Platygyra species have started bleaching throughout May;
• Porites is now in intermediate condition, part-covered by filamentous algae;
• Poicilopora (re-introduced last month) is recovering from bleaching.

In addition, we introduced a new anemone (Heteractis aurora) found at Madhirivadhoo reef, and another soft coral (Sacrophyton sp.)

With the help of the water sports team, we caught 57 new fish during three 2-hour fishing excursions. We now have a school of Orange Basslet juveniles and different juvenile wrasse species, known to be peaceful in captivity. Our aquarium volume is 3 cubic metres, so to avoid any oxygen problems (tank anoxia) we are careful not to exceed a total fish biomass of 30 kg.

New Residents

• Orange Basslet (Pseudanthias squamipinnis)
• Coral Hogfish (Bodianus axillaris)
• Many-spined angelfish (Centropyge multispinis)
• Peacock flounder (Bothus lunatus)
• Chestnut eyelash blenny (Cirripectes castaneus)
• Oriental sweetlips (Plectorhinchus vittatus)
• Nudibranch (Phyllidia varicose)
• Blue-ribbon wrasse (Stethojulis trilineata), Checkerboard wrasse (Hemitautoga hortulanus), Speckled wrasse (Anampses meleagrides), Dusky wrasse (Platyglossus annularis), Queen rainbow wrasse (Allocoris formosa), Checkerboard wrasse (Hemitautoga hortulanus), Exquisite wrasse (Cirrhilabrus exquisitus), Splendid leopard wrasse (Macropharyngodon bipartitus).

Updates July 2017

The increased water temperatures recorded in the aquarium during the last three months have negatively affected the coral life. Some of our coral species (Agaridae, Porites, Platygyra) have shown necrosis and algal growth. The newly introduced Pocillopora colony has also developed some algal growth and our bleached Halomitra (Cap Coral) specimen was returned to the ocean. By contrast, the Acropora specimens have been growing well, which is interesting as this species was the most affected by the 2016 coral bleaching event.

Certain fish species are unsuitable for life in the aquarium, and need releasing back into the ocean after several weeks. This catch-and-release is a lot of work, but provides a showcase to increase public awareness of our diverse Maldivian reef fish. The current population size is 104 fish, and recent new arrivals include:

• Tall-fin Batfish (Platax teira)
• Moorish idol (Zanclus cornutus)
• Powder-blue surgeonfish (Acanthurus leucosternon)
• Long-nose butterflyfish (Forcipiger flavissimus)

Updates August – September 2017

Disaster has struck! Since July, we have hosted a Merten’s sea anemone (Stichodactyla mertensii), the largest of the carpet anemones, with a folded oral disc that can grow up to a diameter of 1m. The anemones can move and even swim to find their ideal living environment. Unfortunately, our specimen found its way into a water-pump, became stuck and stressed, releasing a defensive mucus into the aquarium water which sadly poisoned most of the fish. In less than 1 hour we lost 90% of our fish population. The Clownfish, which produce a protective mucus against the toxins of the anemone, remained unharmed.

So, we have been busy replenishing the aquarium with help from the Kamadhoo fishermen. The new Red sea sailfin tangs and two-colour combtooth blennys are grazers to keep the growth of the filamentous algae under control, which are in competition with the coral life. We also welcomed 8 small herbivorous Zebrasoma; the juveniles are common among staghorn corals in lagoons.

To improve the coral cover and to showcase the coral propagation project, we have started an extra-small coral frame inside the main tank with 8 fragments of Acropora. We can closely observe the growth and development of these coral fragments, along with the 5 fragments from February placed around the main tank on dead coral substrate.

Mini-coral frame in our aquarium

Corals in our aquarium suffering from algal growth

Updates October 2017

Throughout October we have been focusing our efforts to reduce the algal development which started last month. The lighting has been adjusted down to 12h/day, and the grazer fish are playing a great role in the control of algae growth. New residents this month include Orange Basslets (Pseudanthias squamipinnis); the juveniles are bright orange while the males turn red. They are primarily filter feeders, so need plenty zooplankton especially during acclimation.

Unfortunately, the Sacrophyton soft corals died after 9 months, possibly affected by the high temperatures recorded during May. We have now added two new coral specimens, to bring our totals to 7 species of hard corals and 3 species of soft:
– small-coned coral Hydnophora microconus,
– Physogyra bubble coral, known to be hardy for aquaria life, and our existing colony is very healthy and growing well. It is a “near-threatened” species on the IUCN red list.

Updates November 2017

Water parameters of the main tank have remained stable this month, helping to maintain a balanced ecosystem for the welfare of our aquarium’s marine populations. Water temperatures did not exceed 28°C, and our various corals (3 soft and 7 hard coral species) are generally in good health; our new mini-coral frame fragments have taken hold and started to grow. We take regular photographs of our corals to assess health and growth, and hope to identify the species most suitable to be kept and grown in our aquarium.

Updates December 2017

During 2017, we hosted an average 79 individual fish, representing 29 different species from 14 families.  The water parameters were generally stable throughout the year, apart from a 2°C increase in April-May, caused by warm intake water from the lagoon which badly affected the corals. It took a further 5 months for the tank to reach a balanced state.

We created the background of the main tank back in January 2017, with rocks and 10 coral species. From our experiments, we have determined the best-suited healthy corals to be:

• hard corals – Diploastrea heliopore, Goniopora;
• soft corals – Heliopora coreulea, Physogyra.

And the least suitable corals were found to be:

• soft corals – Cladiella, Sacrophytum, Sacrophytum, Cladiella;
• hard corals – Pocillopora, Porites.