Fish Lab & Aquaria – Marine Life in the Maldives

Blue sea dragon (Glaucus atlanticus) Maldives Marine Savers

💙 A beautiful ‘blue sea dragon’ (Glaucus atlanticus, a sea slug / nudibranch) 💙 

At Kuda Huraa, we upgraded our two small marine aquaria with new light systems, and we are trialling a new type of fish food (Hikari Marine-S) to stimulate vibrant colouration of our tank residents.

Plankton Production

  • Algae -the culture was successfully restarted, and volumes have now returned to normal
  • Artemia – production is keeping up with (at 6g of cysts a day), with one 100L algal tub containing nauplii for grow-out
  • Rotifer – volumes remain consistent and stable

Zooplankton Survey Study – We continue to work on the new net trials for our Zooplankton Survey.

Jellyfish – Aurelia aurita – At the start of the year, we emptied and deep-cleaned our large display cylinder. This was then refilled with 400+ jellyfish from the Fish Lab’s Kreisel tank.
At the end of January, we spotted a large bloom of jellyfish in the open ocean, which we sampled and studied in our newly emptied Fish Lab Kreisel. Based on their bell, oral arms and stinging tentacles, we think these ephyra-stage jellyfish are sea nettles (Chrysaora fuscescens). We hope to confirm this as the jellies grow and develop into full medusa-stage with adult colouration.

Fish Lab - tubs of algae

[Left] K2 and K3 tanks of baby shrimp.
[Right] we grow our fish food; here, 2 tubs algae, 1 tub rotifer.

Fish Lab - Maldivian clownfish breeding pair

New breeding pair of Maldivian anemonefish, bonding-phase

Blue Ocean Magic!

Recently, we had some tiny but very special seasonal visitors in our waters …

  • Beautiful ‘blue sea dragons’ (Glaucus atlanticus) – a member of the a sea slug or nudibranch group of gastropod molluscs. Just 3cm (1.2″) long, these fascinating creatures are hermaphrodites (after mating, both individuals lay eggs). They are pelagic, drifting in the open ocean currents, floating on the surface aided by a gas-filled stomach sac. They use sparkly blue colouration as camouflage, and have a defensive sting.
  • Geometrical and artistic ‘blue button jellyfish’ (Porpita porpita) – a marine organism consisting of a colony of hydroids. The blue button is also 3cm in size, has a (mild) sting, floats passively on the ocean surface, but is eaten by blue sea dragons (the two species are sometimes seen together in the Maldives).
  • Bioluminescent plankton washed up on the beach – see below!
Blue sea dragon (Glaucus atlanticus) Maldives Marine Savers

Blue sea dragon (Glaucus atlanticus) [large photo below]

Blue sea dragon (Glaucus atlanticus) Maldives Marine Savers

Blue sea dragons

Ornamental Fish Breeding

Our focus continues, to produce replicable and consistent data for our research paper on Thor amboinensis, and to continue tracking and describing the reproductive cycle of Lysmata amboinensis.
The Donald Duck shrimp (Leander plumosus) was lost, so the tank was cleaned and emptied to best display the 27 sexy shrimp larvae.
A deceased egg-carrying female shrimp (unconfirmed species) was collected from the lagoon and transferred to our Fish Lab in an attempt to hatch the eggs. This was successful for five eggs, producing caridean shrimp larvae (exact species unknown).

  • Clark’s clownfish (Amphiprion clarkii) – There were two spawning events in January, however, all the eggs were eaten by the parents prior to hatching. We have attempted to vary the parental diet to prevent this, but without success.
  • Maldivian clownfish (Amphiprion nigripes) – New pairs were collected, and now all pairs are bonding. The pair in the main display aquarium produced three egg clutches this month.
  • Sexy shrimp (Thor amboinensis) – We collected a further three clutches this month, which continue to develop well, with good survival rates (66% survival after three weeks). The clutches collected in December have all reached pre-settlement stages, with a total of 162 larvae showing swimmerets and stage-8 features. Of these 162, an initial 27 have settled into juveniles and have been introduced to a display tank with a sample of Lobophelia (brain coral) to encourage colonisation.
  • Boxer shrimp (Stenopus hispidus) – Two clutches were produced this month, and left to hatch for observations on ovary development and reproductive cycle.
  • Camel shrimp (Rhynchocinetes durbanensis) – The late stage larvae from December were lost as we attempted to find the appropriate settlement cue for them. This is likely due to the stress of continuous non-transitional moults as they searched for a settlement cue. Our three resident females produced two clutches each, which were left to hatch.
  • Skunk cleaner shrimp (Lysmata amboinensis) – We collected a total of 734 larvae from the two shrimp. The late-stage larvae from last month were lost in their pre-settlement phase, as we trialled different settlement cues (as with R. durbanensis).
Sexy Shrimp (T. amboinensis adult female)

Sexy Shrimp (T. amboinensis adult female)

Sexy shrimp in the egg

Sexy shrimp eggs

Megafauna

We have recorded some interesting megafauna sightings this month! They included hundreds of spinner sharks (Carcharhinus brevipinna) and pink whiptail stingrays (Himantura fai), as well as regular appearances from both tiger sharks (Galeocerdo cuvier), scalloped hammerheads (Sphyrna lewini), and the bottlenose wedgefish (Rhynchobatus australiae).

In confirmation of local reports, we sighted our first ever bull shark (Carcharhinus leucas) – a female measuring 3-4m in length. There was also the notable (if brief) sighting of a single reef manta ray (Mobula alfredi). Typically, mantas are observed in North Malé Atoll from June to September, so it’s likely this individual was migrating to feeding grounds of high planktonic concentration.

Alex Burden marine biologist Reefscapers (5) sharks Maldives
Bioluminescence on the beach Maldives (Kuda/Bodu Huraa)

Bioluminescence was seen at Kuda Huraa and Bodu Huraa

Bioluminescent Dinoflagellate Plankton
(Dinoflagellights 😁)

Recently, we were delighted to experience the famously spectacular Maldives bioluminescence on the shoreline! Although most bioluminescence is attributed to single-celled dinoflagellates (often Noctiluca scintillans), this particular display was actually caused by small ostracods (thanks, Ale!🔬).
These microscopic crustaceans secrete a luminescent mucous (of luciferin and luciferase) that creates blue light either as a defence mechanism or as part of courtship.

Bioluminescence on the beach Maldives Landaa Giraavaru

Bioluminescence on the beach at Landaa Giraavaru, Maldives

Bioluminescence on Maldivian beach caused by OSTRACODS
Blue sea dragon (Glaucus atlanticus) Maldives Marine Savers