We’ve been quite busy the last few weeks, setting up coral nurseries all around the island of Bali, Indonesia. One of our reef restoration sites which is an Ocean Gardener project in Amed, North Bali is starting to attract more and more interesting reef creatures and critters. The last one we were lucky enough to spot and observe was a trio of Halimeda Ghost Pipefish, Solenostomus halimeda.
This fish is so well camouflaged, that only the young eyes of our last female Ocean Gardener instructor could spot it. And even with someone pointing it to me underwater, my weary eyes took a long time to actually be able to make out the fish in its habitat. It has only been than 20 years since the halimeda ghost pipefish was described, although it was known by divers for a lot longer than that.
The specialty of Solenostemus halimeda is to mimic perfectly Halimeda algae leaves. And this very distinctive fish is so good at camouflage that it’s almost impossible to distinguish from the Halimeda algae within which it lives. This level of specialization pushes the level of mimicry to also harbor the same invertebrates that grow on the algae. The different body proportion and ray fin count separates it from the other members of this genus which includes the Ornate (Solenostomus paradoxus), Robust (Solenostomus cyanopterus) Ghost Pipefish.
In this Genus, females differ from male by having large, fused pelvic fins designed to incubate their eggs, unlike Syngnathids like other seahorses and pipefish in which males brood the eggs.
Embryos, enclosed in egg envelopes, are attached to epidermal stalks, termed cotylephores, that occur only in brooding females. Cotylephores are cellular outgrowths of the epithelium on the inside surface of the pelvic fins. This particularity makes this genus really special.
Adjacent calyces of the same cotylephore establish attachments with the envelope of a single egg. Cotylephores are composed of a surface epithelium that is continuous with the skin and a fibrous connective tissue core that contains blood vessels that ramify into an apical capillary plexus. The plexus may function in maternal-embryonic metabolic exchange.
The cotylephores of Solenostomus closely resemble the epidermal stalks (cotylephores) that are the sites of egg attachment in the skin-brooding South American catfish, Platystacus cotylephorus. Based on similarity in structure and probable function, cotylephores in the two groups of fishes are an example of evolutionary convergence. (Wetzel, J., Wourms, J.P. Adaptations for reproduction and development in the skin-brooding ghost pipefishes,Solenostomus . Environ Biol Fish 44, 363–384 (1995). https://doi.org/10.1007/BF00008252)
The females carry multiple ages of eggs/larvae in their ventral fin “pouch”. So they release larvae every day once they are mature. This also explaining why there are often multiple males hanging around a female.
Obviously the habitat is Halimeda algae beds, where it blends perfectly. Halimeda is a genus of green macroalgae which has a body that is composed of calcareous green segments and most herbivorous fish avoid it. This species produces extensive algae beds, and reefs, that can harbor a wide diversity of flora and fauna.
The life cycle of this amazing critters, is short. They spend most of their live hanging in the water column among plankton. They are small and mostly transparent during all these stages, until they settle on the reef, color up, mature, and reproduce. They then die off. That’s why, we can only observe them on the reef for only a few weeks. We start seeing transparent newly settled larvae then they mature and gather together for breeding purposes, get some eggs, and age quickly before disappearing.
This genus was successfully spawned and bred few times already. But the challenge is to keep genetically viable broodstock out of each cycle. Needing a regular input of new genetics into the loop. Thanks to Matt Wandell and Richard Ross for many of these informations.