[Tide Bites]: Pygmy Seahorses – Little Fish With a Big Impact

“Tide Bites” is the monthly newsletter of UW Friday Harbor Laboratories. This month, FHL guest researcher Graham Short discusses his research in Adam Summers’ lab on pygmy seahorses. The application to study in residence at FHL in spring quarter 2019 will be opening in early November, and interested students are encouraged to contact the Marine Biology Adviser for more information.

Hippocampus bargibanti  resembles a miniature version of Daffy Duck (Figure 2), and has been sometimes observed congregating in relatively high numbers on one sea fan (2 to 15 individuals) in which all the males are pregnant.  This might have you thinking of a Daffy Duck Lamaze child birthing convention.

– Dr. Graham Short, Research Associate, California Academy of Sciences

Graham is a research associate at the California Academy of Sciences, a summer resident on San Juan island, and a guest researcher at Friday Harbor Laboratories (FHL). His research interests are focused on the evolutionary relationships, taxonomy, and systematics of fishes in the Syngnathidae family, which include the seahorses, pipehorses, and seadragons. The past two summers Graham has been CT-scanning several species of seahorses, in particular the tiny pygmy seahorses, in Adam Summers’ lab to elucidate the subtle morphological characters that distinguish one species from another.

The family Syngnathidae is a large and diverse group of morphologically unique bony fishes, with 57 genera and 300 described predominantly small-bodied marine species of seahorses, pipefishes, pipehorses, and seadragons. The family occurs worldwide in shallow temperate to tropical waters in a range of habitats, including seagrass beds, estuaries, coral and rocky reefs, and mangroves, and are characterized by a fused jaw, extraordinary crypsis, and their unique and specialized reproductive biology. All syngnathids have male brooding structures, and some genera, such as the iconic seahorse in the genus Hippocampus, evolved true male pregnancy with complete nutrient and oxygen delivery to the developing embryos. There are 43 currently recognized species of seahorses (Lourie et al. 2016), the majority of which are comprised of medium to large species (just under an inch to 14 inches). In contrast, seven species of really tiny seahorses, the pygmy seahorses, are diminutive in size (third of an inch to half an inch: you can fit a few of them on your pinky nail with room to spare) and are morphologically distinct from the more numerous and larger species of seahorses.

Apart from their extremely small size, they have a single gill opening on the back of the head (imagine having your nose on the back of your neck), whereas all other seahorses have a pair of gill openings on either side of the head, and the young are brooded within the male’s trunk rather than a pouch on the tail. Two species of dwarf seahorses are sometimes referred to as pygmy seahorses, but differ by lacking the true pygmy’s single gill opening and trunk brooding. These include the endemic Red Sea seahorse H. debelius which dwells only in soft coral, and H. zosterae, a Western Atlantic species that inhabits seagrass and other submerged vegetation.

Fundamental information on the taxonomy, systematics, ecology, and distribution of pygmy seahorses is still relatively sparse in comparison to the larger seahorse species. Within the first decade of the 21st century six new species of pygmy seahorse were officially described. Bargibant’s pygmy seahorse (Hippocampus bargibanti) was the first species of pygmy seahorse to be discovered. In 1969 a New Caledonian scientist, Georges Bargibant, was collecting specimens of Muricella sp gorgonians for the Noumea museum and upon inspection of a specimen he happened to notice a pair of tiny seahorses. I certainly don’t blame him if he thought he’d too much kava (a South Pacific herbal intoxicant produced by locals masticating the plant root) the previous night. Hippocampus bargibanti resembles a miniature version of Daffy Duck (Figure 2), and has been sometimes observed congregating in relatively high numbers on one sea fan (2 to 15 individuals) in which all the males are pregnant. This might have you thinking of a Daffy Duck Lamaze child birthing convention.

Fig. 2: Hippocampus bargibanti.

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