Eagle-eyed marine scientists behind the discovery and description of a “peculiar” new species of fish have hailed the moment “an excellent opportunity” to study a process called ‘rapid diversification’ – the speed at which new species emerge as others go extinct; an evolutionary process that “may just counteract the loss of biodiversity.”

Last week, scientists from the Liebniz Centre for Tropical Marine Research (ZMT) in Bremen – together with colleagues from Central America – described a new species of fish in the Gulf of Mexico. Called Hypoplectrus espinosai, the new species belongs to the hamlet group – a small predatory fish that lives most commonly among the coral reefs in the Caribbean and the tropical northwestern Atlantic.

This new species was discovered in the Alacrane Reef, a reef complex in the Campeche Bank in the southern Gulf of Mexico, where – using genetic data, geographical records, and a series of photographs – the international team of researchers from Germany, Mexico, and Panama were able to describe the new species before publishing their findings in the scientific journal, Zootaxa.

There are currently 18 recognised species of hamlets – seven of which have been described within the last 14 years. These fish are generally distinguished by their colour patterns, which vary from species to species and are largely genetically determined. 

Spotting a new species of hamlet takes a keen eye. 

“In the past, different hamlets were thought to be diverse colour variants of one species, but now we know that they are individual species,” said Oscar Puebla, a marine biologist at ZMT and a professor of Fish Ecology and Evolution at the Institute for Chemistry and Biology of the Marine Environment (ICBM) at the University of Oldenburg.

“My Mexican colleague, Alfonso Aguilar-Perera from the Autonomous University of Yucatan contacted me some time ago because he had observed a peculiar fish while diving in the Alacranes Reef in the Campeche Bank.”

The colour pattern of this “peculiar” fish resembled two well-known species of hamlets: the butter hamlet (Hypoplectrus unicolor), which is widespread in the Caribbean, and the Veracruz hamlet (Hypoplectrus castroaguirrei) which lives in the western Gulf of Mexico. 

Despite the similarities the newly discovered fish shared with these two, it also – to those eagle-eyed scientists – showed two clear differences.

“It made us curious. We both thought it was a very interesting find, but we also knew that we needed genetic data and a broader geographical perspective to accurately identify this fish,” said Puebla. 

It took an international collaborative effort, but with the help of experts from the University of Michoacana de San Nicolàs de Hidalgo in Mexico and the Smithsonian Tropical Research Institute in Panama, the researchers were able to compile a comprehensive data-set containing the genetic data, geographical records, and the photography they needed to make the description. 

With a black saddle patch on its caudal peduncle, the new species – commonly known as the Campeche Bank Hamlet – one of the smaller species, measuring in at an average size of 11 centimetres. 

“The black saddle patch on the caudal peduncle of the new species distinguishes it from the butter hamlet, whose patch is less extensive and only covers part of the caudal peduncle. The new species also doesn’t have the black eye mask that characterises the Ceracruz hamlet,” said Puebla.

This is all vital information. According to Puebla, the speciation process of hamlets is not yet complete. This new species therefore “offers an excellent opportunity” for scientists to study the “genetic drivers of rapid diversification.”

“How many species there are in the world depends on how quickly new species emerge and how many go extinct,” said Puebla. “The example of the hamlet shows how a natural evolutionary process may counteract the loss of biodiversity.”

Estimates of species extinction rates currently vary. It is generally agreed upon among scientists that we are losing a ‘significant number’ of species each day. Recent studies estimate about eight million species on Earth, of which at least 15,000 are threatened with extinction. While current species extinction rates are highly debated, a common consensus is that today’s extinction rate is hundreds – or even thousands – of times higher than the natural baseline rate.

The researchers behind this study have given the new species the common name ‘Campeche Bank hamlet’ in honour of the species’ geographical distribution area off the north coast of the Yucatan Peninsula in the south-west of the Gulf of Mexico. It’s a description the team behind it believe will highlight the Campeche Bank as an area of interest that harbours endemic reef fish and therefore requires special protection.

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