New to nature No 122 : Jaera tyleri

J. tyleri, discovered feeding on a whale carcass. Photograph: Sven Thatje, courtesy of Dr Katrin Linse

This blind isopod was discovered feeding on a whale carcass deep in the Southern Ocean

Sunday 27 April 2014. Decomposing an enormous carcass in the deep sea is a whale of a problem. There was little organised interest in “whale falls”, as they are known, until the discovery of associated chemoautotroph communities in the late 1980s. Since then, there has been a dramatic increase in systematic studies of the succession of visitors to natural and human-placed whale cadavers to move beyond earlier spotty and anecdotal notes. The story so far suggests three distinct stages in the decomposition of these mammalian remains. First come the mobile scavengers that tear away tissues through active feeding. These include crabs, amphipods, and isopods among invertebrates and hagfish and sleeper sharks among vertebrates. Second are opportunist species, largely invertebrate, that feed on remaining bones and soft tissues that are taking advantage of this temporary nutrient enrichment of their habitat. Finally are the so-called sulphophilic fauna that consist of a diverse collection of bone-feeders, grazers of bacteria, suspension and deposit feeders, and various predators drawn to the action. The anaerobic breakdown of lipids found in the bones results in the release of sulphides that become the chemical basis for a chemoautotrophic “ecosystem”.

Isopods have been observed throughout the stages of decomposition of whales but have rarely been the subject of research projects that more often focus on worms, molluscs, decapods, and fishes. Because no reported isopod visitors to whale falls had ever included members of the genus Jaera, there was no reason to suspect their involvement. This recently changed when a species new to science, Jaera tyleri, was discovered in large numbers feeding on a whale carcass at 1,445m in the Southern Ocean.

Isopods of the family Janiridae are found from the Arctic to the Antarctic and in the Pacific, Indian, and Atlantic oceans between. Its 174 species may or may not be descendants of a common ancestor and are found in many habitats from intertidal to hadal deep sea, including estuaries, salt springs, and caves. Many shallow water species are grazers and herbivores feeding on seaweed, woody materials, and microbial films. For most deep-sea species, almost nothing is known of feeding habits. It is a few species of other genera in this family and those of Munnopsidae that are most frequently reported from whale falls.

While the monophyly of the family is questionable, that of the genus Jaera is not. Data so far suggest that it is monophyletic with its primary distribution in the northern hemisphere. Only five genera in the family have been seen below 1,000m depth, underscoring our ignorance in general of the fauna of the deep.

The new species was introduced in a paper in the online journal PLoS ONE by an international team of German, Russian, and UK researchers led by Katrin Linse of the British Antarctic Survey at Cambridge. In addition to describing the species and verifying its placement in the genus with molecular data, they reviewed all the available geographically precise records for Jaera that they could find, 678 in total. Until the discovery of J. tyleri, all records were from shallow waters in the northern hemisphere. Morphologically, it is easily distinguished from others due to the absence of eyes and short antennae. Reduced eyes have been noted in a complex of species in the Mediterranean, but J. tyleri is unique in its complete blindness.

Individuals of the new species were found on all parts of the whale remains apart from those buried in sediment. The population density was high, with 470 to 6,000 specimens per square metre. Females were slightly more prevalent than males and an analysis of the sizes of specimens suggested the presence of multiple cohorts and continuous breeding. The stories of the ecology of whale falls and the evolution of Janirid isopods will remain incomplete until detailed species surveys, taxonomic revisions and ecological observations are done.

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