[da capo] Of Terms in Bi­ol­ogy: Neuston

[da capo] Af­ter Me­chas' post last Thurs­day on Biocrusts, Christoph re­minded us of Merry's post from Oc­to­ber 2009 on the aquatic equiv­a­lent of biocrusts: Neuston. We felt it most ap­pro­pri­ate to re-post it now. From Merry's and Me­chas' words, it seems both of them had sim­i­lar epipha­nies, dis­cov­er­ing whole new worlds, 14 years apart...

by Merry

When I stum­bled across the term bac­te­ri­oneuston, I dis­covered a whole new world where the air meets the sea. I found that ma­rine neuston had long been used to re­fer to the di­verse flora and fauna in­hab­it­ing the top­most 5 cm of the oceans – a dis­tinctly dif­fer­ent as­sem­blage than found in the wa­ters be­low. This broad group­ing had been fur­ther sub­di­vided. Float­ing or­gan­isms, such as Physalia, the Por­tuguese Man o' War, make up the pleuston (the small or­gan­isms float­ing on or near the sur­face of a body of wa­ter, from the Greek pleustikos, fit for sail­ing). The 40-some species of wa­ter strid­ers are part of the epi­neu­ston (the or­gan­isms liv­ing in the air on the sur­face film of a body of wa­ter). Just be­neath them, liv­ing im­me­di­ately be­low the sur­face film, are the or­gan­isms of the hy­poneuston. There are no hard and fast lines here. A div­ing epineustonic wa­ter strider finds it­self briefly a hyponeu­ston. The plank­to­hy­poneuston gather near the sur­face at night but spend their days be­low. And, of course, the plank­ton float or drift through­out the rest of the wa­ter col­umn. (For these neustonic terms and more, click here.)

Fig. 1. A wa­ter strider. Surely hand­some, al­beit not mi­cro­bial. Source

No­tice how those de­f­i­n­i­tions shifted from the top­most 5 cm to the sur­face mi­cro­layer film as our fo­cus of in­ter­est shifted. To­day, un­adorned neuston is of­ten used to mean the or­gan­isms in the sur­face film. Its et­y­mol­ogy? From the Greek neustos swim­ming, from nein to swim.

The pres­ence of a gelati­nous sur­face mi­cro­layer film had been pro­posed in 1983, based partly on ob­ser­va­tions of the slick as­so­ci­ated with blooms in the Sar­gasso Sea of the fil­a­men­tous cyanobac­terium Tri­chodesmium. (It struck me that the sur­face mi­cro­layer might be a most de­sir­able loca­tion for a fil­a­men­tous, ni­tro­gen-fix­ing, pho­to­syn­thetic cyanobac­terium.)

What about the ocean sur­face film from the mi­cro­bial neuston­ian point of view? It might ap­pear to be an im­mense biofilm stretch­ing from hori­zon to hori­zon. Thick­ness? The au­thors of one pa­per wryly note: In most in­ves­ti­ga­tions, the sur­face mi­cro­layer is op­er­a­tionally de­fined based on the depth of the sam­ple layer col­lected, which is in turn de­pen­dent on the sam­pling method em­ployed. Es­ti­mates of its thick­ness range from 1 to 50 µm, with some of the dif­fer­ence likely due to the vari­able lay­ers of bac­te­ria present. Sur­face layer bac­te­r­ial con­cen­tra­tions are com­monly said to be 10³−10⁵ times higher than in the un­der­ly­ing wa­ter col­umn. One study of the North Sea found that the sur­face layer mi­crobes were pre­dom­i­nantly from two gen­era, Vib­rio and Pseudoal­teromonas, both of which have char­ac­ter­is­tics sug­ges­tive of adap­ta­tion to life in biofilms.

Oh, what about the bac­te­ri­oneuston, where this ar­ti­cle be­gan? This is – of course – the bac­terial com­po­nent of the neuston. So far Google finds no men­tion of an ar­chaea­neuston. The poor Ar­chaea, ig­nored and ne­glected yet once again.

 

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