Sci­en­tists re­port long-term dip in world’s phy­to­plank­ton

Austin American-Statesman - - WORLD & NATION -

LOS AN­GE­LES — The world’s phy­to­plank­ton ap­pears to have been dis­ap­pear­ing at a rate of about 1 per­cent a year for the past cen­tury, re­searchers said Wed­nes­day, a dis­turb­ing long-term trend for the microscopic al­gae that form the ba­sis of the ma­rine food chain and pro­duce much of the world’s oxy­gen.

In re­port­ing their find­ings in the jour­nal Na­ture, the Cana­dian team said that, since 1950, phy­to­plank­ton biomass has shrunk by about 40 per­cent. Sci­en­tists had known the pop­u­la­tion was shrink­ing, but the long-term na­ture of that re­duc­tion came as a sur­prise.

“A global de­cline of this mag­ni­tude? It’s quite shock­ing,” said Dal­housie Uni­ver­sity ma­rine sci­en­tist Daniel Boyce, the study’s lead author.

The new study com­bines his­tor­i­cal records of ocean clar­ity with mod­ern satel­lite data, the lat­ter of which has only been avail­able since the 1970s. To­gether, the mod­ern and his­tor­i­cal in­for­ma­tion pro­vide an ac­cu­rate long-term view of the state of phy­to­plank­ton, some­thing sci­en­tists haven’t had be­fore now.

The his­tor­i­cal data were based on mea­sure­ments of ocean clar­ity, which in­volved low­er­ing what looked like a white din­ner plate into the ocean un­til ob­servers lost sight of it. Wa­ter murk­i­ness in­creases or de­creases depend­ing on the amount of phy­to­plank­ton or, more specif­i­cally, The de­cline in phy­to­plank­ton could have long-term ef­fects on the ma­rine food chain and the world’s oxy­gen sup­ply, re­searchers say. Ma­rine di­atom cells are an im­por­tant group of phy­to­plank­ton. the plant’s green chloro­phyll. The fewer phy­to­plank­ton, the clearer the ocean.

Thus, the sci­en­tists were able to con­vert his­tor­i­cal data into spe­cific mea­sures of phy­to­plank­ton pop­u­la­tions, us­ing it with the mod­ern in­for­ma­tion to cre­ate a time­line of the al­gae over the past cen­tury.

“They’re cre­at­ing a cli­mate record out of some­thing that re­ally wasn’t de­signed to do this, us­ing so­phis­ti­cated tech­niques,” said David Siegel, a Uni­ver­sity of Cal­i­for­nia, Santa Bar­bara, ma­rine sci­en­tist who co-wrote a com­men­tary on the paper.

The sci­en­tists noted that the global de­cline, which was ob­served in eight out of 10 ocean basins, also cor­re­sponded with a rise in ocean tem­per­a­tures dur­ing the past cen­tury.

The sci­en­tists sus­pect that warm­ing near the sur­face of the ocean makes each ocean layer more dis­tinct — pre­vent­ing the bot­tom layer, which is rich in nu­tri­ents, from mix­ing ef­fec­tively with the up­per lay­ers and thus fer­til­iz­ing the phy­to­plank­ton.

Boyce said he hopes the re­search will en­cour­age more study of the de­cline. Look­ing into the past could help sci­en­tists de­ter­mine how to re­verse the de­clines, he said.

“This is the tip of the ice­berg, in some re­spects,” Boyce said. “Phy­to­plank­ton are key to the whole ecosys­tem. In terms of cli­mate changes, the ef­fect on fish­eries, we don’t know ex­actly what these ef­fects will be.”

Karl Brunn

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