Blue-green al­gae spread more and more in Baltic Sea thanks to hu­man ac­tiv­i­ties

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The growth of blue-green al­gae in the Baltic Sea is a his­toric oc­cur­rence. How­ever, it is thanks to hu­man ac­tiv­i­ties that the in­ten­sity of this process con­tin­ues grow­ing, ex­plains head of Marine Ecol­ogy Lab­o­ra­tory of the Univer­sity of Latvia Elmīra Boikova.

She says in­ten­sive growth of blue-green al­gae in hot weather con­di­tions in the Baltic Sea was ob­served a cou­ple of cen­turies ago. This phe­nom­e­non is nat­u­ral for the Baltic Sea. How­ever, it is thanks to hu­man ac­tiv­i­ties, an­thro­pogenic load and agri­cul­tural waste wa­ter that this phe­nom­e­non has been spread­ing more wildly lately, caus­ing ma­jor dam­ages to the ecosys­tem. «Blue-green al­gae have been present in the Baltic Sea for a very, very long time. Growth of these al­gae was ob­served as far back as the 18th cen­tury – when in­ten­sive in­dus­trial ac­tiv­i­ties were not yet present. The ques­tion is scale of growth of these al­gae in the past?» said the re­searcher.

In spring, when river wa­ter car­ries ni­tro­gen and phos­pho­rus to the sea, it causes al­gae that feed of those sub­stances to grow more. In sum­mer, how­ever, when in­or­ganic ni­tro­gen is close to zero, blue-green al­gae be­gin to grow. These al­gae are able to ab­sorb ni­tro­gen from the air, says Boikova. The ex­pert says that as blue-green al­gae grow they be­come buoy­ant, gath­er­ing on the sur­face of the wa­ter. Blue-green al­gae do not present a valu­able source of nu­tri­tion for other or­gan­isms, and they do more harm than good – in large vol­umes they start slowly di­vid­ing and slowly sink­ing to the seabed and us­ing up oxy­gen. This cre­ates anoxic zones. Such zones were pre­vi­ously ob­served in Baltic Sea’s deep­est ar­eas, such as the Got­land Deep. Fin­nish re­searchers have been warn­ing for decades that the spread of anoxic zones have been rapidly spread­ing, and one of the rea­sons for this is the rapid growth of blue-green al­gae, Boikova ex­plains.

Aside from blue-green al­gae, the Baltic Sea still has a fair share of prob­lems – oil pol­lu­tion from in­ten­sive sea­far­ing, pol­lu­tion from phar­ma­col­ogy and cos­met­ics in­dus­try, sewage wa­ter con­tain­ing or­ganic sub­stances that pro­mote the growth of blue­green al­gae, the ex­pert ex­plains.

She adds that the sea, sim­i­lar to hu­mans, has a way of adapt­ing to the chang­ing en­vi­ron­ment – the sea is able to per­form cer­tain self-cleans­ing pro­cesses. But it is cur­rently im­pos­si­ble to say when the Baltic Sea may reach its red line, af­ter which things may very well go tum­bling down. Boikova adds that ev­ery re­gion of the Baltic Sea has a ‘red line’ of its own. Be­cause species va­ri­ety is not large, their ecosys­tem is very sen­si­tive, be­cause each species per­forms its own unique func­tion. This means – the fewer or­gan­isms live there, the eas­ier it is to cause im­bal­ance in the ecosys­tem. Al­though the Baltic Sea is one of the most re­searched seas, there are still many unan­swered ques­tions, said the re­searcher. There is cur­rently noth­ing we can do about the growth of blue-green al­gae, she added. Swedish re­searchers had pre­vi­ously tried pump­ing oxy­gen into the sea to speed up blue-green al­gae blow­ing process, but these ef­forts have come to naught.

To com­bat the prob­lem of blue-green al­gae spread­ing more than they should, ships should not be al­lowed to flush any­thing into the sea, in­clud­ing sewage, the re­searcher rec­om­mends.

Hu­man sen­si­tiv­ity to blue-green al­gae dif­fers from per­son to per­son. Nev­er­the­less, ex­po­sure to this type of al­gae is known to cause con­junc­tivi­tis. Blue-green al­gae do not live for very long, but they do grow quickly – up to five cell di­vi­sions can hap­pen in a day. This is eas­ily ob­served us­ing satel­lite im­ages. Once the heat backs off, blue­green al­gae will stop grow­ing, said Boikova, adding that re­duc­tion of their con­cen­tra­tion re­quires strong waves.

Latvia’s Health In­spec­torate has es­tab­lished re­stric­tions on swim­ming in sev­eral of Latvia’s bathing ar­eas due to in­creased spread of blue-green al­gae.

Pol­ish au­thor­i­ties an­nounced clo­sure of the Baltic Sea coast dues to in­creased con­cen­tra­tion of blue-green al­gae on Wed­nes­day. This week Pol­ish tele­vi­sion showed pho­tos the sea taken from the air show­ing a wide spread of blue-green al­gae. Ac­cord­ing to in­for­ma­tion from the Swedish Me­te­o­rol­ogy and Hy­drol­ogy In­sti­tute, nearly the en­tire cen­tral por­tion of the Baltic Sea is cov­ered in blue-green al­gae. Al­gae cover the Baltic Sea from the Pol­ish coast all the way to Stock­holm and Fin­land. Con­cen­tra­tion of blue-green al­gae is the low­est in the wa­ters near Den­mark, as well as the Gulf of Riga and Both­nian Bay. The largest con­cen­tra­tion of blue-green al­gae in Latvia is found around North­ern Kurzeme.

Žy­gi­man­tas Gedvila/

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