Meet the Sci­en­tist

Ecol­o­gist Stephen Thack­eray re­veals the ef­fects of ‘un­der­wa­ter heat­waves’ on fresh­wa­ter wildlife and the most likely cause of the high tem­per­a­tures we ex­pe­ri­enced through­out June and July this year.

BBC Wildlife Magazine - - Contents - James Fair

Lake ecol­o­gist Stephen Thack­eray on the ef­fects of ‘un­der­wa­ter heat­waves’

S Win­der­mere’s Arc­tic charr be­come stressed at any­thing above 15˚C. T

Daf­fodils flow­er­ing in De­cem­ber, oak trees com­ing into leaf in March and swal­lows ar­riv­ing be­fore spring should prop­erly have sprung – we’ve all no­ticed changes such as these. Less well-known is that cli­mat­e­change-linked phe­nom­ena are also hap­pen­ing be­neath the sur­face of our lakes and rivers, un­her­alded.

As an ex­am­ple of spring’s now un­timely ar­rival be­low the wa­ter line, Stephen Thack­eray, of the Cen­tre for Ecol­ogy & Hy­drol­ogy (CEH), cites how perch in Lake Win­der­mere are spawn­ing ear­lier. “It’s only a few days each decade, but if this is sus­tained over a long pe­riod it can be enough to dis­rupt re­la­tion­ships be­tween species.” The ap­pear­ance of the perch lar­vae moves out of sync with the seasonal pro­lif­er­a­tion of the plank­ton they feed on, lead­ing to poorer sur­vival rates.

Thack­eray is in lit­tle doubt that this is be­ing caused by long-term changes in our cli­mate, which also prob­a­bly contributed to the ex­trem­ity of this sum­mer’s pro­longed heat­wave. But while pro­vi­sional Met Of­fice records sug­gest air tem­per­a­tures in July were 2.2˚C above the 1981–2010 av­er­age, the sur­face wa­ter in Win­der­mere reached 22˚C, 4˚C higher than the long-term av­er­age. This, Thack­eray says, will im­pact species such as Win­der­mere’s Arc­tic charr, a rel­a­tive of salmon and trout. “They be­come stressed at any­thing above 15˚C, so this is far above their ther­mal range,” Thack­eray ex­plains. They can dive (to 64m in Win­der­mere) to cool down but the habi­tat avail­able to them is re­duced.

The prob­lem is com­pounded as warm­ing tem­per­a­tures also fuel the growth of blue-green al­gae – cyanobac­te­ria – which sinks to the bot­tom and de­com­poses, de­plet­ing oxy­gen lev­els. Over the sum­mer, these had de­creased to be­low 7mg per litre, close to the charr’s limit of 5mg per litre. When it breaks down, the al­gae also re­leases tox­ins that can poi­son live­stock, pets and peo­ple.

Field­work for Thack­eray and his team in­volves tak­ing wa­ter sam­ples, record­ing tem­per­a­tures and oxy­gen lev­els and analysing lev­els of nu­tri­ents such as phos­pho­rus. He is also try­ing to de­vise new ways to un­der­stand these ecosys­tems us­ing satel­lite im­agery to spot fresh­wa­ter al­gal blooms – CEH re­cently launched an app, ‘Bloomin’ Al­gae’ so the pub­lic can join in help­ing with this.

Bio­di­ver­sity de­cline has been more rapid in fresh­wa­ter sys­tems than in terrestrial or marine habi­tats. “The Of­fice for National Sta­tis­tics (ONS) val­ues our fresh­wa­ter sys­tems at £39.5bn,” he says. “But what do the im­pacts on them mean for us?” If any­one is go­ing to find an an­swer, it’s most likely to be Thack­eray him­self.

Stephen stud­ies fresh­wa­ter plank­ton in his lab­o­ra­tory. Be­low: Arc­tic charr are im­pacted by in­creas­ing tem­per­a­tures.

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