Scuba Diving - - Currents - BY ROBBY MYERS

In­va­sive species can cause se­ri­ous prob­lems — divers don’t need to look fur­ther than the Caribbean’s li­on­fish in­fes­ta­tion for proof. As the ocean heats up — with the po­ten­tial to rise 37.4 de­grees F by 2100 un­der the In­ter­gov­ern­men­tal Panel on Cli­mate Change’s high­est emis­sions sce­nario — other an­i­mals will find their way into new lo­ca­tions in search of cooler waters. The ma­rine life we are div­ing with to­day could well be the in­vaders of to­mor­row.

Corals rely on a pre­car­i­ous bal­ance of en­vi­ron­men­tal con­di­tions to thrive. NOAA states that the op­ti­mal tem­per­a­ture for co­ral growth is be­tween 73 and 84 de­grees F. (Corals also re­quire ap­pro­pri­ate ph lev­els and a host of other con­sid­er­a­tions.) Reef fish play a part in main­tain­ing this en­vi­ron­ment — her­bi­vores like par­rot­fish and rab­bit­fish scrape away al­gae that would oth­er­wise smother the reef and clear space for new corals to col­o­nize. But what hap­pens when you can’t take the heat? You get out of the kitchen.

A 2014 pa­per in the ICES Jour­nal of Ma­rine Sci­ence by Mi­randa Jones and Wil­liam Che­ung of the Univer­sity of Bri­tish Columbia es­ti­mated that ma­rine fish and in­ver­te­brates will shift with a me­dian rate of 16 miles per decade; these trop­i­cal va­grants al­ready have started ap­pear­ing through­out the world. And when the new kids roll into town, there’s of­ten a clash.

When these trop­i­cal graz­ers find their way to tem­per­ate re­gions, they do what they’ve al­ways done — eat the green stuff. This can have a dev­as­tat­ing ef­fect on kelp forests and sea-grass beds, and dis­rupt lo­cal ecosys­tems. Ac­cord­ing to Na­tional Ge­o­graphic, ex­am­ples can al­ready be found in Ja­pan, Aus­tralia, the Mediter­ranean and the Gulf of Mex­ico. The bar­ren land­scape also acts as a po­ten­tial beach­head for co­ral and an in­va­sion of reef-de­pen­dent life. With­out the kelp, tem­per­ate crit­ters lose shel­ter and food, fac­ing a cri­sis of their own. This mix of en­demic and in­va­sive species will lead to in­creased com­pe­ti­tion, and not ev­ery­one will swim away a win­ner.

Jones and Che­ung’s model es­ti­mates that un­der the high­est emis­sions sce­nario, an av­er­age of 6.5 species will be­come lo­cally ex­tinct for every 0.5 de­gree of lat­i­tude be­tween 10 de­grees north and 10 de­grees south be­tween 2000 and 2050. Those that sur­vive will do so by push­ing into new ter­ri­tory or by adapt­ing to the new nor­mal. What will re­main when the bub­bles set­tle is the ques­tion sci­en­tists are try­ing to an­swer.

“We’re still try­ing to un­der­stand which species will be the win­ners with all this en­vi­ron­men­tal change and which won’t do as well,” say Malin Pin­sky, an ecol­o­gist from Rut­gers Univer­sity study­ing ma­rine com­mu­ni­ties. “Even from a co­ral per­spec­tive, there are some out there that do sur­pris­ingly well when the wa­ter is re­ally hot.”

What species will con­tinue to thrive, and where will they be lo­cated in the not-so-dis­tant fu­ture? Whether corals adapt to heated waters or head for cooler climes, one thing seems cer­tain: The un­der­wa­ter realm we ex­plore to­mor­row could look quite dif­fer­ent from the one we know to­day.

An­i­mals will re­lo­cate, but no one knows which ones, and to where.

Par­rot­fish scrape away al­gae and clear space for new corals.

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