PAR­A­SITES: PROF­IT­ING FROM CLI­MATE CHANGE

Asian Diver (English) - - Science - Text by Dr. Paul Sikkel

Some crea­tures look set ben­e­fit from the rav­ages of a chang­ing cli­mate, at least tem­po­rar­ily…

LIKE SO MANY

divers and ma­rine sci­en­tists of my gen­er­a­tion, I was in­spired by watch­ing count­less hours of The Un­der­sea World of Jac­ques Cousteau: whales sharks, colour­ful co­ral reef fishes, and bril­liant co­ral reefs! My first snorkelling ex­pe­ri­ence came in sev­enth grade when I en­rolled in a free­d­iv­ing course at the local YMCA in La Canada, Cal­i­for­nia. Af­ter that class, I knew that my pro­fes­sional fu­ture be­longed to the ocean. I re­ceived my open-water scuba cer­ti­fi­ca­tion at age

16, and my di­ve­mas­ter and in­struc­tor cer­ti­fi­ca­tion at age 21. I went on to com­plete Bach­e­lor's, Mas­ter's and Ph.D. de­grees in bi­ol­ogy and ma­rine sci­ence. Like the vast ma­jor­ity of divers, my fo­cus when in the water was on the big and the spec­tac­u­lar – things that were eas­ily seen.

My per­spec­tive changed rad­i­cally when in 1997, I ob­served dam­selfish on a co­ral reef in­ter­rupt­ing spawn­ing to visit clean­ing sta­tions at dawn.

As many divers know, cleaner fishes and shrimps re­move par­a­sites from larger fishes. Broadly known as clean­ing sym­bio­sis, these in­ter­ac­tions oc­cur at sta­ble lo­ca­tions on the reef known as “clean­ing sta­tions” that are eas­ily iden­ti­fi­able to divers and to fishes that visit them. Since this chance ob­ser­va­tion, the pri­mary fo­cus of my research has been on the tiny things that make their liv­ing by con­sum­ing parts of larger or­gan­isms such as fishes – par­a­sites, some of which are eaten by clean­ers. Be­cause par­a­sites are dif­fi­cult to see, they are typ­i­cally ig­nored by most divers and even most sci­en­tists. Yet, they rep­re­sent some­thing of a smaller ma­jor­ity – over 50 per­cent of the liv­ing or­gan­isms on co­ral reefs. Ev­ery liv­ing thing that is vis­i­ble to a diver is habi­tat for par­a­sites, and even many par­a­sites have par­a­sites!

THE TICKS OF THE SEA

If one opens the gut of a cleaner fish, what stands out is the large num­bers of a par­tic­u­lar kind of par­a­site called a gnathiid iso­pod. In fact, larger clean­ers such as the cleaner wrasses that are so com­mon in Asian and Australian reefs can eat over 1,000 of these par­a­sites each day.

Gnathi­ids are very sim­i­lar to ticks and mosquitoes on land – the “ticks of the sea”. Like ticks and mosquitoes, gnathi­ids at­tach to their host long enough to se­cure a blood meal. It is dur­ing this feed­ing stage that they can be eaten by clean­ers. Af­ter their blood meal, they drop off and hide in the reef, digest­ing their meal and molt­ing to the next stage, and then feed­ing again. This con­tin­ues un­til they have reached adult­hood (only ju­ve­nile gnathi­ids feed on fish blood), when they do not feed, but re­pro­duce, then die.

Gnathi­ids play a ma­jor role on co­ral reefs. The ir­ri­ta­tion they cause their host fish in­flu­ences the be­hav­iour of co­ral reef fishes such that they increase their in­ter­ac­tion with clean­ers. Large num­bers

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