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Home* Antarctic News → The menu of pen­gu­ins might help to pre­dict chan­ges of their mari­ne habi­tat

The menu of pen­gu­ins might help to pre­dict chan­ges of their mari­ne habi­tat

In the midd­le of the Sou­thern Oce­an the­re is a gre­at wild­life para­di­se: South Geor­gia. The archi­pe­la­go is well known for the lar­ge num­bers of sea birds and seals that are bree­ding here. The land is home for four spe­ci­es of pen­gu­ins: King pen­gu­ins, Gen­too pen­gu­ins, Chin­strap pen­gu­ins and Maca­ro­ni pen­gu­ins.

Bird Island is part of South Geor­gia. This litt­le island lays nor­thwest of the main island. Bri­tish sci­en­tists have been ope­ra­ting a bio­lo­gi­cal rese­arch sta­ti­on here for the last deca­des. This year the rese­ar­chers publis­hed all their know­ledge of the last 22 years on the diet and the popu­la­ti­on deve­lo­p­ment of Gen­too pen­gu­ins and Maca­ro­ni pen­gu­ins.

The sci­en­tists found a trend in a well doing Gen­too popu­la­ti­on ver­sus a less well doing Maca­ro­ni popu­la­ti­on. They descri­be the Gen­too as a gene­ra­list spe­ci­es, fee­ding in the pela­gic zone as well as at the sea bot­tom clo­se to the coast. The Maca­ro­ni is descri­bed as a spe­cia­list spe­ci­es fee­ding all kind of crustace­ans clo­se to the shelf-break regi­on. Howe­ver, the most important and ener­gy rich main food of both pen­gu­in spe­ci­es is the Ant­arc­tic krill (Eup­hau­sia super­ba). But while the Maca­ro­ni pen­gu­in sticks to crustace­ans, the Gen­too is pre­fer­ring various fish spe­ci­es espe­cial­ly during the bree­ding sea­son. One important source is the com­mer­cial­ly used Macke­rel ice­fi­sh (Champ­so­ce­pha­lus gun­nari) .

Life is not dis­tri­bu­t­ed even­ly in the oce­ans. Water mas­ses are com­plex and water fronts are of high impor­t­ance. An important con­ver­gence zone is situa­ted North of South Geor­gia. Here a lay­er of cold, oxy­gen-rich sur­face water from the South meets warm, oxy­gen-poor sur­face water from the North and sinks under­ne­ath it, befo­re the cold water con­ti­nues its way nor­thward as inter­me­dia­te water lay­er. Such zones can be found any­whe­re in the world. Here, the water mas­ses mix. They crea­te a cor­ri­dor full of life whe­re tiny crustace­ans feed on algae and are eaten by other spe­ci­es like fish or sea birds. This zone is so important for the sou­thern mari­ne eco­sys­tem, becau­se it is not inter­rup­ted by any land mas­ses. It also defi­nes the nort­hern bounda­ries of the Sou­thern Oce­an. Depen­ding on the pre­vai­ling winds, win­ter sea ice dis­tri­bu­ti­on or the amount of lar­ge ice­bergs in the area, this rich mixing zone moves fur­ther to the North or to the South. Inte­res­tin­g­ly, the richest Sub-Ant­arc­tic Islands are situa­ted wit­hin this pro­duc­ti­ve belt.

Pen­gu­ins swim dif­fe­rent distan­ces to find their food. The ener­gy inta­ke has to be balan­ced. The food of a fora­ging bout must cover both the ener­gy con­sump­ti­on during the hun­ting trip as well as the time the bird spends on shore. During the bree­ding sea­son the food for the off­spring has to be accoun­ted for as well. If the balan­ce is cor­rect, the popu­la­ti­on is doing well. If the prey chan­ges its whe­rea­bout due to chan­ges in its habi­tat (water tem­pe­ra­tu­re, salini­ty, com­mer­cial fishing), the pen­gu­ins have to swim fur­ther to reach their prey or they will switch to alter­na­ti­ve prey, with less ener­gy out­co­me. The ener­gy brought along may not be suf­fi­ci­ent enough for the off­spring to sur­vi­ve.

Both dis­cus­sed spe­ci­es dif­fer clear­ly in their way loo­king for food. The Gen­too pen­gu­ins with their two chicks are often stay­ing clo­se to the coast. They usual­ly return to the nest after one day fora­ging. The Maca­ro­ni pen­gu­ins use to swim about 150 kilo­me­ters for several days to catch enough food for them­sel­ves and their sin­gle chicks. Both spe­ci­es have the same prey spe­ci­es on the menu. But if they breed tog­e­ther, like on Bird Island, then the Gen­too pre­fer various kind of fish near the coast and the Maca­ro­ni catch dif­fe­rent crustace­ans on the shelf edge.

The sci­en­tists of the stu­dy would now like to under­stand, how chan­ges in the diet com­po­si­ti­on of the pen­gu­ins reflect chan­ges in the mari­ne eco­sys­tem. Krill and fish stocks are play­ing a major role in this food web, sin­ce both are resour­ces for the ani­mal pre­d­a­tors and the fishing indus­try.

Maca­ro­ni pen­gu­ins, South Geor­gia.

Macaroni penguins, South Georgia

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last modification: 2017-05-11 · copyright: Rolf Stange
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