Q14 — Aral Sea Food-Chain Restoration and Salinity Tolerance

Theoretical B Real exam question — full text reproduced under IBO's CC BY-NC-SA 4.0 license

The Aral Sea, located in the southwest of Kazakhstan, was one of the largest salt lakes in the world before drying out. Today, the Aral Sea has two basins: Northern and Southern. Freshwater rivers: Syr Darya flows into the Northern basin and Amu Darya flows into the Southern basin. The water from Amu Darya is overused in agriculture, thus only a small part flows into the sea.

One way of restoring the biota of the Aral Sea is by introducing a food chain of new organisms into the sea. Note that species W and Z are native to the Aral Sea ecosystem, and also inhabit freshwater rivers flowing into the Aral Sea.

Left: two side-by-side satellite photos of the Aral Sea before and after drying out. Right: a graph of salinity and the population quantity of species W and Z over time from before 1970 to 2000s, with an arrow marking an artificial species introduction. Figure 1. A The Aral Sea before and after. B Graph of changes in the salinity of both basins (mg/mL) and quantity metric of adult organisms (arbitrary units). A – salinity, W – species W, Z – species Z. The red arrow indicates the artificial introduction of a community of new species.

On your answer sheet, indicate “T” for true statements and “F” for false ones.

A. A fish species introduced for biota restoration must feed on phytoplankton.

B. Species Z is more resistant to high salt concentrations than species W.

C. It's more likely that the return of species W happened earlier in the Northern Aral than in the Southern.

D. Among the artificially introduced animals, there were organisms that are prey for species Z but not predators of species Z.

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Question reproduced from IBO 2024, Theoretical Exam Part B, licensed under CC BY-NC-SA 4.0 — attributed to the International Biology Olympiad. Open the full exam PDF