The threat posed to native species by water hyacinth (Eichhornia cras…

The correct answer is Option (3) → alien species invasions

An alien species is one that comes from another region. It may be brought in by accident or on purpose. Some alien species become invasive: they spread fast and cause the decline or extinction of native species. Water hyacinth (Eichhornia) is one such invasive weed in Indian water bodies.

Option (1) habitat loss and fragmentation — Incorrect. This is the destruction or breaking up of the places where species live, such as the clearing of tropical rain forests. The threat from water hyacinth comes from a new species spreading, not from the habitat being cleared.

Option (2) coextinctions — Incorrect. Co-extinction is when one species dies out because a species it depends on has become extinct, such as a parasite with its host fish. Water hyacinth is thriving, not dying out.

Option (3) alien species invasions — Correct. Water hyacinth is not native to India. It turned invasive and now threatens native species. This is an alien species invasion.

Option (4) overexploitation — Incorrect. Over-exploitation is over-use of a resource by humans, such as over-harvesting of marine fish. Nobody is over-using water hyacinth.

NCERT Extract:
Loss of Biodiversity – “… (iii) Alien species invasions: When alien species are introduced unintentionally or deliberately for whatever purpose, some of them turn invasive, and cause decline or extinction of indigenous species. … You must be familiar with the environmental damage caused and threat posed to our native species by invasive weed species like carrot grass (Parthenium), Lantana and water hyacinth (Eicchornia).”