What is one of the biggest threats to biodiversity on earth?

• A. Pollution from plastics
• B. The spread of invasive species around the world's seas
• C. Overfishing
• D. Habitat destruction

Answer: (B)

Invasive species that spread around the world’s seas pose a major threat because they can rapidly establish in new marine habitats and disrupt entire ecosystems. Once introduced, these species often face few natural predators, allowing their populations to grow quickly and outcompete native organisms for food and space, prey on native species, or bring new diseases. The result is cascading changes to food webs and habitat structure that can drive native species to local or global extinction and alter ecosystem functions.

In marine settings, global trade and travel create easy pathways for spread—ballast water from ships, hull fouling, aquaculture, and aquarium releases move organisms across oceans. A vivid example is the lionfish in the western Atlantic and Caribbean, which preys on numerous small reef fish and can dramatically reduce native biodiversity and reshape reef communities. This mix of rapid spread, strong ecological impact, and the difficulty of restoration once established makes invasive species a particularly severe threat to biodiversity, even though other issues like pollution, overfishing, and habitat destruction are also serious.