Species globally are shifting their geographic ranges due to changing environmental conditions, altering ecosystems on land and in the ocean. Tropicalization is a specific instance of this, where species from warmer, equatorial zones expand into cooler, temperate regions. This ecological transformation indicates broader environmental shifts.
What is Tropicalization?
Tropicalization describes the process where tropical organisms extend their ranges poleward into temperate ecosystems. This involves species migrating from their native warm habitats into previously cooler zones. It differs from general species migration by specifically highlighting the tropical origin and temperate destination, driven by climate-related changes. This phenomenon is documented in both terrestrial and marine environments, with examples including corals and tropical fish moving into Japanese waters, and mangroves expanding along the Florida coastline.
It is characterized by an increase in warm-affinity species within an ecosystem. This range expansion is linked to a decrease in cold-affinity species.
Drivers of Tropicalization
The primary environmental factor driving tropicalization is rising ocean temperatures. Warmer waters enable tropical species to survive and thrive in regions previously too cold for them. This is particularly evident in marine environments, due to species’ mobility.
Changes in ocean currents also contribute to this expansion. Warm-water boundary currents, like the Kuroshio Current, are shifting poleward, transporting tropical species into temperate latitudes. These currents act as pathways for tropical marine life. The reduction in extreme cold events further supports tropicalization by removing a barrier that previously limited cold-intolerant tropical species.
Ecological Transformations
The arrival of new tropical species alters the ecosystems they colonize. These incoming species can disrupt existing food webs by introducing new predators, competitors, or herbivores. For instance, the expansion of tropical herbivorous fish, such as parrotfish, impacts temperate marine reefs. These fish graze extensively on temperate kelp forests, leading to their degradation and a shift towards dominance by low-biomass turfing algae.
This transformation can lead to a reorganization of the ecosystem’s trophic structure. While some studies show an increase in overall fish species richness and abundance in tropicalized systems, there are significant shifts in the composition of fish assemblages. For example, tropical herbivorous fish have increased in some areas, while temperate-associated planktivores have declined. The Mediterranean Sea is considered a “tropicalization hotspot” due to the increase in tropical species present.
Wider Implications
Tropicalization extends its impacts beyond ecological shifts, influencing human activities and coastal communities. Changes in water temperature and species distribution affect fisheries, altering the abundance and location of commercially valuable species. For example, American lobsters and silver hake are moving into deeper or more northern waters, impacting traditional fishing grounds. Shifts in species can also introduce new species for harvest, requiring adjustments in fishing practices and management strategies.
Coastal communities dependent on fishing and tourism face challenges as these changes unfold. Alterations in marine life can affect tourism, as the types of species attracting divers or recreational fishers may change. The long-term trajectory of tropicalization suggests ongoing transformations, with potential implications for food security, local economies, and cultural practices tied to marine resources.