The 19th-century naturalist Alfred Russel Wallace discovered a peculiar "invisible line" while traveling through the Southeast Asian archipelago. This line cuts through the straits between Bali and Lombok in Indonesia. To the west of the line lived Asian species like orangutans and tigers, while to the east lived Australian species such as tree kangaroos and bird-of-paradise. A mere few dozen kilometers separated what seemed like two different worlds. This “Wallace Line” revealed a deep connection between geography and biology, opening the door for the study of biogeography.
A century later, a similar "ecological boundary" exists in Taiwan's waters. Through long-term surveys in the 1990s, Taiwanese ichthyologist Dr. Kwang-Tsao Shao found a clear north-south difference in fish communities in Taiwan's waters, which led him to propose the concept of "Shao’s Line." This line roughly cuts diagonally from the northeastern tip of Taiwan toward the southwest, extending to the waters near the South Penghu Marine National Park. The formation of this boundary is primarily influenced by the interaction of the Kuroshio and other ocean currents; differences in seawater temperature and salinity create a clear regional distribution of marine life.
However, the stable equilibrium represented by this boundary is being challenged by climate change. As global warming increases sea surface temperatures, the distribution of marine organisms is no longer fixed. This phenomenon is particularly evident in coral reef ecosystems. Dr. Chang-Feng Dai, a pioneer in Taiwanese coral reef research, has witnessed the changes of Taiwan’s corals from thriving to declining over four decades. His research shows that climate change is currently rewriting the ecological boundaries of Taiwan's ocean.
Dr. Dai used climate modeling and coral distribution data to explore the long-term impact of warming on Taiwan’s corals. The results indicate that in the short term (approximately 20 years), as seawater temperatures rise, the waters off eastern and northern Taiwan may become more suitable for coral growth, leading to a northward expansion of coral distribution and a temporary increase in species richness in the north, east, and Penghu.However, this is not a long-term trend. By the middle of this century (around 2055 to 2085), climate models predict that the overall coral distribution in Taiwan will significantly shift northward and shrink. In other words, corals in the southern waters of Taiwan may struggle to recover due to high temperatures and frequent bleaching events, leading to permanent ecological degradation.
This research illustrates that the biological boundaries originally determined by ocean currents and geography are "moving" due to climate change. This shift is not limited to coral reefs but is also observed in other species. For instance, the fishing range for mullet has shown a northward shift in recent years, demonstrating that changes in the marine environment are already tangibly impacting Taiwan’s fisheries and local communities.
Facing these dynamic changes, traditional marine conservation concepts need to be updated. Future protection strategies should be flexible, establishing a connected network of marine protected areas that allows space for potential species migration routes. Simultaneously, it is necessary to integrate observations from local fishers to establish a real-time ecological monitoring system.
From the Wallace Line to Shao’s Line, we see that ocean boundaries are no longer static. As climate change drives these lines to drift northward, we are reminded that changes in the ocean are not just scientific phenomena on a map but a real challenge concerning the future survival of humanity.
