In a groundbreaking interdisciplinary research effort spanning over three years, a team of talented scientists has unveiled a significant breakthrough. Assistant Research Fellow Dr. Chien-Hsiang Lin from the Biodiversity Research Center at Academia Sinica, along with Assistant Professor Dr. Li Lo from the Department of Geological Sciences at National Taiwan University, and Associate Professor Dr. Chih-Lin Wei and Assistant Professor Dr. Sze Ling Ho from the Institute of Oceanography at National Taiwan University, have made a remarkable discovery. Their findings shed light on the intricate relationship between the structure of tropical deep-sea fish communities and fluctuations in seawater temperature.

       Utilizing exceptionally well-preserved fossil fish otoliths (Fig. 1) extracted from a deep-sea core obtained from the Solomon Sea in the southwest edge of equatorial Pacific Ocean, the research team meticulously reconstructed the composition of deep-sea fish communities throughout the past 460,000 years. By conducting comprehensive analyses that combined ancient seawater temperature records with fish diversity and abundance, the team uncovered intriguing insights.

       The study primarily revealed a strong correlation between various fish species in the mid-ocean zone and seawater temperature. During the cooler ice ages, fish diversity soared while their overall abundance decreased. Conversely, during the warmer interglacial periods, fish diversity declined while their abundance increased. Remarkably, the team observed that only a select few heat-tolerant fish species, such as Myctophidae and Bregmacerotidae (Fig. 1), managed to thrive in larger numbers. However, the most significant finding emerged when the researchers discovered a substantial decrease in both fish diversity and abundance in the Super interglacial environment, where seawater temperatures surpassed present-day levels. Intriguingly, the study revealed distinct temperature adjustment gradients for fish diversity and abundance, with a notable difference of approximately 2 degrees in the threshold value (Fig. 2).

       This groundbreaking research represents the first fossil record of fish on such a long timescale and with such high time resolution. Furthermore, it establishes the crucial link between deep-sea fish community and seawater temperatures in the tropics on glacial and interglacial timescales. These findings emphasize the profound sensitivity of deep-sea fish in both oceanic and mesopelagic regions to warming seawater, underscoring the ecological challenges they may face. By enhancing our understanding of the ecosystem impacts resulting from ocean warming, this study serves as an essential and pressing warning for assessing potential repercussions on fish in the future.

       The complete paper has been published in the esteemed open-access journal, Science Advances. To access the full study, visit: https://www.science.org/doi/10.1126/sciadv.adf0656.

Figure 1. The most abundant fish otoliths found in ODP 1115B, a deep-sea core from the Solomon Sea.

Figure 2. Linkage of deep-sea fish abundance and diversity and seawater temperature on glacial/interglacial time scales.

Chien-Hsiang Lin
Assistant Research Fellow

Marine Paleontology