The first study on Chinese marine ostracods revisited: historical ecology of Hong Kong ostracods

Abstract. The pioneering study of Chinese marine ostracods was done by George Stewardson Brady using specimens from Hong Kong in the 19th century. Since then, Robin C. Whatley and Quanhong Zhao restudied Brady's Hong Kong materials by using a scanning electron microscope (SEM) in the 1980s. Whatley and Zhao's studies substantially reduced the taxonomic uncertainty of Brady's Hong Kong species. These studies provide important information on the historical ecology of the less urban 19th-century Hong Kong, especially in comparison with a recent comprehensive survey on Hong Kong ostracods. Here, we (1) show a full list of Hong Kong ostracods studied by Brady with up-to-date taxonomy and then (2) compare Hong Kong ostracod species in Brady's 19th-century study and in a comprehensive 21st-century survey. Our comparison is qualitative and has limitations with uncertainties related to Brady's 19th-century study. Our results nonetheless indicate that four ostracod species known to be sensitive to pollution, eutrophication, or deoxygenation were reported in Brady's study, with only one tolerant species being reported there, whereas tolerant species tend to be much more abundant compared to sensitive species in Hong Kong in the 21st century. Brady also reported >10 species which are now rare in Hong Kong. These species might have been more abundant in the 19th century because of pre-industrial, near-pristine environments. In addition, many of these rare species are known as tropical species, and, at the same time, several temperate species now abundant in Hong Kong were not reported by Brady. Hong Kong's sea surface temperature is known to have been ∼ 1–2 °C higher ∼ 100 years ago than in the present. This recent cooling may have diminished the tropical species and aided the temperate species in subtropical Hong Kong. Our results suggest that the marine environment in 19th-century Hong Kong was much healthier, so the abundance of tolerant species was lower, giving Brady a lower chance to encounter them. He also had a better chance of finding tropical species in subtropical Hong Kong because of warmer sea temperatures at that time. These results highlight the importance of historical ecology by revisiting zoological studies by natural historians in the 19th and early 20th centuries. They documented a “natural baseline” ecosystem before the substantial human presence with industrialization.