DOI: 10.25442/hku.29995246.v1
title: Supporting data for "Integrated approaches in the conservation of foundation species in Hong Kong’s intertidal mudflats"

description: Biodiversity is the basis of healthy and functional ecosystems. Yet, we are currently experiencing a wave of extinction events, threatening many ecosystem functions that our society depends on. Foundation species are species that facilitates local biodiversity by modifying the physical state of their habitat and modulate the availability of resources to other inhabitants of the habitat. By prioritizing the conservation of foundation species, restoration of degraded habitats could be performed in a much more cost-effective manner. In this thesis, I studied the spatial and temporal biodiversity dynamics in two intertidal mudflat habitats shaped by key foundation species: oyster habitats and seagrass meadows.First, I investigated the roles of tropical oyster habitats as modulators of benthic biodiversity across an environmental gradient and across different groups of organisms. Epifaunal diversity in oyster reefs was ~3.7x higher than in adjacent mudflats, while no consistent difference was detected for the sediment infauna. In contrast, the effect of oysters as modulator of benthic bacterial diversity was site dependent. Across all groups of organisms surveyed, the community compositions showed high levels of site dependence.Second, I investigated the species diversity of oysters in ten of Hong Kong’s intertidal mudflats, together with information on their demographics and population genetics. We also examined the species composition of oysters that were farmed commercially in Hong Kong to identify if aquaculture could be a source of larval recruitment for restoration efforts. All oyster habitats surveyed were comprised of multiple oyster species, and a total of nine species of oysters from the genus <i>Magallana</i> and <i>Saccostrea</i> were encountered. In nine out of ten sites surveyed, only one cohort of oysters was present, indicating high mortality of the oysters.Third, I assessed the thermal reaction norm for the growth rate of the seagrass <i>Halophila ovalis</i>, investigating the potential influence of salinity on the shape of this non-linear relationship. I found that <i>H. ovalis</i> exhibits the classic thermal performance curve, with a T<sub>opt</sub> higher (~1°C) than the median summer temperature experienced in its natural habitat. While the broad range of salinity conditions induced variation in the parameters of the thermal performance curve, no significant effect was detected on the overall shape of this reaction norm.Fourth, I studied the population genetics of <i>Halophila beccarii</i> in Hong Kong by sampling specimens from multiple seagrass cohorts in Pak Nai across three years, and genotyped them for detecting changes in genetic composition. Furthermore, specimens from Tanjia Bay, Zhuhai were also genotyped, representing the geographically most proximate <i>H. beccarii</i> population. My data revealed high temporal stability in the genetic composition of the <i>H. beccarii</i> population in Pak Nai, and low level of genetic connectivity between the populations in Pak Nai and Tangjia Bay.Overall, my thesis contributed to advancing our knowledge on the biology and ecology of two key foundation species in Hong Kong’s intertidal mudflats. This knowledge would enable more effective conservation of tropical intertidal mudflat habitats.