Billy K.Y. Kwan

Occurrence, distribution and ecological risk assessment of multiple classes of UV filters in marine sediments in Hong Kong and Japan

Organic ultraviolet (UV) filters are used widely in various personal care products and their ubiquitous occurrence in the aquatic environment has been reported in recent years. However, data on their fate and potential impacts in marine sediments is limited. This study reports the occurrence and risk assessment of eleven widely used organic UV filters in marine sediment collected in Hong Kong and Tokyo Bay. Seven of the 11 target UV filters were detected in all sediment samples (median concentrations: <MLOD-21 ng/g dry weight) with detection frequencies higher in the wet season than in the dry season. Composition profiles showed that BMDM, EHMC and ODPABA were the predominant compounds, accounting for more than 60% of the total UV filter occurrence; this was likely due to their relatively higher octanol-water partition coefficients. Probabilistic ecological risk assessment showed that the likelihood of EHMC causing toxic effects on reproduction in snails was over 84% and 32% based on toxicity data for two species, respectively, suggesting potential risks of UV filters to benthic organisms and possible wider effects on the marine food web. However, more toxicity data for sediment organisms is necessary for better risk assessment of these compounds in benthic communities.

Population Structure and Growth of Juvenile Horseshoe Crabs Tachypleus tridentatus and Carcinoscorpius rotundicauda (Xiphosura) in Southern China

The abundance, population structure and growth of juvenile Asian horseshoe crabs Tachypleus tridentatus and Carcinoscorpius rotundicauda are rarely reported in the literature. This study investigated the density and growth allometry of these sympatric species on the intertidal areas of three spawning and nursery beaches, Xi Bei Ling (XBL), Jin Hai Wan (JHW) and Xi Chang (XC) along the coast of Beibu Gulf, southern China. While T. tridentatus and C. rotundicauda coexisted on JHW and XC beaches, only T. tridentatus was found at XBL. The density of T. tridentatus (0.9–3.2 individuals/100 m2) was significantly higher than that of C. rotundicauda (0.1–1.7 individuals/100 m2) at JHW, but densities were similar at XC. Juvenile T. tridentatus ranged in size (prosomal width) from 14 to 89 mm and were estimated to represent instars 4–12 and ages 2–8 years based on previous studies. C. rotundicauda juveniles were 16–75 mm in prosomal width and represented instars 5–15. The Hiatt growth model on the relationship between pre- and post-molt size data showed similar growth increments in juvenile T. tridentatus and C. rotundicauda. Growth rates for T. tridentatus varied from 4.4 to 19.7 mm/year, depending on instar stage and site. Growth rates were not determined for C. rotundicauda due to lack of data. These data establish a baseline for density and growth allometry of juvenile T. tridentatus and C. rotundicauda horseshoe crabs in Asian waters and will support future monitoring and assessment of juvenile populations and habitat resources.

Preliminary Home Range Study of Juvenile Chinese Horseshoe Crabs, Tachypleus tridentatus (Xiphosura), Using Passive Tracking Methods

Three passive tracking methods, using colored plastic tag (CPT), passive integrated transponder (PIT) tag, and CPT plus PIT were compared to track the movements of juvenile Chinese horseshoe crabs, Tachypleus tridentatus, in summer 2013 on a mudflat in Hong Kong. The study site was re-visited within 2 months after the release of the tagged individuals on ten occasions during low tides. The cumulative recovery rates of the tagged juveniles ranged from 70 to 82 %, with the number of position fixes where each individual was recovered during the repeated field visits varying from one to seven. Based on the adaptive kernel density estimation approach, the mean home range size (indicated by 95 % utilization distribution) tracked by different methods varied between 269 and 462 m2. While the effects of tracking methods on home range size of the juveniles were statistically indistinguishable, PIT tags could be used as a longer-term tracking device for juvenile horseshoe crabs because the tag injected into animal bodies did not cause noticeable effects on survival, growth and molting. Within the body size range of 7th–10th instar juveniles (prosomal width 31–59 mm) used in the present study, no significant correlation was found between body size and home range area. From the analysis of utilization distribution, the juveniles were noted to exhibit residential and nomadic movement patterns, which might be associated with the distribution of food patches on the mudflat. The restricted movements of juveniles in this study suggest potential for high susceptibility to localized habitat disturbance.

Wisdom of Crowds reveals decline of Asian horseshoe crabs in Beibu Gulf, China

Population decline among Asian horseshoe crabs in Asia is increasingly reported, but knowledge of their population and ecological status in China is limited. We conducted community interviews in 30 fishing villages around Beibu Gulf in Guangxi, China, to collect distribution information about the potential spawning/nursery grounds of Tachypleus tridentatus and Carcinoscorpius rotundicauda, and any imminent threats to their populations. Based on the results from 400 respondents we identified 45 potential spawning/nursery grounds distributed widely along the shores of Beibu Gulf. We visited 10 of these sites and verified the presence of juvenile horseshoe crabs by field surveys. Nearly all respondents reported an overall depletion in horseshoe crab populations from these 45 sites, which they attributed mainly to unsustainable fishing practices. Respondents who reported having seen horseshoe crab mating pairs on shores were mostly older people, which may suggest a considerable reduction in horseshoe crabs coming to the shores to spawn in recent years. The mean daily harvest of adult T. tridentatus offshore, as indicated by fishers, has declined from c. 50–1,000 in the 1990s to 0–30 individuals during 2011–2016. Our Wisdom of Crowds approach, supported by confirmatory field surveys, is a cost-effective method for assessing the population status of horseshoe crabs, and the level of threat they face. Similar approaches with other species are likely to be particularly valuable in the Asia–Pacific region, where well-structured population monitoring is largely unaffordable.

Horseshoe crabs as potential sentinel species for coastal health: juvenile haemolymph quality and relationship to habitat conditions

As an interface between terrestrial and marine environments, coastal and estuarine areas are particularly prone to various pollution stresses. Identification of sentinel species is, therefore, essential to provide precautionary information on coastal health conditions. Given their significant ecological roles in estuarine ecosystems, horseshoe crabs are a potential species to indicate the general health status of coastal habitats. The present study demonstrated that the changes in haemolymph composition pattern of two Asian juvenile horseshoe crab species (Tachypleus tridentatus and Carcinoscorpius rotundicauda) are sensitive to reflect heavy metal (lead, nickel and iron) and nutrient (nitrate and ammonia) concentrations of intertidal sediments. In particular, a significant negative correlation was found for the amebocyte viability and ratio of granular–spherical to granular–flattened and degranulated dendritic-like morphological states of amebocytes in juvenile haemolymph with nitrate and lead concentrations respectively. There were also significantly higher concentrations of haemolymph haemocyanin and plasma protein in juvenile C. rotundicauda than in T. tridentatus on the same shore, possibly being related to the difference in foraging habitats of these two horseshoe crab species. Such non-lethal sampling of haemolymph from juvenile horseshoe crabs can be useful for a further development of the monitoring program in assessing potential environmental impacts by anthropogenic activities.

Trophic and growth baseline of dominant subtidal gastropods in contrasting subtropical marine environments

Using 13C/12C, 15N/14N and 18O/16O isotopes, the trophic relationship and growth estimation were analyzed in gastropods Nassarius siquijorensis, Murex trapa and Turritella bacillum and their potential food sources and predators in summer and winter from estuarine and oceanic environments in subtropical Hong Kong. Results of δ13C and δ15N values and isotopic mixing model revealed N. siquijorensis and M. trapa were one trophic level higher than T. bacillum, in which its main food source was particulate organic matter (POM) whereas N. siquijorensis largely consumed POM and polychaetes and M. trapa also preyed on other gastropods. Crabs were the major predator of gastropods. Organisms collected from oceanic waters were more 13C enriched than from estuarine waters, reflecting different carbon food sources from marine or terrestrial origin. The δ18O profile from shell carbonate suggested these gastropods were one to two years old. T. bacillum exhibited faster summer growth than the other two species.