Human impacts and changes in the coastal waters of south China

Spatio-temporal dynamics of phytoplankton community structure in the coastal waters of the Southern Beibu Gulf

This study was conducted during October 2021 (autumn) and April 2022 (spring) to explore the phytoplankton community structure, their distribution characteristics, and the influence of environmental factors in the coastal waters of the Southern Beibu Gulf. The 15 sampling sites were grouped based on the difference in offshore distance to analyze the temporal and spatial differences in community structure and environmental driving in the investigated sea area of the coastal waters of the Southern Beibu Gulf. Permutational multivariate analysis of variance was conducted on the sample data in time and space, revealing that there is no significant difference in space (p > 0.05), but there is significant difference in time (p < 0.05). Notably, water pressure, pH, chemical oxygen demand, nitrite, and labile phosphate were higher in autumn, while total ammonia nitrogen, dissolved oxygen, and suspended solids were significantly higher in spring. Additionally, the study identified 87 phytoplankton species belonging to 6 phyla, dominating by Bacillariophyta, followed by Dinophyta and Cyanophyta. The phytoplankton density, Shannon Weiner's diversity index (H'), Pielou's evenness index (J), and Margalef's richness index (D) ranged from 84.88 to 4675.33 cells L-1, 0.56 to 2.58, 0.26 to 0.89, and 1.21 to 3.64, respectively. Permutational multivariate analysis of variance showed non-significant spatial differences in phytoplankton composition (p > 0.05) but seasonal differences (p < 0.05). Furthermore, canonical correspondence analysis (CCA) identified pH, dissolved oxygen, suspended solids, chemical oxygen demand, nitrite, and labile phosphate as key environmental factors influencing the phytoplankton community structure (p < 0.05). In this study, the dynamic changes of phytoplankton community structure and environmental factors in the southern coastal waters of Beibu Gulf were analyzed in detail from two aspects of time and space. The key environmental factors to protect the ecological environment in the southern coastal area of Beibu Gulf were found out. It provides a reference method and theoretical basis for the management and protection of Beibu Gulf and other tropical marine environment.

Spatially Heterogeneity Response of Critical Ecosystem Service Capacity to Address Regional Development Risks to Rapid Urbanization: The Case of Beijing-Tianjin-Hebei Urban Agglomeration in China

Urban agglomerations have become the new spatial unit of global economic competition. The intense socioeconomic activities attributed to the development of urban agglomerations are bound to cause damage to the ecosystem services of these urban agglomerations. This study adopts the Beijing-Tianjin-Hebei urban agglomeration in China as the research object, analyzes the spatiotemporal evolution of its critical ecosystem service capacity to address regional ++-development risks from 2000–2018, and employs the Moran’s I and geographically weighted regression model to explore the spatial correlation and spatial heterogeneity in the responses of urbanization and ecosystem services. The study indicates that (1) from 2000–2018, the ecosystem services of the Beijing-Tianjin-Hebei urban agglomeration exhibit an increase and then a decline, reaching the highest index in 2015; (2) the ecosystem services reveal obvious spatial heterogeneity with the Yan and Taihang Mountains region as the boundary; (3) built-up area ratio, GDP density, and population density exhibit highly obvious negative correlation driving characteristics on ecosystem services; and (4) the construction land ratio exerts a notable impact on areas with a high ecosystem services, while the spatial response of the effect magnitude of the population and GDP densities is largely influenced by intensive, high-pollution and energy-consuming industries. This article also proposes strategies for the optimization of ecological resources and spatial control, which are dedicated to mitigating the negative impacts of rapid urbanization processes on ecosystem services.

Assessing Coastal Reclamation Success in the East China Coast by Using Plant Species Composition

Quantitative analysis of the species composition and succession law of a plant community in a coastal reclamation area is of great significance for revealing the community construction and species coexistence mechanisms, and provides a basis for the rational use and conservation in coastal reclamation areas. Through the investigation of natural plant communities in Dongtai reclamation area and the adjacent national nature reserves in Jiangsu Province, eastern China, the composition and succession of plant communities were studied. A quantitative method was explored to analyze the process of plant succession and its representative species. The results showed that (1) A total of 65 species were found in the vegetation survey. These belonged to 26 families and 61 genera, and Poaceae is the most common plant species. The plant communities in the unreclaimed areas were mainly composed of Poaceae and Cyperaceae. The plant species increased after reclamation, which were mainly composed of Poaceae and Asteraceae; (2) The plant coverage greatly reduced after three years of reclamation, from 80% of the tidal flat to 37.34%, then gradually increased, and remained generally between 50% and 70%; (3) The above-ground biomass of the plant community was sharply reduced after reclamation, from 1.823 kg/m2 in the tidal flat to 0.321 kg/m2 in three years of reclamation, and then maintained at 0.11~0.27 kg/m2; (4)The species succession process of the plant community in the coastal wetland ecosystem that was affected by the reclamation activities transformed from a halophyte community that was dominated by a salt marsh plant community (Suaeda salsa, Spartina alterniflora, Scirpus mariqueter, and Phragmites australis) to a mesophyte plant community that was constructed with pioneer species such as Setaria viridis, Eleusine indica, etc., and eventually succeeded to a xerophyte plant community that was dominated by Humulus scandens and Cyperus difformis, etc. Reclamation activities have a profound impact on the characteristics and succession rules of natural vegetation communities along coastal wetland ecosystems. The period of seven years is presumed to be the tipping point in the succession of the plant community in coastal reclamation areas. The results of this study can provide a basis and reference for ecological protection and restoration in coastal reclamation areas.

Near future ocean acidification modulates the physiological impact of fluoxetine at environmental concentration on larval urchins

Pharmaceuticals found in human wastes are emergent pollutants that are continuously released into aquatic systems. While exposure to pharmaceuticals alone could adversely impact aquatic organisms, few studies have considered the interactive effects of pharmaceuticals and the future environmental conditions, such as decreasing pH due to ocean acidification. Given the bioavailability of many pharmaceuticals is dependent on these physical conditions, we investigated the effect of environmentally-relevant concentrations of fluoxetine (10 and 100 ng L^-1) under ambient (pH 8.0) and reduced pH conditions (pH 7.7) on physiology, behavior, and DNA integrity of larval sea urchins (Heliocidaris crassispina). Notably, the negative impacts of fluoxetine exposure were attenuated by reduced pH. Larvae exposed to both reduced pH and fluoxetine exhibited lower levels of DNA damage compared to those exposed to only one of the stressors. Similar antagonistic interactions were observed at the organismal level: for example, fluoxetine exposure at 10 ng L^-1 under ambient pH increased the percentage of embryos at later developmental stages, but such effects of fluoxetine were absent at pH 7.7. However, despite the modulation of fluoxetine impacts under ocean acidification, control larvae performed better than those exposed to either stressor, alone or in combination. We also observed that pH alone impacted organismal behaviors, as larvae swam slower at reduced pH regardless of fluoxetine exposure. Our findings highlight the need to consider multi-stressor interactions when determining future organismal performance and that multiple metrics are needed to paint a fuller picture of ecological risks.

Parental whole life cycle exposure modulates progeny responses to ocean acidification in slipper limpets

Multigenerational exposure is needed to assess the evolutionary potential of organisms in the rapidly changing seascape. Here, we investigate if there is a transgenerational effect of ocean acidification exposure on a calyptraeid gastropod such that long-term exposure elevates offspring resilience. Larvae from wild type Crepidula onyx adults were reared from hatching until sexual maturity for over 36 months under three pH conditions (pH 7.3, 7.7, and 8.0). While the survivorship, growth, and respiration rate of F₁ larvae were unaffected by acute ocean acidification (OA), long-term and whole life cycle exposure significantly compromised adult survivorship, growth, and reproductive output of the slipper limpets. When kept under low pH throughout their life cycle, only 6% of the F₁ slipper limpets survived pH 7.3 conditions after ~2.5 years and the number of larvae they released was ~10% of those released by the control. However, the F₂ progeny from adults kept under the long-term low pH condition hatched at a comparable size to those in medium and control pH conditions. More importantly, these F₂ progeny from low pH adults outperformed F₂ slipper limpets from control conditions; they had higher larval survivorship and growth, and reduced respiration rate across pH conditions, even at the extreme low pH of 7.0. The intragenerational negative consequences of OA during long-term acclimation highlights potential carryover effects and ontogenetic shifts in stress vulnerability, especially prior to and during reproduction. Yet, the presence of a transgenerational effect implies that this slipper limpet, which has been widely introduced along the West Pacific coasts, has the potential to adapt to rapid acidification.

Eutrophication control strategies for highly anthropogenic influenced coastal waters

Rapid economic development and urbanization necessitate an understanding of anthropogenic effects on coastal eutrophication. It is a significant challenge for governments to alleviate water degradation and remediate coastal ecosystems. Shenzhen Bay in China, located in a developed and populous area, was selected to analyze the decadal scale influence of anthropogenic activities on eutrophication as well as the effectiveness of governmental remediation strategies. The results showed that the contribution of nutrients from anthropogenic sources accounted for over 80% of the total loads into the bay. Beginning in 1990, increased anthropogenic activities resulted in the loss of environmental capability and resilience, exacerbated eutrophication and water quality degradation. However, the status of eutrophication has been improved since 2005, following the application of intensive management actions implemented in 2000. The practice of eutrophication control suggested that, in view of technical and engineering feasibility, coastal strategies for similar shallow bays should initially reduce phosphorus, followed by nitrogen and eco-remediation to alleviate the serious aquatic situation immediately. The recovery period of eutrophication would be at least five years after governmental actions from Shenzhen Bay's experience. Furthermore, simulated scenarios indicated that eutrophication ranking of Shenzhen Bay could reach and remains medium Moderate, following a 35% reduction in total nitrogen and a 20% reduction in total phosphorus with corresponding eco-remediation.

Metal concentrations in the beach sediments of Bahia Solano and Nuquí along the Pacific coast of Chocó, Colombia: A baseline study

Thirty sediment samples from four different beaches along Bahia Solano and Nuquí (Department of Chocó) of eastern Colombia, with tourism and gold mining activities, were analysed to estimate the concentrations of fourteen different acid leachable metals. Metal distribution patterns showed elevated concentrations of Co, Cr, Cu, Pb and Zn compared with the upper continental crust values. Calculation of geochemical indices confirmed that the enrichment is due to periodic gold mining activities (severe to extremely severe enrichment of Cu, Zn, V, Co, Cr and Pb) along with natural (geological) contributions (minor and moderate enrichment of Ca, Mg, Fe, Ti, Mn and Li). Potential ecological risk index revealed that Pb posed the highest risk. Our results together with a global comparison suggest that the observed metal enrichments are mainly caused by mining and to a lesser extent by tourism in this region, thus instigating continuous monitoring of metal concentrations in this region.

Ocean acidification increases larval swimming speed and has limited effects on spawning and settlement of a robust fouling bryozoan, Bugula neritina

Few studies to date have investigated the effects of ocean acidification on non-reef forming marine invertebrates with non-feeding larvae. Here, we exposed adults of the bryozoan Bugula neritina and their larvae to lowered pH. We monitored spawning, larval swimming, settlement, and post-settlement individual sizes at two pHs (7.9 vs. 7.6) and settlement dynamics alone over a broader pH range (8.0 down to 6.5). Our results show that spawning was not affected by adult exposure (48h at pH7.6), larvae swam 32% faster and the newly-settled individuals grew significantly larger (5%) at pH7.6 than in the control. Although larvae required more time to settle when pH was lowered, reduced pH was not lethal, even down to pH6.5. Overall, this fouling species appeared to be robust to acidification, and yet, indirect effects such as prolonging the pelagic larval duration could increase predation risk, and might negatively impact population dynamics.

Resilience of the larval slipper limpet Crepidula onyx to direct and indirect-diet effects of ocean acidification

Ocean acidification (OA) is known to directly impact larval physiology and development of many marine organisms. OA also affects the nutritional quality and palatability of algae, which are principal food sources for many types of planktonic larvae. This potential indirect effect of OA via trophic interactions, however, has not been fully explored. In this study, veligers of Crepidula onyx were exposed to different pH levels representing the ambient (as control) and low pH values (pH 7.7 and pH 7.3) for 14 days, and were fed with Isochrysis galbana cultured at these three respective pHs. pH, diet, nor their interactions had no effect on larval mortality. Decrease in pH alone had a significant effect on growth rate and shell size. Structural changes (increased porosity) in larval shells were also observed in the low pH treatments. Interactions between acidification and reduced diet quality promoted earlier settlement. Unlike other calcifying molluscs, this population of slipper limpets introduced to Hong Kong in 1960s appeared to be resilient to OA and decreased algal nutritional value. If this robustness observed in the laboratory applies to the field, competition with native invertebrates may intensify and this non-native snail could flourish in acidified coastal ecosystems.