Benthic ecosystem determines jellyfish blooms by controlling the polyp colony development

Copper-induced oxidative stress inhibits asexual reproduction of Aurelia coerulea polyps

OBJECTIVE

Our research aims to investigate the specific mechanisms by which copper inhibits the asexual proliferation of Aurelia coerulea polyps.

METHODS

Aurelia coerulea polyps were exposed to various CuSO4 concentrations to study metamorphosis and budding proliferation. Oxidative stress markers (ROS, MDA, CAT, H2O2, T-AOC, SOD) were measured in polyps and early strobilae. Transcriptomic analysis were used to compare differences in gene expression and enrichment pathways between untreated and copper-exposed polyps. Additionally, RT-qPCR was used to analyze the expression of key molecules. Antioxidant L-Ascorbic acid was applied to determine the role of oxidative stress in asexual reproduction of Aurelia coerulea polyps when exposed to copper.

RESULTS

Copper inhibited strobilization and budding of Aurelia coerulea polyps in a dose-dependent manner, in which oxidative stress was involved. Transcriptomic data suggested that the DNA replication pathway was significantly enriched in early strobilae compared to polyps. However, copper treatment repealed the difference of DNA replication pathway between early strobilae compared and polyps. Transcriptomic data suggested that alanine, aspartate, and glutamate metabolism pathways were enriched in untreated budding polyps compared to copper-exposed polyps. After applying the antioxidant L-Ascorbic acid to copper-exposed polyps, various oxidative indicators changed to different extents, with increases in ROS, MDA, CAT, H2O2, and SOD and a decrease in T-AOC. Further more, the time required for polyps to develop into early strobila was shortened, indicating that the delay in metamorphosis caused by copper exposure was effectively alleviated. And the budding rate increased, indicating that the inhibition of budding proliferation caused by copper exposure was effectively alleviated. The expression of key genes were consist with the transcriptomic sequencing results.

CONCLUSION

Copper exposure causes oxidative stress resulting in the inhibition of asexual reproduction in Aurelia coerulea polyps, including metamorphosis and budding.

Typical Marine Ecological Disasters in China Attributed to Marine Organisms and Their Significant Insights

Owing to global climate change or the ever-more frequent human activities in the offshore areas, it is highly probable that an imbalance in the offshore ecosystem has been induced. However, the importance of maintaining and protecting marine ecosystems' balance cannot be overstated. In recent years, various marine disasters have occurred frequently, such as harmful algal blooms (green tides and red tides), storm surge disasters, wave disasters, sea ice disasters, and tsunami disasters. Additionally, overpopulation of certain marine organisms (particularly marine faunas) has led to marine disasters, threatening both marine ecosystems and human safety. The marine ecological disaster monitoring system in China primarily focuses on monitoring and controlling the outbreak of green tides (mainly caused by outbreaks of some Ulva species) and red tides (mainly caused by outbreaks of some diatom and dinoflagellate species). Currently, there are outbreaks of Cnidaria (Hydrozoa and Scyphozoa organisms; outbreak species are frequently referred to as jellyfish), Annelida (Urechis unicinctus Drasche, 1880), Mollusca (Philine kinglipini S. Tchang, 1934), Arthropoda (Acetes chinensis Hansen, 1919), and Echinodermata (Asteroidea organisms, Ophiuroidea organisms, and Acaudina molpadioides Semper, 1867) in China. They not only cause significant damage to marine fisheries, tourism, coastal industries, and ship navigation but also have profound impacts on marine ecosystems, especially near nuclear power plants, sea bathing beaches, and infrastructures, posing threats to human lives. Therefore, this review provides a detailed introduction to the marine organisms (especially marine fauna species) causing marine biological disasters in China, the current outbreak situations, and the biological backgrounds of these outbreaks. This review also provides an analysis of the causes of these outbreaks. Furthermore, it presents future prospects for marine biological disasters, proposing corresponding measures and advocating for enhanced resource utilization and fundamental research. It is recommended that future efforts focus on improving the monitoring of marine biological disasters and integrating them into the marine ecological disaster monitoring system. The aim of this review is to offer reference information and constructive suggestions for enhancing future monitoring, early warning systems, and prevention efforts related to marine ecological disasters in support of the healthy development and stable operation of marine ecosystems.

Effectiveness of Sampling Techniques in Collecting the Polyp Stage of the Invasive Freshwater Hydrozoan Craspedacusta sowerbii

Current sampling methods for detecting the presence of the invasive freshwater hydrozoan Craspedacusta sowerbii rely mainly on visual confirmation of the medusa stage. Confirming the presence of the polyp stage is equally important for observing medusae since typical late summer/early fall occurrences or observations of medusae are sporadic though are becoming more frequent. The polyp stage is important as it is the organism's primary stage and is present throughout the year depending on water temperatures. Therefore, sampling methods for the polyp stage are, commonly, the collection of substrates such as rocks, plants, or pieces of wood in a given body of water, and these can be cumbersome to examine. Polyps are also small, transparent, and difficult to see on natural substrates. Based on a preliminary culturing of the polyp stage on glass and plastic microscope slides in the laboratory, we designed a sampling methodology based on submerging four substrate types (glass and plastic microscope slides, Hester-Dendy discs, and small glass Petri dishes) to confirm the presence of C. sowerbii polyps in the field. We tested this method in three lakes in the Illinois-Indiana region (USA). Two of the lakes have recorded sightings of medusae but the third has no record of polyps or medusae. The sampling method we designed was effective in that C. sowerbii polyps were found on both plastic and glass slides. While this method can be sufficient for detection of the polyp stage, it also shows potential for improvement; we highlight abiotic and biotic ecological parameters as significant factors influencing the collection of C. sowerbii polyps to be considered for future methodologies.

Biodiversity and distribution patterns of blooming jellyfish in the Bohai Sea revealed by eDNA metabarcoding

BACKGROUND

The mass occurrence of scyphozoan jellyfish severely affects marine ecosystems and coastal economies, and the study of blooming jellyfish population dynamics has emerged in response. However, traditional ecological survey methods required for such research have difficulties in detecting cryptic life stages and surveying population dynamics owing to high spatiotemporal variations in their occurrence. The environmental DNA (eDNA) technique is an effective tool for overcoming these limitations.

RESULTS

In this study, we investigated the biodiversity and spatial distribution characteristics of blooming jellyfish in the Bohai Sea of China using an eDNA metabarcoding approach, which covered the surface, middle, and bottom seawater layers, and sediments. Six jellyfish taxa were identified, of which Aurelia coerulea, Nemopilema nomurai, and Cyanea nozakii were the most dominant. These three blooming jellyfish presented a marked vertical distribution pattern in the offshore regions. A. coerulea was mainly distributed in the surface layer, whereas C. nozakii and N. nomurai showed a upper-middle and middle-bottom aggregation, respectively. Horizontally, A. coerulea and C. nozakii were more abundant in the inshore regions, whereas N. nomurai was mainly distributed offshore. Spearman's correlation analysis revealed a strong correlation between the eDNA of the three dominant blooming jellyfish species and temperature, salinity, and nutrients.

CONCLUSIONS

Our study confirms the applicability of the eDNA approach to both biodiverstiy evaluation of blooming jellyfish and investigating their spatial distribution, and it can be used as a supplementary tool to traditional survey methods.