Search

A warm-water doliolid species Dolioletta gegenbauri (Uljanin, 1884) was firstly recorded in Jiaozhou Bay (JZB) during the autumn of 2019–2020. As a warm-water species, its native habitat lies in the East China Sea Shelf, >1000 km south of JZB. Distribution, abundance, stage composition, size frequency distribution, and relationships with environmental factors were studied. Both asexual and sexual reproduction stages were observed. Gonozooids generally dominated the population, indicating an active population development status. Abundance was significantly correlated to temperature. Water temperature in the two consecutive years was among the highest levels during the recent 3–4 decades. The continuous warming trends both in the China coastal seas and JZB likely expanded the biogeographic range. The sub branches of a boundary current, the Kuroshio Current, especially the Yellow Sea Warm Current, may play a central role during the northward extension. Moreover, its feeding, growth, reproduction, and recruitment could also be benefited from the neritic food environment. Finally, when the temperature dropped below 15 °C in the early winter, it disappeared in JZB. The seasonal expansion of D. gegenbauri in JZB could be facilitated by current transportation, warming, and the neritic environment. [ABSTRACT FROM AUTHOR]

Scyphozoan polyp colonies are typically patchily distributed on substrate surfaces at varying densities in the natural environment. We investigated the differences in Aurelia coerulea and Nemopilema nomurai colony proliferation and biofouling invasion at high and low in situ polyp densities in Jiaozhou Bay, China, to explore potential polyp density-dependent effects. The study found that in situ A. coerulea polyp colonies on settling plates consistently survived at high initial density (24.4 ± 2.8 ind•cm−2) over a one-year experiment, but 60% of colonies disappeared at low initial density (0.6 ± 0.1 ind•cm−2). Polyp density in these colonies constantly fluctuated with a significant difference between the two treatments, decreasing by 71.5 ± 37.0% relative to the original level at high initial density by the end of the experiment, but increasing by 237.4 ± 662.7% at low initial density. In contrast, all N. nomurai polyps, whether at high or low initial density (1.9 ± 0.6 ind•cm−2 and 0.2 ± 0.0 ind•cm−2), died after approximately six weeks. Strobilation occurred in A. coerulea , but not in N. nomurai owing to the untimely die-off of polyp colonies. No significant differences in strobilation percentage, number of discs strobila−1 and the calyx diameter of polyps were observed between the two density treatments. Macro-fouling organisms (e.g. , ascidians and bryozoans) invaded the settling plates one week after the start of the experiment. Their coverage percentage was significantly lower at high initial polyp density in A. coerulea in a year, but there was no significant difference between both treatments in N. nomurai polyps. Nudibranch predators were discovered in the biofouling communities during the summer, with no significant differences in their numbers between the two treatments for each polyp species. The results indicated that density-dependent effects may play an important role in regulating in situ polyp colony proliferation and combatting biofouling invasion in A. coerulea , but not in N. nomurai. High colony survival and low levels of biofouling invasion at high initial polyp densities in A. coerulea might favor their extensive colonization in natural environment over extended periods of time. • Polyp colonies of Aurelia coerulea in situ survived 100% and 40% in a year at high and low initial densities, respectively. • All in situ Nemopilema nomurai polyps died after approximately six weeks at both initial densities. • Coverage percentage of macro-fouling organisms significantly decreased at high initial polyp density for A. coerulea. • Density-dependent effects may be important in regulating polyp colony proliferation and biofouling invasion in A. coerulea. [ABSTRACT FROM AUTHOR]

As mariculture expands offshore in response to the increasing demand for seafood, a new set of ecological concerns arises. We report on presented phosphate and silicate deficiencies in spring in the Zhangzi Island area, northern Yellow Sea, used for farming scallops. Silicon limitation was observed at up to 77.3% of stations, with an average silicate concentration as low as 1.7 μM in March 2014. Average phosphate concentration decreased from 0.12 to 0.05 μM from March to May. Stoichiometric ratios and absolute concentrations indicate that 78%-90% of stations showed phosphate limitation. Correspondingly, the phytoplankton community shifted from predominately diatoms to dinoflagellates. The higher frequency of nutrient limitation in farmed areas, compared with unseeded areas and northern Yellow Sea in general, imply intensified bottom-up controls on scallop production. The "bottle-neck" effect of limited food availability in spring suggests that carrying capacity was originally overestimated, when calculated from annual primary production., (Copyright © 2019 Elsevier Ltd. All rights reserved.)