Effects of salinity, light intensity and biofouling on planula settlement and subsequent development to polyps in Cyanea nozakii (Cnidaria: Scyphozoa)

Abstract

AbstractCyanea nozakii is a scyphozoan jellyfish that causes problematic blooms in Chinese coastal waters, whilst its polyps have never been found in the field. This laboratory study examined the effects of salinity, light intensity and biofouling on planula settlement and subsequent development to polyps for narrowing the potential polyp habitat with regard to these factors. Planulae of C. nozakii could complete settlement, metamorphosis through planulocysts and development into 4-tentacle polyps within 5 days over a broad salinity range from 13 to 32. The planulae were photonegative with significantly lower settlement success at 1700 lx compared to 80 lx and darkness. The settlement was severely inhibited by the exacerbation of biofoulings mainly consisted of ascidians and bryozoans; it was blocked completely on substrates with heavy biofouling (covered area: ≥95%, mean wet weight: 1400 mg·cm−2) and substantially on those with light biofouling (50%, 16.5 mg·cm−2). The settled polyps were outcompeted by the biofouling proliferation and finally eliminated. These imply that neither salinity nor light intensity is a limiting factor but the availability of proper hard substrates with no or scarce biofouling is a bottleneck for C. nozakii polyps to establish the population in Chinese coastal waters