A model for the transportation and distribution of jellyfish Rhopilema esculentum for stock enhancement in the Liaodong Bay, China

A numerical model for jellyfish Rhopilema esculentum stock enhancement is developed for the first time. The model is based on an operational ocean circulation-surface wave coupled forecasting system for the seas off China and adjacent areas and uses a Lagrangian particle-tracking scheme to track the trajectories of released jellyfish. The Jellyfish are modeled as particles with diel vertical migration and are passively drifted by the current and dispersion due to the sub-grid processes. A comparison between the simulation and survey results demonstrate that the model can capture the primary distribution patterns of the released jellyfish. The model results show that the ocean current and indirect wind impact are the main drivers controlling the jellyfish transport. A connectivity matrix between the release sites and fishing grounds indicates the top of the bay is better than the eastern and western coasts for jellyfish fishing. The matrix also shows that only 45% and 27% of the jellyfish released from Wafangdian(WFD) can enter the fishing ground in 2008 and 2010; thus, the site near WFD is not an advisable location for jellyfish release. A Lagrangian probability density function based on a nine-year tracing experiment validates the results and further provides a "climatology" distribution of the released jellyfish.Several experiments are conducted to examine the sensitivity of the model to random walk schemes and to release conditions. The model requires a random walk but is insensitive to the random walk scheme. The experiments with different habitat depths show that if the jellyfish are fixed on the bottom of the water, most of them will be transported to the center, or even out of the bay, by the bottom circulation.

Rotifer community structure and its response to environmental factors in the Backshore Wetland of Expo Garden,Shanghai

We investigated rotifer community structure in the Backshore Wetland of the Expo Garden in Shanghai from September 2009 to August 2010.We identified 116 rotifer species,determined the dominant species and their relationships with environmental factors,and community diversity indices.Polyarthra trigla was the most common species over the four seasons and proportionally most dominant in spring and autumn,whereas Cephalodella exigua and Keratella cochlearis were the most dominant species in winter and summer,respectively.There was seasonal variability in species numbers,with the highest numbers in summer,followed by autumn and winter.The mean annual density was 815±1346 ind./L and the biomass was 0.3649±0.4940 mg/L.There were significant differences between months:the highest density(2723±2926 ind./L)and biomass(0.7938±0.8197 mg/L)occurred in June,while the lowest density(238±271 ind./L)and biomass(0.0476±0.0429 mg/L)occurred in May.Canonical correspondence analysis(CCA)indicated that temperature,pH,nitrite nitrogen(NO2-N),and total phosphorus(TP)were the most important abiotic factors affecting rotifer distribution.Our research showed that the adaptability of the rotifers to temperature was the important factor.