Range Of Annual Variation Research Articles

Characteristics and possible causes of sea level anomalies in the Xisha sea area

Based on the analysis of wind, ocean currents, sea surface temperature (SST) and remote sensing satellite altimeter data, the characteristics and possible causes of sea level anomalies in the Xisha sea area are investigated. The main results are shown as follows: (1) Since 1993, the sea level in the Xisha sea area was obviously higher than normal in 1998, 2001, 2008, 2010 and 2013. Especially, the sea level in 1998 and 2010 was abnormally high, and the sea level in 2010 was 13.2 cm higher than the muti-year mean, which was the highest in the history. In 2010, the sea level in the Xisha sea area had risen 43 cm from June to August, with the strength twice the annual variation range. (2) The sea level in the Xisha sea area was not only affected by the tidal force of the celestial bodies, but also closely related to the quasi 2 a periodic oscillation of tropical western Pacific monsoon and ENSO events. (3) There was a significant negative correlation between sea level in the Xisha sea area and ENSO events. The high sea level anomaly all happened during the developing phase of La Nina. They also show significant negative correlations with Nino 4 and Nino 3.4 indices, and the lag correlation coefficients for 2 months and 3 months are–0.46 and–0.45, respectively. (4) During the early La Nina event form June to November in 2010, the anomalous wind field was cyclonic. A strong clockwise vortex was formed for the current in 25 m layer in the Xisha sea area, and the velocity of the current is close to the speed of the Kuroshio near the Luzon Strait. In normal years, there is a “cool eddy”. While in 2010, from July to August, the SST in the area was 2–3°C higher than that of the same period in the history.

Feeding behavior of the mussel Mytilus galloprovincialis (L.) in a Mediterranean estuary: A field study

The feeding behavior of the mussel Mytilus galloprovincialis was investigated in the field on top of a mussel raft in Alfacs Bay, NW Mediterranean Sea. The experiments were performed in November 2006 and February, April and July 2007 using a flow-through filter feeding device. Total particulate matter (TPM), particulate organic matter (POM) and particulate inorganic matter (PIM) were calculated for the bay water, as well as the feces and pseudofeces of the mussels. These were used with the biodeposition method to estimate several feeding-physiological parameters, such as the clearance rate (CR), rejection rate through pseudofeces production (RP), organic ingestion rate (OIR), absorption rate (AR) and absorption efficiency (AE). The results showed that the characteristics of available suspended matter for mussels in terms of particle concentration (TPM: mg/l) and organic content ( f defined as POM/TPM) ranged 1.03–2.30 mg/l, and 0.48 to 0.73 respectively throughout the study period. This indicates a rather stable feeding environment of low concentrations of high organic content particles despite the wide range of temperatures recorded (from 10 to 26 °C). However, a characteristic of such a variation pattern of particle suspension (TPM and f) was that short-term variations (in the course of days) covered the whole range of annual variation. Accordingly, physiological parameters characterizing both food acquisition and absorption in mussels were found to respond to short-term variations in food regime. Pseudofeces production in mussels was low (less than 5% in most cases) and they tended to reduce their clearance rate instead of increasing their pseudofeces production in response to rising particle concentration. The absorption efficiency was positively related to the organic content of the seston particles. There was also a positive correlation between clearance rate and absorption efficiency. The reduction of clearance, ingestion and absorption rates obtained in July highlights a negative influence of high water temperatures upon feeding and digestive processes of mussels.

Variability patterns differ between standing stock and process rates

Standing stocks are typically easier to measure than process rates such as production. Hence, stocks are often used as indicators of ecosystem functions although the latter are generally more strongly related to rates than to stocks. The regulation of stocks and rates and thus their variability over time may differ, as stocks constitute the net result of production and losses. Based on long-term high frequency measurements in a large, deep lake we explore the variability patterns in primary and bacterial production and relate them to those of the corresponding standing stocks, i.e. chlorophyll concentration, phytoplankton and bacterial biomass. We employ different methods (coefficient of variation, spline fitting and spectral analysis) which complement each other for assessing the variability present in the plankton data, at different temporal scales. In phytoplankton, we found that the overall variability of primary production is dominated by fluctuations at low frequencies, such as the annual, whereas in stocks and chlorophyll in particular, higher frequencies contribute substantially to the overall variance. This suggests that using standing stocks instead of rate measures leads to an under- or overestimation of food shortage for consumers during distinct periods of the year. The range of annual variation in bacterial production is 8 times greater than biomass, showing that the variability of bacterial activity (e.g. oxygen consumption, remineralisation) would be underestimated if biomass is used. The P/B ratios were variable and although clear trends are present in both bacteria and phytoplankton, no systematic relationship between stock and rate measures were found for the two groups. Hence, standing stock and process rate measures exhibit different variability patterns and care is needed when interpreting the mechanisms and implications of the variability encountered.