Description: Continuous Plankton Recorder data suggest that the Irminger Sea supports a major proportion of the surface-living population of the copepod Calanus finmarchicus in the northern North Atlantic, but there have been few studies of its population dynamics in the region. In this paper, we document the seasonal changes in the demographic structure of C. finmarchicus in the Irminger Sea from a field programme during 2001/2002, and the associations between its developmental stages and various apparent bio-physical zones. Overwintering stages were found widely at depth (〉500 m) across the Irminger Sea, and surviving females were widely distributed in the surface waters the following spring. However, recruitment of the subsequent generation was concentrated around the fringes of the Irminger Sea basin, along the edges of the Irminger and East Greenland Currents, and not in the central basin. In late summer animals were found descending back to overwintering depths in the Central Irminger Sea. The key factors dictating this pattern of recruitment appear to be (a) the general circulation regime, (b) predation on eggs in the spring, possibly by the surviving G0 stock, and (c) mortality of first feeding naupliar stages in the central basin where food concentrations appear to be low throughout the year. We compared the demographic patterns in 2001/2002 with observations from the only previous major survey in 1963 and with data from the Continuous Plankton Recorder (CPR) surveys. In both previous data sets, the basic structure of G0 ascent from the central basin and G1 recruitment around the fringes was a robust feature, suggesting that it is a recurrent phenomenon. The Irminger Sea is a complex mixing zone between polar and Atlantic water masses, and it has also been identified as a site of sporadic deep convection. The physical oceanographic characteristics of the region are therefore potentially sensitive to climate fluctuations. Despite this, the abundance of C. finmarchicus in the region, as measured by the CPR surveys, appears not to have responded to climate factors linked to the North Atlantic Oscillation Index, in contrast with the stocks in eastern Atlantic areas. We speculate that this may because biological factors (production and mortality), rather than transport processes are the key factors affecting the population dynamics in the Irminger Sea.

Description: The influence of copepod prey size and behaviour upon Aurelia aurita medusae predation rates was investigated. There was no significant difference in predation rates across a 4-fold (250 to 987 μm) prey size range (heat-killed developmental stages of Acartia tonsa ). Any behavioural differences (e.g. swimming speed, escape response) across live A. tonsa developmental stages had no significant effect upon their susceptibility to predation. In addition, Aurelia aurita ingestion rates were similar upon adult males and females of a copepod that exhibit similar swimming speeds ( A. tonsa ), as well as upon both adult sexes of a copepod with contrasting swimming behaviour ( Oithona similis ). An encounter model indicated that the size and speed of Aurelia aurita overwhelmed the differences in size and swimming speeds of these prey by largely determining encounter rates. However, overall, heat-killing prey lead to significantly higher predation rates than those upon live prey. This may be attributed to the escape response of live prey, which is not included in the encounter model. The capture efficiency of Aurelia aurita was low (〈9%), but high ingestion rates may be achieved through the large encounter rates of this cruising predator.

Description: Most ectothermic organisms mature at smaller body sizes when reared in warmer conditions. This phenotypically plastic response, known as the “temperature-size rule” (TSR), is one of the most taxonomically widespread patterns in biology. However, the TSR remains a longstanding life-history puzzle for which no dominant driver has been found. We...

Description: Estimating growth and production rates of mesozooplankton, and copepods in particular, is important in describing flows of material and energy though pelagic systems. Over the past 30 years, the Moult Rate (MR) method has been used to estimate juvenile copepod growth rates in ~40 papers. Yet the MR method has been shown to have serious flaws. Here we re-examine the results from the majority of published MR method studies and re-estimate growth rates using the modified Moult Rate (MMR) method, which ascribes changes in mass to the appropriate time period over which it was accrued. The MR method has typically over-estimated growth rates (on 80% of occasions) for life stages where the subsequent stage is actively moulting; the median and mean MR values are 138 and 164%, respectively, of the corrected MMR values. We were unable to correct the original data for life stages that are followed by a non-moulting stage, e.g. copepodite stage 5 to adult. We performed experiments with Calanus pacificus to estimate growth of stage C5 using an alternative method. We found that the error size and sign varied between mass type (i.e. DW, C and N). Recommendations for practical future assessments of growth in copepods are made.