S. H. Coombs

Marine Ecosystem Response to the Atlantic Multidecadal Oscillation

Against the backdrop of warming of the Northern Hemisphere it has recently been acknowledged that North Atlantic temperature changes undergo considerable variability over multidecadal periods. The leading component of natural low-frequency temperature variability has been termed the Atlantic Multidecadal Oscillation (AMO). Presently, correlative studies on the biological impact of the AMO on marine ecosystems over the duration of a whole AMO cycle (∼60 years) is largely unknown due to the rarity of continuously sustained biological observations at the same time period. To test whether there is multidecadal cyclic behaviour in biological time-series in the North Atlantic we used one of the worlds longest continuously sustained marine biological time-series in oceanic waters, long-term fisheries data and historical records over the last century and beyond. Our findings suggest that the AMO is far from a trivial presence against the backdrop of continued temperature warming in the North Atlantic and accounts for the second most important macro-trend in North Atlantic plankton records; responsible for habitat switching (abrupt ecosystem/regime shifts) over multidecadal scales and influences the fortunes of various fisheries over many centuries.

Spawning season and temperature relationships for sardine (Sardina pilchardus) in the eastern North Atlantic

Spawning temperature preferences for sardine (Sardina pilchardus) in the eastern North Atlantic were determined from egg survey data. These were compared with climatological temperature cycles (1986 2002) derived from satellite observations, by geographical region, to predict spawning seasons. Optimum spawning temperatures were determined as 14.0-15.0°C from the English Channel to Portugal and 16.0-18.0°C for all north-west African regions. Spawning seasons were closely related to the general latitudinal trend of the annual temperature cycle, with modification by upwelling in the western Iberian and north-west African regions. Some differences between temperature-based spawning season predictions and field observations were related to variations in seasonal plankton production. Correlations in the annual time-series of favourable spawning temperatures suggested relatively strong linkages between the southern areas from Portugal to Senegal. There was no consistent relationship between annual variations in extent of temperature-predicted spawning seasons and observed field abundance of eggs.

A comparison of LHPR and OPC data from vertical distribution sampling of zooplankton in a Norwegian fjord

Abstract Sampling was carried out using a double Longhurst-Hardy Plankton Recorder (LHPR) system (200 µm and 53 µm mesh nets) in June 1993 in Storfjorden on the west coast of Norway to describe the vertical distribution of zooplankton. The results are compared with concurrent Optical Plankton Counter (OPC) data. Zooplankton was most abundant in a superficial (0–30 m depth) layer ofwarrn (8 to 12 °C), low salinity (23 to 34) water. Included in this shallow distribution were cladocerans, which comprised 62.7 % of all zooplankton identitied in the 200 µm LHPR samples. Most of the small zooplankton taken in the 53 µm LHPR samples was distributed in the upper 50 m of the water column|abundant amongst these small organisms were adult Microsetella norvegica together with nauplii and early copepodite stages of other copepods. Both the number and biovolume of particles recorded by the OPC were consistently about 4 times higher throughout the water column than for an equivalent size range of zooplankton identified in the 200 µm LHPR samples. A comparison of particulate size frequency distributions from the OPC and the 200 µm LHPR samples suggests that this difference could be due partly to the detection of flocculants and detritus by the OPC. However, the 53 µm LHPR results indicate that there was also significant under-representation of zooplankton < 0.35 mm Equivalent Spherical Diameter (ESD) in the 200 µm LHPR samples due to extrusion through the liltering mesh.