Assessing the variability of hydrographic processes influencing the life cycle of the Sicilian Channel anchovy, Engraulis encrasicolus, by satellite imagery

Three oceanographic surveys carried out in the Sicilian Channel during the spawning season (June to July) of anchovy (Engraulis encrasicolus) showed a close relationship between anchovy reproductive strategy and important hydrographic structures. A time series of satellite‐derived sea surface temperature images of the Sicilian Channel were analysed by means of empirical orthogonal functions and the dominant empirical modes were studied in detail. The first empirical mode captured much of the original variance and reproduced the trajectory of the Atlantic Ionian Stream (AIS), the principal hydrodynamic feature of the area. The time coefficients of modes 1 and 2 had seasonal signals which, when combined, accounted for the enhancement of the thermal front, clearly visible off Cape Passero (southernmost coast of Sicily) during summer. As the area constituted the principal nursery ground of the Sicilian Channel anchovy, the combination of the time coefficients of these modes was considered a potential indicator of the food particle concentration usually associated with oceanic fronts, which provided the energy requirements for larval growth. Mode 3 described the north/south displacements of the mean AIS trajectory, which modified the surface temperature regime of the anchovy spawning habitat. Therefore, the time coefficients of this mode were used as a potential indicator of anchovy spawning habitat variability. The capability of time coefficients of modes 2 and 3 to modify the main pattern depicted by mode 1 were tested successfully against in situ oceanographic observations.     

Effect of habitat conditions on reproduction of the European anchovy (Engraulis encrasicolus) in the Strait of Sicily

The aims of this study were to describe the reproductive cycle of the European anchovy (Engraulis encrasicolus) off the south coast of Sicily and determine whether intra‐ and inter‐annual reproductive trait variations, if any, are adaptive responses which maximize reproductive success under environmental fluctuations. Biological data were collected from purse seine and mid‐water pelagic trawl commercial catches landed in Sciacca (Sicily) over 6 yr (1997–2002) at fortnightly intervals, analysing a total of 84 581 individuals. No inter‐annual changes in length at first reproduction were observed, with a mean pooled value of 11.26 cm for both sexes being found. Spawning intensity, indicated by gonadosomatic index, condition factor and length–weight relationships, seem to be governed by food availability prior to spawning. Anchovy reproductive investment was limited by the area's low primary production. There was a synchrony between reproductive cycle and temperature. Water warming marks the onset of a period of high water stability in the area, and its later cooling marks the onset of a period with low water stability. The relationship between reproductive cycle and temperature is therefore probably a reproductive strategy having evolved to ensure that spawning takes place during the period of the year when water column stability is higher, favouring food concentration and egg and larval retention in the spawning areas.     

Influence of field burning and soil treatments on growth of wheat after Kentucky bluegrass, and effect of Rhizoctonia cerealis on bluegrass emergence and growth

Studies were conducted to assess the importance of soil-borne pathogens as impediments to the production of direct-drilled wheat following Kentucky bluegrass in rotation. Bluegrass sods were collected as cores from commercial seed fields in October (after open-field burning) and in December and March (after exposure to normal freezing and thawing), treated with glyphosate after a 2- to 3-week period of green-up in the glasshouse, and then planted to wheat 21 days later. Wheat seedlings in the 3- to 4-leaf stage were stunted and spindly in either burned or nonburned sods collected in October, but grew significantly better in burned than nonburned sods collected in December and March. Fumigation (methyl bromide), simulated tillage, and application of metalaxyl as a drench, singly or as combined treatments, improved the growth of wheat in nonburned sods. Growth of wheat in nontreated burned sods collected after frost had penetrated the upper portions was equivalent to that in fumigated sods. Experimental freezing at −20°C for up to 96 h, of burned and nonburned sods collected in October, followed by thawing also improved the growth of wheat subsequently sown directly into these sods. The stunted and spindly seedlings had roots girdled and severed by lesions typical of Rhizoctonia root rot. Isolates of Rhizoctonia cerealis were recovered from these roots and caused poor seedling emergence and stunted root and shoot growth of both wheat and bluegrass. The results suggest that both R. cerealis and Pythium spp. are potentially important soil-borne pathogens of wheat when following Kentucky bluegrass in rotation and that burning done routinely to improve the yield of bluegrass seed can also reduce the potential for damage caused by Rhizoctonia and Pythium root rots of wheat seeded directly into bluegrass sod.