THE VERTICAL-DISTRIBUTION OF EGGS OF MAUROLICUS-MUELLERI

The vertical distribution of eggs of the sternoptychid Maurolicus muel leri from different localities worldwide was analysed on the basis of apparently conflicting literature and new data. Although the vertical distribution has been classified as ''variable'', most data from hydro graphically comparable areas were similar. Differences at both larger and smaller geographical scales were mainly a consequence of environme ntal variability and to a minor extent the result of sampling limitati ons. In North Atlantic waters of average salinity and with a temperatu re range of 8-10-degrees-C, eggs generally occur deep because of their relatively high density. In less saline waters off New Zealand and al so perhaps off Japan the same has been found. In highly saline waters such as those of the Mediterranean Sea, the eggs have a much shallower distribution. In areas without vertical motion of water masses, the d epth of occurrence depends directly on the density of seawater. The eq uilibrium densities are not uniform worldwide and some density ranges are given. In areas with lower salinities, eggs show adaptations via a larger ''perivitelline space'', which results in reduced specific gra vity. Eggs cannot compensate for high seawater densities. In upwelling ecosystems, eggs are found shallower than would be expected from the equilibrium density range present. Alternative hypotheses are discusse d, that in upwelling systems spawning occurs shallower, or that eggs a re transported upwards with upwelling waters. In the Benguela upwellin g system, shallow distributions could coincide with high mortality of eggs.