Animal Plankton of the Norwegian Coast Warers and the Open Sea. I - Production of Calanus finmarchicus (Gunner) and Calanus hyperboreus (Krøyer) in the Lofoten Area

Abstract

1) The general part of the present work contains a discussion of the general laws controlling the geographical distribution and the production within a certain marine area of zooplanctonic species, illustrated by investigations of Calanus finmarchicus and Calanus hyperboreus. 2) Chapter I contains a morphological description of biological groups, eggs and larval stages of Calanus hyperboreus and Calanus finmarchicus 3) Chapter II shows how the larval stages of the two species cannot be distinguished by measurements of the total length. By measurising the carapace it has been possible to find a method for separating the larval stages and of determining them quantitatively in the samples. 4) Chapter III deals with the biology of Calanus hyperboreus on the basis of experimental studies and analyses of samples from the coast of Norway from the various seasons of the year. 5) Chapters IV and V deal with investigations of the two species from the Lofoten area. 6) The two species spend the winter in the Lofoten area at great depths. Calanus hyperboreus in the winter condition is so deeply distributed that its horisontal extent is restricted only to the inner areas where the great depths occur. Calanus finmarchicus, which is somewhat less deeply distributed, is not so sharply restricted to the inner parts as the foregoing species, some few percents of the stock are also found outside the area where the greater depths occur. 7) The winter condition is for both species interrupted by an annual vertical migration. This is as regards Calanus finmarchicus completed about the middle of March and as regards Calanus hyperboreus about the middle of April. 8) During the completion of and after the vertical migration there takes place a change in concentration in those parts of the area in which a winter stock existed. This change in concentration is due to the circumstance that the individuals after reaching the higher layers of water are carried away by strong convection currents from the winter localities out over the coastal banks. 9) The changes in concentration of various dimensions in the different parts of the area investigated. In well protected parts some of the stock remains, but in winter localities among the skerries, where there is no protection, the stock is completely carried away by the convection currents. 10) Calanus hyperboreus has a very restricted spawning area which may be limited to the surface isotherms for 2°-3° C. 11) This restriction to isotherms does only apply vertically. Within the prescribed area spawning takes place in layers of water with a temperature up to 7° C., the highest temperature observed in the area during spawning. Experimentally, spawning has been observed at temperatures between -1°.5 to 7°.5 C. 12) The development of eggs takes place as regards. Calanus hyper- boreus before the annual vertical migration. 13) Spawning takes place at different rates in the upper water layers and in deep water. Experiments appear to show that both certain conditions of light and low temperatures have a stimulating effect upon the rate of spawning. Spawning is therefore probably dependent upon the annual vertical migration. 14) The extent of the spawning area as regards this species is mainly dependent upon one factor, viz. the extent of the winter area of distribution. 15) The spawning area of Calanus finmarchicus is not so sharply defined as that of Calanus hyperboreus. This is connected with the circumstance that the horisontal distribution of the species in the winter condition is not as restricted as that of Calanus hyperboreus. 16) About 19/20 of the stock of Calanus finmarchicus spawn inside the surface isotherms for 3°.5 C, but spawning takes place both horisontally and probably also vertically at all the temperatures represented in the area during the investigations. Spawning takes place with almost the same intensity everywhere where females ready to spawn are present. 17) In Calanus finmarchicus the development of eggs takes place after the completion of the annual vertical migration. The period of spawning is much more protracted than that of Calanus hyperboreus. 18) The circumstance that 19/20 of the stock spawn within definite isotherms and isohalines is due to the determination of the spawning area by two factors, 1) The horisontal distribution during Winter. 2) the dispersion of the winter stock by surface currents during the time between the annual vertical migration and the development of the fullgrown eggs. 19) It is possible that the development of the new generation of Calanus hyperboreus into the later stages can only take place at low temperatures, a circumstance which will be of great importance in future investigations of the geographical distribution of the species and of the production of the species in various parts of the ocean. 20) Damas (1905) was able to localise a spawning area for Calanus finmarchicus in the southern part of the Norwegian Sea. It is most probable that the phenomenon shown by Damas is due to a numerical difference in the occurrence of spawning animals as in the Lofoten area. Helland-Hansen and Nansen (1909) show that the 3 species Calanus hyperboreus, Calarnus finmarchicus and Pseudocalanus elongatus are stationary in more stationary water exposed to movements in various directions and for each species of different origin. CaLanus hyperborelrs in water of pure Arctic origin, Calanus finmarchicus in water consisting of a mixture of Arctic and Atlantic water, and Pseudocalanus in water of pure Atlantic origin. From the investigations in the Lofoten area we may conclude that the species are only stationary during the winter condition. It seems to be extremely probable that we from the investigations now carried out can establish the following rules for the geographical distribution and the production of marine pelagic animals: 21) When a species is stationary in an area of the sea, also the water of this area will have to be comparatively stationary. 22) When a species occur in waters where convection currents are prevailing a deficiency (p. 18) due to changes in ecological factors will be found. 23) The age of the water masses in their biological area is a factor of dominant influence in the production of marine pelagic animals of different areas of the northern seas.