Phytoplankton biomass and zooplankton abundance on the south coast of Portugal (Sagres), with special reference to spawning of Loligo vulgaris

The importance of the south-west coast of Portugal as a spawning ground for the long-finned squid, Loligo vulgaris, was investigated between May 1993 and May 1994 at a site 3 Km East of Sagres. Hydrographic (temperature and salinity) observations were registered in situ and water samples were collected for laboratory determinations of chlorophyll a. Zooplankton was sampled with a 500 mm plankton net during 10mn trawls. Hydrographic and biological information was related to the occurrence of L. vulgaris egg masses at the site. The values of water temperature ranged from 13.0º C in January to 19.2º C in July, and the salinity varied between 35.3o/oo in May of 1993 and 38.0 o/oo, in November, December and March. The highest values for phytoplankton biomass were recorded in September and May, whereas the maximum zooplankton abundance was recorded between July and September. The most important zooplankton groups included cladocerans, copepods, crustacean larvae, fish eggs and appendicularians. We have concluded that the highest values for zooplankton abundance were recorded when the greater number of egg masses of L. vulgaris were observed