Improved sea-urchin embryo bioassay for in situ evaluation of dredged material.  Sediments usually contain many contaminants derived from human activities. In case of dredging activities, these sediment-bound contaminants arise following the excavation and remobilization of sediments. Previous studies have used different species of clam, crabs, lugworms, etc. for the evaluation of dredged material in situ, but there are not studies that use acute bioassays for these purposes. The sea-urchin embryo bioassay has been chosen to characterize biological effects in situ in two ports of the southwest of Spain, the Port of Huelva and the Port of Cadiz. The sea-urchin embryo bioassay has been adapted for in situ evaluation of seawater quality in coastal areas, however, they are necessary for further improvements to take into account differences of temperature between sites. This temperature variation is one of the principal reasons (other than pollution) of larval mortality and the slow down in the growth rate of the urchin. In the present study a bioassay was conducted in both field and laboratory conditions, in order to compare the effects in situ with the effects under controlled conditions of temperature, salinity and oxygen dissolved. Results showed a good correlation between samples obtained in situ and in the laboratory, but in the field the percentage of normal pluteus larvae is less than under laboratory conditions.