Abstract Zooplankton samples were collected at Ras Tanura and Safaniya on the Saudi Gulf coast in April 1992. Both are known spawning areas of penaeid shrimp including Penaeus semisulcatus. Zooplankton and penaeid larval abundance in 1992 are compared with data collected from the same localities during the same period in the 1970s. At Ras Tanura, mean penaeid larval abundance was significantly lower in 1992 (0.275 m −3) than 1976 (6.77 m −3), whereas mean zooplankton abundance showed no significant change. Data also suggest that penaeid larval abundance at Ras Tanura was lower in 1992 than 1975, 1977, and 1978. At Safaniya, both mean zooplankton and penaeid larval abundance were significantly lower in 1992 (0.128 ml m −3 and 0.009 m −3) than in 1978 (0.77 ml m −3 and 16.70 m −3). Possible reasons for the observed patterns include natural environmental changes, ‘normal’ background impacts (e.g. coastal reclamation, dredging, oil pollution) and impacts arising from the 1991 Gulf War. Mathews et al. (1993) provides evidence that the war had a major impact on spawning stock size, which was reduced to very low levels in early 1992. It is suggested that a combination of several factors, rather than any single one, may have been involved.