STUDIES ON THE BARNACLE BALANUS AMPHITRITE DARWIN, 1854 (CIRRIPEDIA) FROM IN THE

BY

SALMA H. A. SHALLA1), ABDUL F. A. GHOBASHY1) and RICHARD G. HARTNOLL2) 1)Department of Zoology, Suez Canal University, Ismailia, Egypt 2) Port Erin Marine Laboratory (University of Liverpool), Port Erin, Isle of Man, British Isles ABSTRACT The reproductive seasonality and the growth rate of Balanus amphitritewere studied in Lake Timsah in the mid-region of the Suez Canal. Some nauplius larvae were recorded in each month, but they were abundant only from April to October. Cyprid larvae were most abundant from July to August, and settlement from June to October. At different stations in the lake, frequency of settlement was related to biotic rather than abiotic factors. Growth rate was faster in summer than winter, and was related to water quality. The scasonal pattern of reproduction in Lake Timsah reflected the marked seasonality in environmental conditions.

RÉSUMÉ La saison de reproduction et le taux de croissance de Balanusamphitrite ont été étudiés dans le lac Timsah, dans la région moyenne du canal de Suez. Quelques nauplii ont été recueillis chaque mois, mais ils n'étaient abondants que d'avril à octobre. C'est en juillet et août que les larves cypris étaient les plus abondantes, et, pour les fixations, c'était de juin à octobre. En différentes stations, la fréquence des fixations était plutôt liée à des facteurs biotiques qu'a des facteurs abiotiques. Le taux de croissance était plus élevé en été qu'en hiver, et était en relation avec la qualité de l'eau. En ce qui concerne les époques de reproduction dans le lac Timsah, elles reflétaient le caractère saisonnier très marqué des conditions d'environment.

INTRODUCTION

During the course of its passage from the Mediterranean Sea to the Gulf of Suez the Suez Canal passes through several lakes. It first crosses the shallow Lake Manzalah, the channel of the Canal being separated from the lake by embankments on either side. At 78 km from Suez it enters Lake Timsah, some 5 km long, with the city of Ismailia on its northern shore: the Canal forms a dredged channel through the eastern side of the lake. After a further 15 km the Canal passes for some 35 km through the much larger Bitter Lakes, before the final stretch leading to Suez. The main features mentioned are shown in fig. 1. The hydrography of Lake Timsah is unusually complex, since it results from the interaction of several factors. These factors have undergone changes during the period since the Canal was built, and are also subject to seasonal changes. They can be outlined briefly. Prior to the construction of the Canal, Lake Timsah was a marshly depres- sion, which was intermittently reached by flood waters from the via the 504

Fig. 1. A map to show the general features of the Suez Canal. The inset shows Lake Timsah, with the (three) sampling stations numbered, and arrows to indicate the major freshwater inputs.

Wadi Tumilat. During the construction of the Canal it was initially filled with Mediterranean water, but once the Canal was completed it received water from several sources. One was an input of high salinity waters from the Bitter Lakes. This high salinity resulted from the solution of salt deposits on the lake bed, but the salinity steadily fell as they dissolved, before stabilizing when this process was completed by the sixties. Nevertheless, the prevailing northerly water flow through the Canal for most of the year means that high salinity water, further concentrated by evaporation in the Bitter Lakes, continues to reach Lake Timsah via the Canal. A second major factor is the input of fresh water directly into Lake Timsah. This water originates from the Nile via a freshwater canal, and enters Lake Timsah as direct overflow, sewage effluent and agri- cultural drainage. Until the freshwater canal was extended northwards to Port