Journal of American Science, 2011; 7(1) http://www.americanscience.org Factors Associated with the Distribution of the Invasive Bivalve Clams" Donax Variabilis (Say,1822)" at the Area of the Mediterranean Coast Preferred by Marine Fish Larvae, New Damietta, Egypt El-Ghobashy, A.E. 1 ; Mahmad, S.Z. 2 ; Kandeel, S.K. 3 and El-Ghitany, A.H. *1 1 Zoology Department, Faculty of Science (Damietta), Mansoura University, Egypt. 2 Oceanography Department, Faculty of Science, Suez Canal University, Egypt. 3 Zoology Department, Faculty of Science (Fayoum), Fayoum University, Egypt. * asmaa_haris222@yahoo.com Abstract: New Damietta shore is one of the important areas for collection of the clams as well as mullet, seabass and seabream larvae which are reliable for marine aquaculture in Egypt. Donax variabilis was recorded for the first time in Egypt and because of its presence in the area of Damietta Maritime Port, larvae has come stuck with ships from the Atlantic Ocean where they were registered there. The density of D.variabilis increased in site I (718 / m ) than in site II (415 / m ). Water salinity (33.43 ± 4.59 mg/ L) in 2 2 site I was less than the salinity of the sea, while it was almost similar to the salinity of the sea (36.94 ± 3.45 mg/ L) at site II. Nutrients concentration at site II were higher than that at site I, where it averaged 0.02 ± 0.01, 0.05 ± 0.03 and 0.26 ± 0.16 at site I and 0.05 ± 0.03, 0.34 ± 0.41 and 0.46 ± 0.36 mg/l at site II for NO 2 , NO 3 and PO 4 respectively. Measured Chlorophyll a was high at site II (0.25 0.12 mg/m ) 3 compared to site I (0.25 0.12 mg/m ), revealing the increase 3 in phytoplankton biomass at site II. Crustaceans and molluscs were the most groups associated with clam's beds. D.variabilis cohorts appeared during summer months, this indicates that the population consists of only one spawning event. Length frequency of D.variabilis was essentially bimodal during the period of study. Three modes were recorded in June, 2008 at size classes of 7, 11and 20 mm of shell length. [El-Ghobashy, A.E.; Mahmad, S.Z.; Kandeel, S.K. and El-Ghitany, A.H. Factors Associated with the Distribution of the Invasive Bivalve Clams" Donax Variabilis (Say,1822)" at the Area of the Mediterranean Coast Preferred by Marine Fish Larvae, New Damietta, Egypt. Journal of American Science 2011; 7(1):1051- 1062]. (ISSN: 1545-1003). http://www.americanscience.org . Key wards: Mediterranean coast- Donax variabilis- A biotic factors- Biotic factors 1. Introduction: A bivalvia can acquire an important role in solving the problem of shortage and high price of animal protein in Egypt. Egyptian beaches has extended over long distances and it has become necessary to look at how the exploitation of bivalvia inhabiting these beaches. Bivalve molluscs are conspicuous members of sandy beaches (McLachlan et al., 1996). The family Donacidae inhabits exposed intertidal sandy beaches and form worldwide, by far, the largest group living in such highly dynamic environments (Ansell, 1983; Brown & McLachlan, 1990). Since this group is present in the seaside which is unstable and have continuous environmental changes. Biotic (food availability and intraspecific interactions) and a biotic (beach slope, swash energy, sand particle size, salinity, and chemical cues) factors play predominant roles in regulating alongshore distribution patterns (Defeo & de Alava, 1995; McLachlan, 1996; Gime´nez & Yanicelli, 2000 and Lastra et al., 2006). Also human activity may represent an additional regulatory agent, acting either directly, by removal of individuals, or indirectly, by removal or disturbance of potential competitors (Defeo and de Alava, 1995; Defeo, 1996a; Schoeman, 1996 and Brazeiro & Defeo, 1999). Ecological preferences of Donax have been studied by Ansell & Lagardere, 1980 and Guillou & Bayed, 1991. McLachlan & Jamarillo (1995) have reviewed the zonation of organisms on sandy shores and have emphasized the strong control exerted on distribution by physical factors and the temporal variability of the component communities. As well as, the population dynamics of Donax species have been examined by Guillou, 1982; Maze & Laborda, 1988; Maze, 1990 and Tirado & Salas, 1998. Clams are important recreational and commercial resources in many countries (McLachlan, et al., 1996). Donax sp. spreading in the northern coast of Egypt and be the favorite food among the population in coastal cities. Inshore waters of the Damietta region (North coast of Egypt) support nursery (larval or fry) areas for several commercially important species, especially http://www.americanscience.org editor@americanscience.org 1051