Ecological observations on talorchestia brito (stebbing, 1891)‎ and allorchestes plumicornis (heller, 1866)‎ (amphipoda, talitridae)‎ inhabiting the Red Sea coast, Egypt

Abstract EN

The abundance, population structure and their relations with the ambient environmental conditions of two talitirid amphipod species; Talorchestia brito and Allorchestes plumicornis were studied at two sites in the Egyptian Red Sea Coast; site 1 is Marine Biological Station (MBS) and site 2 is Safaja Fishermen Harbour (SFH).

Samples were collected monthly during the warm period (April- August, 2007) from the two sites.

Individuals were subdivided according to sex and length and abundance was calculated for each species in each sampling site.

Abundance of Talorchestia brito varied during the study period with a marked decrease in April.

Sex ratio was female biased.

The males of T.

brito grow larger than females; the males reached a maximum length of 13 mm while females reached 10 mm.

On the other side, males of Allorchestes plumcornis were more abundant than females throughout the study period.

The sex ratio fluctuated between 0.54 during August and 0.86 in July.

The unusual dominance of males of A.

plumcornis may be attributed to high mortality of females as a result of hard conditions during the warm period.

Females and males of A.

plumcornis become distinguishable at 5mm.

The absolute length range recorded for A.

plumcornis was 2-5 mm for juveniles, 5-9 mm for females and 5-10 mm for males.

The results revealed that, temperature was the most important factor affecting the occurrence of A.

plumcornis population while, it was insignificant for T.

brito.

The early stages of T.

brito were more sensitive to dissolved oxygen concentrations while those of A.

plumcornis were sensitive to salinity variations.

On the other side, the adult forms of the two species showed the reverse pattern.