Résumé:
This study interests the state of health of Posidonia oceanica meadows of Mostaganem coasts.
Shoot density was measured and phenological parameters were followed from February to July
2011 at Stidia and Hadjadj areas at - 3 m mean depths. In order to study the feeding behavior of
the aspidochirotid Holothurians inhabiting the Posidonia oceanica meadows and to have an idea
on relationship between the Posidonia and the holothurians component, organic matter throughout
digestive tract, faecal matter and into the preferred biota of Holothuria (H.) tubulosa, Holothuria
(L.) poli, Holothuria (P.) forskali and Holothuria (P.) sanctori were analyzed and granulometrics
analysis of the sediment particles ingested by Holothuria (L.) poli and into the biota was realized,
in order to access the selectivity degree of this species by calculating the electivity index.
Posidonia meadow of Stidia is installed on rocky substratum, whereas Hadjadj one is installed on
soft substratum. At Hadjadj area average densities of (505.6 ± 316.9), (193.6 ± 59.13) and (379.2
± 157.50) have been respectively obtained for HS1, HS2, HS3 stations and in Stidia area the
average densities (181.4 ± 75.40), (350.8 ± 188.57) where obtained for stations SS1 and SSM
respectively. This means that the Posidonia oceanica meadows of Stidia and Hadjadj areas have
abnormal densities. At both localities, the studied phenological parameters shows an increase from
the end of the winter - early spring (February and March) to late spring - early summer (May and
June). Seagrasses beds of both localities show a slight sign of disturbance. However, the seagrass
bed is in better health in Hadjadj area.
Aspidochirotid holothurians species show organic matter selectivity. Holothuria (P.) sanctori is
the most selective species, followed by Holothuria (P.) forskali, Holothuria (L.) poli and
Holothuria (H.) tubulosa. Faeces are richer in organic matter than the surrounding sediment.
Holothuria (L.) poli prefer the fine and very fine sediment fractions, which are richest in organic
matter. The results support "optimal foraging" theory and show that these holothurians species
recognize the richer organic coated particles and that Holothuria (L.) poli can distinguish between
sediment particle with or without organic matter.
