World Congress of Malacology Antwerp ... - Unitas Malacologica

Can response to water flow explain the distributions of extant and extinct aquatic Melanopsis
spp. in the Jordan valley?
Dussart, G. 1 ; Heller, J. 2 ; Dussart, A. 1
1. Ecology Research Group, Canterbury Christ Church University, Imperial College at Wye, Wye,
Ashford, Kent TN25 5AH,
Email: gbd1@cant.ac.uk
2. Department of Evolution, Systematics and Ecology, The Hebrew University of Jerusalem, Givat
Ram, Jerusalem,
Email: heller@vms.huji.ac.il
Relationships between shell morphology and river flow might explain the ecological distributions of
Melanoides and Thiara in Guadeloupe (Pointier & Dussart, 1999). Grossowicz, Silvan and Heller et
al. observed in 2003 that Melanopsis species hybridised in a narrow ecotone between gently running
stream outlets (M. buccinoidea ) and wave-affected lake shore (M.costata) in the Jordan valley. They
also suggested that the distribution of elongate, small mouthed forms of costata correlated with rivers
and lakes with weak currents and rich aquatic vegetation, as on the banks of the River Jordan and the
sub-recent lake Hula.
The aim of the work presented here was therefore to investigate whether relationships seen in
Guadaloupe might also apply to Jordan valley Melanopsis species. Thirty shells of extant populations
of each of M.buccinoidea, M.costata costata, M. costata jordanica and M.saulcyi were tested for
their response to water flow in the laboratory.
Each taxon showed a similar response pattern between flows of 1.18m/s and 1.48 m/s. For each
taxon, the pattern changed as flow rate increased, probably as shell sculpture caused a change from
laminar to turbulent flow. For all four taxa, smaller shells showed a lower response to flow than
larger shells. The response was not linear; M.buccinoid showed a smooth, sinuous response whereas
M.costata costata and M. costata jordanic showed intricate changes in response for shells with a
cross sectional profile between 35-45 mm 2 and between 58-62 mm 2 . Small specimens of M.saulcyi
responded strongly to changes in flow rate.
These results might contribute to an understanding of the Pleistocene biogeography of
M.buccinoidea, M. costata, M.obediensis, M.multiformis, M.corrugata and M.turriformis in the
Jordan valley as revealed by sediment cores. It might also help to explain the evolutionary ecology of
extant Melanopsis in this region.
Reproductive strategies of cultivated and wild oysters, Crassostrea gigas, in relation to
environmental variations in a high-turbidity intertidal mudflat (Bourgneuf, France)
Dutertre, Mickaël; Beninger, Peter G; Barillé, Laurent
Laboratoire d’Écophysiologie Marine Intégrée EA 2663, Faculté des Sciences et des Techniques, BP
92208, 2 rue de la Houssinière, Nantes, F-44322 France,
Email: mickael.dutertre@univ-nantes.fr; peter.beninger@univ-nantes.fr; laurent.barille@univnantes.fr
Gametogenesis and reproductive effort were investigated in Pacific oysters, Crassostrea gigas, in
relation to the seasonal variations of their habitat using quantitative histological methods and
continuously-recording environmental monitors. Cultivated and wild oysters were installed in
February 2005 in two farming sites mainly characterized by different annual mean suspended
particulate matter (SPM) concentrations, ranging from 34 mg.l -1 to 154 mg.l -1 , and sampled monthly
between February 2005 and February 2006. Environmental monitors recorded water temperature,
SPM and chlorophyll a concentrations, salinity, oxygen content and immersion time throughout the
study. The acinal structure of the gonad persisted throughout the year. Spermatocytes and oocytes
were respectively observed in males and in females from March when water temperature (