IN SITU ORIENTATION OF THE MANILA CLAM RUDITAPES PHILIPPINARUM (, ) : PRELIMINARY RESULTS J.-M Defossez, J Daguzan

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J.-M Defossez, J Daguzan. IN SITU ORIENTATION OF THE MANILA CLAM RUDITAPES PHILIPPINARUM (BIVALVIA, VENERIDAE) : PRELIMINARY RESULTS. Vie et Milieu / Life & Environment, Observatoire Océanologique - Laboratoire Arago, 1996, pp.21-24. ￿hal-03100518￿

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IN SITU ORIENTATION OF THE MANILA CLAM RUDITAPES PHILIPPINARUM (BIVALVIA, VENERIDAE) : PRELIMINARY RESULTS

J.-M. DEFOSSEZ1 and J. DAGUZAN2 'Laboratoire d'Ecologie, Systématique et Morphologie Animales, Université de Liège, 22, quai van Beneden, B-4020 Liège, Belgium Station de Biologie Marine de l'île Bailleron, Université de Rennes, F-56860 Séné, France

SUSPENSION FEEDERS ABSTRACT. - The in situ orientation of 226 mature Manila clams Ruditapes ORIENTATION philippinarum (Adams & Reeve) was recorded. The results show that 88 % of FILTRATION thèse typical suspension feeders présent an orientation at an angle of 22.5 to 67.5 degrees with the crossflow. We propose an hypothesis in order to explain this unexpected observation and we point out the importance of such a basic adaptation regarding nutrition efficiency.

SUSPENSIVORES RÉSUMÉ. - L'orientation in situ de 226 Palourdes japonaises adultes Ruditapes ORIENTATION philippinarum (Adams & Reeve) révèle que 88 % de ces suspensivores typiques FILTRATION s'orientent suivant un angle compris entre 22,5° et 67,5° par rapport au courant. Une hypothèse est avancée afin d'expliquer cette observation inattendue et l'attention est attirée sur l'importance que peut avoir un tel comportement sur l'efficacité nutritionnelle.

INTRODUCTION avoiding refiltration as changes of siphon height, siphon pair orientation and adjustment of siphonal excurrent speed with the flow have been proposed Suspension feeders receive increasing attention but were based on a model siphon pair connected as key factors in coastal ecosystem dynamics (Of- to a pump (Monismith et al., 1990). Nevertheless, ficer et al, 1982; Cohen et al, 1984; Nichols, only few observations have been done in the field. 1985). Indeed, because they collect particles from Our results describe the in situ orientation of sea water and release filtered water and biodepo- the locally very abundant Ruditapes philippina- sits, they seem able to control the phytoplankton rum (= Tapes japonica) recently introduced along biomass and take part in nutrient cycling (see Loo the French coast (Laruelle et al., 1994). The ob- and Rosenberg, 1989 and Demers et al., 1989 servations presented in this paper should invite to among others). It is clear that the importance of pay more attention to basic adaptations of mature this rôle within the ecosystem is proportional to suspension feeding animais and the part they play the quality and quantity of seston présent in the regarding the actual exchanges occurring within water that suspension feeders pump. Moreover, in the ecosystem. the point of view of their nutrition efficiency, it is critical that suspension feeders avoid as much as possible from pumping again the water they have already filtered. As récent studies showed that local seston depletions may occur when sus- MATERIALS AND METHODS pension feeders are filtering (Fréchette and Bour- get, 1985; Peterson and Black, 1987; Fréchette et al, 1989), ail adaptations allowing to limit this The study was conducted on a muddy tidal flat on diluting effect appear to be of the first importance the south point of the Bailleron island (golfe du Mor- both for individual growth as well as for the bihan, Brittany, France) where hydrodynamic characte- interactions between the entire population and the ristics are simple and constant : the mean directions of ecosystem. the currents are from East to West at ebb and inversely at flow with a maximal déviation of ± 5 degrees Regarding this problem, bivalves have received (Fig. 1). The mean current speed was of 0.1 m s"1 to the main attention. Some possible stratégies for 0.15 m s'1. 22 DEFOSSEZ, DAGUZAN

RESULTS

The figure 3 shows that, regarding the cross- flow direction, neither the parallel (axes 6 and 18) nor the normal (axes 0 and 12) orientation is observed (except for the axis 18 chosen by 3 animais). On the contrary, 46% of the individuals are orientated following the axes 3, 9, 15 and 22. The other animais occupy intermediate orienta- tions with a higher frequency for the axes closer to axes 3, 9, 15 and 22 than to the others. 250m Moreover, we have observed that the shell orientation is similar to the direction given by the Fig. 1. - Localisation of the sampling site near the south alignment of the two siphons of each . point of the Bailleron island and mean orientation of Therefore, our results show that not only the shell the tidal currents (maximal déviation : ± 5 degrees). but also the siphon pair of R. philippinarum ex- hibits preferred orientations. When the axis are converted into degrees, it appears that an angle 226 individuals longer than 4 cm were randomly of 22.5 to 67.5° between the alignment of the two sampled on a restricted area (25 m2) during low tides siphons and the crossflow (at flow or at ebb) is in August 1994. Such animais were considered as ma- the most frequently observed (88 %), while an ture (Lamelle et ai, 1994). The sédiment was gently orientation from 0 to 22.5° between the alignment removed from around the upper half of the shell and the orientation of the sagittal plane of the shell was of the siphons and the current direction or its determined as the bearing of a line running from the perpendicular represents only 12%. Such orienta- dorsal to the ventral side of the clam, which corres- tions seem stable because observations on undis- ponds to that running from the exhalent to the inhalent turbed animais reveals that their orientation siphon. Thèse orientations are presented by means of a remains unchanged from low tides to low tides 24 axes circular histogram with a class interval of 15° during 5 tidal cycles. (Fig. 2). The axes 0 and 6 point to North and East respectively.

Fig. 2. - A, Représentation of the 24 axes used to record the in situ orientation. B, An example is given for one Ruditapes philippinarum oriented as defined in the text following the axis 3. ORIENTATION OF RUDITAPES PHILIPPINARUM 23

West East

Crossfiow direction Crossfiow direction at flow at ebb

n =226

= 5 individuals

Fig. 3. - Circular histogram of the in situ orientation of Ruditapes philippinarum (class interval 15°) as observed near the south point of the Bailleron island (golfe du Morbihan, Brittany, France).

DISCUSSION tration by vertical entrainement and by mixing with the water the particles présent on the sédi- How does one explain such results ? One of the ment surface. With such an hypothesis, the orien- major points from the study of Monismith et al. tation observed can be interpreted as follows : (1990) about the bivalve siphonal current is the when the animais are oriented normal to the cur- proof that refiltration of the excurrent siphon may rent, they prevent from refiltration (at flow or at be significant when the incurrent is downstream. ebb) but they could not pump this hypothetical Therefore, the fact that R. philippinarum is rarely particle richer water présent along the excurrent observed with its siphons positioned parallel to siphon jet. An orientation following an angle of the current may be seen as a strategy to avoid 22.5 to 67.5 degrees would allow to collect this refiltration. This proposition is in agreement with water (at flow or at ebb) without a too significant the observations of Tevesz and Cornélius (1985) refiltration. and Vincent et al. (1988) in Lampsilis radiata We may conclude that R. philippinarum shows luteola and Mya arenaria respectively. Thèse bi- obviously preferential orientations to the current. valves were found to be positioned preferentially As such a strategy can greatly affect the nutrition with their siphons normal to the current. However, efficiency, hydrodynamic investigations are requi- the situation seems more complex with R. philip- red in order to evaluate more correctly the précise pinarum. It is clear that the parallel orientation is part played by infaunal bivalve suspension feeders rarely chosen but the complète geometrical alter- within the coastal ecosystem dynamics. native position (i.e. the normal orientation) is also ACKNOWLEDGMENTS - This research was supported never observed. In fact, it is just the intermediate by the National Fund of Scientific Research of Belgium orientation between the parallel and the normal to J.-M. Defossez. Spécial thanks are due to Miss CE. one which prédominâtes. We hypothesize that lo- Maurin for her help during the work, to Dr. M. Poulicek cal turbulences occur.along the excurrent siphon for his comments on the manuscript and to Mrs C. jet and induce local increases of seston concen- Allano who drew the figures. 24 DEFOSSEZ, DAGUZAN

REFERENCES MONISMITH, S. G., J. R. KOSEFF, J. K. THOMP- SON, C.A. O'RIORDAN and H. M. NEPF, 1990. A study of model bivalve siphonal currents. Limnol. COHEN, R. R. H., P. V. DRESSLER, E. J. PHILIPS Océan. 35 : 680-696. and R. L. CORY, 1984. The effect of the Asiatic NICHOLS, F. H., 1985. Increased benthic grazing : an clam, Corbicula fluminea, on the phytoplankton of alternative explanation for low phytoplancton bio- the Potomac River, Maryland. Limnol. Océan. 29 : mass in northern San Fransisco Bay during the 1976- 170-180. 1977 drought. Estuar. Coast. Shelf Se. 21 : 379-388. DEMERS, S., J.-C. THERRIAULT, E. BOURGET and OFFICER, C. B., T. J. SMAYDA and R. MANN, 1982. H. DESILETS, 1989. Small-scale gradients of phy- Benthic filter feeding : a natural eutrophication toplankton productivity in the littoral fringe. Mar. control. Mar. Ecol. Prog. Ser. 9 : 203-210. Biol. 100 : 393-399. PETERSON, C. H. and R. BLACK, 1987. Resource FRÉCHETTE, M. and E. BOURGET, 1985. Food limi- depletion by active suspension feeders on tidal flats : ted growth of Mytilus edulis L. in relation to the influence of the local density and tidal élévation. benthic boundary layer. Can. J. Fish. Aqua. Se. 42 : Limnol. Océan. 32 : 143-166. 1166-1170. TEVESZ M. J. S. and D. W. CORNELIUS, 1985. Life, FRÉCHETTE, M., C. A. BUTMAN and W. R. GEYER, habits and distribution of the riverine Lampsilis ra- 1989. The importance of boundary-layer flows in diata luteola (, Bivalvia). Kirtlandia, 41 : supplying phytoplankton to the benthic suspension 27-34. feeder Mytilus edulis L. Limnol. Océan. 34 : 19-36. VINCENT, B., G. DESROSIERS and Y. GRATTON, LARUELLE F, J. GUILLOU and Y. M. PAULET, 1994. 1988. Orientation in the infaunal bivalve Mya are- Reproductive pattern of the clams, Ruditapes decus- naria L. in relation to local current direction on a satus and R. philippinarum on intertidal flats in tidal flat. J. Exp. Mar. Biol. Ecol. 124 : 205-214. Brittany. J. Mar. Biol. Ass. U. K. 74 (2) : 351-366. Reçu le 3 mars 1995 ; received March 3, 1995 LOO, L.-O. and R. ROSENBERG, 1989. Bivalve sus- Accepté le 27 novembre 1995 ; accepted November 27, 1995 pension feeding dynamics and benthic-pelagic cou- pling in an eutrophicated marine bay. J. Exp. Mar. Biol. Ecol. 130 : 253-276.