Physiological Response of <Emphasis Type="Italic">Spisula Subtruncata
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Hydrobiologia 475/476: 505–511, 2002. E. Orive, M. Elliott & V.N. de Jonge (eds), Nutrients and Eutrophication in Estuaries and Coastal Waters. 505 © 2002 Kluwer Academic Publishers. Printed in the Netherlands. Physiological response of Spisula subtruncata (da Costa, 1778) to different seston quantity and quality Jose L. Rueda∗ & Aad C. Smaal Netherlands Institute for Fisheries Research (RIVO). P.O. Box 77, 4400 AB Yerseke, The Netherlands ∗Present address: Marine and Estuarine Ecology Unit, Department of Zoology and Entomology, University of Queensland, St. Lucia, Qld 4072, Australia E-mail: [email protected] Key words: bivalve, feeding behaviour, filtration, ingestion, regulation Abstract Individuals of the bivalve Spisula subtruncata were fed a mixed diet comprising of sea water enriched with the diatom Phaeodactylum tricornutum and ashed silt within a range of concentrations, simulating natural conditions above pseudofaeces threshold. The designed ranges for total particulate matter were between 10 and 30 mg l−1and organic content of seston 15–40%. Filtration rate, rejection rate, ingestion rate and absorption rate were measured at those different conditions. Filtration rate and rejection rate were significantly correlated to total particulate matter and percentage of organic matter, with higher rates at higher values of total particulate matter and lower values of percentage organic matter. Ingestion rate was maintained at similar levels in all the treatments and organic enrichment of the ingested food occurred due to preingestive selection of the filtered material. A differential absorption rate occurred at different levels of organic matter in the diet with high rates at high values of the organic content of the diet. S. subtruncata showed different physiological responses to changes of the food conditions: (1) Increase of pseudofaeces production at increasing levels of particulate matter, (2) preingestive selection of organic material which enriched the organic fraction of ingested food, (3) stabilized ingestion rate and (4) increase of the absorption rate at high organic levels of the seston. Introduction ditions, season or location within the coast. The effects of the variability of suspended particles in the water Spisula subtruncata (da Costa, 1778) is a common column has never been studied up to date in S. sub- bivalve which lives in coastal areas of Europe with truncata, but it has been described for other bivalve a distribution from Norway to the Mediterranean and species both in temperate (Bayne et al., 1989; Iglesias the Atlantic coast of Morocco (Tebble, 1966). The et al., 1996; Navarro & Widdows, 1997) and tropical habitat of this species in the North Sea (sandy bot- waters (Yukihira et al., 1999; Wong & Cheung, 1999). toms between 2 and 30 m) represents an environment There is a controversy about the effects of the where the concentration of suspended particulate mat- quantity and quality of seston in the feeding processes ter (seston) may be variable in time as a result of of bivalves. Jørgensen (1990, 1996) have suggested resuspension of fine sediments during periods of high that responses to environmental changes are determ- current velocity, wind-wave activity and storm events, ined solely by the physical properties of the cilliary especially in the shallow bottoms. For example, in the mechanisms of pumping and filtration. On the other Dutch coastal area, seston concentrations in the wa- hand, several authors (Bayne et al., 1989, 1993; Ig- ter column can vary between 2 and 150 mg l−1, with lesias et al., 1992, 1998; Navarro et al., 1996; Navarro values between 5 and 10 mg l−1 being most frequent & Widdows, 1997; Hawkins et al., 1998; Yukihira et (RIKZ, 1999). Between 5 and 40% of this seston may al., 1999; Wong & Cheung, 1999; Pouvreau et al., be organic in nature, with Chlorophyll concentrations 2000) have observed bivalve filter feeding resulting in between 0 and 11 µgl−1, depending on weather con- relative constancy of rates of absorption and ingestion. 506 Table 1. Number (N), shell length (SL: mm) and ash free dry weight (AFDW: mg) of the animals used in the different experiments (Exp) at different levels of total particulate − matter (TPM: mg.l 1) and percentage of organic matter (%OM). Date (year/month/day). Mean value ± standard deviation Exp Date TPM %OM N SL AFDW 1 990804 12.59 ± 0.67 16.21 ± 1.33 7 25.4 ± 1.5 130.0 ± 19.7 2 990805 11.49 ± 0.41 26.41 ± 2.05 7 25.3 ± 1.1 118.6 ± 15.4 3 990802 10.66 ± 1.76 35.71 ± 1.65 7 25.3 ± 1.4 114.3 ± 16.0 4 990720 22.44 ± 0.95 17.53 ± 2.07 7 24.5 ± 1.2 103.6 ± 9.8 5 990723 18.98 ± 0.08 25.13 ± 0.63 7 25.3 ± 1.3 113.2 ± 21.2 6 990730 21.52 ± 0.56 43.66 ± 4.18 7 25.6 ± 1.6 119.4 ± 45.8 7 990719 29.48 ± 2.64 14.34 ± 0.99 7 24.8 ± 1.5 92.8 ± 22.5 8 990803 30.28 ± 0.8 25.17 ± 1.72 7 25.4 ± 1.5 132.0 ± 17.3 9 990729 30.31 ± 2.57 39.17 ± 1.41 7 24.7 ± 0.8 116.9 ± 33.5 The following modes of regulating the ingestion rate lands) during June and July 1999 and transported of food have been described: (1) changing the pump- to the Field station of RIKZ at Jacobahaven (Oost- ing or the clearance rate (Navarro et al., 1992, 1994; erschelde, S.W. Netherlands) where the experiments Iglesias et al., 1996; Navarro & Widdows, 1997), or were executed. Selected individuals for experiments (2) increasing rejection of pseudofaeces above a cer- had a shell length of around 25 mm (Table 1). Ac- tain threshold of seston quantity and quality (Iglesias climatisation to laboratory conditions proceed for one et al., 1992; Navarro et al., 1992; Navarro & Wid- week. During this time the animals were placed in a dows, 1997). There are other mechanisms to increase container with fine sand and natural sea water pumped the food ingestion and absorption by a preingestive se- continuously from the coast. Parameters from the wa- lection of organic matter from filtered material (Bayne ter were similar to those from the place of collection et al., 1993; Navarro & Iglesias, 1993; Iglesias et al., of the animals. Afterwards 7 individuals of S. subtrun- 1996; Hawkins et al., 1998; Wong & Cheung, 1999) cata were placed in experimental chambers and fed on and adjustment of the absorption efficiency to changes experimental diets for 5 h prior to start of the meas- in gut passage time (Bayne et al., 1989; Navarro et al., urements. Collection of biodeposits were carried out 1994) or the gut content (Hawkins et al., 1990). Little 8 h after the start of the experiment. Two samples of information about feeding and ecophysiology of Spi- biodeposits were collected for each individual on each sula subtruncata is available (Møhlenberg & Riisgård, experiment. 1979; Kiørboe & Møhlenberg, 1981; Møhlenberg & Kiørboe, 1981). Research related to its growth in the North sea has been carried out recently (Degraer, 1999). Experimental diets The aim of the experiment reported here is to de- Dietary composition included the following compon- termine how physiological rates are affected in Spisula ents: (1) Cells of the pelagic diatom Phaeodactylum subtruncata by different diets. The hypothesis is that tricornutum and (2) silt particles (<50 µm) previously this filter feeder is able to respond to variation in food ashed for removing the organic material. The mixtures quality and quantity by adjustments of physiological of algaes and silt were added to natural sea water di- rates. luted with filtered sea water in a reservoir tank. A mixer was placed in the bottom and suspension of Material and methods particles was promoted by aeration. A pump provided a flow of water through each chamber (2.8 l h−1) Collection and maintenance in which the depletion of particles by the clams was below 30% of the total. For making and controlling Individuals of Spisula subtruncata were dredged from the diets, the concentration of particles was monitored populations in the Molengat (North of The Nether- with a Coulter Counter fitted with a 100 µm tube. 507 The designed ranges for the diets were: total par- (f=p) and when SE = 1, there is a complete selection ticulate matter (TPM: mg l−1) 10–30 mg l−1 and per- and ingestion of organic particles. centage organic matter of seston 15–40%. Details of the different experimental diets are shown in Table 1. Size standardization of physiological rates In each experiment, 3 water samples were taken during the experimental period from the inflow of the control Once the physiological measurements were com- chambers. For determinations of TPM, water samples pleted, shell length of each individual was recorded to (1 l) were filtered onto pre-ashed (450 ◦C for 4 h) and the nearest 0.1 mm as well as the ash-free dry weight of the soft tissues (weight after dry the soft tissues at weighed GFC filters, rinsed with sea water-isotonic ◦ ◦ ammonium formate and dried at 80 ◦C. The dry weight 80 C during 24 h − weight after calcination at 520 C of retained material gave the TPM and the weight loss during 4 h). Rates were assumed to scale with body on ignition at 450 ◦C for 4 h gave the ash weight or size, and consequently, measurements were standard- particulate inorganic matter (PIM: mg l−1) from which ised to an equivalent of 150 mg ash free dry tissue of − ∗ the particulate organic matter (POM: mg l 1)wasde- S. subtruncata by using the formula Ys = Ye (150/ b rived (POM = TPM − PIM).