THE VELIGER TheVeliger49(0:15-18 (March 30, 2007) i: CMS. Inc., 2006 Effects of Photoperiod Manipulation on Reproductive Condition of the Northern Bay Scallop, Argopecten irradians irradians (Lamarck, 1819) PETER N. DESANCTIS, M.D.,' KIM TETRAULT,' and STEPHEN T. TETTELBACH^ ' Southold Project in Aquaculture Training (SPAT), Cornell Cooperative Extension of Suffolk County, NY Southold, 11971 -Marine Science Program, Southampton College, Long Island University, Southampton, NY 11968; new address: Dept. of Biology, C.W. Post Campus of Long Island University, Brookville, NY 11548 (e-mail: Stephen.tettlbach(@,liu.edu) Abstract. Recentstudiessuggestthatphotoperiodmayplayanimportantroleinreproductivedevelopmentofcertain scallopspecies, but similarinvestigationshavenotbeen donepreviouslyforthebayscallop. Inthisstudy, weexposed bay scallops,Argopecten irradiansirradians(Lamarck, 1819), duringlatereproductivedevelopmentbut priorto spawning, to three different light regimens (24 hr light, 24 hr dark, and ambient light) in the laboratory. Scallops from all treatments showed increases in reproductive condition over a 4-week period, but those held under continuous light showedastatisticallygreaterincreaseinreproductiveconditionasearlyas6 daysafterthestartoftheexperiment. Our data suggest that photoperiod may play a significant role in affecting the reproductive condition ofbay scallops. INTRODUCTION week period, from mid-May to mid-June 2003, by exposing 0+ yr hatchery-reared scallops which had Changes in water temperature and food availability are been overwintered in Goose Creek, Southold, New gtheanteracluley trheegaprrdoecdestso obfe rtehperomdaujcotriveexodgeevneoluospmfeancttorisn aYmobrike,ntUlSigAht (tdoiurtnharleesudnilfifgehrtenatpplriogahtchirneggimmeanxsi:mu(1m) temperate bivalve mollusks (Sastry, 1963, 1966, 1968; Sastry & Blake, 1971; Bayne, 1976; Newell et al., 1982; day-length in late June), (2) continuous darkness MacDonald & Thompson, 1985). Photoperiod has (effected with light impermeable fiberglass tanks and usually been viewed as playing a minor role, or no role coovveerrhs)e,adabndank(3)ofcofnotuirnu1o.u2s3 mliglhotng(,pr4o0v-idweadttbyCooaln whatsoever, in gametogenesis ofbivalves, but given the wmtthieoaolutnln-tldi(iegDnvhetegvlapotluphaceayhdtselnpalahnteoutiro&meppeoorfrMititoahndnegtapmneratcot,ylienbii1end99esi1yc)mea.p,lolirotEptviasirnpdetreponribconaedbutlchi-ees gWolorphnoaiguqtpueXes®,0off.fil6bueosmrrcgeallsdalcesoeespnpstr)a(cslniuegpwhpat=lyitet9uda5bn)ewski)swt.ha(0sEu.a9nfhcimehlltdweorifeiddne,thsXaeempb2at.irh5earntemtee reproductive development of such pectinid species as flowing seawater from Cedar Creek at the Southold Pecten maximus (Paulet & Boucher, 1991; Devauchelle Marine Environmental Learning Center in Southold, & Mingant, 1991; Saout et al., 1999), Placopecten New York. Flow rate was 113.61 (=30 gal)/inin; magellanicus (Couturier & Aiken, 1989), and Argopec- temperature ranged from 14.4-18.9°C, while salinity ten circularis (Villalejo-Fuerte & Ochoa-Baez, 1993). remained at —28 ppt during the study period. All While reproduction has been extensively studied in the tanks were cleaned on a weekly basis, following bay scallop, Argopecten irradians (see review by Barber removal ofscallops, with a strong stream ofwater. At & Blake, 1991); effects of photoperiod on gonadal the time of initial collection on 14 May 2003, shell maturation have not been investigated. The purpose of heights of 15 scallops were measured to the nearest this study was to examine how manipulation of mm (X = 48 mm; SD = 3.3 mm) and a baseline of photoperiod affected gonad weight and reproductive reproductiveconditionoftheseanimalswasdetermined (gonadal) index during the late stages of reproductive via measurement of gonad dry weight (GDW) and development, prior to spawning, of the northern bay gonadal index (GI = (gonad dry weight) / (total tissue scallop, Argopecten irradians irradians. dry weight) X 100) (Barber & Blake, 1991). Shell heights, GDW, and GI of 15 bay scallops sacrificed MATERIALS AND METHODS from each of the three photoperiod treatments (ambi- ent, dark, light) were similarly measured at approxi- Effects of photoperiod manipulation on bay scallop mately weekly intervals during the ensuing 4-week reproductive development were monitored over a 4- period. Page 16 The Veliger, Vol. 49, No. 1 ^^^^M AmbientLight AA AmbientLight 24hrDark B B 24hrDark 24hrLight BAB 24hrLight AAB ^-' 1.5 X s: •aa> AA G> c BE a n I c a o c O rca 20 OO 0-5 5/14 5/20 5/27 6/5 6/10 5/14 5/20 5/27 6/5 6/10 Date Date Figure 1. Temporal changes in gonad index (GI) of Figure 2. Temporal changes in gonad dry weight (GDW) of hatchery-reared 0+ yr bay scallops. Argopccteii inaclicms hatchery-reared 0+ yr bay scallops, Argopecteu inadians irradiaiis, exposed to three different light regimens (ambient ivradiaus. exposed to three different light regimens (ambient light, 24 hrdark, 24 hr light) in the laboratory from 14 May- light, 24 hrdark, 24 hr light) in the laboratory from 14 May- 10 June 2003. Bars represent mean values + 1 SD; n = 15 10 June 2003. Bars represent mean values + 1 SD; n = 15 individuals per group, per sample date. Statistical differences individuals per group, per sample date. While there were between means for a given date, as determined via Kruskal- statistical differences (at P < 0.04) between means on 5/20. 6/ Wallis non-parametric ANOVA, are shown above the bars; 5, and 6/10, as determined via Kruskal-Wallis non-parametric ** = P < 0.01; *** = F < 0.001. Letters shown above the ANOVA's, there were no statistical differences (at P < 0.05) bars signify results of Tukey-type non-parametric multiple shown in any of the Tukey-type non-parametric multiple comparisons; dates having the same letter are not statistically comparisons. different at P < 0.05. that GI of scallops held under 24-hr light was RESULTS significantly higher, at P < 0.01, than GI of ambient scallops on 20 May, significantly higher than GI of Bay scallops held under each of the three different both ambient and 'dark' scallops on 27 May, and photoperiod treatments (ambient, 24 hr dark, 24 hr significantly higher than those of 'dark' scallops on light) showed progressive increases in reproductive both 5 June and 10 June. Comparable Kruskal-Wallis condition, as evidenced by increases in mean GI and ANOVA's ofGDW versusphotoperiodtreatmentwere mean GDW by the end of the 4-week study period significantly different, at P < 0.04, for the 20 May, 5 (Figures 1, 2). Scallops held under the 24-hr light June, and 10 June sample dates, but were not different regimen showed a consistent increase in both GI and on 27 May {P = .0651). Tukey-type multiple compar- GscaDllWopsahteledacuhndeorf atmhbeiefnoturphsoatmoppleirnigodpoerricoodnst,inwuhoiulse iPso<ns,0.h0o5w,evbeert,wedeind nGotDrWeveaolfssicganlilfoipcsantfrdoifmfetrehnecetsh,reaet darkness showed an increase in GI and GDW for the treatment groups on any of the four sampling dates. first 2 weeks, but some fluctuation thereafter. There No differences in shell heights of scallops were was no evidence that extensive spawning occurred in apparent during the coAurNseOVofAthe study, as revealed any of the scallop groups, as would have been by a 2-way parametric of shell height versus evidenced by a sharpdecline in GI and GDW following photoperiod treatment (/* = 0.0911), sample date a steady increase (Barber & Blake, 1991). {P = 0.1267), and treatment X date interaction (P = 0.234). No scallop mortality was recorded during Significant differences in reproductive condition of scallops from the three groups were apparent as early the study. as 6 days after exposing scallops to the different DISCUSSION photoperiods (Figures 1, 2). Raw and transformed GI GDW and values were non-nonnal, so parametric Our data suggest that photoperiod may play a signifi- analyses were precluded, but Kruskal-Wallis non- cant role in affecting the reproductive condition ofbay parametric ANOVA's (Zar, 1984) of GI versus scallops, Argopecteu irrculians inadians. Effects of photoperiod treatment, at each of the four sampling photoperiod manipulation were also manifested rapid- dates, were each statistically significant at P < 0.01 ly, asearly as 6 days afterdeployment ofscallops under (Figure 1). Following these analyses, Tukey-type non- the three different photoperiod regimens. Bay scallops parametric multiple comparisons (Zar, 1984) showed exposed to the different photoperiods all showed p. N. DeSanctis et al., 2006 Page 17 increases in reproductive condition (both GI and Devauchelle & Mingant (1991). In our study, the mean GDW) over the course of the 4-week study, but, GI values for scallops exposed to continuous light for relative to initial values, scallops exposed to 24-hr light between 2^ weeks (53.3-63.4) were considerably had significantly higher GI levels than those ofscallops higher than maximum mean GI values reported for exposed to ambient light or 24 hr dark conditions. The 0+ yr scallops from natural populations (Epp et al., GDW lack of clear statistical differences amongst of 1988: 29.2-32.0; Tettelbach et al., 1999: 33.1-38.0; scallops in the three photoperiod treatment groups was Tettelbach et al., 2002: 37.0-44.5) and hatchery stocks likely due to variability of gonad weights of scallops (Davidson, 2000: 30.1-34.1; Tettelbach et al., 2002: used in the experiment. 35.2-35.8) sampled from the field in eastern Long Photoperiod was the only variable manipulated in Island, New York at comparable times in the re- our experiments, and thus we conclude that the productive cycle, mid-May to mid-June. While the high manipulation of photoperiod was directly responsible GI levels that we observed may be reflective of for the observed differences in scallop reproductive differences in relative reproductive investment of development. A potential indirect effect of light scallops from different source populations (Parsons et manipulation might have been an elevated level of al., 1992), they also appear to reflect the positive effects algal growth, and hence food, in experimental tanks of exposure to longer photoperiod. Further investiga- exposed to longer photoperiods. Walls of the 24 hr- tion of the effects of light on the reproductive light tanks qualitatively appeared to have a heavier development of bay scallops should provide further biofilm layer than those ofthe other tanks at the time scientific insight as well as potentially useful applica- oftheweeklycleanings. Given theflow ratein thetanks tions to aquaculture. h(1a1v3e.6a1f(f=ec3t0edgasle)s/tmoinn)l,evheolwseivnert,heittiasnuknsl.ikWehliyltehibsecnotuhlidc Acknowledgments. We thank the staffofCornell Cooperative mbiacyrsocaallglaoepsm(aDyavbiesp&otMeanrtsiahlallyl,im1p9o63r)t,anittdtooesthneotdiseteeomf pExrtoegnrsaimonwohfoSuafssfiosltkedCoinuntthye caunldtuortihnegromfesmcbalelrosps.ofthe SPAT likely that this nutritional source would have been LITERATURE CITED significantly different in the three tanks due to the frequency with which tanks werecleaned. Thompson et Barber, B. J. &N. J. Blake. 1991. Reproductive physiology. al. (1994) showed that larvae ofPatinopecteuyessoensis EPpc.ol3o7gy7^&28AqIuna:cuS.ltEu.reS.hEulmsewvaieyr:(eNd.e).wSYcoarllko.ps: Biology, (= P. caurinus yessoensis) grew faster and were larger Bayne, B. L. 1976. Reproduction in bivalve molluscs under after 18 d when fed phytoplankton (Pavlova lutheri or environmentalstress. Pp. 259-277In: F. J. Vernberg(ed.). Chaetoceros simplex) grown under high vs. low light Physiological EcologyofEstuarineOrganisms. University levels; they concluded that this difference was due to ofSouth Carolina Press: Columbia, South Carolina. the higher levels ofshort-chain saturated fatty acids in Couturier, C. & D. E. Aiken. 1989. Possible Role of the algae grown under high light conditions. Again, Photoperiod in Sea Scallop Reproduction. Proceedings of the Annual Meeting, 1989, Aquaculture Association of given thehigh fiow rateandvery briefresidencetime of Canada Symposium 89(3):65-67. phytoplankton in our tanks, it is unlikely that the Davidson, M. C. 2000. The Effects of Stocking Density in different light regimens affected the biochemical Pearl Nets on Survival, Growth, and Reproductive composition of the ambient phytoplankton species Potential of the Bay Scallop, Argopecten imidiaiis while in the tanks. irradians. M.S. Thesis, State University ofNew York at repOruorduccotnicvleusidoenvselaobpomuetnttheienffecAtrsgoopfepchtoetnopeiriiraoddiaonns DaviSst,onRy. BL.ro&okN,.54Maprp.shall. 1961. 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