The effect of sedimentation on the settlement behavior of the American lobster

1. The effect of sedimentation on the settlement behavior of the American lobster (Homarus americanus). Benoit Bruneau & Gilles Miron Université de Moncton, Moncton, Nouveau-Brunswick, Canada, E1A 3E9 INTRODUCTION RESULTS AND DISCUSSION • Most benthic marine invertebrates have a complex life cycle involving a pelagic dispersal phase followed by a benthic settlement phase. The latter is often dependent on preferred substrate availability. • Lobster settlement • During stage IV (postlarvae) • Leads to a behavioural transition : pelagic benthic/cryptic (Factor 1995) • On gravel and/or rocks (Botero & Atenna 1982, Pottle & Elner 1982) • Ecosystem modifications • Climate change : Extreme weather events more frequent (IPCC 2012) • Anthropic activities : Agriculture, waterway dredging, … • Sedimentary load and regimes affected : • sedimentation over gravel and rocky substrate • Age(Figure 1) : • D-2: Surface time tend to decrease as sedimentation levels increase while time spent in the water column increases • D-4: Surface time tend to increase as sedimentation levels increase • D-2 and D-4: Time spent on bottom tend to decrease as sedimentation levels increase • D-3: Patterns show no trend • High interindividual variability • More consistent D-4 settlement behaviours • Substrate(Figures 2 and 3) : • Effect of substrate type is more apparent for D-4 larvae. • Sedimentation = Total bottom time • Sedimentation = Frequency of bottom contacts Work in progress Subject to change • Objectives: • Determine at which age the settlement behaviour is best developed in stage IV postlarvae. • Measure the effect of sedimentation over preferred substrate on the settlement behaviour. Figure 1. Time Budget (%) for each larval age (D-2, D-3 and D-4) by treatment (Gravel, low sedimentation, medium sedimentation, high sedimentation). Behaviors are related to larvae position in the aquarium (Bottom, Water Column and Surface). Standard-errors are presented as upper intervals. MATERIAL AND METHODS Work in progress Subject to change Work in progress Subject to change 1. Postlarva: • Day 2, 3 and 4 of stage IV postlarvae • Larva provided by the Coastal Zones Research Institute (CZRI) Figure 3. Time series of larvae age D-4 on high sedimentation substrate. Time budget is presented as stacked barplot . Figure 2. Time series of larvae age D-4 on gravel substrate. Time budget is presented as stacked barplot. 2. Experimental Design: • 4 types of substrate: • A better understanding of the American lobster life cycle and recruitment processes is not only important for fishery management but also in itself as part of an ecosystemic view of the potential effect of climate change on benthic populations and the industries that depend on them. • Larval deposition : • Critical phase of the life cycle - Survival increase • Affects population growth and sustainability • Sedimentation : • Detrimental on settlement behaviour of stage IV lobsters (postlarvae) • Increase in sedimentation leads to pelagic behaviours (ex. swimming) • Behaviours better defined for D-4 postlarvae • Behaviours less homogeneous for D-2 and D-3 than D-4 postlarvae : may be related to the transition between pelagic and benthic behaviours (Factor 1995) • More results will soon be available to complete this study. The new data will help shed some light on the different behaviours observed among stage IV postlarvae aged from 2 to 4 days over different substrates . Literature cited • Botero, L. and Atema, J. 1982: Behavior and substrate selection during larval settling in the lobster Homarus americanus. J. Crustacean Biol 2(1): 59-69 • Factor, R. J. 1995. Introduction, Anatomy, and Life Historyal and Postlarval Ecology. p. 1–11. In Biology of the Lobster Homarus americanus. l R. Factor (éd.). San Diego, CA: Academic Press. xiii + 528 p. • IPCC, 2012: Managing the Risks of Extreme Events and Disasters to Advance Climate Change Adaptation. A Special Report of Working Groups I and II of the Intergovernmental Panel on Climate Change [Field, C.B., V. Barros, T.F. Stocker, D. Qin, D.J. Dokken, K.L. Ebi, M.D. Mastrandrea, K.J. Mach, G.-K. Plattner, S.K. Allen, M. Tignor, and P.M. Midgley (eds.)]. Cambridge University Press, Cambridge, UK, and New York, NY, USA, 582 pp. • Miron G, L. J. Walters, R. Tremblay and E. Bourget. 2000. Physiological condition and barnacle larval behavior: a preliminary look at the relationship between TAG/DNA ratio and larval substratum exploration in Balanus amphitrite. Mar. Ecol. Prog. Ser. 198: 303–310 • Pottle, R.A. and Elner, R.W. 1982: Substrate preference behavior of juvenile American lobsters, Homarus americanus, in gravel and silt-clay sediments. Can. J. Fish. Aquat. Sci. 39: 928-932 CONCLUSION Gravel (preferred lobster ground) Low Sedimentation over Gravel Medium Sedimentation over Gravel High Sedimentation over Gravel • 4 replicates • 1 hour focals (duration of observations) • Temperature is kept at 20˚C (rearing temperature) • Experiments carried out on each batch produced (one batch presented) 3. Measurements: • Time budget: • time at 1) surface, 2) water column, 3) bottom • Cephalotorax length, total weight • Lipid analysis (Miron& al. 2000)