This study examined the role of maternal provisioning in controlling interpopulation variation in hatching size in nine isolated populations of the intertidal gastropod Nucella ostrina, in which development to the early juvenile stage takes place within an egg capsule. Variation among populations was almost entirely due to the ratio of nurse eggs to embryo, which explained 65% of the variation in hatching size. Egg size was not a significant predictor of hatching size. Differences among seven of these populations in the nurse egg/embryo ratio were entirely due to the number of nurse eggs allocated per capsule; these populations allocated different numbers of nurse eggs per capsule but allocated the same number of embryos. Intriguingly, the two most wave-sheltered populations allocated significantly more nurse eggs and more embryos to each capsule than did the seven other populations, but they maintained nurse egg/embryo ratios consistent with patterns observed in the other populations. Inter- and intrapopulation variation in hatching size appears to be controlled largely by different mechanisms: within-population variation being controlled mainly by differences in allocation of embryos per capsule, whereas most among-population variation being due to differences in allocation of nurse eggs per capsule.

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Measurements of larval vertical distributions at high temporal and spatial resolutions as well as larval behavioural responses to environmental characteristics are needed to parameterize bio-physical models of larval dispersal or transport. We studied larval vertical distribution for 7 taxonomic groups (gastropods, bivalves, polychaetes, bryozoans, asteroids, carideans and brachyurans), with different morphology, swimming abilities and life-history strategies, and examined whether these vary with physical or biological factors and periodic cycles (diel period and tidal state) in the field. Using a pump, we collected plankton samples at 6 depths (3, 6, 9, 12, 18 and 24 m), over a 36 and a 26 h period. Temperature, salinity, fluorescence and current velocity were measured concurrently. Larval vertical distribution varied among taxonomic groups, but 4 patterns could be distinguished: (1) larvae exclusively in the mixed layer (asteroids), (2) larvae predominantly below the thermocline, halocline and pycnocline (gastropods, bivalves, polychaetes), (3) larvae associated predominantly with the fluorescence maximum (bryozoans and carideans) and (4) larval distribution varying dielly (gastropods, polychaetes, carideans and brachyurans). Based on flow velocities and depending on distribution, asteroid larvae were likely to be transported farther than those of bryozoans and carideans, while direction and magnitude of transport varied for the other larvae. For most taxonomic groups, behaviour observed in the field agreed with measured laboratory responses to relevant cues. For asteroids and bivalves, simple beha vioural parameters can be generated that can be utilized to improve the accuracy of biophysical models.KEY WORDS: Vertical migration · Temperature · Fluorescence · Diel period · Water column structure · Larval behavior · Larval transport · Biophysical model parameters Resale or republication not permitted without written consent of the publisherMar Ecol Prog Ser 469: [37][38][39][40][41][42][43][44][45][46][47][48][49][50][51][52] 2012 Horizontal currents can ad vect larvae of coastal species offshore, leading to failure of recruitment to nearshore habitats (Shanks 1995).Meroplankton are capable of movement against vertical currents, as their swimming or sinking speeds are greater than weak vertical current velocities (0.1 cm s −1 ) (Chia et al. 1984, Metaxas 2001. Larval movement between layers of different velocities can alter the horizontal direction and magnitude of larval transport and dispersal (DiBacco et al. 2001, Metaxas 2001. Through changes in buoyancy or propulsion by ciliary or muscular activity, some crustacean and bivalve larvae can cover large distances vertically, in some cases many times a day (Cronin & Forward 1986, dos Santos et al. 2008. Larval movement can possibly be triggered through an innate behavioural response to physical and/or chemical stimuli. Consequently, sensory detection of the environment can potentially affect larval direction of movement and/or swimming be haviour (...

Marine gastropods form a diverse taxonomic group, yet little is known about the factors that affect their larval distribution and abundance. We investigated the larval vertical distribution and abundance of 9 meroplanktonic gastropod taxa (Margarites spp., Crepidula spp., Astyris lunata, Diaphana minuta, Littorinimorpha, Arrhoges occidentalis, Ilyanassa spp., Bittiolum alternatum and Nudibranchia), with similar morphology and swimming abilities, but different adult habitats and life-history strategies. We explored the role of physical (temperature, salinity, density, current velocities) and biological (fluorescence) factors, as well as periodic cycles (lunar phase, tidal state, diel period) in regulating larval vertical distribution. Using a pump, we collected plankton samples at 6 depths (3, 6, 9, 12, 18 and 24 m) at each tidal state, every 2 h over a 36 and a 26 h period, during a spring and neap tide, respectively, in St. George's Bay, Nova Scotia. Concurrently, we measured temperature, salinity, density, fluorescence (as a proxy for chlorophyll, i.e. phytoplankton density), and current velocity. Larval abundance was most strongly related to temperature, except for Littorinimorpha and Crepidula spp., for which it was most strongly related to fluorescence. Margarites spp., A. lunata, Ilyanassa spp. and B. alternatum exhibited either diel or reverse-diel vertical migration during 1 or both lunar phases. For Crepidula spp., Littorinimorpha, A. occidentalis and Nudibranchia, larval vertical distribution differed between lunar phases. Only the larval vertical distribution of Margarites spp., D. minuta and Ilyanassa spp. varied with tidal state during 1 or both lunar phases. The key factors determining the vertical distribution of gastropod larvae were temperature, fluorescence, and light, although the importance of each factor varied among taxa. Differences in vertical distribution may enable these larvae to partition over a wide range of potential habitats for settlement.