Predation of cockles (Cerastoderma edule) by the whelk (Buccinum undatum) under laboratory conditions

The feeding rate and behaviour of whelks (Buccinum undatum)offered cockles (Cerastoderma edule) in laboratory experimentswere examined. When presented with cockles in a range of sizes(10–40 mm), 14 B. undatum (34.6–88.3 mm),held individually in aquaria, consumed a wide size range ofcockles. Small whelks (<40 mm) consumed cockles (<23 mm),whereas large whelks, (>60 mm) ate a greater numberof larger cockles (>30 mm) and a wider size range ofcockles (12–40 mm) than smaller whelks. The majority(90%) of the shells of the predated cockles were undamaged andthe few (<10%) that were damaged showed only slight abrasionsto the anterior and posterior shell margin. Filmed observationsof B. undatum feeding on C. edule showed a method of attackthat has not previously been reported and involved the use ofthe whelk's foot to asphyxiate the cockle or to pull the shellvalves apart. No filmed evidence was found for the previouslyreported shell ‘wedging’ technique for prising openthe closed shell valves of C. edule, although 10% of the shellsof consumed cockles in feeding experiments had damaged shellmargins. (Received 4 April 2007; accepted 30 June 2007)     

FEED PREFERENCES OF NUCELLA CRASSILABRUM AND JUVENILE CONCHOLEPAS CONCHOLEPAS (GASTROPODA: MURICIDAE) FROM A ROCKY SHORE IN SOUTHERN CHILE

The feeding preferences of two molluscan predators, Nucellacrassilabrum and Concholepas concholepas, from southern Chilewere studied by means of laboratory and field experiments. Bothpredators preferred Semimytilus algosus to Perumytilus purpuratus.Small C. concholepas selected mussels less than 5 mm, similarsized N. crassilabrum preferred individuals of 5-10 mm. LargerC. concholepas did not consume mussels above 10 mm whereas largeN. crassilabrum preferred the 15-20 mm size but also took musselsup to 30 mm. Individuals rarely consumed more than one musselin a 7 day period. Both predators consumed the barnacle Chthamalusscabrosus, larger items being taken more frequently than smallerones. Field experiments confirmed laboratory results, but barnacleconsumption was 30% higher in the field. Although considerabledietary overlap is evident between these two predators, thereare clear differences in their selection of prey species andsizes. This might provide a mechanism for reducing competitionwhich may result from changes in prey abundance. (Received 17 July 1990; accepted 28 August 1990)     

ASPECTS OF THE LIFE CYCLE, POPULATION DYNAMICS,GROWTH AND SECONDARY PRODUCTION OF THE EDIBLE SNAIL HELIX LUCORUM LINNAEUS, 1758 (GASTROPODA, PULMONATA) IN GREECE

This paper examines the biology and ecology of Helix lucorumL. which lives in mainland Greece, as well as its growth andsecondary production. A demographic study revealed that (a)3 cohorts exist at any time during the year (when adults ofall generations belong to the same cohort) (b) egg-laying andhatching occur during the months of July and August respectively,(c) the most rapid growth takes place during spring. Study ofH. lucorum genitalia in relation to age showed that the snailsaxe sexually mature 3 years after hatching, when the largestdiameter of their shell (D) is equal to or greater than 35 mm Von Bertallanffy's method suggests that Helix lucorum may liveup to 14 years or more in order to reach its possible maximumsize (48.80 mm) The study of relative growth of D in relation to P_s (peristomesurface) of Helix lucorum shows that D grows faster than P_swhen D12.50 mm; juveniles change their growth rate when theirD arrives at 22.05 mm, and growth becomes slower when adultsarrive at 36.27 mm Annual secondary production calculated by the size frequencymethod gave a mean annual density of 3.39 individuals per m²,a mean annual crop (biomass) of 4.04 g-m^–2 and an annualproduction (P) of 5.02 g · m^–2. The annual turnoverratio (P//b) is equal to 1.24 (Received 23 June 1987;     

COMPARISONS OF LIFE-HISTORY TRAITS AND SEXUAL DIMORPHISM BETWEEN ASSIMINEA JAPONICA AND ANGUSTASSIMINEA CASTANEA (GASTROPODA: ASSIMINEIDAE)

Life histories of two sympatric assimineid gastropods, Assimineajaponica and Angustassiminea castanea, were investigated ata reed marsh in northern Japan. Size frequency distributionsrevealed that growth curves of females and males differed inboth species resulting in sexual dimorphisms in shell size.In A. japonica, the shell height of females was larger thanthat of males, whereas in A. castanea males attained a biggershell than females. Mating behaviour of A. japonica was observedmainly from February to June, while that of A. castanea wasobserved from May to August. The diameter of deposited eggsof A. japonica was 200 to 250 mm, whereas that of A. castaneawas 125 to 150 mm. The length of the veliger larva of A. japonicaat hatching was approximately 200 mm, whereas that of A. castaneawas approximately 125 mm. Longevity, age at sexual maturityand opportunities for reproduction during life time were estimatedin the field. For A. japonica, sexual maturity was establishedby the age of 17 months and longevity was about three years.Opportunities for reproduction of A. japonica occurred twiceduring a lifetime. For A. castanea, sexual maturity was establishedby the age of 10 months and longevity was almost five years.Opportunities for reproduction of A. castanea occurred fivetimes during a lifetime. The differences of life-history traitsand sexual dimorphism between species and possible explanationsof evolutionary factors are discussed. To whom correspondence should be addressed. (Received 21 January 1999; accepted 8 September 1999)     

Age and growth of planktonic squids Cranchia scabra and Liocranchia reinhardti (Cephalopoda, Cranchiidae) in epipelagic waters of the central-east Atlantic

Statolith microstructure was studied in two abundant planktoniccranchiids, Cranchia scabra (56 specimens, 38–127 mm mantlelength, ML) and Liocranchia reinhardti (34 specimens, 99–205mm ML) sampled in epipelagic waters of the western part of theGulf of Guinea (tropical Atlantic). Growth increments were revealedin ground statoliths of both species. It was possible to distinguishtwo growth zones in statolith microstructure by their colourin reflected light of the microscope: the translucent postnuclearzone and pale white opaque zone. Assuming that growth incrementsin statoliths were produced daily, ages of the largest immatureC.scabra and L.reinhardti were 166 and 146 days, respectively.Both cranchiids are fast-growing squids with growth rates inlength resembling those of juveniles of tropical ommastrephidsand Thysanoteuthis rhombus. Liocranchia reinhardti grows faster:its growth rate in ML is approximately twice that of same-agedC.scabra. The life cycle of both cranchiids consists of twophases. During their epipelagic phase, C.scabra and L.reinhardtifeed and grow rapidly from paralarvae to immature young in theepipelagic waters, attaining 120–130 and 170–200mm ML by ages of 4–5 months, respectively. Then they changetheir life style to a deepwater phase.     

Zooplankton prey selection by juvenile fish in Nova Scotian Shelf basins

The stomach contents of fish <100 mm standard length (SL)and fish >100 mm SL collected during June and October intwo deep basins on the Scotian Shelf, showed that juvenile co(and silver hake fed primarily on the two most abundant speciesof zooplankton in the basins: Calanus finmarchicus and Meganyctiphanesnorvegica. These zooplankton were abundant in the basin: duringthe 2 months, forming high concentrations at depths below 200m during the day. In June fish (<100 mm SL) concentratedin the upper 50 m during both day and night. Cod and wolffislcollected between 195 and 240 m had a large percentage of C.finmarchicusin their stomachs suggesting that these fish exploited the highconcentrations of C.finmarchicus below 200 m depth There wasno evidence that Calanus hyperboreus was eaten by any juvenilefish species. Calanus finmarchicus was the most common preyof cod feeding in the top 50 m, but the percentages o C.finmarchicusstages IV and V were lower in the stomachs than in the watercolumn. Cod showed ; strong preference for M.norvegica, withthis prey species having a modified Ivlev's index of 1 indicatingthat cod were highly selective for this species. There was noevidence that C.hyperboreus. stage IV was eaten by any of thespecies offish. Silver hake and dogfish (>100 mm SL) bothfeed oi M.norvegica and C.finmarchicus in the deep regions ofthe basins. In October, silver hake was the most common juvenilefish in the basins, feeding primarily on small stages of M.norvegica.The populations of fish (>100 mm SL) in the basins were mainlyspecies known to feed heavily or euphausiids. The two basinsare unique regions of the shelf because of the large populationsof Calanus copepods and M.norvegica they contain all the yeararound, thereby providing an atrractive feeding ground for manyspecies of fish, particularly silver hake.     

PREDATOR-PREY INTERACTIONS BETWEEN LEPSIELLA (BEDEVA) PAIVAE (GASTROPODA: MURICIDAE) AND KATELYSIA SCALARINA (BIVALVIA: VENERIDAE) IN PRINCESS ROYAL HARBOUR, WESTERN AUSTRALIA

On a sandy beach at Shoal Bay in Princess Royal Harbour, Albany,southwestern Western Australia, lives a small muricid gastropodthat feeds virtually monotonically on the overwhelmingly dominantresident bivalve Katelysia scalarina. Lepsiella paivae livesburied in the sand and attacks its prey within it. Because ofits small size (<13 mm shell height), bivalve prey isalso small and this study demonstrates a preference for K. scalarinaof 5 mm shell length, i.e. juveniles. Laboratory experimentsalso suggested a possible preference for attack of the rightvalve. Lepsiella paivae can and does, however, attack largerprey (up to 15 mm shell length), but cannot consume themcompletely. A second visit to Princess Royal Harbour in theAustral winter, when there was no juvenile K. scalarina present,showed L. paivae to be attacking at the sand surface, also bydrilling, the small (<4 mm) gastropod Hydrococcus brazieri(Hydrococcidae). SEM studies of experimentally determined drillholes of L. paivae show them to be of variable form, some straightsided, others bevelled (like a naticid) and <500 µmin diameter. On this sheltered Southern Ocean beach, therefore,L. paivae has specialized to attack juvenile bivalves by burrowingafter them. It can, however, attack other species opportunisticallyon the sand surface when seasonally favoured juvenile bivalveprey are not present. (Received 8 January 2005; accepted 16 March 2005)     

ECOLOGY OF THE INTRODUCED SNAIL MELANOIDES TUBERCULATA (GASTROPODA: THIARIDAE) IN RELATION TO BIOMPHALARIA GLABRATA IN THE MARSHY FOREST ZONE OF GUADELOUPE, FRENCH WEST INDIES

Melanoides tuberculata was introduced to several types of aquatichabitat occurring in the marshy forest zone, Guadeloupe, asa competitor of the snail host, Biomphalaria glabrata, of Schistosomamansoni. Colonization by the competitor was successful in allhabitats, but the impact on the snail host was variable accordingto the site. Evolution of global prevalences, intensities andabundances of Schistosoma mansoni in the reservoir host, Rattusrattus, did not show any significant changes during the eightyears following the introduction of the competitor. The analysisof size distribution of M. tuberculata in a release plot showedthat maximum reproduction took place during the rainy seasonbetween June and November. The thiarid snail needed 4.5 monthsto reach a size of 10 mm, 14 months to reach 15 mm, and morethan 30 months to reach 20 mm. Calculated life expectancieswere 0.74 year at the first year of age, 0.9 year at the secondyear, and 0.5 year at the third year. (Received 21 September 1992; accepted 5 January 1993)     

Population dynamics of Aurelia aurita (Scyphozoa) from an isolated brackish lake, with particular reference to sexual reproduction

The annual cycle of abundance, growth and sexual reproductionof the scyphomedusa Aurelia aurita was examined over a 12 monthperiod in an isolated, shallow, brackish, man-made body of water:Horsea Lake, England. Strobilation started in December and ephyraewere present through June in varying numbers, suggesting a 7month period of near-continuous recruitment. Horsea Lake hasa dense A.aurita population, with the peak abundance of 24.9m^–3 occurring in mid-May. Medusae (>10 mm) were presentin the water column from March through January. Maximum belldiameter of 105 mm was observed in late September. However,medusa growth was very poor (G ranged between –0.03 and0.07 day^–1 over a 12 month period), and monthly mean belldiameters were typically <50 mm. For most of the year, theabundant A.aurita population was most likely severely food limitedas a result of a numerically and species-poor mesozooplanktoncommunity dominated by the calanoid copepods Acartia margalefiand Acartia tonsa. Nevertheless, the very small A.aurita medusaewere still able to attain sexual maturity and reproduce. Ripefemale medusae carrying fertilized eggs and planula larvae werefirst observed in May and June, although the main period ofplanula larva production was September-December. In November,all females were ripe, the smallest being 19–20 mm belldiameter. At both Horsea Lake and a nearby productive estuary,Southampton Water, planula larva production increased linearlywith wet weight, although compared with the larger A.auritamedusae from Southampton Water, reproductive output at HorseaLake was low. Aurelia aurita in Horsea Lake showed plasticityin its population characteristics in response to environmentalconditions, with both fecundity and size to maturity varyingon a seasonal basis. Medusae appeared to partition the availablefood resources into either somatic growth when food was abundantor reproductive effort when food was scarce.     

Statolith microstructure and age of early life stages of planktonic squids Galiteuthis phyllura and Belonella borealis (Oegopsida, Cranchiidae) from the northern North Pacific

Statolith morphology and microstructure were studied in twocommon species of panktonic cranchiid squids, Belonella borealis[four juveniles with mantle length (ML) 375–450 mm] andGaliteuthis phyllura (13 paralarvae and juveniles, ML 9–235mm),caught near the bottom and in pelagic layers over the continentalslope of Siberia in the northwest Bering Sea. The total numberof growth increments within the statoliths ranged from 277 to294 in B.borealis and from 10 to 209 in G.phyllura. Assumingthat these increments were produced daily, both species growrapidly in length (daily growth rate = 1.13mm day^–1 duringthe first 8–10 months of their juvenile phase in the mesopelagiclayers, prior to migration into deeper waters for maturation.     

Diet-shifts and food-dependent survival in Engraulicypris sardella (Cyprinidae) larvae from Lake Malawi, Africa

The diet of Engraulicypris sardella (Cyprinidae) larvae wasdeterinmed from the open waters of Lake Malawi, Africa. Theguts of first-feeding larvae of 2–3 mm total length (TL)usually contained many cells of 5–9 µm diametertentatively identified as a non-colonial green alga (Chlorophyta).The number of these cells in the guts of larvae declined aslarvae increased in size, and were not found in larvae greaterthan 9 mm TL. Other types of phytoplankton were rarely seenin the guts of larvae. Copepod nauplii were eaten by larvaegreater than 4 mm TL, and copepodite copepods and cladoceansby larvae greater than 5 mm TL. The biomass of open water crustaceanzooplankton and E.sardella larvae were determined over a 2-yearsampling programme. The mortality rate of E. sardella was negativelycorrelated with zooplankton biomass, but was not significantlycorrelated with the amount of zooplankton food in the guts oflarvae.     

PREDATION ON THE BIVALVE CHOROMYTILUS MERIDIONALIS (KR.) BY THE GASTROPOD NATICA (TECTONATICA) TECTA ANTON

The effects of a population of the boring gastropod Natica tectaon the bivalve Choromytilus meridionalis were investigated atBailey's Cottage, False Bay, South Africa. In July 1979 theN. tecta density on the mussel bed averaged 69 m^–2 andthe population consisted mainly of reproductively mature individualsbetween 20–33 mm shell width. Laboratory experiments on N. tecta showed that prey size selectionis an increasing function of predator size. The prey size rangetaken by large N. tecta is also greater than that taken by smallindividuals. The position of the borehole on the mussel shellis a function of the way in which the shell is held by the footduring the boring process. Consumption rates measured in thelaboratory showed an increase from approximately 1 kJ per weekin 18 mm N. tecta to 4.5 kJ per week in 28 mm individuals. Populationconsumption in the field was calculated as 663 kJ m^–2month^–1. It was estimated that at this rate the standingcrop of mussels in the pool would be eliminated within 10 months.Field measurements showed significant depletion after 6 months. New spat settlement of mussels occur every 4–6 years.The growth curve shows that after one year the population meansize exceeds 30 mm shell length, which is beyond the prey selectionsize range of small N. tecta. It was concluded that at the timeof a new mussel settlement a niche is provided for the simultaneoussettlement and growth of juvenile N. tecta in high densities.However, within one year the increase in prey size, togetherwith depletion due to over-exploitation, limits population growthand density in N. tecta. (Received 14 March 1980;     

Vertical distribution and seasonal abundance of Aglantha digitale (O.F. Muller) (Coelenterata: Trachymedusae) and other planktonic coelenterates in the northeast Atlantic Ocean

The vertical distribution and seasonal variability in abundanceof the hydromedusa Aglantha digitale (O.F. Müller) andother coelenterates from the north-east Atlantic Ocean are described.The coelenterates were abundant from May to September and reachedpeak numbers in June, July and September when concentrationof 40 individuals m^–1 were recorded. A. digitale numericallydominated the codenterate population and accounted for over80% of the dry weight biomass in hauls taken from 1971 to 1974.The data suggests a 2 month development period for this medusafrom egg to mature adult (8 mm) which supports previous publisheddata. During the growth of the medusa there were considerablechanges in the ratios of wet to dry weights. At a bell-heightof 1 mm the mean dry weight was 22% of mean wet weight and at8 mm the mean dry weight was 5% of mean wet weight; the percentagedecreased further in the largest specimens to 2% at 25 mm. Themajority of A. digitale occurred in the upper 100 m but in lateJuly the larger specimens extended their distribution to thelimit of sampling (500 m). The two most abundant siphonophores, Dimophyes arctica(Chun) and Nanomia cara A. Agassiz, werefound deeper than the main population of A. digitale. It issuggested that coelenterates could be an important source ofnitrogen for the development of the late bloom of phytoplanktonin the north-east Atlantic Ocean.     

Predation, production and the organization of an estuarine copepod community

The copepod community of the estuaries near Beaufort, NC underwenta consistent seasonal succession from a spring assemblage dominatedby the medium-sized copepod Acartia tonsa (1 mm) to a summer—fallassemblage dominated by the small-bodied copepods Parvocalanuscrizsrirostris and Oithona colcarva (both 0.5 mm). However,in enclosure experiments during this period, A. tonsa dominatedthe community, due to higher growth rates and its predationon the nauplii of other species. Nutrient additions enhancedthe dominance by A. tonsa. The decline in abundance of A. tonsain the estuary was associated with increased abundance of planktivorousanchovies and silversides. In other enclosure experiments, planktivorousfish eliminated A. tonsa and other large copepods, althoughthey persisted in enclosures lacking fish. I conclude that predationby size-selective planktivorous fish prevents dominance by A.tonsa during summer—fall. ¹Present address: Institute of Marine Sciences, University ofNorth Carolina, 3407 Arendell Street, Morehead City, NC 28557,USA     

Action Potential in Luffa cylindlica and its Effects on Elongation Growth

The action potential of the non-seismonastic plant, Luffa cylindrica,was studied and characterized. Single action potentials of 30to 60 mV were evoked by electrical or cooling stimuli appliedto the stem internode. Action potentials were transmitted withoutdiminution along stimulated internodes shorter than 40 mm inlength. No difference in velocity between acropetal and basipetaltransmission was observed. This behavior is very similar tothat of Mimosa and Biophytum. The velocity of transmission ofaction potentials along internodes of Luffa was dependent upondistance from the point of stimulation; 10 to 20 mm sec^–1upto 40 mm, and 70 mm sec^–1 at around 50 mm from the pointof stimulation. The action potential was not transmitted tothe neighboring internode. Action potentials were also observedin the petiole and leaf. Beyond the threshold stimulus, theamplitude of the transmitted action potential depended on thestrength of the stimulus. The absolute and relative refractoryperiods for the transmission of action potentials were 2 minand 2 to 5 min, respectively. Elongation growth of the stem, recorded using a differentialtransformer, decreased after the generation of a single actionpotential in the upper most internode. This decreased growthrate continued for more than 5 min. (Received March 10, 1986; Accepted June 11, 1986)     

Population dynamics of the scyphomedusa Aurelia aurita in Southampton Water

The population dynamics of the scyphomedusa Aurelia aurita inSouthampton Water is characterized. Strobilation, indicatedby the presence of 1 mm ephyrae, occurred from the end of Januaryto the middle of March. Maximum abundances of up to 8.71 m^–3occurred soon after ephyrae release, after which numbers declinedsteadily until the end of June, when the population was absentfrom Southampton Water. The residence time of 3–4 monthsis somewhat less than that reported in many other areas, includingKiel Bight and Gullmarfjord. The carbon biomass of A.auritaaccounted for 92–97% of the predominant gelatinous biomass(A.aurita, Pleurobrachia pileus and Phialidium hemisphericum)in the upper estuary, and this reached a maximum of 30.2 mgC m^–3 in May 1990 and 27.6 mg C m^–3 in June 1991.Coincident with increased water temperature and mesozooplanktonabundance during May, growth rates increased from 0.02–0.30mm day^–1 to a peak of 4.8 mm day^–1, with a maximumbell diameter of 120–140 mm reached in late May/earlyJune. Size to maturity was variable, although the smallest medusaobserved to be ‘ripe’, i.e. containing dividingeggs and planula larvae in the brood sacs on the oral arms,were 64–71 mm. Aurelia aurita is believed to be endemicto Southampton Water, but because of the double high water inthe area, short flushing rates of between 4.5 and 20 days maybe responsible for such short residence times of Aurelia medusae.The effects of strong NE winds were considered as factors governingthe distribution of medusae in years of atypical temporal abundance.     

NUTRITION OF TRIDACHIA CRISPATA (MORCH) (SACOGLOSSA)

Autotrophic nutrition plays an important role in adult Tridachiacrispata in the western Atlantic Ocean and results from an endosymbioticassociation between the sacoglossan and the kleptoplastids ofChlorophyta. A series of living specimens 7-80 mm in length was studied inthe laboratory. After a body length of 10 mm has been attained,the parapodial lobes of the two sides meet and fuse. Microscopicexamination of faecal strings of specimens undergoing this transitionrevealed that algal remains were produced only by juvenilesless than 13 mm long. Larger specimens defaecated only rarelyand the diminutive faecal strings contained no recognizablealgal debris. This transition probably parallels the physiologicaltransition between juvenile heterotrophic nutrition and adultautotrophic nutrition. Microscopic examination of the radulae of transitional specimensshowed no diminution of the size, number or morphology of theteeth. This indicates that in an emergency heterotrophic nutritionmay be resumed. Growth rates of Tridachia were measured in the laboratory, withand without light and the provision of algal foods. Unfed animalslost weight rather rapidly in captivity, whereas those fed uponsuitable algae (Halimeda discoidea, Caulerpa verticillata, C.racemosa and Chaetomorpha sp) did not.Caulerpa sertularioideswas suitable for food for a limited time, but proved toxic afterabout a week. Of the other species tested, Caulerpa verticillatawas the least suitable, while Halimeda, Chaetomorpha and Caulerparacemosa were the best. Ironically, C. verticillata was theonly one of the algal species tested which is known to be takenin the natural diet in Floridean waters. These experiments confirmedthat heterotrophic feeding will be resumed in Tridachia if theculture-conditions do not favour autotrophic nutrition.     

Ecological investigations on the zooplankton community of Balsfjorden, northern Norway: population dynamics of the euphausiids Thysanoessa inermis (Kroyer), Thysanoessa raschii (M.Sars) and Meganyctiphanes norvegica (M.Sars) in 1976 and 1977

The population dynamics of the euphausiids Thysanoessa inermis(Kröyer), T. raschii (M.Sars), and Meganyctiphanes norvegica(M.Sars) have been followed in Balsfjorden in 1976 and 1977.Seasonal variations in length-frequency distributions, growthin carapace length, sex-ratio, and spermatophore productionand attachment are presented and discussed in relation to changesin hydrography and phytoplanlcton standing-crop. An annual generationof T. inermis and T. raschii was spawned in April and May. Eggsand larvae of M. norvegica were not found in Balsfjorden, indicatingthat recruitment occurs from outside the fjord. T. inermis andT. raschii reached maximum carapace lengths of 7–8 mmand 6–7 mm respectively and had life-spans of c. 2 years3 months. M. norvegica had a life-span of c. 2 years 6 monthsand reached a maximum carapace length of c. 12.5 mm. In bothT. inermis and T. raschii 0-group underwent the greatest lengthincreases from May to October, I-group from March to Augustand II-group from April to June. The population structure, growthpatterns and growth periods of M. norvegica were difficult todiscern. The phytoplanlcton cycle appears to be the dominantfactor regulating both growth and spawning of the Thysanoessaspp in Balsfjorden, while temperature has no obvious influence.     

Motion behavior of nauplii and early copepodid stages of marine planktonic copepods

The goal of this study was to quantify periods of activity andvelocities of late naupliar and early copepodid stages of planktoniccopepods occurring regularly on the southeastern continentalshelf of the USA. We obtained quantitative information on eightspecies, including adult females of Oithona plumifera. All studieswere conducted at food concentrations near or above satiationlevels. Activities ranged from 0.85% (adult females of O.plumifera)to 100% of time (nauplii and copepodids of various calanoidspecies). Motion velocities (excluding escape motion) coveredmore than one order of magnitude: from 0.39 mm s^–1 fornauplii of Temora stylifera to 5.24 mm s^–1 for naupliiof Oncaea mediterranea. Ranges of activities of species rangefrom occasional for early juveniles to adult females of O.plumiferato 100% for the same range of T.stylifera, the latter creatinga feeding current from N III onwards, the former not at all.Of notable interest is Centropages velificatus which moves intermittentlyas a late nauplius, continuously as an early copepodid and intermittentlyas an adult. All observed calanoid late nauplii and copepodidsmove in three dimensions, excluding copepodids of the shelfbreak/oceanicParacalanus aculeatus. The results indicate not only significantdifferences in motion behavior between cyclopoids and calanoids,but also between calanoid species. Yet, some calanoid speciesshow little ontogenetic changes at all.