Distribution and drift of the crab Carcinus maenas (L.) (Decapoda, Portunidae) larvae over the continental shelf off northern Portugal in April 1991

The coastal distribution and abundance of Carcinus maenas larvalstages were studied from plankton samples collected in a gridof 79 sampling station organized into six cross-shore transectsextending from the coast to –170 km offshore, betweenthe Mondego and Ave rivers, on the northwest coast of Portugal.The samples were collected in April 1991 with a modified Bémultinet plankton sampler, which was towed from a maximum depthof 200 m and provided a vertical resolution of up to five standardstrata at each station. Current and wind data were availablefor a period that extended beyond the period covered by theobservations All the species' larval stages were found in thesamples, but their distribution was confined to the inner andmiddle shelf stations Vertically, 88% of the larvae occurredin the top 30 m and another 11% in the 30–60 m stratum.The zonal stages I and II were concentrated (–90%) inthe surface layer, but a gradual ontogenic displacement to deeperwaters was observed from then on, the megalopa being equallydistributed between the 0–30 and the 30–60 m strata.Horizontally, there was a dear association of the first zoeawith the estuarine inlet while the older meal stages were dispersedprogressively offshore. Evidence was found that the megalopaexperienced an onshore transport that did not affect the previousstages.This transport is wnsistent with the observation of anonshore flow component at 40 m. It was not possible, however,to examine the hypothesis that this flow conveys the last larvalstage to the coast, but not the previous ones. The dependenceof the along-shore flow component on wind stress lends supportto the hypothesis that the larvae are advected from the northas the upwelling season progresses.     

Population structure, reproductive biology and maintenance of Euphausia lucens in the southern Benguela Current

This study investigates the population structure and reproductivebiology of the euphausiid Euphausia lucens in relation to temporaland spatial variations in the abiotic and biotic environmentin the St Helena Bay region off the west coast of South Afnca.This is an area of high biological productivity and is importantfor recruitment to the pelagic fishery. Gravid females (stageIV) and young larvae were collected throughout the year, suggestingcontinuous breeding. Spawning was most intense from August toOctober (late winter to early spring) just prior to the onsetof upwelling and an associated increase in phytoplankton. Recruitmentwas high until early summer (August-January) and decreased toa low level throughout autumn and early winter (February-June).The proportion of gravid females increased with distance offshoredespite relatively low chlorophyll a concentrations offshore.Multiple spawning is inferred from the high frequency of gravidfemales in the population. The reproductive strategy and verticaldistribution of all developmental stages of E.lucens is relatedto the current regime of the study site in order to formulatemechanisms most likely to play an important role in maintainingcoastal populations of E.lucens in the southern Benguela Current.     

Mesoscale advection of Upogebia pusilla larvae through an upwelling filament in the Canaries Coastal Transition Zone (CTZ)

Larval transport has a strong influence on marine populations and ecosystem function. Traditional hypotheses establish that larvae of coastal species are swept offshore during strong upwelling periods producing low recruitment rates; however, recent studies have demonstrated that this hypothesis is not supported by larval distribution data. The present study examines the influence of upwelling filaments on larval advection and wastage. During August 1993, the transport of Upogebia pusilla was analysed in relation to an offshore filament off Northwest Africa. This mesoscale structure was generated by a trapped, quasi-permanent cyclonic eddy located between the Canary Islands and the African shelf and extended 150?km westward into the oligotrophic open ocean waters. The horizontal distribution depicted by U. pusilla larvae was strongly influenced by the oceanographic features of the Canaries Coastal Transition Zone (CTZ). Specifically, the larvae were closely associated with upwelling front and filament position, showing that these neritic larvae can be advected 10–100s of kilometres offshore through the filament. However, the low larval densities observed in the samples suggest that many larvae might remain close to the coast, thus avoiding seaward transport. This implies that filaments probably do not significantly affect the recruitment success of intertidal invertebrates such us U. pusilla in upwelling systems.     

Optimal wind patterns for biological production in shelf ecosystems driven by coastal upwelling

Major upwelling systems around the world provide marine productivity and fishery yield out of proportion to their area. Upwelling winds have the counteracting effects that stronger winds upwell more nutrients to the surface for higher production, but they also transport that production off continental shelves where it may not be consumed by shelf-dwelling species. Because the patterns of wind fluctuations vary in these systems, we determined the conditions for maximal biological production using a simple conveyor belt model. The conditions are that: (1) the average cross-shelf velocity produced by the winds be the value that provides the maximum production with constant winds and (2) that the wind pattern be periodic with period equal to the cross-shelf transport time that results from maximizing production with constant winds. Examination of an example using winds in central California indicated wind patterns optimal for phytoplankton occurred more frequently than those for zooplankton.     

Fortnightly periodicity in the abundance of diatom and dinoflagellate taxa at a coastal study site

From 3 July to 15 September 2000, plankton samples were collected roughly every 2 days at three stations within 1.5 km from shore at Sunset Bay, OR. In these samples we enumerated Coscinodiscus-like diatoms, Protoperidinium spp., and the potentially toxic phytoplankter, Pseudo-nitzschia spp. Using time series analysis, the abundance of these phytoplankters was compared to wind stress, tidal range, and sea surface temperature (SST). SST was significantly cross-correlated with wind stress (lower SST occurred during upwelling favorable winds) and maximum daily tidal range (cold and warm anomalies in SST occurred around the neap and spring tides, respectively). We found no significant cross-correlations between wind stress (upwelling vs. downwelling winds) and the abundance of any of the taxa. Significant cross-correlations were found between phytoplankton abundances and the maximum daily tidal range (peak concentrations occurred between the neap and spring tides) and SST (peak concentrations occurred during periods of warmer SST). We hypothesize that this pattern of abundance may be caused by shoreward transport of offshore phytoplankton populations by internal tidal waves.     

Phytoplankton distribution and composition off the coast of Galicia (northwest of Spain)

During October 1977, phytoplankton iamples were collected alongwith other hydrographic and biological data from a grid of stationslocated off Galicia (NW of Spain), between the coast and about100 km offshore. Chlorophyll a distribution and phytoplanktoncomposition were studied and related to hydrographic and geographicfeatures of the area. The higher phytoplankton biomasses werefound off the western coast and were conditioned by the presenceof the rias - flooded tectonic valleys of moderate depth functioningas positive estuaries - and the occurrence of coastal upwelling,which allows the injection of nutrient rich water along thebottom of the rias. The qualitative composition of the phytoplanktonreflected principally the influence of the rias but appearedalso to show variability related to the distribution of watermasses. The patterns of circulation of the surface and sub-surfacewaters were likely to reinforce the phytoplankton differencesbetween the northern and western coasts of Galicia.     

Influence of Typhoon Matsa on Phytoplankton Chlorophyll-a off East China

Typhoons can cause strong disturbance, mixing, and upwelling in the upper layer of the oceans. Rich nutrients from the subsurface layer can be brought to the euphotic layer, which will induce the phytoplankton to breed and grow rapidly. In this paper, we investigate the impact of an intense and fast moving tropical storm, Typhoon Matsa, on phytoplankton chlorophyll-a (Chl-a) concentration off East China. By using satellite remote sensing data, we analyze the changes of Chl-a concentration, Sea Surface Temperature (SST) and wind speed in the pre- and post-typhoon periods. We also give a preliminary discussion on the different responses of the Chl-a concentration between nearshore and offshore waters. In nearshore/coastal regions where nutrients are generally rich, the Chl-a maximum occurs usually at the surface or at the layer close to the surface. And, in offshore tropical oligotrophic oceans, the subsurface maxima of Chl-a exist usually in the stratified water column. In an offshore area east of Taiwan, the Chl-a concentration rose gradually in about two weeks after the typhoon. However, in a coastal area north of Taiwan high Chl-a concentration decreased sharply before landfall, rebounded quickly to some degree after landfall, and restored gradually to the pre-typhoon level in about two weeks. The Chl-a concentration presented a negative correlation with the wind speed in the nearshore area during the typhoon, which is opposite to the response in the offshore waters. The phenomena may be attributable to onshore advection of low Chl-a water, coastal downwelling and intensified mixing, which together bring pre-typhoon surface Chl-a downward in the coastal area. In the offshore area, the typhoon may trigger increase of Chl-a concentration through uptake of nutrients by typhoon-induced upwelling and entrainment mixing.     

Across-shelf transport of gastropod larvae in the central Bahamas: rapid responses to local wind conditions

Surveys for veliger larvae of the large gastropods Strombusgigas and Strombus costatus were carried out in duplicate transectsrunning offshore (0.26–5 km) from Lee Stocking Island,Exuma Cays, Bahamas. The across-shelf distribution of the larvaeduring the 1991 spawning season was highly variable over periodsof 3–6 days. Larvae of both species are known to inhabitthe upper few meters of the water column, and analysis of windstress patterns over the study period showed that across-shelfdistribution of the larvae was affected by wind forcing. Seaward(recruitment-unfavorable) transport near Lee Stocking Islandwas most highly correlated with wind stress toward the north-northwest(335–357). The resultant wind stress during the studywas toward 279, suggesting that recruitment of conch to nurserygrounds on the Great Bahama Bank in the Exuma Cays occurs underanomalous summer wind conditions. The correlation between theacross-shelf distribution of conch veligers and wind stresswas highest with extinction coefficients of 0.17–0.23in the exponentially filtered wind stress. This indicates thatlarval distribution over the 5-km-long transects responded rapidlyto changes in wind stress. Over 75% of the effective wind stressoccurred over just 6–8 h preceding collections; therefore,short-term changes in wind stress, such as afternoon strengtheningof the trade winds, may have a significant influence on across-shelflarval transport. ³Present address: Northeast Fisheries Science Center, NationalMarine Fisheries Service NOAA, 74 Magruder Road, Highlands,NJ 07732, USA     

Counterintuitive effects of global warming‐induced wind patterns on primary production in the Northern Humboldt Current System

It has been hypothesized that global warming will strengthen upwelling‐favorable winds in the Northern Humboldt Current System (NHCS) as a consequence of the increase of the land–sea thermal gradient along the Peruvian coast. The effect of strengthened winds in this region is assessed with the use of a coupled physical–biogeochemical model forced with projected and climatological winds. Strengthened winds induce an increase in primary production of 2% per latitudinal degree from 9.5°S to 5°S. In some important coastal upwelling sites primary production is reduced. This is due to a complex balance between nutrient availability, nutrient use efficiency, as well as eddy‐ and wind‐driven factors. Mesoscale activity induces a net offshore transport of inorganic nutrients, thus reducing primary production in the coastal upwelling region. Wind mixing, in general disadvantageous for primary producers, leads to shorter residence times in the southern and central coastal zones. Overall, instead of a proportional enhancement in primary production due to increased winds, the NHCS becomes only 5% more productive (+5 mol C m^?2 year^?1), 10% less limited by nutrients and 15% less efficient due to eddy‐driven effects. It is found that regions with a initial strong nutrient limitation are more efficient in terms of nutrient assimilation which makes them more resilient in face of the acceleration of the upwelling circulation.     

Rapid palaeoceanographic changes in the Benguela Upwelling System for the last 160,000 years as indicated by abundances of planktonic foraminifera

Two sediment cores retrieved from the continental slope in the Benguela Upwelling System, GeoB 1706 (19°33.7′S 11°10.5′E) and GeoB 1711 (23°18.9′S, 12°22.6′E), reveal striking variations in planktonic foraminiferal abundances during the last 160,000 years. These fluctuations are investigated to assess changes in the intensity and position of the upwelling centres off Namibia. Four species make up over 95% of the variation within the core, and enable the record to be divided into episodes characterized by particular planktonic foraminiferal assemblages. The fossil assemblages have meaningful ecological significance when compared to those of the modern day and the relationship to their environment. The cold-water planktonic foraminifer, Neogloboquadrina pachyderma sinistral [N. pachyderma (s)], dominates the modern-day, coastal upwelling centres, and Neogloboquadrina pachyderma dextral and Globigerina bulloides characterize the fringes of the upwelling cells. Globorotalia inflata is representative of the offshore boundary between newly upwelled waters and the transitional, reduced nutrient levels of the subtropical waters. In the fossil record, episodes of high N. pachyderma (s) abundances are interpreted as evidence of increased upwelling intensity, and the associated increase in nutrients. The N. pachyderma (s) record suggests temporal shifts in the intensity of upwelling, and corresponding trophic domains, that do not follow the typical glacial-interglacial pattern. Periods of high N. pachyderma (s) abundance describe rapid, discrete events dominating isotope stages 3 and 2. The timing of these events correlates to the temporal shifts of the Angola-Benguela Front (Jansen et al., 1997) situated to the north of the Walvis Ridge. Absence of high abundances of N. pachyderma (s) from the continental slope of the southern Cape Basin indicates that Southern Ocean surface water advection has not exerted a major influence on the Benguela Current System. The coincidence of increased upwelling intensity with the movement of the Angola-Benguela Front can be interpreted mainly by changes in strength and zonality of the trade wind system.     

SEABIRDS OF THE SENEGAL UPWELLING AND ADJACENT WATERS

Seabird distributions were observed off Senegal during the upwelling season there, in February-March 1976, and are interpreted against an oceanographic background. Gannets Sula bassana , Pomarine Skuas Stercorarius pomarinus , Great Skuas Catharacta skua , Lesser Black-backed Gulls Larus fuscus , Black-headed Gulls L. ridibundus , Sandwich Terns Sterna sandvicensis and Royal Terns S. maxima were the dominant species on the shelf and slope adjacent to the inshore upwelling zone. Grey Phalaropes Phalaropus fulicarius were the only seabirds associated with an oceanic 'front' farther offshore; it is suggested that this and similar boundary zones are important feeding areas during the pelagic phase of this species' annual cycle.
Leach's Storm-Petrels Oceanodroma leucorhoa were seen east to 20W, but the predominant storm-petrel of the waters between 23W and the continental slope was the Madeiran O. castro. It is suggested that the hatching period of Madeiran Storm-Petrels on the Cape Verde Islands is timed to take advantage of the arrival there of young fish in the surface waters, spawned off the African coast and drifted offshore. However Madeiran Storm-Petrels make no direct use of the coastal upwelling; nor do Little Shearwaters Puffinus assimilis or White-faced Storm-Petrels Pelagodroma marina , the other winter-breeding Cape Verdes seabirds, which probably feed close to the Islands.
The Senegal upwelling is underexploited by seabirds, in contrast to comparable upwelling systems elsewhere. It is suggested that this is due to the seasonal timing of the upwelling, the scarcity of secure nest-sites for breeding seabirds, and the competing attractions of the Benguela upwelling in the South Atlantic.     

The Influence of Ekman Transport on Zooplankton Biomass Variability off Southern Brazil

Cross- and long-shelf Ekman transport components were correlatedwith the variability of zooplankton biomass from 1977 to 1990off the southern Brazilian coast (27°S to 35°S and 46°Wto 54°W). During warm months the dominant cross-shelf Ekmantransport was oriented offshore, where an increase in zooplanktonbiomass occurred with intervals of 2–3 months. The presenceof the South Atlantic Central Water (SACW; the water mass thattypically upwells at the continental shelf) was confirmed byseasonal temperature–salinity diagrams. The high zooplanktonbiomass values observed in this study were frequently causedby salps, which play an important ecological role in the pelagiccommunity in upwelling zones that has not been investigatedyet.     

A mechanism for offshore initiation of harmful algal blooms in the coastal Gulf of Maine

A combination of observations and model results suggest a mechanismby which coastal blooms of the toxic dinoflagellate Alexandriumfundyense can be initiated from dormant cysts located in offshoresediments. The mechanism arises from the joint effects of organismbehavior and the wind-driven response of a surface-trapped plumeof fresh water originating from riverine sources. During upwelling-favorablewinds, the plume thins vertically and extends offshore; downwellingwinds thicken the plume and confine it to the nearshore region.In the western Gulf of Maine, the offshore extent of the riverplume during upwelling conditions is sufficient to entrain upward-swimmingA. fundyense cells germinated from offshore cyst beds. Subsequentdownwelling conditions then transport those populations towardsthe coast.     

Sur quelques zooplanctontes abondants dans l'upwelling de Cabo Frio (Bresil)

On some zooplankters common in the Cabo Frio (Brazil) upwelling.In the waters off Cabo Frio zooplankton maxima are observedbetween February and April, which is the period of upwellingoccurrence. Copepods are highly diversified; we identified 96species at a single collecting station during one year. In summerCalanoides carinatus, Paracalanus parvus and Oncea media areabundant, whereas we observed dominance of Temora stylifera,Clausocalanus furcatus, C. arcuicomis, Oithona plumifera andgreat quantity of Creseis acicula during winter. Chaetognatha(Sagitta enflata), Appendicularia (Oikopleura longicauda), Ostracoda(Conchoecia spp.) and Pteropoda (Limacina sp.) are permanentthroughout the year, and maximum in summer. The vertical distributionof zooplankton depends on the hydrological structure, i.e. natureof the water mass and degree of mixing between different waters.Brazil current water, with low quantity of organisms and dominanceof copepods (Clausocalanus furcatus, Mecynocera clausi, Corycaeidae,Oithonidae, Oncaeidae) accompanied by Evadne spinifera and Lucifertypicus. South Atlantic Central Water (upwelling water) characterizedby rare deep copepods and abundance of Calanoides carinatusand Ctenocalanus vanus which are excellent indicator speciesfor upwelling occurrence. Coastal water, with low salinity,where some species with brackish affinity are observed, likeOithona ovalis and Podon polyphemoides.     

Nutrient and phytoplankton dynamics in the Queen Charlotte Islands (Canada) during the summer upwelling seasons of 2001-2002

The Queen Charlotte Islands, Canada, lie at the northern extremeof the coastal upwelling system of the eastern North PacificOcean (51–54°N). In this study, the first observationsof spatial and inter-annual patterns in nutrient inventories,chlorophyll (Chl) a and phytoplankton assemblages are reportedand related to oceanographic conditions in near-shore watersof the island archipelago. Stronger and more persistent upwellingin 2002 coincided with higher nutrient and Chl a standing stockscompared to 2001 and a higher proportion of diatoms. Dinoflagellateswere more prevalent in 2001, including several potentially harmfulspecies. At sub-seasonal scales, Chl a concentrations were greatestduring downwelling conditions and smallest during upwellingconditions. On the west coast, weak water column stratification,high relative proportions of diatoms and large nutrient inventoriesaccompanied upwelling-favourable conditions, whereas on theeast coast, there was no direct relationship between the BakunUpwelling Index and water column stability. According to redundancyanalysis, variability in species composition was best explainedby sea surface temperature, the depth of the euphotic zone andnutrient inventories. The east coast supported blooms of coccolithophoreswithin protected bays, confirming previous satellite observationsthat showed bright patches in these areas. The data illustratethat moderate upwelling can have an important influence on near-shorealgal standing stocks and species composition at the northernextreme of the upwelling system off the west coast of NorthAmerica, and that topographical complexity may be importantfor the development of phytoplankton blooms.     

Vertical migrations of fish larvae: Eulerian and Lagrangian observations in the Eastern English Channel

The Eastern English Channel is known for its strong hydrodynamics.Tidal and residual currents are reinforced by the south-westerndominant wind and drift waters from the English Channel to theNorth Sea. Previous spatial studies have shown that the advectionof larvae could differ from one species to another. Flounder(Pleuronectes flesus) larvae were found offshore, drifting tothe north until the fins were formed; then they were found nearthe coast. However, sole (Solea solea) larvae remained in coastalwaters during their development. The difference in larval spatialdistribution is assumed to be related to the interaction betweenvertical migration and advection by alternative tidal currents,leading to a selective tidal stream transport. To describe thevertical distribution of these larvae, two strategies were used.First, a Eulerian study was carried out with samples taken atthe same geographical location every 1.5 h for 41 h. Ichthyoplanktonwere collected in the water mass using a Bongo net and witha suprabenthic multi-net sledge, at four layers above the seabed, between 0.1 and 1.4 m. Secondly, to enable water movementto be disregarded, a Lagrangian study was carried out by usinga Bongo net every 3 h, following a drifting buoy for 3 days.The results show that even during the youngest stages, solelarvae are able to perform tidal and diel vertical migration.We assume that they may limit their advection to the North Seabecause of their upward migration during ebb and at night, whichmay enable them to remain in the same area dealing with thecurrents. Flounder larvae begin their vertical migration atthe stage of notochord flexion, which ends their drift to thenorth. The larvae reach the bottom of the water column, particularlyduring ebb when they are concentrated in the first 40 cm abovethe bottom. This behaviour favours their advection during flow,leading to efficient and fast transport towards the coast.     

Study and modelling of the development of Euterpina acutifrons (Copepoda: harpacticoida)

The larval development of populations initially composed ofnauplii Nl of Euterpina acurifrons (Copepoda: Harpacticoida)is studied in the laboratory. A first experiment in which temperatureis the only varying parameter allows an assessment of inherentvariability of development. A simple mathematical model thenaccounts for the effect of temperature on development. We findresidence times to be almost identical for all developmentalstages, and higher mortality rates in the case of stages N6and Cl. The model also accounts for latency times observed inthe development of populations including larval stages. A secondexperiment, run at constant temperature, shows that a deficientfood supply increases the average residence time of early stages,as well as their variance. Data obtained on a population bredin tanks under unregulated trophic and temperature conditionsshow that the variation with time of the stage composition ofthe population modulates the effect of external factors on thegrowth of the population.     

Maintenance of Coastal Surface Blooms by Surface Temperature Stratification and Wind Drift

Algae blooms are an increasingly recurrent phenomenon of potentially socio-economic impact in coastal waters globally and in the coastal upwelling region off northern Baja California, Mexico. In coastal upwelling areas the diurnal wind pattern is directed towards the coast during the day. We regularly found positive Near Surface Temperature Stratification (NSTS), the resulting density stratification is expected to reduce the frictional coupling of the surface layer from deeper waters and allow for its more efficient wind transport. We propose that the net transport of the top layer of approximately 2.7 kilometers per day towards the coast helps maintain surface blooms of slow growing dinoflagellate such as Lingulodinium polyedrum. We measured: near surface stratification with a free-rising CTD profiler, trajectories of drifter buoys with attached thermographs, wind speed and direction, velocity profiles via an Acoustic Doppler Current Profiler, Chlorophyll and cell concentration from water samples and vertical migration using sediment traps. The ADCP and drifter data agree and show noticeable current shear within the first meters of the surface where temperature stratification and high cell densities of L. polyedrum were found during the day. Drifters with 1m depth drogue moved towards the shore, whereas drifters at 3 and 5 m depth showed trajectories parallel or away from shore. A small part of the surface population migrated down to the sea floor during night thus reducing horizontal dispersion. The persistent transport of the surface bloom population towards shore should help maintain the bloom in favorable environmental conditions with high nutrients, but also increasing the potential socioeconomic impact of the blooms. The coast wise transport is not limited to blooms but includes all dissolved and particulate constituents in surface waters.     

A Fuzzy Logic Model to Describe the Cyanobacteria Nodularia spumigena Blooms in the Gulf of Finland, Baltic Sea

A fuzzy logic model to describe the seasonal evolution of Nodularia spumigena blooms in the Gulf of Finland was built and calibrated on the basis of monitoring data. The model includes three phosphate sources: excess phosphate after the annual spring bloom and parameterised phosphate transport to the upper mixed layer by turbulent mixing and upwelling events. Surface layer temperature and wind mixing form the physical conditions controlling the growth of N. spumigena. Model simulations revealed that phosphate input caused by turbulent mixing and upwelling have to be taken into account to achieve the best fit with observed data. Testing the fuzzy model for early prediction of maximum N. spumigena biomass about a month before the usual occurrence of blooms, gave good results. The potential use of the model for prediction of bloom risk at a certain location along the Estonian or Finnish coast was tested. The bloom transport velocities used in the fuzzy model were pre-calculated by a 3D numerical circulation model for different wind regimes.     

Coastal intrusion of copepods: mechanisms and consequences on the population biology of Rhincalanus nasutus

In contrast to its usual habitat as a copepod that may occurin shelf or slope waters with low oxygen content between depthsfrom the surface to >2000 m, Rhincalanus nasutus was foundin a shallow (<60 m) embayment, the Arauco Gulf in Chile.Here, we document the complex life history of this copepod wheredid and ontogenetic vertical migratory behavior was co-ordinatedwith the circulation pattern which helped to retain a summerresident population in the vicinity of the gulf. With the onsetof the upwelling season in the southern summer, the mid-depthEquatorial Sub Surface Waters intrude into the gulf, leadingto the formation of a strong thermocline at 10–20 m andthe development of a two-layer circulation pattern. CopepoditesI, C.II and C.III (first stage to exhibit migratory behavior)were found within the gulf in the layer where the net transportwas at a minimum while chlorophyll-a concentrations were ata maximum. Older stages (C.IV-C.VI females and males) migratefrom their daytime depth in the bottom, shoreward-moving, low-oxygenlayer, to their night-time depth in the shallow seaward-movinglayer. The population of copepods retained in the area thuslyreproduce, as reflected in the sequential pulses of differentdevelopmental stages. Because coastal intrusions such as thisof R.nasutus have been documented for several other speciesduring the seasons of maximum phytoplankton production (upwelling),they may form part of a more widespread reproductive strategyof the larger zooplankton of coastal upwelling systems thanpreviously suspected.