Shelf Waters Off Research Articles

Does otolith macrostructure record environmental or biological events? The case of black hake ( Me rluccius polli and Merluccius senegalensis)

Fish age determination using otoliths requires a prior understanding of growth mark deposition patterns (translucent rings, TR) as well as their connection with internal or external events experienced by the fish. This study analysed the macrostructural seasonal ring deposition pattern observed in transversal sections of black hake otoliths. A total of 793 black hake otoliths were collected in autumn and spring 2007 from research and commercial surveys carried out in continental and shelf waters off Mauritania. Most of the Merluccius polli otoliths presented narrow and wide translucent rings (NTR and WTR, respectively) regardless of fish size, whereas Merluccius senegalensis otoliths only showed NTR. This seemed to be a sign of ontogenetic discrepancy between the two black hake species, whose otoliths confirmed the existence of significant differences in their growth patterns. The frequency distributions of the number of TR counted along the ventral radius (VR) of the otolith from the nucleus (birth date) and from the ventral edge (death date) were analysed to ascertain whether a specific endogenous event ( Hypothesis A) or a precise environmental event ( Hypothesis B) could restrain growth leading to the formation of TR. The general TR frequency distribution pattern was somewhat similar for both hake species, which showed marked TR at comparable distances. Within each species, TR frequency distributions of their distances from the nucleus along the otolith VR were quite similar between sexes, seasons, and fish sizes. Our results support the idea of a coincident biological event, such as first maturity, slowing down the growth process and thus provoking the formation of TR in otoliths of both species. This study also experience difficulty using the complex and highly variable macrostructural pattern of black hake otoliths to establish age interpretation criteria for these two species.

On- and off-shelf diving effort of juvenile elephant seals from Península Valdés determined by light loggers

The shallow Patagonian Shelf off Peno´nsula Valdes limits the dive depth of southern elephant seals (Mirounga leonina )t o,100 m, an unusual circumstance for this deep-diving species. Beyond the shelf water depths of .1,000 m enable the seals to forage deeper and use the entire water column. We compared the diving pattern of 10 juveniles instrumented with light-temperature loggers to determine if diving effort, measured as dive durations longer than the estimated aerobic dive limit, differed between on-shelf and off-shelf waters. The productive Patagonian Shelf, an environment where juveniles showed lower diving effort, also was used commonly by older seals, which likely displaced juveniles off-shelf periodically, where they exhibited increased diving effort.

Trace Metal Dynamics in Marine Shrimps from the Southwest Coast of India

Concentrations of Fe, Co, Ni, Cu, Zn, Cd and Pb in the muscle tissue of marine shrimps, Penaeus mondon, Penaeus japonicus, Penaeus indicus, Penaeus mergniensis, Parapenaeopsis hardwickii and Parapenaeopsis stylifera, collected from the continental shelf waters off Kochi on southwest coast of India were determined. Inter species-specific tissue metals loads were appreciable within the Penaeid shrimps for the region. The ranges of higher concentrations of Fe (756.8 to 1288.5 mg/g), Co (8.8 to 18.6 mg/g), Ni (12.8 to 24.7 mg/g), Cu (32.8 to 46.8 mg/g), Zn (52.6 to 88.7 mg/g), Cd (5.8 to 9.6 mg/g), and Pb (0.8 to 1.9 mg/g) were observed in P. mondon, P. japonicus, P. indicus, P. mergniensis, and P. hardwickii characterized with an estuarine-sea life history when compared with the lowest concentrations of Fe (725.8 mg/g), Co (8.5 mg/g), Ni (10.6 mg/g), Cu (28.6 mg/g), Zn (44.8 mg/g), Cd (3.6 mg/g), and Pb (0.6 mg/g) found in P. stylifera with only a sea life history. This difference is possibly due to the favoring uptake of differently bioavailable metals from the associated food chain bioaccumulation processes within the estuarine and shelf waters off Kochi. The higher bioaccumulation factors 555867, 442857, 171528, 33621, 42933, 48731 and 4750 of the analyzed metals (Fe, Co, Ni, Cu, Zn, Cd & Pb) in the shrimp species P. mondon compared with others will support ecologists to use it as a bioindicator for metal pollution.

Distribution of life-history stages of the salp Thalia democratica in shelf waters during a spring bloom

Swarms of the salp Thalia democratica periodically occur off southeast Australia follow- ing the austral spring bloom of phytoplankton. The present study aimed to determine the abundance and size/stage distribution of T. democratica and their relationship with copepods in 3 water types of the western Tasman Sea. Samples were taken from vertical net hauls along 4 cross-shelf transects spaced along 200 km of the New South Wales coast, from the East Australian Current (EAC) sepa - ration zone, around 32.5° S, to off Sydney (34° S). Temperature-salinity signatures grouped stations into 3 distinct water types: inner shelf water, EAC and upwelled water. Although common across all stations, T. democratica was significantly more abundant in inner shelf waters compared to both EAC and upwelled water. Analysis of population structure (aggregate buds, aggregate females, aggregate males, immature solitaries and mature solitaries) also identified higher proportions of reproductive aggregates and their offspring in inner shelf water. This salp population structure was significantly different in the EAC regions, characterised by a paucity of the solitary stages, higher temperatures and lower chlorophyll a concentrations. A weak negative correlation was identified between T. demo- cratica and copepod abundance. In the present study, the maximum abundance of T. democratica was twice the highest globally recorded abundance and 10-fold greater than maximum abundances sampled from the continental shelf and slope waters off southeast Australia during the period from 1938 to 1942.

Thread-drifting juvenile Mytilus spp. in continental shelf waters off Coos Bay, Oregon, USA

ABSTRACT: On 4 sample dates in summer 2007, vertically stratified zooplankton samples and oceano-graphic data were collected at 7 stations located from 0.5 to 28 km from shore near Coos Bay, Oregon,USA. Two of the sample dates (27 June and 14 August) were characterized by upwelling conditionsand the other two (3 and 18 July) by downwelling or relaxation. We identified larval and thread-drifting Mytilus californianus and M. trossulus/galloprovincialis . Thread-drifting M. californianus and M. trossulus/galloprovincialis ranged in size from 306 to 627 μm and from 305 to 832 μm, respectively.On all sample dates, larval and thread-drifting mytilids were rare in surface waters (0 to 10 m depth),abundant below these depths at the 3 inshore stations (0.7 to 4.5 km offshore) and rare or absent at alldepths at more seaward stations. Thread drifters were caught within 10s of meters of the bottom.There was no relationship between either the strength of the alongshore currents or wave energy andthe abundance of thread drifters. Thread drifters were significantly more abundant during down-welling/relaxation events than during upwelling events. The higher abundances during downwellingmay be due to favorable conditions for thread drifting within the benthic boundary; density instabilitygenerated by the downwelling circulation interacting with the cross-shelf density gradient createsvertical currents, which may aid lift-off of thread drifters from the bottom.KEY WORDS:

Movements and diving behavior of Atlantic bluefin tuna Thunnus thynnus in relation to water column structure in the northwestern Atlantic

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 400:245-265 (2010) - DOI: https://doi.org/10.3354/meps08394 Movements and diving behavior of Atlantic bluefin tuna Thunnus thynnus in relation to water column structure in the northwestern Atlantic Gareth L. Lawson1,2,*, Michael R. Castleton1, Barbara A. Block1 1Tuna Research and Conservation Center, Stanford University, Hopkins Marine Station, 120 Oceanview Boulevard, Pacific Grove, California 93950, USA 2Present address: Biology Department, Woods Hole Oceanographic Institution, Woods Hole, Massachusetts 02543, USA *Email: glawson@whoi.edu ABSTRACT: We analyzed the movements and diving behavior in relation to water column structure of 35 electronically tagged Atlantic bluefin tuna (176 to 240 cm in length at tagging) during their spring–fall period of occupancy of the Gulf of Maine, Canadian Shelf, and neighboring off-shelf waters from 1999 to 2005. Tagged fish arriving in this study region in March–April initially occupied weakly stratified off-shelf waters along the northern Gulf Stream. As waters over the continental shelf warmed in June, the fish shifted onto the shelf. Sea surface temperatures occupied were relatively constant in both off- and on-shelf waters (April–September monthly medians varying from 16.1 to 19.0°C). Dives made in the stratified waters of the shelf during summer and fall were significantly more frequent (up to 180 dives d–1) and fast (descent rates up to 4.1 m s–1) than in weakly stratified off-shelf waters occupied during spring, defining dives as excursions below tag-derived estimates of the surface isothermal layer depth (ILD). The duration and depth of dives also decreased significantly in association with changing water column structure, from medians in off-shelf waters during April of 0.45 h and 77.0 m, respectively, to 0.16 h and 24.9 m in August. Analyses of tag measurements of internal body temperature and feeding proxies suggest that both the horizontal movement of the fish onto the continental shelf and the dives made from the warm surface layer into colder waters at depth represent a balance between the maintenance of preferred ambient temperatures and foraging opportunities. KEY WORDS: Atlantic bluefin tuna · Thunnus thynnus · Electronic tagging · Gulf of Maine · Diving behavior Full text in pdf format Supplementary material PreviousNextCite this article as: Lawson GL, Castleton MR, Block BA (2010) Movements and diving behavior of Atlantic bluefin tuna Thunnus thynnus in relation to water column structure in the northwestern Atlantic. Mar Ecol Prog Ser 400:245-265. https://doi.org/10.3354/meps08394Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 400. Online publication date: February 11, 2010 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2010 Inter-Research.

Optical properties and optical constituents of the Faroe Islands shelf and off-shelf waters, North East Atlantic

The study comprises a data set of CTD, optical properties—K 0(PAR), c p, a(PAR), b(PAR)—and optical constituents—Chl a, SPM, CDOM—from 72 shelf and off-shelf stations in the Faroe Islands (62°N, 7°W) North East Atlantic, in early spring 2005. Results showed that shelf waters surrounding the islands were cold and low saline, whereas off-shelf waters were warmer (~1°C) and more saline (~0.05) PSU. A pronounced oceanographic front separated the two waters, and diffuse light attenuation K 0(PAR), beam attenuation c p, Chl a, absorption a(PAR), and scattering coefficient b(PAR) were all significantly higher on the shelf. Analyses showed that off-shelf light attenuation K 0(PAR) was governed by Chl a, shown by a high (r 2 = 0.64) Chl a–K 0(PAR) correlation, whereas light attenuation on the shelf was governed by both Chl a, SPM, and CDOM in combination. A Chl a specific diffuse attenuation coefficient $$ K_{0}^{*} \left( {\text{PAR}} \right) $$ of 0.056 (m2 mg−1 Chl a) and a Chl a specific beam attenuation ( $$ c_{\text{p}}^{*} $$ ) of 0.27 (m2 mg−1 Chl a) coefficients were derived for the off-shelf. It is pointed out that Chl a is the single variable that changes over time as no rivers with high SPM and CDOM enter the shelf area. Data were obtained in early spring, and Chl a concentrations were low ~0.5 mg Chl a m−3. Spring bloom Chl a are about 10 mg Chl a m−3 and estimations showed that shelf K 0(PAR) will increase about 5 times and beam attenuation about 10 times. The Faroe Islands shelf–off-shelf waters is a clear example where physical conditions maintain some clear differences in optical properties and optical constituents. The complete data set is enclosed.

Trace metal dynamics in fishes from the southwest coast of India

The concentration of Fe, Co, Ni, Cu, Zn, Cd, and Pb in the muscle tissue of marine fishes like Lates calcarifer, Nemipterus japonicus, Caranx melampygus, Rastrelliger kanagurta, and Cyanoglossus macrostomus was estimated from samples collected in the continental shelf waters off Kochi and Mangalore on southwest coast of India. Species-specific and spatially heterogeneous patterns of tissue metals loads were apparent within the pelagic and demersal fish species for the two regions. The concentration ranges of Fe (541.60 to 649.60 ppm), Ni (12.12 to 13.92 ppm), and Cu (3.09 to 3.62 ppm) were higher in the demersal species C. melampygus, whereas Co (9.10 to 11.80 ppm) and Zn (79.30 to 84.30 ppm) were higher in the pelagic species L. calcarifer and Cd (4.35 to 6.38 ppm) were higher in the demersal species N. japonicus, possibly due to enhanced bioavailability of these metals from ecological processes associated with upwelling during the summer monsoon. The fish species showed a great capacity to accumulate metals, with highest bioaccumulation for the essential element iron and lowest bioaccumulation for the non-essential element lead. Among the demersal species, C. melampygus and N. japonicus had high concentration factors for the metals Fe (280,268 to 322,808), Ni (88,252 to 96,891), Cu (2,351 to 2,600), and Cd (29,637 to 32,404). In contrast, the pelagic species L. calcarifer and R. kanagurta had high concentration factors for the metals Zn (40,812 to 46,892), Co (280,285 to 423,037), and Pb (854 to 1,404).

Transequatorial Migrations by Basking Sharks in the Western Atlantic Ocean

The world's second largest fish, the basking shark (Cetorhinus maximus), is broadly distributed in boreal to warm temperate latitudes of the Atlantic and Pacific oceans from shallow coastal waters to the open ocean. Previous satellite archival tagging in the North Atlantic has shown that basking sharks move seasonally, are often associated with productive frontal zones, and may make occasional dives to mesopelagic depths. However, basking sharks are thought to be restricted to temperate latitudes, and the extent to which they exploit deeper-water habitat remains enigmatic. Via satellite archival tags and a novel geolocation technique, we demonstrate here that basking sharks are seasonal migrants to mesopelagic tropical waters. Tagged sharks moved from temperate feeding areas off the coast of southern New England to the Bahamas, the Caribbean Sea, and onward to the coast of South America and into the Southern Hemisphere. When in these areas, basking sharks descended to mesopelagic depths and in some cases remained there for weeks to months at a time. Our results demonstrate that tropical waters are not a barrier to migratory connectivity for basking shark populations and highlight the need for global conservation efforts throughout the species range.

Elevated Fe(II) and Dissolved Fe in Hypoxic Shelf Waters off Oregon and Washington: An Enhanced Source of Iron to Coastal Upwelling Regimes

There has been a growing interest in the cause and impact of hypoxic regions known as "dead zones" that have increasingly appeared along the west coast of the United States and have caused widespread destruction to the crab and fishing industry in this upwelling region. Here, we present results that demonstrate that the hypoxic conditions in the water column over the continental shelf result in a marked increase in iron(II) concentrations, which contribute to elevated dissolved and labile particulate iron concentrations. These elevated dissolved iron(II) concentrations result from two factors: (1) the hypoxic water column allows extremely elevated iron(II) concentrations in reducing porewaters to exist close to the sediment water interface, leading to an increased flux of iron(II) from the sediments; (2) the low oxygen, low pH, and low temperatures within the bottom boundary layer act in concert to markedly slow down the oxidation rate of Fe(ll). During upwelling conditions, this process can result in a greatly enhanced source of Fe available to upwell to surface waters, potentially increasing phytoplankton productivity, which can, in turn, lead to enhanced export flux, driving the system further into hypoxic or suboxic conditions.

Larval fish assemblages along the south‐eastern Australian shelf: linking mesoscale non‐depth‐discriminate structure and water masses

AbstractWe present findings of the first mesoscale study linking larval fish assemblages and water masses along shelf waters off south‐eastern Australia (southern Queensland‐New South Wales), based on vertical, non‐depth discriminate data from surveys in October 2002 and 2003 (spring) and July 2004 (winter). Clustering and ordination were employed to discriminate between larval assemblages and, for the first time, to define water masses from water column temperature frequencies. Surveys yielded 18 128 larval fishes comprising 143 taxa from 96 identifiable families, with small pelagics accounting for 53% of the total. Three major recurrent larval assemblages were identified during the study, each of which matched one of three water masses, namely East Australian Current to the north (EAC; 20.5–23.4°C), Tasman Sea to the south (TAS; 14.8–17.5°C), and mixed EAC–TAS water in between (MIX; 18.3–19.9°C). All three assemblages were present in spring, whereas only EAC and MIX occurred in the more northerly constrained winter survey. Furthermore, boundaries between the EAC, MIX and TAS assemblages were found to be dynamic, with locations shifting temporally and spatially depending on EAC extent. Assemblage composition differed significantly between water masses across surveys, with EAC–TAS being most dissimilar. Such contrast was due to the presence of tropical/temperate taxa in EAC, primarily temperate‐associated taxa in TAS, and a combination of EAC–TAS taxa within MIX consistent with the convergence of both waters. Results highlight the strength of employing larval assemblages as indicators of water masses, particularly in view of the potential effect of climate change on spawning habitats of shelf fishes.

Faroe Shelf Water

Faroe Shelf Water (FSW) is the water mass that occupies the shallow parts of the Faroe Shelf, surrounding the Faroe Islands (62°N, 7°W). Intensive tidal mixing induces a high degree of homogeneity and the circulation system allows a partial isolation from surrounding waters. This water mass, therefore, supports a unique ecosystem of great importance for commercial fish stocks and studies have shown a clear dependence of the ecosystem on the physical processes that maintain this system and control the exchange between the FSW and the off-shelf waters. In order to identify and quantify these processes, a large observational dataset has been analysed and related to alternative theories. From this analysis, the extent and properties of the FSW have been quantified and the degree of stratification explained in terms of the Simpson–Hunter theory. The residual clockwise circulation system, which is responsible for the partial isolation from off-shelf waters, is shown to be mainly generated by tidal rectification. The typical exchange rate of water between the FSW and the off-shelf regimes has been determined by the use of simple models based on the heat and the salt budgets but the actual exchange rate is found to vary considerably in time and space. These results support earlier suggestions that this exchange is the main limiting factor for the phytoplankton spring bloom on the Faroe Shelf and that variations in exchange rate are responsible for the large inter-annual variation in spring bloom timing and intensity. The observations indicate that the on-shelf/off-shelf exchange intensity is not symmetrically distributed around the shelf, but rather concentrated around the narrow southern tip of the Faroe Shelf, where off-shelf waters during intensive exchange events may be imported all the way to the shore.

Segregation between the sexes: Antarctic fur seals, Arctocephalus gazella, foraging at South Georgia

Antarctic fur seals show extreme sexual size dimorphism and their breeding strategies place very different constraints on the behaviour of males and females. Whereas the foraging behaviour of lactating females is well studied, very little is known about males. We tracked 14 adult males during a period when they are observed around South Georgia to compare their behaviour with that of 41 lactating females tracked from the same island. There was significant spatial segregation between the sexes in both the horizontal and the vertical dimensions. Female fur seals foraged near the surface, mostly at night, concentrating their efforts at the shelf break and in deeper off-shelf waters. Males foraged closer to the breeding beaches and their time at sea was concentrated in waters over the continental shelf. Males dived significantly deeper and longer and spent longer in the bottom phase of a dive than females. Females dived mostly at night, whereas males dived much more during the day and overall had greater variability in their behaviour within a trip. Sex was a better predictor of dive durations than mass when depth was considered. Categorizing dives into three types showed that males often foraged on or near the bottom, a behaviour not observed in females. We suggest that body size dimorphism causes sexual differences in foraging behaviour (e.g. dive depth, duration, etc.) but how this is manifested (i.e. trip distance, foraging location) is dependent on the local environment and the related prey resources.

Bayesian analysis of allozyme markers indicates a single genetic population of kingklip Genypterus capensis off South Africa

Kingklip Genypterus capensis inhabit deep continental shelf and slope waters off southern Africa and are now largely harvested as a bycatch in trawl and longline fisheries for Cape hakes Merluccius spp. Regional differences in growth, vertebral count and otolith morphology indicate that kingklip may consist of three stocks. In this study, allozyme markers are used to test whether the two southern stocks, the putative Cape and South Coast stocks, are genetically distinguishable. Standard electrophoretic methods detected Mendelian polymorphisms at six (23%) of 26 enzyme-encoding loci in five samples extending from about 29°S on the West Coast to about 25°E on the South Coast. No deviations from Hardy-Weinberg proportions were observed in the samples or in the pooled sample. Gene diversities (heterozygosity) ranged from HS = 0.039 to 0.042 among samples, and averaged 0.041. Genetic differentiation among localities was remarkably small, FST = 0.003, and did not differ significantly from zero. A Bayesian analysis of population structure, based on detecting departures from Hardy-Weinberg proportions and gametic phase equilibria between loci, indicated with a high likelihood that the five samples were drawn from a single genetic population. In combination, these results are consistent with the occurrence of a single population off South Africa. However, the most conservative management strategy is to set harvest quotas individually on the Cape and South Coast stocks.

Climatic effects on plankton and productivity on the Faroe Shelf

Abstract Previous investigations have shown that new primary production on the Faroe Shelf during the spring bloom varies considerably from one year to another, both with regard to timing and intensity. It has also been found that variations in new primary production are transmitted up the food chain to top predators such as cod and haddock. An observed inverse relationship between new primary production and zooplankton biomass, especially Calanus finmarchicus, might be due to grazing, but could also reflect a dependence of both new primary production and C. finmarchicus import on the horizontal exchange between waters on the shelf and off it. Here, we investigate this question, using observations and an idealized numerical model. We find that the large variability in new primary production is most likely due to the direct effect of variable horizontal exchange rates on phytoplankton reproduction (horizontal Sverdrup mechanism), rather than grazing. Enhanced horizontal exchange flushes phytoplankton from the shallow areas and limits primary production. Horizontal exchange rate seems most sensitive to horizontal density differences between on-shelf and off-shelf waters, which is governed by atmosphere–ocean heat exchange and precipitation. For the primary observational period from 1990 to 2003, a close relationship was found between air temperature in January–April and new primary production. Cold winters produced large density differences, small horizontal exchange rates, and intensive new primary production. Other, less direct, evidence indicates, however, that this relationship may not have been valid in a period before 1990.

Seasonal and inter-annual variability of SeaWiFS-derived chlorophyll a concentrations in waters off the Washington and Vancouver Island coasts, 1998–2002

Abstract Seasonal and inter-annual variability in satellite-derived estimates of near-surface chlorophyll a concentration and primary production were examined in three regimes (shelf, slope and deep oceanic waters) off Washington and Vancouver Island from 1998 to 2002. Wind-induced upwelling predominates in late spring and summer, coinciding with the maximum in solar radiation, leading to increased accumulations of phytoplankton biomass. Shelf chlorophyll concentrations varied from 2 to 10 mg m−3 and were generally lower in April and May and maximal in September. Chlorophyll concentrations on the slope followed a similar seasonal pattern (ranging from 0.5 to 4 mg m−3); however, concentrations were always greater on the Vancouver Island slope compared to the Washington slope for any 30-day period. Oceanic chlorophyll concentrations were generally less than 1 mg m−3 and averaged approximately 0.3 mg m−3. The Pacific Northwest is often cloud covered; data density maps provide an index of confidence in the ‘regional’ applicability of the summary statistics. One consequence of the 1997–1998 El Nino appears to be a reduction in chlorophyll concentration, and inferred rates of primary productivity, in slope and oceanic waters off Vancouver Island in 1998. An increased frequency of El Nino events may lead to a reduction in offshore carbon transport and sequestration, and these results help develop an understanding of the variability in carbon cycling in this dynamic upwelling region. Six-month median chlorophyll concentrations were maximal in 2002 for all subregions off Vancouver Island and for shelf and slope regions off Washington. The dramatic increases in chlorophyll concentrations seen in 2002 are consistent with hypothesized increased advection of nutrient-rich Subarctic waters into the California Current.

Seasonal and inter-annual variability of SeaWiFS-derived chlorophyll a concentrations in waters off the Washington and Vancouver Island coasts, 1998–2002

Seasonal and inter-annual variability in satellite-derived estimates of near-surface chlorophyll a concentration and primary production were examined in three regimes (shelf, slope and deep oceanic waters) off Washington and Vancouver Island from 1998 to 2002. Wind-induced upwelling predominates in late spring and summer, coinciding with the maximum in solar radiation, leading to increased accumulations of phytoplankton biomass. Shelf chlorophyll concentrations varied from 2 to 10 mg m−3 and were generally lower in April and May and maximal in September. Chlorophyll concentrations on the slope followed a similar seasonal pattern (ranging from 0.5 to 4 mg m−3); however, concentrations were always greater on the Vancouver Island slope compared to the Washington slope for any 30-day period. Oceanic chlorophyll concentrations were generally less than 1 mg m−3 and averaged approximately 0.3 mg m−3. The Pacific Northwest is often cloud covered; data density maps provide an index of confidence in the ‘regional’ applicability of the summary statistics. One consequence of the 1997–1998 El Niño appears to be a reduction in chlorophyll concentration, and inferred rates of primary productivity, in slope and oceanic waters off Vancouver Island in 1998. An increased frequency of El Niño events may lead to a reduction in offshore carbon transport and sequestration, and these results help develop an understanding of the variability in carbon cycling in this dynamic upwelling region. Six-month median chlorophyll concentrations were maximal in 2002 for all subregions off Vancouver Island and for shelf and slope regions off Washington. The dramatic increases in chlorophyll concentrations seen in 2002 are consistent with hypothesized increased advection of nutrient-rich Subarctic waters into the California Current.

Habitat selection of overwintering Calanus finmarchicus in the NE Norwegian Sea and shelf waters off Northern Norway in 2000–02

AbstractThe abundance and distribution of overwintering Calanus finmarchicus in the NE Norwegian Sea and shelf waters off North Norway was studied during January for 2000–02. Depth integrated distribution of C. finmarchicus CV showed aggregations with high abundances in the Lofoten Basin and southwest of Tromsøflaket for all three years. The exact location of the aggregation areas and the maximum abundances did, however, vary between the years. The concentrations southwest of Tromsøflaket were almost twofold higher in 2000 at 150 000 ind. m−2 compared to 70 000 and 90 000 ind. m−2 in 2001 and 2002, respectively. Vertical distribution of the animals was similar for the three years, with most of the CVs of the population residing in the depth interval between 700 and 1200 m. Peak abundances of 350 ind. m−3 were found at 850–1000 m west of Tromsøflaket in 2000, whereas in 2001 the maximum abundances were located in the Lofoten Basin at 700–900 m, in the order of 150 ind. m−3. In 2002, the highest concentration of animals was found west of Vesterålen between 1100 and 1200 m, with a concentration of 385 ind. m−3. The vertical and horizontal distribution of C. finmarchicus CV closely followed the hydrographic structures in the area, with the highest abundances associated with cold (<2°C), less saline (34.85–34.9) water with a density of 27.95–28. The patches of high abundance were located in confined areas along the continental shelf slope and in the Lofoten Basin, indicating that the animals may have been extracted from the highly flushed surface areas in late summer during their ontogenetic descent, and trapped in mesoscale physical features in the deep‐water masses throughout the winter. We argue that deep‐water mesoscale anticyclonic eddies, which are frequently formed along the continental slope and in the Lofoten Basin, may provide favourable retention areas for the overwintering population of C. finmarchicus. Consequently, the impact of ocean climate as well as more regional and local effects on the creation and persistence of these mesoscale features is likely to influence the Calanus abundance and advection paths in the following spring and summer.

Variations in phytoplankton pigments, size structure and community composition related to wind forcing and water mass properties on the North Carolina inner shelf

Variations in phytoplankton pigments, size structure and community composition were examined in inner shelf waters off North Carolina in relationship to water mass properties subject to the influence of low salinity outflow from the Chesapeake Bay, alternations in wind forcing and interactions with shelf water masses. Observations were made aboard the R/V Edwin Link during May 1997. Episodes of upwelling-favorable conditions were accompanied by detachment of the low salinity outflow plume from the coast, and enhanced dispersion and mixing with shelf waters. Distinct water masses were identified using cluster analysis of temperature–salinity ( T–S) properties. Two major clusters, distinguished on the basis of relatively high and low salinities, were identified as ambient coastal water (A) and modified bay water (B). Each of these could be further separated into two water mass types characterized by relatively high and low temperatures. The pigment and taxonomic composition of these water masses were examined. The carotenoid fucoxanthin was generally the most abundant accessory pigment. Zeaxanthin and chlorophyll b were also relatively abundant at most stations. Ratios to chlorophyll a of 19′-hexanoyloxyfucoxanthin and peridinin were higher for the high salinity clusters. A shift to downwelling-favorable conditions toward the latter part of the cruise gave rise to a narrow, southward flowing jet of low salinity Chesapeake Bay water corresponding to the low salinity, relatively high temperature water mass identified by cluster analysis. Fucoxanthin dominated the accessory pigments in this low salinity feature. Proportions of chlorophyll a associated with different phytoplankton classes, as estimated using CHEMTAX software (Mar. Ecol. Prog. Ser. 144 (1996) 265), varied among groups in a manner consistent with pigment composition. A diverse assemblage of diatoms, cyanobacteria, cryptophytes and prasinophytes accounted for the majority of chlorophyll a at most stations. Haptophytes and dinoflagellates were relatively more abundant in warmer, higher salinity stations. The low salinity jet exhibited high biomass and low diversity compared to other water masses. Its phytoplankton population was dominated by diatoms larger than 8 μm in diameter. The results demonstrate that phytoplankton community composition varies substantially among the different water masses in this coastal region and is subject to event scale (i.e., days to weeks) changes in relation to wind forcing and shelf circulation processes.

Phytoplankton spectral absorption as influenced by community size structure and pigment composition

Assessments were made of the relative importance of package effects and pigment composition in contributing to variations in spectral absorption in shelf waters off North Carolina during May 1997 and off west Florida during October 1998. Measurements of spectral absorption of size-fractionated particulate material on glass fibre filters were made using two methods, the transmittance-reflectance (T-R) method and the quantitative filter technique (QFT). Spectral absorption of phytoplankton pigments was decomposed into a series of 13 Gaussian absorption bands, and absorption band peak heights were related to concentrations of major pigment classes. Maximum weight-specific pigment absorption coefficients for individual absorption bands (p* m ) derived from the fit of a hyperbolic tangent function to the data were found to be similar for North Carolina and west Florida shelf waters. The values were used to reconstruct spectral absorption in the absence of pigment packaging, which was then compared to measured absorption to provide an assessment of pigment packaging. Package effects were found to be responsible for up to a 62% reduction in the amplitude of major absorption bands, particularly for samples from low-salinity waters and for populations dominated by larger (>3 μm) phytoplankton. Variations in pigment composition were also found to have an impact, although it was smaller (10-28%), on variations in total absorption. Potential bio-optical applications of the Gaussian decomposition approach include the estimation of pigment concentrations from in situ or remotely sensed ocean colour observations. Alternatively, where pigment concentrations are known, it may be possible to estimate absorption. Successful application of such techniques may necessitate characterizations of coefficients specific to a given region and time.