Chlorophyll <Emphasis Type="Italic">a</Emphasis> as a measure of seasonal coupling between phytoplankton and the monsoon periods in the Gulf of Oman

We present data from a long time-series study to describe the factors that control phytoplankton population densities and biomass in the coastal waters of Oman. Surface temperature, salinity, nutrients, dissolved oxygen, chlorophyll a (Chl a), and phytoplankton and zooplankton abundance of sea water were measured as far as possible from February 2004 through February 2006, at two stations along the southern coast of the Gulf of Oman. The highest concentrations of Chl a (3 mg m⁻³) were recorded during the southwest monsoon (SWM) when upwelling is active along the coast of Oman. However, results from our study reveal that the timing and the amplitude of the seasonal peak of Chl a exhibited interannual variability, which might be attributed to interannual differences in the seasonal cycles of nutrients caused either by coastal upwelling or by cyclonic eddy activity. Monthly variability of SST and concentrations of dissolved nitrate, nitrite, phosphate, and silicate together explained about 90% of the seasonal changes of Chl a in the coastal ecosystem of the Gulf of Oman. Phytoplankton communities of the coastal waters of Oman were dominated by diatoms for most part of the year, but for a short period in summer, dinoflagellates were dominant.     

Identification of the coastal zone of the central and eastern Gulf of Finland by numerical modeling,measurements, and remote sensing of chlorophyll <Emphasis Type="Italic">a</Emphasis>

A combination of numerical modeling results with measurement and satellite imagery data was used during the biologically active period for the determination of the coastal zone extent in the central and eastern Gulf of Finland. Adopting the approach that the coastal zone can be identified by the spatial distribution of biotic parameters, spatial variations and gradients of chlorophyll a (chl-a) concentrations were analyzed. The results showed that chl-a concentrations vary in a wide range over the biologically active period. During heavy blooms, the coastal zone may appear occasionally and depend on the spatial distribution of the bloom. On average, clear limits of the coastal zone could be defined for the central and eastern Gulf of Finland. In the central Gulf of Finland, water and material exchange are rather intensive, and the coastal zone is narrower than in the eastern Gulf. In the easternmost part of the Gulf of Finland, chl-a concentrations were permanently high in an area of about 100 km width due to the discharge of the Neva River. The study has shown that gradients of chl-a spatial distribution can be applied for determining limits of the coastal zone extent. The standardized gradient of zero is shown to be a threshold separating the coastal zone (standardized gradients > 0) from the open sea (standardized gradients < 0). Guest editors: J. H. Andersen & D. J. Conley Eutrophication in Coastal Ecosystems: Selected papers from the Second International Symposium on Research and Management of Eutrophication in Coastal Ecosystems, 20–23 June 2006, Nyborg, Denmark     

Ocean color observations of a surface water transport event: Implications for Pseudo-nitzschia on the Washington coast

A persistent patch of high biomass water, associated with the Juan de Fuca Eddy, is often observed in surface chlorophyll a images off the southwest coast of Vancouver Island, Canada. Outbreaks of toxic Pseudo-nitzschia spp. along the Washington, USA, coast are believed to correlate with the transport of waters from Juan de Fuca Eddy southward to Washington beaches. A time series of Sea-viewing Wide Field-of-view Sensor (SeaWiFS) satellite ocean color images from late May 1999 of coastal waters off Washington and Vancouver Island, processed for surface chlorophyll a concentration and spectral remote sensing reflectance, captured a transport event where water from the Juan de Fuca Eddy was transported onto the Washington shelf. Strong upwelling-favorable winds appeared to deform the patch over an 8-day period and move it southward into Washington coastal waters with surface velocities of approximately 8–16 km d⁻¹. SeaWiFS and sea surface temperature imagery showed the local phytoplankton response to wind-driven coastal upwelling restricted to a narrow (10–15 km) region along the Washington coast. Although we did not observe transport of high biomass water originating in the Juan de Fuca Eddy to Washington beaches in May 1999, transport of Pseudo-nitzschia cells could occur following a rapid shift to downwelling-favorable conditions. Tracking the trajectory of surface waters from the Juan de Fuca Eddy by remote sensing could be used to trigger conditional sampling for domoic acid along the Washington coast.     

Phytoplankton Spring Bloom Intensity Index for the Baltic Sea Estimated for the years 1992 to 2004

We introduce an index for estimating the annual phytoplankton spring bloom intensity in the Baltic Sea. It is based on chlorophyll a estimates calculated from automatically sampled fluorescence and chlorophyll a measurements on board cargo ships from 1992 to 2004. The intensity is described by an index including information on the chlorophyll a concentration and duration of the spring bloom period. In all of the years studied, the spring bloom was most intense in the Gulf of Finland. In the Gulf of Finland and the Northern Baltic Proper there was a slight tendency for the bloom to start earlier in the spring.     

The Concentrations of Trace Metals in the Soft Tissues of the Mytilid Mollusk <Emphasis Type="Italic">Septifer bilocularis</Emphasis> (Linnaeus, 1758) as a Possible Indicator of Water Quality at Coastal Coral Reefs of Vietnam

The variability of Fe, Mn, Zn, Cu, Pb, Cd, and Ni concentrations was studied in soft tissues of the common mytilid mollusk Septifer bilocularis collected in May 2013 at the coral reefs along the entire Vietnamese coast from the Gulf of Siam to Ha Long Bay. The salinity, suspended solids, and nutrients were determined during the sampling; these hydrochemical characteristics of the surrounding waters were controlled by the river runoff and the content of chlorophyll a. The concentration of Mn in the mollusk S. bilocularis was elevated under the river runoff effect. However, concentrations of Cd and Zn in S. bilocularis were the lowest within the areas of river influence and increased in waters of central Vietnam and the Gulf of Siam, where upwellings are an important driving force. A comparison of our data with those obtained for Mytilidae from other regions showed that the mussel S. bilocularis can be recommended for biomonitoring of the concentrations of trace metals in the waters of coral ecosystems along the Vietnam coast.     

Decadal weakening of the wind-induced upwelling reduces the impact of nutrient pollution in the Bay of Málaga (western Mediterranean Sea)

The hypothesis that nitrate versus phosphate regulates the coastal primary production has been assessed at different time scales in the northwest Alboran Sea. Time series of temperature, salinity, nutrients and chlorophyll a obtained at three stations located off Málaga city (the greatest coastal urban core along the Alboran Sea shoreline) from 1992 to 2006 have been analysed. At the decadal scale, temperature increased linearly while salinity decreased. These changes were related to a shift in the wind regime suggesting that coastal upwelling became steadily weaker. In contrast to phosphate, nitrate was positively correlated with salinity at the seasonal scale and decreased linearly from 1992 to 2006. Seasonal and decadal changes in chlorophyll a were correlated with nitrate (and uncorrelated with phosphate). However, non-regular variability in chlorophyll a was correlated with phosphate. Consequently, the results demonstrate that nitrate controls the phytoplankton biomass at the inter-annual scale while both nitrate and phosphate do so at a shorter time scale. The Bay of Málaga receives elevated entries of domestic waste waters that release high loads of phosphate compared to nitrate. Our analysis indicates that the expected impact of this pollution on chlorophyll a at the inter-annual scale is reduced in comparison with the effects of atmospheric forcing.     

Community development and modes of phosphorus utilization in a late summer ecosystem in the central Gulf of Finland, the Baltic Sea

The development of a filamentous, nitrogen-fixing cyanobacterial bloom was followed during July–August 1990 in a stratified basin in the central Gulf of Finland, Baltic Sea. Hydrography, dissolved inorganic, particulate and total nutrients, chlorophyll a, alkaline phosphatase activity, ³²PO₄-uptake and phytoplankton species were measured. The study period was characterized by wind-induced mixing events, followed by marked nutrient pulses and plankton community responses. Phosphate uptake was highest throughout the study period in the size fraction dominated by bacteria and picocyanobacteria (< 2 µm) and the proportion of uptake in the size fraction 2–10 µm remained low (2–6%). Higher phosphate turnover times were observed in a community showing signs of enhanced heterotrophic activity. The bloom of filamentous, nitrogen-fixing cyanobacteria Aphanizomenon flos-aquae was promoted by a nutrient pulse with an inorganic nutrient ratio (DIN:DIP) of 15. The results show that the quality, frequency and magnitude of the physically forced nutrient pulses have an important role in determining the relative share of the different modes of phosphorus utilization and hence in determining the cyanobacterial bloom intensity and species composition in the Baltic Sea.     

The influence of upwelling,coastal currents and water temperature on the distribution of the red tide dinoflagellate, <Emphasis Type="Italic">Noctiluca scintillans</Emphasis>, along the east coast of Australia

Quasi-synoptic surveys along the east coast of Australia between 28 and 34°S show that the heterotrophic dinoflagellate, Noctiluca scintillans, occurs along this entire stretch of the coast. Areas of relatively high abundance of Noctiluca were observed downstream of regions predisposed to current-induced upwellings as a consequence of alongshore topographic variations. High-resolution temporal and spatial sampling of upwelling events showed that Noctiluca was abundant (up to 28 cells l^?1) within mature upwelled waters. A high proportion (>80%) of fed Noctiluca cells (cells with prey in their vacuoles) was observed in the mature upwelled waters indicating that the observed increase in abundance of Noctiluca was associated with increased feeding activity. The absolute abundance of Noctiluca in upwelled waters was, however, found to vary from one upwelling location to another and between seasons. In particular, highest abundances of Noctiluca were recorded south of 31.5°S, where the East Australian Current (EAC) characteristically separates from the coast. The high abundances partly arise from southward advection and retention of the Noctiluca cells, and partly from upwelling inshore of the separated EAC driven by cross-shelf boundary layer fluxes. The temperature of the EAC was also found to influence absolute abundances. Surface water temperatures during our summer cruise were anomalously high due to a strong La Niña phase, and up to 4°C warmer than during our spring cruise. We found that the warmer surface water temperatures were associated with relatively lower average abundances of Noctiluca in the near shore zone.     

An extensive Cochlodinium bloom along the western coast of Palawan, Philippines

A massive fish kill and water discoloration were reported off the western coast of Puerto Princesa, Palawan, Philippines in March 2005. Phytoplankton analysis revealed a near monospecific bloom of the dinoflagellate, Cochlodinium polykrikoides, with cell concentrations ranging from 2.5 × 10⁵ to 3.2 × 10⁶ cells per liter. Ground truth data were supplemented by processed satellite images from MODIS Aqua Level 2 data (1 km resolution) from January to April 2005, which revealed high surface chlorophyll-a levels (up to 50 mg/m³) offshore of west and southwest Palawan as early as February 2005. The bloom extended 310 km in length and 80 km in width at its peak in March off the central coast (Puerto Princesa). By April, the bloom declined in intensity, but was still apparent along the northern coast (El Nido). Fluctuations in chlorophyll levels off the western coast of Sabah, Malaysia and Brunei during this time period suggested that the bloom was not limited to the coast of Palawan. Satellite imagery from Sabah in late January revealed a plume of chl-a that is believed to be the source of the C. polykrikoides bloom in Palawan. This plume drifted offshore, advected northward via the basin-wide counterclockwise gyre, and reached nutrient-rich, upwelled waters near Palawan (due to a positive wind stress curl) where the dinoflagellate bloomed and persisted for 2 months from March to April 2005.     

Phytoplankton ecology in the Southern Benguela current. I. Biochemical composition

Investigations on phytoplankton communities in a nearshore region off the Cape Peninsula revealed three types of upwelled water. During active upwelling temperatures were < 10 °C and concentrations of inorganic nutrients were high (Type 1). Maturing upwelled water was characterized by temperatures > 10°C and nitrate concentrations varying between 2 and 15 μg-at. NO₃-N · 1^?1 (Type 2), while aged upwelled water (Type 3) contained low concentrations of nitrate (<2 μg-at. NO₃-N · 1^?1) at temperatures > 10°C. During the summer of 1978–1979 diatoms dominated the communities from October to January but microflagellates were dominant in February and March. In both types of community, low concentrations of ATP, chlorophyll a, protein and carbohydrate were measured in Type 1 water with protein/carbohydrate ratios being > 1. In Type 2 water concentrations of chlorophyll a, ATP and protein were high and the protein/carbohydrate ratio was > 1. Concentrations of chlorophyll a and ATP remained high in Type 3 water but the protein/carbohydrate ratio decreased to < 1 due to an increase in the concentration of acid-soluble glucan. It was concluded that the communities were in an active phase of growth in Type 1 and Type 2 water when adequate nutrients were available, but were in a slow-growing phase in Type 3 water when nitrate concentrations were low. Correlation coefficients, simple linear regressions and stepwise multiple regressions between biochemical and environmental variables confirmed that nitrate was the nutrient most closely related to the biochemical composition of phytoplankton. Using linear regression equations of biochemical variables on glucan it was estimated that chlorophyll a existed in a ratio of ≈ 1: 1 between living phytoplankton and bacteria/detritus, while the percentage of ATP was high in the phytoplankton component of Type 1 water but low in that of Type 2 water. The percentage of protein in detritus was greater than in living phytoplankton, and the carbohydrate content of living phytoplankton increased as the upwelled water matured from Type 1 and Type 2 to Type 3.     

SEA-BIRD OBSERVATIONS OFF SOMALIA

The oceanography of the coastal waters of eastern Somalia was investigated by R.R.S. ‘Discovery’ during August and September 1964. The oceanographic findings are briefly described. Although upwelling was in progress north of 8^oN, plankton, sea-birds and other signs of a high rate of organic production were notably scarce. Previous knowledge of the marine ornithology of the Somali coast is poor and some unpublished notes ot ine late M. E. W. North are given in full. In 1964 both the warm Somali current and the upwelling area between Ras Mabber and Cape Guardafui supported few sea-birds, though they were largely different species. The only area with abundant sea-birds was at the boundary between the cool upwelled water and the warm water spreading from the Gulf of Aden. It is suggested that the former may sink before the final stages of the ecological succession are reached, so that food for sea-birds is scarce. Summaries of the distributions of each species are given and these are compared with previous observations.     

Size-fractionated phytoplankton chlorophyll in an Eastern Mediterranean coastal system (Maliakos Gulf, Greece)

The dynamics of phytoplankton biomass were studied in an Eastern Mediterranean semi-enclosed coastal system (Maliakos Gulf, Aegean Sea), over 1 year. In particular, chlorophyll a (chl a) was fractionated into four size classes: picoplankton (0.2–2 μm), nanoplankton (2–20 μm), microplankton (20–180 μm) and net phytoplankton (>180 μm). The spatial and temporal variation in dissolved inorganic nutrients and particulate organic carbon (POC) were also investigated. The water column was well mixed throughout the year, resulting in no differences between depths for all the measured parameters. Total chl a was highest in the inner part of the gulf and peaked in winter (2.65 μg l^–1). During the phytoplankton bloom, microplankton and net phytoplankton together dominated the autotrophic biomass (67.2–95.0% of total chl a), while in the warmer months the contribution of pico- and nanoplankton was the most significant (77.5–93.4% of total chl a). The small fractions, although showing low chl a concentrations, were important contributors to the POC pool, especially in the outer gulf. No statistically significant correlations were found between any chl a size fraction and inorganic nutrients. For most of the year, phytoplankton was not limited by inorganic nitrogen concentrations. Electronic Publication     

Why no red tide was observed on the West Florida Continental Shelf in 2010

Over the past two decades, the two most anomalous years for water properties on the west Florida continental shelf were 1998 and 2010. In both instances, the shelf was ventilated by relatively cold, nutrient-rich waters of deep ocean origin, which reset the background state underlying shelf ecology. The ventilation in both of these years derived from prolonged interactions of the Gulf of Mexico Loop Current with the shelf slope near the Dry Tortugas located on the southwest corner of the shelf. By contacting relatively shallow isobaths, the boundary current interactions there set the entire shelf into motion, facilitating upwelling across the shelf break, even to DeSoto Canyon some 500 km away, and then across the shelf to the near shore. Such prolonged and intense upwelling of nutrient-rich water in 2010 contrasted with the more typically occurring locally wind driven upwelling conditions, whereby waters upwelled at the near shore are from the inner shelf, versus the deep ocean. Thus not all upwelling scenarios have similar consequences. Whereas the typical wind driven upwelling scenario is necessary for Karenia brevis red tide blooms to manifest along the coastline, the rarer, deep ocean induced upwelling scenario (as occurred in 1998 and particularly in 2010) acts to suppress K. brevis red tides because of the elevated inorganic nutrient conditions that they facilitate. Hence, minimal cell counts above background were observed in 1998, and no cell counts above background were observed in 2010. We conclude that the lack of red tide along the west coast of Florida in 2010 was due to anomalously large and protracted upwelling of nutrient-rich waters of deep ocean origin caused by Loop Current and eddy interactions with the shelf slope.     

Influence of upwelling on the chaetognath community along the Southeastern Arabian Sea

Community structure and distribution of chaetognaths were investigated along the upwelled and non-upwelled waters of Southeastern Arabian Sea (SEAS) from the coastal, shelf and open ocean regions. With the onset of monsoon, intense upwelling along the southern part of SEAS (8° 28′ N) and a weak coastal upwelling along the northern counterpart (15° 30′ N) was evident. Zooplankton biomass was observed to be high in the upwelled waters with the dominance of copepods. Chaetognaths were also observed in significant numbers all along the SEAS, however maximum numerical abundance was observed in the southern upwelled waters. Chaetognaths belonging to 10 genera were identified of which genus Flaccisagitta (54%) made the most dominant group along the entire study area followed, in order of abundance, by Serratosagitta (20%), Mesosagitta (18.2%), Sagitta (12.3%), Ferosagitta (11%) and Krohnitta (6.4%). Flaccisagitta were observed to be abundant in the upwelled waters along with Pterosagitta, Serratosagitta, Sagitta, Krohnitta and Ferosagitta whereas genus Mesosagitta dominated the non-upwelled waters of northern transects.

     

Temporal and spatial variability of chlorophyll <Emphasis Type="Italic">a</Emphasis> concentration in Lake Taihu using MODIS time-series data

In order to predict the distribution of chlorophyll a synoptically in Lake Taihu from 2006 to 2008, a common empirical algorithm was developed to relate time series chlorophyll a concentrations in the lake to reflectance derived as a function of band 2 MODIS data (r ² = 0.907, n = 145) using time series from 2005. The empirical model was further validated with chlorophyll a data from a 2008 to 2009 dataset, with RMSE < 7.48 μg l⁻¹ and r ² = 0.978. The seasonal and inter-annual variability of the surface chlorophyll a concentration from 2006 to 2008 was then examined using Empirical Orthogonal Function (EOF) analysis. The results revealed that the first four modes were significant, explaining 54.0% of the total chlorophyll a variance, and indicated that during the summer, algal blooms always occur in the northern bays, Meiliang Bay and Gonghu Bay, while they occur along the southwestern lakeshore during early summer, fall, and even early winter. The inter-annual variance analysis showed that the duration of algal blooms was from April to December of 2007, which was different from the bloom periods in 2006 and 2008. The results of EOF analysis show its potential for long-term integrated lake monitoring, not only in Lake Taihu but also in other large lakes threatened by accelerating eutrophication.     

Changes in style and intensity of production in the Southeastern Atlantic over the last 70,000 yr

Accomplishing reliable paleo-reconstructions of productivity and upwelling conditions in eastern boundary current systems requires the use of cores collected in a basin-wide spatial pattern. Based on diatom assemblage analysis and the concentration and the bulk biogenic components of three gravity cores recovered from the Benguela Upwelling System (BUS) between 19° and 25°S, I describe rapid paleoceanographic changes that occurred during the last 70 ka B.P. in the southeastern Atlantic. The pattern of biogenic production and accumulation differs to varying degrees among the three core sites along the SW African coast. The highest sedimentation and accumulation rates at 25°S off Lüderitz conform with the present-day, well-known pattern of highest productivity and most intense coastal upwelling. Highest diatom values at 25°S during MIS3 points to more intense upwelling due to the combination of strong seaward-extending upwelling filaments, shoaling of the upwelled water, and the influence of silicate-rich waters of Antarctic origin. Productivity decreased along the central BUS throughout MIS2, when the siliceous–calcareous productivity regime shifted toward a system dominated by calcareous producers. Although intensity and strength of winds created adequate conditions for upwelling during MIS2, diatom production decreased. The complete replacement of the upwelling-associated diatom flora by a non-upwelling-related diatom community during MIS1 reflects weakened upwelling, weakened seaward extension of the upwelling filaments, and dominance of warmer surface waters. Combining changes in the composition of the diatom assemblage and variations of the bulk biogenic components allows for reliable reconstruction of paleoproductivity and upwelling changes for the SE Atlantic during the last 70 ka B.P.     

Hydrography and characteristics of the phytoplankton in shelf and oceanic waters off southeastern Brazil during winter (July/August 1982) and summer (February/March 1984)

The physical and chemical environment, and the phytoplankton primary production of southeastern Brazil were studied in relation to the general oceanographic structure during two research cruises (winter and summer). In each cruise, a total of 91 stations were occupied. Data were collected on the spatial distribution of nutrients, phytoplankton biomass and photosynthetic capacity over the coastal, shelf and oceanic areas off São Paulo, Paraná and Santa Catarina States.During wintertime, the mixing processes between tropical warm waters of the Brazil Current and subantarctic waters of the Malvinas Current formed strong environmental gradients. The drainings of Rio de La Plata and Lagoa dos Patos are transported northwards by coastal currents, enriching the shelf waters off Santa Catarina State with inorganic nutrients and consequently increasing the chlorophyll a to the highest concentrations (> 3.5 mg m ^–3) measured during the two cruises. In slope waters chlorophyll values were always low (0.05–0.45 mg m ^–3). The chlorophyll within the euphotic layer varied from 8.8–36.7 and 1.2–18.5 mg m^–2 during winter and summer, respectively.The surface photosynthetic rates during winter and summer cruises ranged respectively from 0.21–9.17 and 0.66–19.60 mgC/mgChl.a/h. The mean rates were higher in nearshore waters and decreased seaward.The thermal structure of the water column affected the vertical distribution of chlorophyll a and photosynthesis within the euphotic zone; During unstratified periods (winter) they were uniformly distributed but the occurrence of subsurface peaks of chlorophyll and strong photosynthetic inhibition of low light adapted cells in deeper layers are associated to the seasonal thermocline. Occasionally, upwelling of deep waters from shelf break enriched the deeper euphotic layers in offshore areas. Intensive upwelling was observed off Paranagua Bay (Parana State) and the mechanisms of its formation are discussed.     

Estuary–ocean connectivity: fast physics,slow biology

Estuaries are connected to both land and ocean so their physical, chemical, and biological dynamics are influenced by climate patterns over watersheds and ocean basins. We explored climate‐driven oceanic variability as a source of estuarine variability by comparing monthly time series of temperature and chlorophyll‐a inside San Francisco Bay with those in adjacent shelf waters of the California Current System (CCS) that are strongly responsive to wind‐driven upwelling. Monthly temperature fluctuations inside and outside the Bay were synchronous, but their correlations weakened with distance from the ocean. These results illustrate how variability of coastal water temperature (and associated properties such as nitrate and oxygen) propagates into estuaries through fast water exchanges that dissipate along the estuary. Unexpectedly, there was no correlation between monthly chlorophyll‐a variability inside and outside the Bay. However, at the annual scale Bay chlorophyll‐a was significantly correlated with the Spring Transition Index (STI) that sets biological production supporting fish recruitment in the CCS. Wind forcing of the CCS shifted in the late 1990s when the STI advanced 40 days. This shift was followed, with lags of 1–3 years, by 3‐ to 19‐fold increased abundances of five ocean‐produced demersal fish and crustaceans and 2.5‐fold increase of summer chlorophyll‐a in the Bay. These changes reflect a slow biological process of estuary–ocean connectivity operating through the immigration of fish and crustaceans that prey on bivalves, reduce their grazing pressure, and allow phytoplankton biomass to build. We identified clear signals of climate‐mediated oceanic variability in this estuary and discovered that the response patterns vary with the process of connectivity and the timescale of ocean variability. This result has important implications for managing nutrient inputs to estuaries connected to upwelling systems, and for assessing their responses to changing patterns of upwelling timing and intensity as the planet continues to warm.     

Response of Tetraselmis suecica to nutrient and grazer manipulation

Three methods of algal quantification (direct cell counts, chlorophyll a extraction, in vivo fluorescence) were used to evaluate the response of the unicellular green flagellate Tetraselmis suecica to nutrients and grazers. Nutrient enrichment enhanced total cell counts, chlorophyll a concentration and in vivo and DCMU-fluorescence. Photosynthetic efficiency was reduced in the complete F2 medium as indicated by the high level of in vivo fluorescence, whereas photosynthetic efficiency was increased by the introduction of mussels to the F2 medium. The addition of mussels significantly increased the proportion of non-motile cells, but did not reduce the total cell count. The effect of mussel grazing on algae could be underestimated if only total cells were counted or only the chlorophyll a concentration was measured. The results indicate that these three methods measure different properties of an algal culture and are complementary to each other in assessing the quality and quantity of an algal population. Direct algal counting offers a reliable numerical assessment for cell population abundance. Chlorophyll a concentration was closely correlated to the total cell count. In the presence of mussels, in vivo fluorescence did not correlate with either algal cell counts or chlorophyll a concentration, indicating that the measurement of in vivo fluorescence may be misleading for estimating algal abundance under different culture conditions. This revised version was published online in August 2006 with corrections to the Cover Date.     

Temporal variability in egg production rates of Acartia tonsa Dana in Long Island Sound

The relationship between week-by-week variations in the in situ egg production rates of Acartia tonsa Dana and changes in chlorophyll concentration in several size fractions was investigated by incubating adult females in natural sea water for 24-h periods. Our results indicate that the egg production of A. tonsa in Long Island Sound was better related to the 10 μm chlorophyll size fraction than to the total chlorophyll concentration. The < 10 μm size fraction comprised the greatest percentage of the chlorophyll during July and August when the water column was stratified. Egg production rates were lowest (8.7 eggs · female⁻¹ · day⁻¹) in early August when less than 0.5 μg chlorophyll 1 ⁻¹ was observed in the 10 μm chlorophyll a size fraction. Following destratification in late August, the “fall” diatom bloom occurred and egg production rates increased to the maximum observed rate of 56.6 eggs · female⁻¹ · day⁻¹. At this time, the concentration of the 10μm chlorophyll size fraction was 5.5 μg 1⁻¹. Maximum egg production rates were observed at chlorophyll concentrations as low as 0.8 μg 1⁻¹ in the 10 μm size fraction.