Comparison of the sedimentation of a diatom spring bloom and of a subsurface chlorophyll maximum

The seasonal pattern of sedimentation was determined over a 8-mo investigation period covering the productive season at a permanent station in the Southern Kattegat (Denmark) in 1990. The phytoplankton succession was characterised by a 4-mo long subsurface maximum associated with the pycnocline which was entirely dominated by the dinoflagellate Gyrodinium aureolum. The bulk sedimentation of organic matter took place during this period and accounted for >60% of the annual particulate organic carbon (POC) and particulate organic nitrogen (PON) sedimentation. The spring bloom period contributed 60% of the sedimentation of intact phytoplankton cells, but only 20% of the POC and PON sedimentation. A minor fraction of the sedimenting matter from the subsurface phytoplankton maximum consisted of intact phytoplankton (<20%), suggesting that the phytoplankton was processed by heterotrophs and that it was mainly products from this activity which contributed to thevertical flux of organic matter. The variation in oxygen concentration below the pycnocline coincided with the pattern of sedimentation with a delay of 3 to 6 wk.     

An approach for particle sinking velocity measurements in the 3–400?μm size range and considerations on the effect of temperature on sinking rates

The flux of organic particles below the mixed layer is one major pathway of carbon from the surface into the deep ocean. The magnitude of this export flux depends on two major processes—remineralization rates and sinking velocities. Here, we present an efficient method to measure sinking velocities of particles in the size range from approximately 3–400?μm by means of video microscopy (FlowCAM^?). The method allows rapid measurement and automated analysis of mixed samples and was tested with polystyrene beads, different phytoplankton species, and sediment trap material. Sinking velocities of polystyrene beads were close to theoretical values calculated from Stokes’ Law. Sinking velocities of the investigated phytoplankton species were in reasonable agreement with published literature values and sinking velocities of material collected in sediment trap increased with particle size. Temperature had a strong effect on sinking velocities due to its influence on seawater viscosity and density. An increase in 9?°C led to a measured increase in sinking velocities of ~40?%. According to this temperature effect, an average temperature increase in 2?°C as projected for the sea surface by the end of this century could increase sinking velocities by about 6?% which might have feedbacks on carbon export into the deep ocean.     

Sedimentation and benthic mineralization of organic detritus in a Norwegian fjord

The supply of particulate material to the sea-bed as well as the oxygen consumption and the redox potential of the sea-bed were measured during a one-year period (1979/1980) at 60 and 90 m depth in the inner part of a west Norwegian fjord, Fanafjorden. At both sites, uniform sedimentation rates of total particulate material (825 and 885 g m^-2 yr^-1, respectively) and particulate inorganic material (576 and 616 g m^-2 yr^-1, respectively) were found. The sedimentation rates of particulate organic carbon (96 and 107 g m^-2 yr^-1, respectively) and particulate organic nitrogen (10 and 12 g m^-2 yr^-1, respectively) were low in winter, higher in summer and autumn, with maxima in May/June, reflecting similar maxima in the phytoplankton biomass in the area, with 6 to 8 wk delay. The oxygen consumption of the sea-floor was lowest in winter/spring and highest in summer. Thirtytwo and 38 g C m^-2 yr^-1 (respiration quotient=0.85) were metabolized by the sediment at 60 and 90 m, respectively. The simultaneous measurements of sedimentation rates and sediment oxygen uptake throughout a whole year demonstrated that the benthic mineralization is governed by the sedimentation over a longer time-scale, but that seasonal imbalances do occur. A box-model of the flux of particulate organic carbon to the sediment surface is presented, and includes the relevant processes and some quantitative estimates.     

Mass encystment and sinking of dinoflagellates during a spring bloom

The decline of a spring bloom dominated by dinoflagellates and the mass sedimentation of dinoflagellate cysts was documented in a coastal area of the northern Baltic Sea, SW Finland in 1983. The exceptionally large spring phytoplankton bloom was observed in early May. After depletion of nitrate phytoplankton biomass declined rapidly. The bloom was followed by intense sedimentation of spherical cysts and of organic matter at the end of May. These cysts were presumably hypnozygotes of Peridinium hangoei Schiller. Sedimentation of dinoflagellate cysts was estimated to correspond to ca. 45% of the maximum sedimentation of particulate organic carbon at this time, although most of the dinoflagellate biomass disintegrated already in the water column and was deposited as organic detritus or washed away by advection. It is concluded that the life cycle strategies of the dominant vernal phytoplankton species have a major impact on the sedimentation of the spring bloom.     

Bacterioplankton in the coastal euphotic zone: Distribution,activity and possible relationships with phytoplankton

Bacterioplankton were studied in the euphotic zone of the Southern California Bight, USA, with special attention to biological factors affecting bacterial distribution and activity. Measurements were made of bacterial abundance, thymidine incorporation into acid insoluble material, primary production (particulate and dissolved), chlorophyll, phaeopigments, total microbial ATP, particulate organic carbon and nitrogen, dissolved organic carbon, dissolved primary amines, and glucose and thymidine turnover rates. The data were analyzed by pairwise rank correlations with significance tested at the P<.005 level. Bacterial abundance and thymidine incorporation both declined progressively with increasing distance from shore (to 100 km); similar trends occurred for the phytoplankton, with several stations having subsurface maxima. Bacterial abundance, thymidine incorporation, and thymidine and glucose turnover rates were all significantly correlated to each other, suggesting they are comparable as relative measures of bacterial activity. Thymidine incorporation per cell, an indicator of specific growth rate, was not correlated to bacterial abundance, suggesting density independent specific growth rates. Bacterioplankton growth rate was evidently influenced more by the standing stock of phytoplankton than by the primary production of the phytoplankton. Thus, bacterial growth may possibly be stimulated by leakage of dissolved organic matter not so much from healthy photosynthesizing cells as from phytoplankton being disrupted and incompletely digested during predation by the zooplankton and nekton.     

Sedimentation of organic detritus in Lochs Etive and Creran,Argyll, Scotland

The rates of sedimentation of organic detritus were measured at 3 stations in two Scottish sea lochs, Loch Etive and Loch Creran, using sedimentation jars exposed at various depths. Details are given of the seasonal and depth distribution of sedimenting material, and its composition for a 1-year period. Differences in the pattern of sedimenting material collected at different depths and in the seasonal patterns of sedimentation at the different stations suggested that, in each case there were differences in the relative importance of detritus from various sources. At all stations, phytoplankton production made a relatively small contribution to the total detritus collected, either directly as dead cells, or indirectly as the faeces of zooplankton organisms. Near the head of Loch Etive there were contributions by filamentous algae and Enteromorpha sp., but a major source of detritus was terrestrial debris, mainly carried into the loch in the waters of the River Etive. In the lower basin of Loch Etive, terrestrial detritus also contributed to the total sedimenting near the surface, but at greater depths much of the material collected in the sedimentation jars probably resulted from short-term resuspension and re-deposition of bottom material, reflecting a net transport of fine sediment from the shallower to the deeper areas of the loch. Secondarily resuspended material was also a major source of material collected in the jars exposed in Loch Creran.     

Benthic response to sedimentation of a spring phytoplankton bloom: Process and budget

The response of benthos to sedimentation of the spring phytoplankton bloom in the Kiel Bight (Western Baltic Sea) is described in terms of biomass (ATP) and activity (heat production and ETS-activity). Input of the bloom (11.5 g C m^-2) over a period from March 25 to April 19, 1980 to the sediment surface was in the form of cells and fresh phytodetritus as indicated by low C/N ratios (7) and high energy charge values (0.78). Benthic microbial activity was immediately stimulated by this input as heat production doubled and the activity of ETS tripled over winter values within 12 d in the absence of a significant increase in ambient temperature. A comparison of the two activity parameters suggests that anaerobic metabolism is more important during the winter (February and March) than after input of the bloom. Meiofauna was not able to take part in the first activity outburst. Benthic ATP-biomass (excluding macrofauna) doubled in late April due to microbial production, and doubled again in early May when meiofauna started reproductive activity. For macrofauna a general statement was not possible, although the sediment surface feeder Macoma baltica commenced a build up of glycogen and lipid resources immediately following bloom input whereas Nephtys ciliata, feeding on sediment and small macrofauna, showed a less pronounced and delayed effect from this input. An energy budget based on heat production measurements was calculated. A daily heat loss of the benthic community of 21.7 KJ m^-2 d^-1 (35.5 KJ m^-2 d^-1) was found, when a depth of 3 cm sediment (5 cm) was assumed. Heat production of macrofauna contributed less than 5% of this activity. The input of the bloom was burned within 21 (13) d. Preliminary estimations for an annual budget suggest that the vertical transport of particulate organic matter via sedimentation can only explain 25% (15%) of the benthic activity in the shallow water ecosystem of the Kiel Bight. This indicates the presence of other sources of organic carbon such as benthic primary production or other transport processes providing carbon to the sediments.Publication No. 384 of the Joint Research Program of Kiel University (Sonderforschungsbereich 95)     

Effects of rising temperature on pelagic biogeochemistry in mesocosm systems: a comparative analysis of the AQUASHIFT Kiel experiments

A comparative analysis of data, obtained during four indoor-mesocosm experiments with natural spring plankton communities from the Baltic Sea, was conducted to investigate whether biogeochemical cycling is affected by an increase in water temperature of up to 6?°C above present-day conditions. In all experiments, warming stimulated in particular heterotrophic bacterial processes and had an accelerating effect on the temporal development of phytoplankton blooms. This was also mirrored in the build-up and partitioning of organic matter between particulate and dissolved phases. Thus, warming increased both the magnitude and rate of dissolved organic carbon (DOC) build-up, whereas the accumulation of particulate organic carbon (POC) and phosphorus (POP) decreased with rising temperature. In concert, the observed temperature-mediated changes in biogeochemical components suggest strong shifts in the functioning of marine pelagic food webs and the ocean’s biological carbon pump, hence providing potential feedback mechanisms to Earth’s climate system.     

Organic detritus of a tropical estuary

Organic detritus of the Cochin Backwater (India) is largely composed of fine silt and sand particles around which organic matter adheres and forms aggregates. In addition to plankton, large quantities of benthic algae, rooted plants, animal matter, suspended soft mud and the material brought down by the rivers and land runoff constitute the main sources of detritus. Detritus sedimentation in the estuary attains its maximum from April to June. Detritus forms a major portion of seston, while phytoplankton productivity constitutes 0.1 to 1.0% of settled detritus. Detrital pigments include degraded chlorophyll (phaeophytin), which has a marked seasonal variation; detrital carbon, phosphorus and nitrogen show little change during the year. The caloric value of detritus, calculated from protein, carbohydrate and lipid fractions and also from total carbon, indicates that sedimented detritus does not have a high nutritional value. However, being a readily available material, its entry into the food chain seems to increase the efficiency of energy transfer from one trophic level to another.     

Mechanisms of production and fate of organic phosphorus in the northern Adriatic Sea

In the period from 1980 to 1984 organic phosphorus, nutrients, primary production rates (¹⁴C), chlorophyll a (chl a) standing crops, and basic oceanographic parameters were measured during 23 cruises at six stations in the open waters of the northern Adriatic Sea. These waters are significantly influenced by polluted Po River discharge. Organic phosphorus was correlated with several parameters which characterize phytoplankton activity and organic matter decomposition processes. In the late winter-spring period, organic phosphorus is produced during phytoplankton blooms. It is hypothesized that microzooplankton grazing is the main factor increasing the organic phosphorus concentrations in summer (up to 1.1 mol 1^-1). Fall and winter had much lower values (below 0.3 mol 1^-1) due to remineralization processes and an increased water mass exchange between the northern and central Adriatic regions. The direct contribution of organic phosphorus by freshwater discharge was not found to be significant. The higher organic phosphorus concentrations that can occur in low salinity waters are most likely due to their increased capability to support primary production.     

Sea ice microbial production supports Ross Sea benthic communities: influence of a small but stable subsidy

Diversity in guilds of primary producers enhances temporal stability in provision of organic matter to consumers. In the Antarctic ecosystem, where temporal variability in phytoplankton production is high, sea ice contains a diatom and microbial community (SIMCO) that represents a pool of organic matter that is seasonally more consistent, although of relatively small magnitude. The fate of organic material produced by SIMCO in Antarctica is largely unknown but may represent an important link between sea ice dynamics and secondary production in nearshore food webs. We used whole tissue and compound-specific stable isotope analysis of consumers to test whether the sea ice microbial community is an important source of organic matter supporting nearshore communities in the Ross Sea. We found distinct gradients in delta13C and delta15N of SIMCO corresponding to differences in inorganic carbon and nitrogen acquisition among sites with different sea ice extent and persistence. Mass balance analysis of a suite of consumers demonstrated large fluxes of SIMCO into the nearshore food web, ranging from 5% to 100% of organic matter supplied to benthic species, and 0-10% of organic matter to upper water column or pelagic inhabitants. A delta13C analysis of nine fatty acids including two key biomarkers for diatoms, eicosapentaenoic acid (EPA, 20:5omega3), and docosahexaenoic acid (DHA, 22:6omega3), confirmed these patterns. We observed clear patterns in delta13C of fatty acids that are enriched in 13C for species that acquire a large fraction of their nutrition from SIMCO. These data demonstrate the key role of SIMCO in ecosystem functioning in Antarctica and strong linkages between sea ice extent and nearshore secondary productivity. While SIMCO provides a stabilizing subsidy of organic matter, changes to sea ice coverage associated with climate change would directly affect secondary production and stability of benthic food webs in Antarctica.     

Meiobenthos distribution pattern in the tropical East Atlantic: indication for fractionated sedimentation of organic matter to the sea floor?

To test the extent to which sea surface productivity governs the distribution pattern of benthic organisms, meiobenthic standing stocks were investigated on the shelf, continental margin and the adjacent abyssal plains off the western African coast between Guinea (10°N) and Angola (18°S). The area of investigation is characterized by gradients in surface productivity due to spatially and seasonally varying coastal upwelling. Reflecting the dependency of deep-sea organisms on organic matter input from the euphotic zone, similar gradients ought to be expected within the benthos. Meiofaunal abundances and biomasses (including Foraminifera) from a total of 57 stations along 13 transects across the continental margin showed a fairly close correlation with sediment-bound chloroplastic pigment concentrations, indicating the sedimentation of particulate organic matter from phytoplankton production. However, certain discrepancies in faunal and pigment distribution patterns were found in regions apart from the centres of enhanced primary␣productivity, i.e. apart from the upwelling centres: whereas pigment concentrations in the sediments were still comparably high, meiofaunal numbers in those peripheral areas were generally lower. It is suggested that smaller/lighter phytodetritial matter, transported over long distances by subsurface currents and exposed to ongoing microbial degradation during its passage, probably does not have the same energy content as the relatively fast-sinking, larger phytodetritus aggregates (“marine snow”), which are found in centres of enhanced primary productivity and support extensive benthic stocks. Thus, meiobenthic abundances in relation to sediment-bound pigment concentrations on the western African continental margin may indicate fractionated sedimentation of organic matter to the sea floor. Received: 28 May 1997 / Accepted: 14 July 1997     

Trophic structure of deep-sea macrobenthos

The effect of the trophic factor on large-scale distributional patterns of deep-sea macrobenthos inhabiting the floor of the World Ocean has been studied. Two hundred and twenty-eight bottom trawl samples collected by Soviet research vessels in the Pacific and Indian Oceans at depths ranging from 3000 to 6000 m were analyzed. For each sample, the weight of animals with a similar mode of feeding was determined to find the weight ratio of representatives of three main trophic groups, i.e., deposit-feeders, suspension-feeders and carnivores. These data, indicating predominance of alternate groups as well as data on their geographic distribution, were related to feeding conditions which depend on: (1) rates of sedimentation, (2) nature of sediments, (3) content of organic carbon, (4) degree of transformation of organic matter on and within sediments, and, when available, (5) data on redox potential, biochemical oxygen consumption, and state of heterotrophic microflora in the sediments. In dealing with the feeding conditions of deep-sea macrobenthos in the Atlantic Ocean, biological characteristics were deduced from literature data on the composition of sediments, their redox potential and organic carbon content. As a result of this research, eutrophic and oligotrophic regions on the floor of the World Ocean have been distinguished and their boundaries defined. Eutrophic regions lie within areas with high biological productivity of surface-water layers, and cover the peripheral and equatorial parts of the oceans; they are characterized by quantities of labile (digestible) organic matter within sediments which are sufficient for deposit-feeders to predominate in eutrophic regions everywhere, except on considerable bottom elevations. Oligotrophic regions are confined to open areas of the oceans lying beyond the equatorial belt; they are characterized by very low rates of sedimentation and, consequently, by scarce quantities of deposited organic matter. Here, suspension-feeders predominate, although their population density is very low.     

RETRACTED ARTICLE: Removal of lead and cadmium ions from aqueous solutions using the macroalga Caulerpa racemosa

Sediment bulk parameters and fatty acid biomarkers were used to investigate the relative contribution of major sources of particulate organic matter during upwelling and non-upwelling conditions, at organic enriched sites on the south-eastern Brazilian coast. The degradation state of the organic material and its implications for benthic food webs were also evaluated. Temperature and salinity values indicate the intrusion of the South Atlantic Central Water in spring with a strong influence at station 4S. C:N ratios and fatty acid biomarkers suggest that sedimentary particulate organic matter is mainly autochthonous and originated from phytoplankton, zooplankton and bacteria, with a minor terrestrial contribution. Short-chain saturated fatty acids predominated, indicating the prevalence of partially degraded detritus. An exception was station 4S, where polyunsaturated fatty acids dominated, indicating the input of labile organic matter linked to upwelling of the South Atlantic Central Water. Fatty acid concentrations and the organic carbon content of the sediments suggest that food quantity is not a limiting factor for benthic fauna. Despite the high organic background of the sediments, the sporadic inputs of labile organic matter associated with South Atlantic Central Water intrusions may produce an important impact on benthic fauna and on the biogeochemistry of the sediments.     

Phytoplankton carbon dynamics during a winter-spring diatom bloom in an enclosed marine ecosystem: primary production,biomass and loss rates

Phytoplankton production, standing crop, and loss processes (respiration, sedimentation, grazing by zooplankton, and excretion) were measured on a daily basis during the growth, dormancy and decline of a winter-spring diatom bloom in a large-scale (13 m³) marine mesocosm in 1987. Carbonspecific rates of production and biomass change were highly correlated whereas production and loss rates were unrelated over the experimental period when the significant changes in algal biomass characteristic of phytoplankton blooms were occurring. The observed decline in diatom growth rates was caused by nutrient limitation. Daily phytoplankton production rates calculated from the phytoplankton continuity equation were in excellent agreement with rates independently determined using standard ¹⁴C techniques. A carbon budget for the winter bloom indicated that 82.4% of the net daytime primary production was accounted for by measured loss processes, 1.3% was present as standing crop at the end of the experiment, and 16.3% was unexplained. Losses via sedimentation (44.8%) and nighttime phytoplankton respiration (24.1%) predominated, while losses due to zooplankton grazing (10.7%) and nighttime phytoplankton excretion (2.8%) were of lesser importance. A model simulating daily phytoplankton biomass was developed to demonstrate the relative importance of the individual loss processes.     

Seasonal Fluctuations in the Nutritional Value of Particulate Organic Matter in A Lagoon

Water samples were collected on a fortnightly basis in the lagoon of S. Gilla (Sardinia, Mediterranean Sea) in order to study seasonal nutritional fluctuations of particulate organic matter. the lagoon is characterized by high quantities of suspended matter throughout the year. Thermohaline conditions had no effect on particulate matter quantity and composition, but the quantity as well as quality of suspended particles was drastically affected by the wind, the major effecter of sediment resuspension. As a result of sediment resuspension, seston was always richer in inorganic fraction. However, throughout the year of investigation, most particulate organic carbon was quite appealing for filter feeding communities, although the best POM quality was available during phytoplankton blooming. the phytoplankton pool of suspended matter was just a small fraction of the bulk, accounting for only 13% on average of particulate organic carbon. in terms of energy available in the seston, the highest amount was stored in organic matter heterotrophic fraction, whilst the smallest was to be found in living phytoplankton.     

Sedimentation of particulate matter during a phytoplankton spring bloom in relation to the hydrographical regime

Data presented and discussed here were collected continuously during April/May 1975 in the Bornholm Basin of the Baltic Sea. Sedimentation rates of particulate matter were recorded with 5 multisample sediment traps from different depths in the water column at 2 positions 170 km apart. Current meter data collected during the same period and depths indicated that the positions remained hydrographically distinct during the investigation. Particulate matter from the euphotic zone including diatom cells formed the bulk of the material collected by all traps. This flux of organic particles to the bottom was unimpeded by the strong density stratification present in the water column. The upper traps always collected less material than lower ones. This paradox has been ascribed to diminishing current speeds with depth, concomitant with an increase in sinking rates of phytoplankton and phytodetritus. Both factors influence the sampling efficiency of sediment traps, which are thought to have underestimated actual sedimentation rates here. A time lag of 2 to 3 weeks in bloom development seemed responsible for the characteristic differences between the two positions. The phase of major sedimentation at one position covered about 18 days, and a distinct sequence in the composition of the material collected by the 6 glasses of each trap indicated phases of a progressively deteriorating phytoplankton population in the water column contributing the particulate material. A total of 6.2 g C m^-2 in 34 days was recorded at this station. Apart from a trap situated in an oxygen deficient layer which collected 0.44 g C m^-2 of zooplankton corpses, zooplankton mortality was overestimated by the traps. Large-scale sedimencation of fresh organic matter produced by the spring bloom is probably a regular feature in areas with low over-wintering zooplankton populations and, as such, possibly has a direct stimulatory effect on growth and reproduction of the benthos.Contribution No. 185 of the Joint Research Programme 95, Kiel University.     

Hydrographic and biological aspects of algal bloom in the Adriatic Sea in 1988

The interaction of hydrological, chemical and biological factors in a defined time may cause an excess bloom of phytoplankton in an ecosystem, which can persist over a long period or occur from time to time.

This phenomenon has been recorded from the northern Adriatic and coastal enclosed basins along the eastern Adriatic coast (Ka?tela Bay, Split) for a long time now.

During 1988 this phenomenon of increased production was recorded from almost the entire northern and middle Adriatic with some traces even in its southern part. Some preliminary results for that period point to the fact that this was caused very likely by exceptionally warm and dry weather, with no significant precipitations and wind. Such conditions affect horizontal and vertical stratification of water masses.

High photosynthetic radiation, increased quantities of alochthonous organic matter, either in the form of particulate or dissolved organic matter, either in the form of particulate or dissolved organic carbon (POC or DOC), influx of nutrients (via rivers, municipal sewage or upwelling) are the main causes of sudden bloom and rapid reproduction rate of phytoplankton species (Diatoms) to the large quantities to which the pollution of the entire coastal area is due.     

Carbon budget for the spring bloom in Auke Bay,Alaska

This paper describes a carbon budget for the spring phytoplankton bloom in Auke Bay, a subarctic bay in southeastern Alaska. The budget was constructed using semiweekly data on carbon production, particulate carbon in the water column, and cumulative sedimentation of carbon, chlorophyll a, and pheopigments. From these measured parameters, seasonal carbon consumption, utilization, and import/export terms were derived. The chlorophyll and pheopigment data were used to partition carbon sinking out of the photic zone between phytoplankton cells and fecal material. The difference between total carbon production and carbon available for consumption was attributed primarily to carbon import/export related to advection of water masses into and out of the bay. Separate budgets were developed for each of five sampling years (1985–1989). An average of 130±16 g C/m² were produced by phytoplankton during each spring. Our model suggests that an average of 70% of this carbon was available for consumption by grazers within the bay; the remaining 30% is assumed to have been exported from the bay by advective transport. Of the available (non-exported) carbon, an average of 55% was consumed by grazers, 34% sank out of the photic zone in the form of uneaten algae, and about 11% remained at the end of the sampling period in the form of phytoplankton standing stocks. Overall, about 27% of the carbon produced each spring in Auke Bay (35 gC/m²) was used for growth and respiration by first-order consumers within the bay.     

Picophytoplankton responses to changing nutrient and light regimes during a bloom

The spring bloom in seasonally stratified seas is often characterized by a rapid increase in photosynthetic biomass. To clarify how the combined effects of nutrient and light availability influence phytoplankton composition in the oligotrophic Gulf of Aqaba, Red Sea, phytoplankton growth and acclimation responses to various nutrient and light regimes were recorded in three independent bioassays and during a naturally-occurring bloom. We show that picoeukaryotes and Synechococcus maintained a “bloomer” growth strategy, which allowed them to grow quickly when nutrient and light limitation were reversed. During the bloom picoeukaryotes and Synechococcus appeared to have higher P requirements relative to N, and were responsible for the majority of photosynthetic biomass accumulation. Following stratification events, populations limited by light showed rapid photoacclimation (based on analysis of cellular fluorescence levels and photosystem II photosynthetic efficiency) and community composition shifts without substantial changes in photosynthetic biomass. The traditional interpretation of “bloom” dynamics (i.e., as an increase in photosynthetic biomass) may therefore be confined to the upper euphotic zone where light is not limiting, while other acclimation processes are more ecologically relevant at depth. Characterizing acclimation processes and growth strategies is important if we are to clarify mechanisms that underlie productivity in oligotrophic regions, which account for approximately half of the global primary production in the ocean. This information is also important for predicting how phytoplankton may respond to global warming-induced oligotrophic ocean expansion.