Plankton Community Production Research Articles

Long-term dynamics of forage base and food supply for nekton in the upper epipelagic layer of the western Bering Sea. Part 1. Composition and abundance of zooplankton and small-sized nekton

An updated concept for the state, dynamics, and production of plankton communities in the upper epipelagic layer of the western Bering Sea is presented based on the timeseries for 1986–2020. The zooplankton biomass in summer exceeded the biomass in fall season in 1.3–2.1 times for the layer of 0–50 m and in 1.1–1.8 times for the layer of 0–200 m, mostly because of decreasing abundance of copepods and chaetognaths that was not compensated by slight increase of the euphausiids and amphipods biomass. Interannual variations were higher and reached 2–3 times and 4–5 times, respectively. Abnormal blooming of certain ecological groups of zooplankton (either warm-water or cold-water) occurred in the anomalous years. Species structure of zooplankton community varied in dependence on oceanographic conditions, generally toward higher abundance in warmer environments. In spite of considerable impact of thermal regime, this dependence was not close and even was absent in some cases that indicated a complex organization of zooplankton communities subjected to influence of many environmental factors. Mean total biomass of large-sized zooplankton and micronekton (prey for large-sized nekton) in the upper epipelagic layer of the western Bering Sea is estimated as 41 . 106 t in summer and 24 . 106 t in fall season, its total production as 101 . 106 t and 67 . 106 t, respectively. In summer, production of non-predatory zooplankton (phyto- and euryphages) prevailed over the predatory zooplankton production, with exception of 2009 and 2013. On the contrary, production of zoophages prevailed in autumn due to successive seasonal changes in the epipelagic plankton communities. These modern data on biomass and production of the zooplankton communities indicate significant reserves of food resources for fish and squids in the deep-water Commander Basin, western part of the Aleutian Basin, and in the area at Cape Navarin.

Factors controlling plankton community production, export flux, and particulate matter stoichiometry in the coastal upwelling system off Peru

Abstract. Eastern boundary upwelling systems (EBUS) are among the most productive marine ecosystems on Earth. The production of organic material is fueled by upwelling of nutrient-rich deep waters and high incident light at the sea surface. However, biotic and abiotic factors can modify surface production and related biogeochemical processes. Determining these factors is important because EBUS are considered hotspots of climate change, and reliable predictions of their future functioning requires understanding of the mechanisms driving the biogeochemical cycles therein. In this field experiment, we used in situ mesocosms as tools to improve our mechanistic understanding of processes controlling organic matter cycling in the coastal Peruvian upwelling system. Eight mesocosms, each with a volume of ∼55 m3, were deployed for 50 d ∼6 km off Callao (12∘ S) during austral summer 2017, coinciding with a coastal El Niño phase. After mesocosm deployment, we collected subsurface waters at two different locations in the regional oxygen minimum zone (OMZ) and injected these into four mesocosms (mixing ratio ≈1.5 : 1 mesocosm: OMZ water). The focus of this paper is on temporal developments of organic matter production, export, and stoichiometry in the individual mesocosms. The mesocosm phytoplankton communities were initially dominated by diatoms but shifted towards a pronounced dominance of the mixotrophic dinoflagellate (Akashiwo sanguinea) when inorganic nitrogen was exhausted in surface layers. The community shift coincided with a short-term increase in production during the A. sanguinea bloom, which left a pronounced imprint on organic matter C : N : P stoichiometry. However, C, N, and P export fluxes did not increase because A. sanguinea persisted in the water column and did not sink out during the experiment. Accordingly, export fluxes during the study were decoupled from surface production and sustained by the remaining plankton community. Overall, biogeochemical pools and fluxes were surprisingly constant for most of the experiment. We explain this constancy by light limitation through self-shading by phytoplankton and by inorganic nitrogen limitation which constrained phytoplankton growth. Thus, gain and loss processes remained balanced and there were few opportunities for blooms, which represents an event where the system becomes unbalanced. Overall, our mesocosm study revealed some key links between ecological and biogeochemical processes for one of the most economically important regions in the oceans.

Catchment vegetation and temperature mediating trophic interactions and production in plankton communities.

Climatic factors influence the interactions among trophic levels in an ecosystem in multiple ways. However, whereas most studies focus on single factors in isolation, mainly due to interrelation and correlation among drivers complicating interpretation and analyses, there are still only few studies on how multiple ecosystems respond to climate related factors at the same time. Here, we use a hierarchical Bayesian model with a bioenergetic predator-prey framework to study how different climatic factors affect trophic interactions and production in small Arctic lakes. Natural variation in temperature and catchment land-cover was used as a natural experiment to exemplify how interactions between and production of primary producers (phytoplankton) and grazers (zooplankton) are driven by direct (temperature) and indirect (catchment vegetation) factors, as well as the presence or absence of apex predators (fish). The results show that increased vegetation cover increased phytoplankton growth rate by mediating lake nutrient concentration. At the same time, increased temperature also increased grazing rates by zooplankton. Presence of fish increased zooplankton mortality rates, thus reducing grazing. The Arctic is currently experiencing an increase in both temperature and shrub vegetation cover due to climate change, a trend, which is likely to continue. Our results point towards a possible future general weakening of zooplankton grazing on phytoplankton and greening of arctic lakes with increasing temperatures. At the same time, the impact of the presence of an apex predator indicate considerable local variation in the response. This makes direction and strength of global change impacts difficult to forecast.

Seasonal dynamics of autotrophic and heterotrophic plankton metabolism and PCO2 in a subarctic Greenland fjord

We measured net planktonic community production (NCP), community respiration (CR), and gross primary production (GPP) in September, February, and May in a subarctic Greenland fjord influenced by glacial meltwater and terrestrial runoff. Potential controls of pelagic carbon cycling, including the role of terrestrial carbon, were investigated by relating surface‐water partial pressure of CO2 (PCO2), NCP, GPP, and CR to physicochemical conditions, chlorophyll a (Chl a) concentration, phytoplankton production, inventories of particulate (POC) and dissolved organic carbon (DOC) and vertical flux of POC. The planktonic community was net heterotrophic in the photic zone in September (NCP 5 ‒21 ± 45 mmol O2 m‒2 d‒1) and February (NCP 5 ‒17 mmol O2 m‒2 d‒1) but net autotrophic during a developing spring bloom in May (NCP 5 129 ± 102 mmol O2 m‒2 d‒1). In September, higher temperatures, shorter day lengths, and lower Chl a concentrations compared with May caused increased rates of CR, lower GPP rates, and net heterotrophy in the photic zone. The GPP required to exceed CR and where NCP becomes positive was low (in May: 1.58 ± 0.48 µmol O2 L‒1 d‒1 and September: 3.06 ± 0.82 µmol O2 L‒1 d‒1) and in the range of open ocean values, indicating that allochtonous carbon did not stimulate CR. The PCO2 in the surface water was below atmospheric levels (September average 25.0 ± 0.71 Pa, February 35.4 ± 0.40 Pa, and May 19.8 ± 1.21 Pa), rendering the ecosystem a sink of atmospheric CO2. NCP was identified as an important driver of surface PCO2 , with high rates of autotrophy and vertical export of POC reducing surface PCO2 during summer. In winter, net heterotrophy added CO2 to the water column, but this postive effect on PCO2 was balanced by simultaneous cooling of the water column, which decreased PCO2 because of increased solubility of CO2. High autochthonous production implies a relatively limited influence of allochthonous carbon on pelagic carbon balance and CO2 dynamics in the fjord.

UV sensitivity of planktonic net community production in ocean surface waters

AbstractThe net plankton community metabolism of oceanic surface waters is particularly important as it more directly affects the partial pressure of CO2 in surface waters and thus the air‐sea fluxes of CO2. Plankton communities in surface waters are exposed to high irradiance that includes significant ultraviolet blue (UVB, 280–315 nm) radiation. UVB radiation affects both photosynthetic and respiration rates, increase plankton mortality rates, and other metabolic and chemical processes. Here we test the sensitivity of net community production (NCP) to UVB of planktonic communities in surface waters across contrasting regions of the ocean. We observed here that UVB radiation affects net plankton community production at the ocean surface, imposing a shift in NCP by, on average, 50% relative to the values measured when excluding partly UVB. Our results show that under full solar radiation, the metabolic balance shows the prevalence of net heterotrophic community production. The demonstration of an important effect of UVB radiation on NCP in surface waters presented here is of particular relevance in relation to the increased UVB radiation derived from the erosion of the stratospheric ozone layer. Our results encourage design future research to further our understanding of UVB effects on the metabolic balance of plankton communities.

Distribution and production of plankton communities in the subtropical convergence zone of the Sargasso Sea. I. Phytoplankton and bacterioplankton

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 426:57-70 (2011) - DOI: https://doi.org/10.3354/meps09001 Distribution and production of plankton communities in the subtropical convergence zone of the Sargasso Sea. I. Phytoplankton and bacterioplankton Lasse Riemann1,7,*, Torkel Gissel Nielsen2,6, Theis Kragh3, Katherine Richardson4, Hjalte Parner5, Hans Henrik Jakobsen6,2, Peter Munk6 1Department of Natural Sciences, Linnaeus University, 39182 Kalmar, Sweden 2National Environmental Research Institute, Aarhus University, Department of Marine Ecology, 4000 Roskilde, Denmark 3Freshwater Biological Laboratory, University of Copenhagen, Helsingørsgade 51, 3400 Hillerød, Denmark 4University of Copenhagen, Center for Macroecology, Evolution and Climate, 2200 Copenhagen N, Denmark 5International Council for the Exploration of the Sea (ICES), 1553 Copenhagen V, Denmark 6National Institute of Aquatic Resources, DTU Aqua Section for Oceanecology and Climate, Technical University of Denmark, DTU Kavalergården 6, 2920 Charlottenlund, Denmark 7Marine Biological Section, University of Copenhagen, Strandpromenaden 5, 3000 Helsingør, Denmark *Email: lriemann@bio.ku.dk(Second superscript numbers indicate present addresses) ABSTRACT: Elevated levels of biomass and productivity are often associated with ocean frontal systems. The Subtropical Convergence Zone (STCZ) in the southern Sargasso Sea shows pronounced and stable thermal fronts, but little is known about the ecological consequences of these hydrographic features. With the aim of improving the understanding of physical and lower trophic level processes in the area, we carried out field studies of physical, chemical and biological characteristics along 3 transects crossing thermal fronts associated with the STCZ in March to April 2007. Thermal and chemical stratification were evident at all stations within the STCZ, and a depletion of nitrate was measured in the upper ~150 m. The phytoplankton biomass was dominated by Prochlorococcus spp. with highest abundance, up to >400000 cells ml–1, at the chlorophyll a (chl a) maximum at 100 to 150 m depth. Synechococcus spp. were generally located higher in the water column. Picoalgae were less abundant, up to 8000 cells ml–1, but explained most of the variation in chl a. Even though diatoms and dinoflagellates were few, the biomass of larger phytoplankton equalled or exceeded that of picoplankton at a few stations. Bacterial biomass was roughly equal to half of the phytoplankton biomass. We did not find elevated levels of primary production or biomass of specific phytoplankton groups associated with the STCZ, probably due to a pronounced variability between stations along transects. Nevertheless, distinct increases in chl a were associated with the zone and thermal fronts bordering the STCZ. KEY WORDS: Sargasso Sea · Picoalgae · Bacteria · Prochlorococcus · Synechococcus · Convergence zone Full text in pdf format PreviousNextCite this article as: Riemann L, Nielsen TG, Kragh T, Richardson K, Parner H, Jakobsen HH, Munk P (2011) Distribution and production of plankton communities in the subtropical convergence zone of the Sargasso Sea. I. Phytoplankton and bacterioplankton. Mar Ecol Prog Ser 426:57-70. https://doi.org/10.3354/meps09001Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 426. Online publication date: March 28, 2011 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2011 Inter-Research.

Distribution and production of plankton communities in the subtropical convergence zone of the Sargasso Sea. II. Protozooplankton and copepods

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 426:71-86 (2011) - DOI: https://doi.org/10.3354/meps09047 Distribution and production of plankton communities in the subtropical convergence zone of the Sargasso Sea. II. Protozooplankton and copepods Nikolaj G. Andersen1,4, Torkel Gissel Nielsen1,2,*, Hans Henrik Jakobsen2,1, Peter Munk2, Lasse Riemann3,4 1National Environmental Research Institute, Aarhus University, Department of Marine Ecology, 4000 Roskilde, Denmark 2National Institute of Aquatic Resources, DTU Aqua Section for Oceanecology and Climate, Technical University of Denmark, DTU Kavalergården 6, 2920 Charlottenlund, Denmark 3Department of Natural Sciences, Linnaeus University, 39182 Kalmar, Sweden 4Marine Biological Section, University of Copenhagen, Strandpromenaden 5, 3000 Helsingør, Denmark *Corresponding author. Email: tgin@aqua.dtu.dk(Second superscript numbers indicate present addresses) ABSTRACT: The oligotrophic Sargasso Sea in the western part of the North Atlantic Ocean is influenced by a complex set of oceanographic features that might introduce nutrients and enhance productivity in certain areas. To increase our understanding of the variability in plankton communities and to determine the potential reasons why Atlantic eels Anguilla spp. use this area for spawning, we investigated the distribution and productivity of the zooplankton community across the Subtropical Convergence Zone (STCZ) in the Sargasso Sea in March and April 2007. The vertical and horizontal distributions of protozoans and metazooplankton were investigated at 33 stations along 3 north to south transects ranging from 64 to 70°W to a depth of 400 m. Copepods dominated the metazooplankton, while heterotrophic athecate dinoflagellates dominated the protozoan biomass. Other important groups were appendicularians, gastropod larvae and ostracods. Most of the recorded metazoan groups responded numerically to the frontal features (i.e. the surfacing of the isotherms) with high abundance in the STCZ compared with areas north and south of this. Juvenile copepod growth and egg production peaked in the STCZ, with a weight-specific growth rate of juvenile copepods ranging from 0.09 to 0.21 d–1, and a much lower specific egg production in the order of 0.01% d–1. The Sargasso Sea is described as oligotrophic, but the availability of athecate dinoflagellates and ciliates in the STCZ potentially leads to an enhanced mesozooplankton secondary production, which may in turn be available to organisms at higher trophic levels such as larvae of Atlantic eels. KEY WORDS: Sargasso Sea · Ciliates · Heterotrophic dinoflagellates · Copepods · Convergence zone Full text in pdf format PreviousNextCite this article as: Andersen NG, Nielsen TG, Jakobsen HH, Munk P, Riemann L (2011) Distribution and production of plankton communities in the subtropical convergence zone of the Sargasso Sea. II. Protozooplankton and copepods. Mar Ecol Prog Ser 426:71-86. https://doi.org/10.3354/meps09047Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 426. Online publication date: March 28, 2011 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2011 Inter-Research.

Net plankton community production in the Arabian Sea based on O2 mass balance model

Monthly net community production (NCP) rates were computed using oxygen mass balance model for the euphotic zone in the eastern (EAS) and western Arabian Sea (WAS). NCP showed large seasonal and spatial variability in the Arabian Sea, and it is consistent with gross productivity. Net autotrophic conditions were found during high productive seasons, while net heterotrophic conditions were prevalent during non‐monsoon seasons in both EAS and WAS. Though gross productivity is higher during SW monsoon (June to September), NCP decreased from June to September due to increase in grazing pressure. This suggests that production to respiration ratio controls NCP in the Arabian Sea. NCP is found to be higher in the WAS compared to the EAS and it is consistent with gross productivity. Incubation experiments suggested that phytoplankton growth was higher than zooplankton grazing in the WAS due to high concentrations of nutrients and it is opposite in the EAS, suggesting that a different ecosystem exists in the east and west probably due to existence of different physical forcing. In general, picoplanktons are more dominant in the EAS, whereas diatoms are major contributors to primary production in the WAS due to low nitrate concentration in the former region. As a result, most of the produced carbon is recycled in the euphotic zone in the EAS, whereas it is exported to the deeper layers in the WAS. These results are consistent with the sinking fluxes of carbon at 100 m depth in both the regions. On an annual scale, WAS is net autotrophic, whereas EAS is net heterotrophic. NCP amounts to approximately one fourth of the gross primary production, and it is consistent with the new production estimated using f‐ratios in the Arabian Sea.

Planktonic community production and respiration and the impact of bacteria on carbon cycling in the photic zone of Lake Kinneret

AME Aquatic Microbial Ecology Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsSpecials AME 34:43-55 (2004) - doi:10.3354/ame034043 Planktonic community production and respiration and the impact of bacteria on carbon cycling in the photic zone of Lake Kinneret T. Berman*, A. Parparov, Y. Z. Yacobi Yigal Alon Kinneret Limnological Laboratory, Israel Oceanographic and Limnological Research, PO Box 447, Migdal 14 950, Israel *Email: berman@amiad.org.il ABSTRACT: The following parameters were determined in the photic zone of Lake Kinneret from January 2001 through December 2002: primary production (PP), community respiration (CR), bacterial biomass production (BBP), bacterial numbers (BN) and biological oxygen demand (BOD5). Average values over the 2 yr period for these parameters in the photic zone (0 to 15 m) were PP, 1539 mgC m-2 d-1; CR, 1653 mgC m-2 d-1; BBP, 887 mgC m-2 d-1; BN, 4.6 × 106 cells ml-1; and BOD5, 6366 mgC m-2. We used these data together with literature-based assumptions about the ratio of net to gross primary production, bacterial and zooplankton respiration to estimate bacterial growth efficiencies (BGE) ranging from 44 to 64%. Bacterial specific growth rates averaged 0.33 d-1, ranging from 0.13 to 0.93 d-1. CR was significantly correlated with both PP and BBP. A significant correlation was found between BBP and BOD5, suggesting that the indigenous bacterial populations were strongly dependent on substrates measured by BOD5. The potentially labile fractions of TOC, as quantified by BOD5, were rapidly cycled by heterotrophic bacteria, within ~4 d on average. With the exception of 6 to 8 wk in early summer, the photic zone of this warm mesotrophic-eutrophic lake, with low inputs of allochthonous organic carbon, was net autotrophic. BBP and BGE values were high in comparison to those reported from even more eutrophic aquatic systems. Our results indicate that bacteria are by far the major biological agents of organic carbon cycling in Lake Kinneret, and contradict the general perception that the microbial loop plays a less important role in carbon cycling in eutrophic than in oligotrophic aquatic systems. KEY WORDS: Bacterial production · Growth efficiency · Community respiration · Primary production · BOD5 · Lake Kinneret Full article in pdf format PreviousNextExport citation RSS - Facebook - Tweet - linkedIn Cited by Published in AME Vol. 34, No. 1. Online publication date: January 16, 2004 Print ISSN: 0948-3055; Online ISSN: 1616-1564 Copyright © 2004 Inter-Research.

Influence of nutrients and mixing on the primary production and community respiration in the Gulf of Riga

Rates of plankton community production and respiration in relation to wind, solar radiation, biomass and nutrients were measured in the mixed layer during a late spring, a mid-summer and an early autumn situation in the Gulf of Riga. System metabolism was estimated by the in vitro oxygen method and from oxygen mass balance directly in the water. Gross production (GPP) remained fairly stable throughout the investigation periods with a mean of 1.8 g C m −2 day −1 (range: 0.5–3.9 g C m −2 day −1). Community respiration varied from 0.5 to 6.4 g C m −2 day −1 during the two summer studies (the high respiration rates ranging from 3.0 to 10.4 g C m −2 day −1 found during the autumn cruise were probably overestimates). Respiration rates generally exceeded GPP indicating that the system was apparently net-heterotrophic during the three investigation periods. The predominant limiting factor for phytoplankton growth were nutrients during spring and summer. In autumn the combination of low light levels and high vertical mixing due to wind lead to conditions of light limitation. However, growth conditions were affected by the stabilizing (solar heating) and destabilizing (wind) forces acting on the water column in all three situations. Depending on the relative strength of these forces, day-to-day primary production could vary considerably. Under conditions of nutrient limitation mixing may increase photosynthesis; this is a consequence of improved exploitation of incident light and of available nutrients in the mixed layer. The strong dependency of mixing on primary production implies that measurements based on in vitro incubations may underestimate “real” production.

Microbial dynamics in coastal waters of East Antarctica:plankton production and respiration

The rates of plankton community production and respiration were determined from in vitro changes in dissolved inorganic carbon and dissolved oxygen and the incorporation of (NaHCO3)-C-14 at a coastal site in East Antarctica between 16 December 1993 and 12 February 1994. The breakout of seasonal fast ice was associated with a succession of dominant phytoplankton from Cryptomonas to Phaeocystis to a diatom assemblage. Gross production reached 33 mmol C m(-3) d(-1) and C-14 incorporation peaked at 24 mmol C m(-3) d(-1) on 23 January 1994, at the time of the chlorophyll a maximum (22 mg chi a m(-3)). Dark community respiration reached its maximum (13 mmol C m(-3) d(-1)) 4 d later. Photosynthetic rates calculated from C-14 incorporation were significantly lower (17 to 59%) than rates of gross production. The derivation of plankton processes from changes in both dissolved oxygen and dissolved inorganic carbon allowed the direct measurement of photosynthetic and respiratory quotients. A linear regression of all data gave a photosynthetic quotient of 1.33 +/- 0.23 and a respiratory quotient of 0.88 +/- 0.14. Concurrent determinations of bacterial, heterotrophic dinoflagellate, nanoflagellate and ciliate respiration could account for 15 to 58% of measured dark-community respiration. This study has improved the sparse data set of plankton respiration measurements, confirmed that heterotrophic respiration is a significant process in the carbon flux of coastal Antarctic waters and achieved a first apportionment of community respiration to the major microbial groups in this region

Characteristics of plankton communities in Chinese integrated fish ponds: effects of excessive grazing by planktivorous carps on plankton communities

Biomass and production of plankton communities were investigated in two Chinese integrated fish culture ponds in August, Dianshanhu Pond (with high density of planktivorous carp) and Pingwang Pond (with low density of planktivorous carp). The plankton communities were composed of rotifers, protozoans, phytoplankton ( 40 µm), cladocerans and copepods were rare because of grazing pressure by the carp. The density or biomass of bacteria (1.93 × 107 and 2.20 × 107 cells ml−1 on average in Dianshanhu and Pingwang Ponds, respectively), picophytoplankton (24.6 and 18.5 mg m−3 Chla on average) and rotifers (5372 and 20733 ind. 1−1 on average) exceeded the maximum values reported for natural waters.

Seasonal and regional variations in plankton community production and respiration for Chesapeake Bay

Plankton community production and respiration rates were examined at 3 stations representmg distinct regions along the estuanne gradient in the main stem of Chesapeake Bay, USA. Rates were measured as in vitro changes in oxygen concentration, as determined by Winkler titration with an automated photometric end-point detection system. At each station rates of both processes exhibited annual patterns which followed that of water temperature. There were distinct differences, however, among the 3 stations in the relative magnitude of metabolic rates measured. Annual rates of daytime net plankton community production were estimated to be 265, 1680, and 2040 g O2 n r 2 yrW1, while annual night-time plankton community respiration rates in the upper water column were estimated as 130, 1090, and 490 g 0; m 2 y r l at the upper, middle and lower Bay stations, respectively. Thus, whereas rates of net daytime production increased substantially moving downbay, highest measured rates of community respiration were, m fact, found in the middle region of the Bay. Annual cycles of production and respiration rates were significantly related to each other at the upper and middle stations, but unrelated at the lower station. Integrated estimates of net plankton community metabolism (production minus respiration) at the 3 stations exhibited seasonal patterns departing from balanced metabolism (production = respiration) during winter-spring and converging on zero net metabolism in summer-fall. During the cooler months net plankton metabolism was negative (net heterotrophic) at the upper station and positive (net autotrophic) at the middle and lower stations. Over the annual cycle, the 3 stations showed a longitudinal pattern of increasing die1 net plankton community metabolism, progressing from a net heterotrophy of -70 g O2 m 2 y r l in the turbid, upper Bay, to shghtly positive metabolism of 160 g 0; m-2 yr-I m the mid-region, to strong net autotrophy of 760 g Oa m 2 y r l in the less turbid, lower Bay. KEY WORDS' Plankton. Production Respiration. Net community metabohsm . Oxygen. Chesapeake Bay

New Zealand lakes research, 1967–91

Abstract Research on New Zealand lakes over the past 25 years has focused mainly on eutrophication, measures of water quality, patterns, processes and production in plankton communities, and the spread and growth of submerged adventive macrophytes. Compared with most northern temperate lakes many New Zealand lakes show: low levels of inorganic nitrogen (N) and frequent N‐limitation of phyto‐plankton growth; diffuse, rather than point source, nutrient inflows; a great diversity of optical properties; unusual and often variable timing of plankton growth (attributed to the pervasive influence of New Zealand's oceanic climate); low productivity and biomass of zooplankton, which appear to be limited by food rather than predators; and sensitivity to invasion by adventive macrophytes. Notable research develop‐ments include improved methods of measuring nutrients, empirical predictive models that relate indices of eutrophication to nutrient loading, and significant advancements in methods of quantifying and measuring water colour and clarity.