Showing papers on "Productivity (ecology) published in 1990"

Carbon and nitrogen economy of 24 wild species differing in relative growth rate.

Abstract: The relation between interspecific variation in relative growth rate and carbon and nitrogen economy was investigated. Twentyfour wild species were grown in a growth chamber with a nonlimiting nutrient supply and growth, whole plant photosynthesis, shoot respiration, and root respiration were determined. No correlation was found between the relative growth rate of these species and their rate of photosynthesis expressed on a leaf area basis. There was a positive correlation, however, with the rate of photosynthesis expressed per unit leaf dry weight. Also the rates of shoot and root respiration per unit dry weight correlated positively with relative growth rate. Due to a higher ratio between leaf area and plant weight (leaf area ratio) fast growing species were able to fix relatively more carbon per unit plant weight and used proportionally less of the total amount of assimilates in respiration. Fast growing species had a higher total organic nitrogen concentration per unit plant weight, allocated more nitrogen to the leaves and had a higher photosynthetic nitrogen-use efficiency, i.e. a higher rate of photosynthesis per unit organic nitrogen in the leaves. Consequently, their nitrogen productivity, the growth rate per unit organic nitrogen in the plant and per day, was higher compared with that of slow growing species.

Effects of Different Resource Additions of Species Diversity in an Annual Plant Community

Abstract: A commonly observed phenomenon in plant communities is that the ad- dition of a limiting resource leads to an increase in productivity and a decrease in species diversity. We tested the hypothesis that the mechanism underlying this pattern is a dis- proportionate increase in mortality of smaller or shade-intolerant species in more produc- tive sites caused by reduction of light levels. We added water and/or one of three nutrients (nitrogen, phosphorus, and potassium) to a 1 st-yr old-field community dominated by weedy annuals and measured effects on productivity, species composition, diversity, and light levels after one growing season. Diversity was not clearly related to productivity in this experiment. Watering increased productivity, but, contrary to expectations, had no effect on density of surviving plants, species diversity, or abundance of low-growing species. Almost all the increase in biomass with watering was due to a positive response by Ambrosia artemisiifolia, an upright annual that was the most common species in the canopy in all treatments. The addition of nitrogen had only a small positive effect on productivity, but strongly decreased density of surviving plants, species diversity, and abundance of most low-growing species. Only Ambrosia increased in abundance with nitrogen addition. The phosphorus and potassium additions had little effect on the community. We suggest that the high mortality and low diversity in the nitrogen addition plots, but not in the more productive watered plots, was due to limitation by nitrogen earlier than limitation by water during the growing season. The consequence was earlier canopy closure and greater mortality due to light limitation.

Dissipative Beaches and Macrofauna Communities on Exposed Intertidal Sands

Abstract: This study was undertaken primarily to test the hypotheses that (I) the intertidal fauna of exposed sandy beaches occupy four distinct zones and (2) that dissipative (flat) beaches support faunas of high abundance and diversity. The benthic macrofauna of three high energy, dissipative beaches on the Oregon coast was quantitatively surveyed and found to comprise an assemblage of 16-21 species and 50-290*10 9 individuals per meter per beach. This fauna exhibited zonation four zones being distinguished by 3-4 characteristic species each. Zonation appeared to be related to both interstitial moisture levels in the sand at low tide and tide levels or inundation times. These data together with similar data from a range of beaches in southern Africa and western Australia were analyzed for changes in faunal diversity, total abundance and biomass and mean individual mass in response to physical changes in sand particle size, wave height, beach slope and beach type. The biological parameters showed good correlations with all the physical parameters, but beach slope and type gave the best fits for abundance and diversity. Biomass was however best correlated with wave energy. This is interpreted as meaning (l) that wave energy which may control surf zone productivity and food availability, controls intertidal biomass and (2) that although sand particle size and wave climate may have some direct effects the type of fauna developing on a beach is primarily determined by the total swash "climate" of the beach face as reflected in beach slope and beach type.

A 5-yr Record of Aerial Primary Production and Stand Characteristics of Spartina Alterniflora

Abstract: The purpose of this paper is to document and explain the interannual variability in aboveground primary productivity from salt marshes at North Inlet, South Carolina. A census method of measuring production was applied to salt marsh sites vegetated by the grass Spartina alterniflora, and a statistically significant relationship between stem age and cumulative leaf loss was used to estimate leaf turnover. Aboveground productivity was 2.3 times as large as the positive increment in standing biomass density due to the turnover of stems and leaves, with stem turnover accounting for 33% and leaf turnover 23% of total aboveground productivity. A numerical simulation demonstrated the sensitivity of destructive harvest methods to sampling errors that are propagated by spatial variability. Monthly measurements, made at one site for >5 yr, document a twofold variation in annual aboveground production, which has important implications for the biogeochemistry and trophic dynamics of estauries. Positive correlations i...

Changes in productivity and distribution of nutrients in a chronosequence at Glacier Bay National-Park, Alaska

Abstract: By assessing productivity and ecosystem nutrient distribution, this work extends the early classic studies of the influence of N 2 fixers and conifers on soil development and nitrogen accumulation in a primary succession chronosequence at Glacier Bay, Alaska, U.S.A. The nitrogen-fixing shrub Alnus sinuata (Sitka alder) dominates recently deglaciated sites along Glacier bay but is replaced by Picea sitchensis (Sitka spruce) after about 80 years. While Alnus dominated, soil organic matter and nitrogen (N) increased very rapidly (...)

Quantitative assessment of the major limitations on productivity ofSpirulina platensis in open raceways

Abstract: This work represents an attempt to assess the relative contribution of the factors limiting productivity ofSpirulina platensis in open raceways throughout the year. Temperature of the culture during daylight exerted the predominant effect on productivity and elevating the temperature resulted in a significant rise in productivity even in summer. Photoinhibition had a decisive role in summer in determining productivity ofSpirulina in open raceways in that growth almost ceased after mid-day. Contamination by other microorganisms, particularlyS. minor andChlorella sp. was estimated to reduce the net biomass yield by at least 15 to 20%, but measures to curtail the establishment of these species in the raceway have been devised. The effect of harvest time during the day on the yield of dry mass was examined: no conclusion could be drawn except in mid-summer, when evening harvesting resulted in a significant increase in the output rate of dry weight over morning harvesting.

Quantifying the impact of periphytic algae on nutrient availability for phytoplankton

Abstract: SUMMARY. 1 Recent laboratory studies demonstrate that periphytic algae growing on the sediment surface reduce nutrient availability in the overlying water. Consequently, periphytic algae may competitively reduce growth of phytoplankton. 2 The aim of this study was to quantify the competitive impact of sediment-attached periphytic algae on phytoplankton in the presence of all other factors simultaneously affecting nutrient dynamics in natural systems. 3 In enclosure experiments, performed in three lakes of different productivity, the periphytic algal biomass was manipulated. When compared to enclosures with high biomass of periphytic algae, those with reduced biomass showed an increase in total phosphorus concentration in the water of 32–44%. Extrapolation of the experimental results to whole lakes predicts an increase in original total phosphorus concentration of between 1.5% and 8.0%. According to existing regressions between total phosphorus and phytoplankton chlorophyll, the potential increase in original phytoplankton biomass will be between 2.5% and 12.6%. 4 With respect to the shallow parts of lakes, my results support the conclusions revealed from laboratory studies that periphytic algae have a significant impact on the phosphorus concentration in the overlying water. However, when considering whole-lake dynamics, the competitive impact of periphytic algae on phytoplankton biomass development is probably of minor importance. 5 Rather, the main competitive advantage of growing on the sediment surface, compared to in the water, may be the exclusive access to nutrients in the sediment.

Mangrove ecology, aquatic primary productivity, and fish community dynamics in the Teacapán-Agua Brava Lagoon-Estuarine system (Mexican Pacific)

Abstract: Aquatic primary productivity, mangrove ecology, and fish community dynamics were investigated in the Teacapan-Agua Brava lagoon-estuarine system, the most extensive mangrove ecosystem on the Pacific coast of Mexico with three species of mangroves distributed heterogeneously (Laguncularia racemosa, Rhizophora mangle, andAvicennia germinans). Tree density was 3,203 trees ha−1 and basal area was 14.0 m2 ha−1. Litterfall was 1,417 g m−2 yr−1, characteristic of a productive riverine forest. The degradation constant forLaguncularia racemosa leaves varied from 1.71 to 4.7 yr−1 and mean annual net aquatic productivity was 0.41 g C m−3 d−1. There were high concentrations of humic substances (up to 150 mg l−1) early in the wet season. Seasonal variations of the above parameters seemed closely related to the ecology of fish populations. There were 75 fish species distributed in two principal assemblages associated with wet and dry seasons. Diversity and biomass analysis indicated 18 dominant species. Total biomass of the community in this coastal system was estimated at 10 g wet wt m−2. The highest biomass occurred in the wet season. The most common fish species wereMugil curema, Achirus mazatlanus, Galeichthys caerulescens, Arius liropus, Diapterus peruvianus, Lile stolifera, Centropomus robalito, andEucinostomus sp., all of which have fishery importance. Primary productivity and fish community ecology are controlled by habitat characteristics, river discharge, and climatic seasonality.

Periphyton Responses to Higher Trophic Levels and Light in a Shaded Stream

Abstract: The effects of higher trophic levels on benthic primary producers were examined in the context of light limitation in a shaded headwater stream Abundance (presence or absence) of a predatory fish Semotilus atromaculatus and a grazing snail Elimia clavaeformis were manipulated with in situ Plexiglas channels, while spatial variability in ambient light was related to variability in primary productivity among channels Indirect effects of fish on periphyton were insignificant, possibly because grazers that are vulnerable to fish predation were scarce during the experiment, or because fish preyed upon other predators of grazers Snails had compensatory effects within the periphyton: they diminished biomass and productivity in the loosely attached layer, but stimulated productivity in the tightly attached layer Snails appeared to mitigate shading of the tightly attached layer by the loosely attached layer Benthic primary productivity was highly correlated with ambient light levels, accounting for 42% of the

Plankton community respiration along a nutrient gradient in a shallow Danish estuary

Abstract: Plankton community respiration was examined in a shallow, very eutrophic Danish estuary during April to September. Maximum rates (3.98 g O2 m-3 d-l) were measured during the phytoplankton spring bloom in the most eutrophicated inner parts. Community respiration was significantly related to biomass and gross productivity of phytoplankton and net production of bacterioplankton. The relationship was weak to temperature and bacterial biomass. Regression analysis suggested that phytoplankton and bacteria, on average, accounted for 64 to 83 % of the community respiration at the 2 most eutrophic localities. The regressions also provided estimates of mean phytoplankton respiration (0.76 mg O2 mg-l chlorophyll a h-', 6.0 % of gross productivity), mean bacterial respiration (1.4 times net production) and mean bacterial growth yield (42 %). Pelagic respiration exceeded benthic respiration and became proportionally larger with increasing eutrophication and phytoplankton productivity in the inner parts of the estuary. These results stress the importance of phytoplankton blooms for pelagic respiration, overall oxygen balances and oxygen depletion phenomena.

Comparisons of sponge populations across the Barrier Reefs of Australia and Belize: evidence for higher productivity in the Caribbean

Abstract: Sponge populations were compared along transects from land-influenced, inner-shelf reefs to ocean-influenced reefs of the 2 largest barrier reefs in the Pacific and Atlantic Oceans. Sponge biomass on Belize reefs in the Caribbean is greater than on comparable reefs of the central Great Barrier Reef (GBR), whereas individual abundance and species richness are simllar in the 2 regions. Inner-shelf sponge populations are comparable in trophic structure with approximately twice as much biomass and rate of carbon consumption on Belize reefs. Sponge populations on clean water reefs of the 2 regions, however, are fundamentally different. With approximately 6 t ~ m e s the blomass, Belize sponges are large and almost totally heterotrophic and consume on average 15 tlmes more organic carbon per unit area than GBR sponge populations, of which ca 50 ''h of the biomass consists of small phototrophic species. The fundamental differences in species colnposition and mode of nutrition of the sponge populations are a result of long temporal and spatial separations of the 2 reglons. The difference In abundance of phototrophic sponges follows a pattern of a greater evolution of symb~oses In the more oligotrophic Pacific Ocean. The greater sponge hiomass and rates of carbon consumption on these Caribbean reefs are suggestive of higher oceanic productivity compared with that of the Pac~fic. lncreascs in the biomass of heterotrophic sponges are proposed as an early warning slgnal for organlc pollution on coral reefs.

Primary productivity and particulate organic matter flow in an estuarine mangrove-wetland in Hong Kong

Abstract: Net primary productivity and organic matter flow of a mangrove-dominated wetland was estimated by following production and detritus dynamics in a tidal pond in north west Hong Kong in 1986–1988 (9.1 ha). Total productivity was 12.47 t dry wt ha−1 yr−1, of which >90% was from emergent macrophytes (the mangroveKandelia candel and the reedPhragmites communis). High turbidity and high summer temperatures probably limited respective production by phytoplankton and benthic macroalgae (dominated byEnteromorpha crinata). Despite the high total productivity, little detritus was exported from the emergent macrophyte stands, due to the low inundation frequency. This created a net water column carbon deficit which was provided for by the high organic matter import (mean = 4.42 g ash free dry wt m−2 d−1) from the incoming water. This same sediment and particulate organic carbon input giving a high accretion rate of 1.7 cm yr−1 was probably also the force behind progressive dis-coupling of emergent macrophyte production from water column consumers. This resulted in a tendency to retain production in the emergent macrophyte stands while the water column community increasingly relied on allochthonous carbon. This shift from a net exporter to a net importer of carbon in landward wetlands is probably characteristic of the transition into nutrient-conservative terrestrial systems.

Microbial biomass in the coastal plume of Chesapeake Bay: Phytoplankton-bacterioplankton relationships

Abstract: Turnover rate of suspended organic matter (POC) increased seasonally with temperature as the proportions of POC accounted for by bacterioplankton increased relative to phytoplankton. The proportion of phytoplankton productivity that cycled through bacterioplankton averaged 13% and showed little seasonal variability. These results imply changes in the pathways and rates by which phytoplankton and bacterioplankton production were consumed or exported from the plume. Time series of 1–3 d next to surface drifters within the plume provided some insight into the nature of these changes. In February when the turnover rate of POC was low, phytoplankton biomass declined relative to bacterioplankton due to sedimentation of large diatoms. Low bacterioplankton biomass was associated with high rates of predation by heterotrophic microflagellates. In August when POC was turning over rapidly, phytoplankton biomass declined relative to bacterioplankton due to selective grazing by copepods. High bacterioplankton biomass appeared to be a consequence of enhanced DOC flux associated with high copepod grazing and POC turnover rates as well as with low predation by heterotrophic microflagellates.

Interannual fluctuations in primary production: Direct physical effects and the trohic cascade at Castle Lake, California

Abstract: Direct physical effects and cascading trophic interactions operate together to determine interannual variability in the seasonal pattern .of primary productivity at Castle Lake, California. Principal component analysis was used to investigate the depth-time distributions of productivity for summers 196 l-l 986. Two characteristic patterns were found, together accounting for 60-70% of the year-to-year variability. The first pattern corresponds to the deep productivity maximum that forms in the hypolimnion in June and July. Variability in this first pattern arises from the direct effects on phytoplankton populations of year-to-year changes in timing of ice breakup and hydraulic flushing in spring. The first pattern is unusually strong or weak, compared to the longterm average, during the phenomenon of El Niiio-Southern Oscillation. A second characteristic pattern corresponds to the mixed-layer productivity maximum that develops in August and September. Variability in this second pattern arises from trophic interactions at higher levels: rainbow trout feed on late-summer Daphnia rosea populations, which in turn graze on the mixed-layer algal community. In addition, some of the variability in the rainbow trout population arises from yearto-year differences in angling pressure from humans. These results demonstrate how interannual variability in an ecosystem property (primary productivity) can be controlled by forces acting simultaneously through the top and the base of the food web.

Primary and bacterial productivity of tropical seagrass communities in the Gulf of Carpentaria, Australia

Abstract: Plant and bacterial productivities were compared at different seasons in 3 communities of seagrass in the Gulf of Carpentaria. Australia, in 1985. Seagrass biomass and shoot density were very variable, with no seasonal trend. The gross primary productivity of the seagrasses in each of the communities (Syringodium isoetifoliurn with Cymodocea serrulata in a bay, Halodule uninervis at a river mouth, and Thalassia hernprichii with Cymodocea rotundata on a reef flat) were determined seasonally from rates of lacuna1 gas production. Productivity varied seasonally, being lowest in winter (July). Values ranged from 0.6 to 1.0 g C m-2 d-' for C. serrulata, 0.3 to 8.1 for S. isoetifolium, 0 9 to 3.5 for H. uninervis, 0.2 to 0.4 for T henlprichii and 0.1 to 1.0 for C. rotundata. Gross community primary productivity, measured from diurnal changes in oxygen concentration in the water column, ranged from 3.3 in winter to 9.3 g C m-2 d-' in summer at the bay site, 2.7 to 4 at the river mouth and 3.3 to 8.4 on the reef flat. Bacterial productivity was determined using the rate of tritiated thymidine incorporation into DNA. Most (90 to 95 %) bacterial biomass was produced in the sediment. Between winter and summer, total bacterial productivity (including water column) ranged from 1.0 to 4.8 g C m-2 d-I in the bay, 0.6 to 2.5 at the river mouth and 0.6 to 3.7 on the reef flat. Bacterial productivity averaged 43 O/ O (range 10 to 90 %) of gross primary productivity, and thus would account for about half of the primary production if their growth efficiency were 50 %. Animals appeared to have an impact on bacteria at the sediment surface in summer, when specific growth rates and productivity were high, but numbers were low.

A fading recovery: the role of roach (Rutilus rutilus L.) in maintaining high phytoplankton productivity and biomass in Lake Vesijarvi, southern Finland

Abstract: For 60 years, Lake Vesijarvi, especially the Enonselka basin (2600 ha), received sewage water discharge from the City of Lahti. In 1976 the municipal sewage loading was diverted from the lake. Initially, the recovery of the lake proceeded well but after some years summer blooms of blue-green algae (Aphanizomenon, Microcystis) increased again. High biomass of roach (Rutilus rutilus L.) was considered to play an important role in maintaining high algal productivity and biomass in the lake water. Field experiments in mesocosms (22–24 m3) with different densities of roach suggested that fish biomass should be less than 30 g m−2, or 300 kg ha−1, to ensure a significant reduction in the current productivity and biomass of phytoplankton. Bioturbation of sediments and recycling of nutrients, rather than zooplanktivory, seemed to be the main factors linking roach to water quality in the mesocosms. The applicability of the mesocosm results to the management of Lake Vesijarvi is discussed.

Spectral photosynthesis, quantum yield and blue-green light enhancement of productivity rates in the diatom Chaetoceros gracile and the prymnesiophyte Emiliania huxleyi

Abstract: The photosynthetic properties of white and blue-green light grown cultures of a diatom, Chaetoceros gracile, and a prymnesiophyte, Emiliania huxleyi, were compared. The aim of the study was to quantify chromaticity effects on the spectral properties of chromophytes which significantly impact bio-optical predictions of in situ primary production. The comparisons emphasized the spectral dependency of cell pigmentation, absorption, quantum yield and rates of photosynthesis. Concentrations of chlorophylls and carotenoids were similar for the white light cultures of C. gracile and E. hrudeyi. While the absorption spectra for the chromophytes were similar, E. huxleyi exhibited a higher quantum efficiency and hence a higher photosynthetic rate, than C gracile. The pattern of blue-green light adaptation was quite distinct for the 2 phytoplankters. The &atom exhibited little change in pigmentahon, but relative quantum yleld increased slightly as did overall rates of photosynthesis. In the prymnesiophyte, total cell pigmentation was reduced by half, lowerlng cell absorption while increasing in situ chlorophyll-specific rates of photosynthesis. Carbon action spectra were made with and without background blue-green light in order to assess the potential errors produced by restricted 'Emerson enhancement effects' which are inherent in the measurement of photosynthetic action spectra. Rates of photosynthesis increased 17 to 36 % when enhancement effects were taken into account. These direct measures of photosynthesis were in good agreement with bio-optlcal model predictions based on the spectral properties of chron~ophytes.

The role of recruitment in the dynamics of a sierran subalpine bird community

Abstract: The species richness and number of territories of all species combined in a 1km2 Sierran subalpine study area fluctuated dramatically over the seven summers of 1979-1985 and were highly correlated with the timing of snowmelt. Over the same period, productivity (as determined by the number of young fledged per breeding territory) remained relatively constant, with dominant species tending to show higher and more constant productivity than did rare species. No significant correlations were found, at least for dominant species, between productivity and either the total number of breeding territories or species richness, suggesting that productivity did not strongly depend on either the potential intraspecific or interspecific competitive regime. Data collected annually on the return rates of 96 breeding adult birds banded in 1979 failed to detect changes in their winter survival rates. These patterns suggest that the recruitment of new breeders, particularly young, is a major factor controlling the populatio...

Bacterial growth rates, production and estimates of detrital carbon utilization in deep-sea sediments of the Solomon and Coral Seas

Abstract: Surface (0–5 mm) sediments at 10 bathyal and abyssal (695–4350 m) stations were sampled to determine variations in bacterial densities, productivity (tritiated thymidine incorporation at simulated in situ conditions) and specific growth rates (μ) in relation to environmental conditions and phytodetritus in the Solomon and Coral Seas. bacterial direct counts ranged from 2.5 to 60.6 × 108 cells g−1 sediment dry wt, but did not decline significantly with ocean depth or correlate with any other variables measured. Bacterial productivity was generally low, ranging from 34 to 7010 μg C m−2 d−1, but specific growth rates varied widely, ranging from 0.001 to 0.12 d−1. Incubation of samples at in situ temperature and atmospheric pressure at two stations resulted in either no detectable growth or significantly decreased thymidine incorporation, indicating a barophilic response. Quantities of macroalgal detritus were found at stations closest to reefs, whereas vascular plant and wood debris were found at most of the other stations, indicating that some detrital material transported from adjacent reefs and by massive riverine export from Papua New Guinea reaches the deep-sea floor in both seas. Significant quantities of sedimentary chlorophyll α and phaeo-pigments also were detected, indicating some deposition of phytoplankton-derived detritus. The fluxes of phytoplankton-derived, detrital carbon to the benthos were estimated (using available plankton data and the flux equation of Suess) as on the order of 2–23 mg C m−2 d−1. Assuming a median carbon assimilation efficiency of 50%, utilization of this material by sedimentary bacteria was estimated to vary widely (2–97%), averaging 40% oof total detrital carbon flux. Rates of bacterial productivity declined significantly with water depth and correlated with no other factors, but specific growth rates correlated positively with the standing amounts of macroalgal debris and were comparatively rapid (= turnover times of 6–63 days) only at the sites where this detritus was found. These results suggest that factors traditionally invoked as regulating bacterial activity in the deep sea may not always be applicable, particularly for habitats receiving significant quantities of fresh algal detritus.

Components of breeding productivity in a marine bird community: key factors and concordance

Abstract: We estimated components of annual breeding productivity for eight species of marine birds on the Semidi Islands in the western Gulf of Alaska. Mortality of eggs and young, caused primarily by avian predators, accounted for most of the annual variation in productivity. Failure to produce eggs, clutch size variation, and the hatchability of eggs were generally less important. The stage of breeding at which annual productivity was most strongly regulated differed among species. In murres, chick-rearing success accounted for the largest share of annual variation in overall productivity, whereas incubation success was the key factor in fulmars, kittiwakes, and puffins. Although avian predators were the dominant proximate cause of egg and chick losses in some species, food supply seemed ultimately responsible for variation in all the major components of productivity. Concordance of productivity among species was low for the marine bird community as a whole, but selected pairs of species exhibited a greater tend...

Primary productivity of angiosperm and macroalgae dominated habitats in a New England Salt Marsh: a Comparative analysis

Abstract: Net primary productivity estimates were made for the major macrophyte dominated habitats of the Nauset Marsh system, Cape Cod, Massachusetts. Above-ground primary productivity of short form Spartina alterniflora , the dominant habitat of the system, was 664 g m −2 y −1 . Productivity of the other dominant angiosperm ( Zostera marina ) was estimated to range from 444–987 g m −2 y −1 . The marsh creekbank habitat was dominated by an intertidal zone of fucoid algae ( Ascophyllum nodosum ecad. scorpioides , 1179 g m −2 y −1 ; Fucus vesiculosus , 426 g m −2 y −1 ), mixed intertidal filamentous algae (91 g m −2 y −1 ), and a subtidal zone of assorted macroalgae (68 g m −2 y −1 ). Intertidal mudflats were dominated by Cladophora gracilis , with net production ranging from 59–637 g m −2 y −1 . These angiosperm and macrophyte and macrophyte dominated habitats produce over 3 × 10 6 kg y −1 of biomass (1·2 × 10 6 kg carbon y −1 ). Twenty-eight per cent (28%) of this carbon production is derived from the Zostera and macroalgae habitats. Although S. alterniflora is considered the major macrophyte primary producer in Nauset Marsh and other north temperate salt marshes, it is concluded that other habitats also contribute significantly to total system carbon production.