Production Of Benthic Communities Research Articles

Alternative substrate types promote eastern oyster recruitment and benthic community productivity

Alternative substrate types promote eastern oyster recruitment and benthic community productivity

Space–time analyses of sediment composition reveals synchronized dynamics at all intertidal flats in the Dutch Wadden Sea

Intertidal mudflat systems are shaped by geological processes and an interplay of hydrodynamics, sediment availability and ecological processes. All around the world these systems are affected by relative sea level rise (RSLR), changing climate and by human activities such as sediment nourishments, dredging, hydrological engineering and bottom trawling. These kinds of perturbations cause changes in morphology and sediment composition which may cause shifts in the composition, spatial distribution and productivity of benthic communities. We analysed the spatial and temporal variability of the sediment grain size of more than 900 km2 intertidal flats in the Dutch Wadden Sea in the period 2009–2019. The large scale coverage was achieved by yearly grid sampling at more than 4000 stations. Spatial panel data models were used to analyse changes in median grain size and mud content between years and to estimate the effects of resuspension due to wind and the accumulation of silt during summer. We show that between years the sediments of the intertidal flats changed synchronously throughout the study area and that the flats became coarser during the period 2011–2015 and muddier again between 2015 and 2019. The system wide changes and the absence of clear local deviations leads to the hypothesis that a large scale factor like changing hydrodynamic regime (e.g. due to RSLR), variability in the composition of suspended sediment in the North Sea or changing microphytobenthic productivity were causally involved in the coarsening of intertidal flats. Our data and analysis provides a base for further scientific enquiry but longer time series on higher temporal resolution of both sediment data and the physical and ecological environment are required. Models simulating the environment may provide further insight into possible development of sediment composition of the intertidal flats of the Wadden Sea.

Diversity, structures assemblages and production of benthic communities on artificial reefs, a comparative case study in the English Channel

In this study, the diversity and structures assemblages of benthic communities present on artificial reefs (AR) immersed for 5 years were monitoring during a full year in 2020. The comparison of two different sites Bernières in the Bay of Seine and Cherbourg in the central part of the English Channel brings innovative results on the efficiency of such structures. Benthic fauna and macroalgae communities were studied; several biotic indices like Shannon-Wiener diversity index were calculated. Benthic fauna was classified according to their trophic group and the biomass was estimated. Our results pointed out strong differences for several indicators between sites and seasons. Benthic fauna was more abundant in the Bay of Seine and more diversified than in the Bay of Cherbourg. Primary producers’ diversity and biomass were higher in the Bay of Cherbourg and dominated by Rhodophyceae species. Primary production results showed that the Bay of Cherbourg was a more productive system than the Bay of Seine. This study highlighted the efficiency of such structures to create habitats and promote biomass and diversity of associated living communities. In comparable conditions, different systems were highlighted: a “primary producer reef” and a “primary consumer reef”.

Review and syntheses: Impacts of turbidity flows on deep-sea benthic communities

Abstract. Turbidity flows – underwater avalanches – are large-scale physical disturbances that are believed to have profound and lasting impacts on benthic communities in the deep sea, with hypothesized effects on both productivity and diversity. In this review we summarize the physical characteristics of turbidity flows and the mechanisms by which they influence deep-sea benthic communities, both as an immediate pulse-type disturbance and through longer-term press-type impacts. Further, we use data from turbidity flows that occurred hundreds to thousands of years ago as well as three more recent events to assess published hypotheses that turbidity flows affect productivity and diversity. We find, unlike previous reviews, that evidence for changes in productivity in the studies was ambiguous at best, whereas the influence on regional and local diversity was more clear-cut: as had previously been hypothesized, turbidity flows decrease local diversity but create mosaics of habitat patches that contribute to increased regional diversity. Studies of more recent turbidity flows provide greater insights into their impacts in the deep sea, but without pre-disturbance data, the factors that drive patterns in benthic community productivity and diversity, be they physical, chemical, or a combination thereof, still cannot be identified. We propose criteria for data that would be necessary for testing these hypotheses and suggest that studies of Kaikōura Canyon, New Zealand, where an earthquake-triggered turbidity flow occurred in 2016, will provide insights into the impacts of turbidity flows on deep-sea benthic communities as well as the impacts of other large-scale disturbances such as deep-sea mining.

Impacts of the non-native alga Sargassum horneri on benthic community production in a California kelp forest

The arrival of Sargassum horneri throughout the Southern California Bight and the Baja Peninsula has raised concern regarding kelp forest resilience and ecosystem function following the invasion of this non-native species. To understand how S. horneri impacts native algal abundance and community production, we removed S. horneri from experimental plots over a period of 11 mo. We measured impacts on native algal communities and community productivity using SCUBA surveys and benthic chambers equipped with oxygen, temperature, and light sensors. We observed a nearly 4-fold increase in recruitment of Macrocystis pyrifera and a 9-fold increase in adult M. pyrifera stipe density in S. horneri removal plots, but no discernable changes in net community production among treatments. We found ephemeral increases in gross community production and community respiration in the non-removal plots that coincided with periods of peak S. horneri biomass. To understand the temporal dynamics of community production, we deployed benthic chambers across a rocky reef dominated by S. horneri. Here, temporal variation in community production was most strongly related to corresponding variation in water temperature and changes in S. horneri biomass related to its annual lifecycle. Overall, our study indicates that S. horneri presence contributed to ephemeral increases in gross community production and community respiration, but it did not affect net community production. Moreover, S. horneri removal can lead to increases in native algal abundances given favorable abiotic conditions. We suggest that S. horneri thrives in a disturbed ecosystem rather than being a driver of ecosystem change.

Loss of seagrass results in changes to benthic infaunal community structure and decreased secondary production

Seagrass beds have decreased in abundance and areal coverage over the past several decades. Although previous studies have examined the importance of seagrass for benthic community assemblages and abundances, the effect of seagrass on deep-dwelling, large (high-biomass) infauna and the importance for benthic secondary production in Chesapeake Bay have not been addressed. Using benthic suctions and push cores, we compared density, diversity, and secondary productivity of benthic communities in seagrass to those in other shallow-water habitats and estimated benthic secondary productivity lost in the York River due to loss of seagrass from 1971 to 2016. We examined four habitat types in the York River: unvegetated, Gracilaria spp., mixed seagrass (multiple seagrass species), and Zostera marina L. seagrass. Physical characteristics of habitat types and biomass of organisms were assessed, and annual secondary productivity was calculated using biomass and production-to-biomass ratios. Benthic density, diversity, secondary productivity, sedimentary chlorophyll a, and percent sand were all highest in seagrass beds with Z. marina alone. Approximately 35% of benthic secondary productivity, or 1.51 × 108 g C yr–1, was lost in the York River in 1971–2016 due to the loss of seagrass beds to unvegetated substrate. The loss of seagrass in the York River over time and the associated decrease in benthic secondary productivity that we estimated could have negative consequences for the productivity of epibenthic predators. Our data emphasize the importance of conservation and restoration of seagrass.

The onset of the Ordovician evolutionary radiation of benthic animals in the Baltic Region: Explosive diversity of attachment structures of stalked echinoderms, substrate revolution and the role of cyanobacterial communities

The study of the Ordovician holdfasts of the Baltic Paleobasin revealed an explosive increase in the morphological diversity of echinoderms of the Baltic Paleobasin, up to 12 major morphological types in the Volkhov Regional Stage (Dapingian), reflecting an explosive growth in the taxonomic and morphological diversity of stalked echinoderms in general, but primarily crinoids. A sudden increase in the size and diversity of holdfasts at that time suggests a considerable increase in calcite production by stalked echinoderms and their adaptation to a wide distribution of a new type of substrate — hardgrounds and firm coarse-grained bioclastic substrates. The possibility of wide distribution of such substrates was due to a considerable increase, of at least an order of magnitude, in the carbonate productivity of benthic communities, whereas the rapid distribution of a new type of substrate and an explosive increase in the diversity and abundance of their inhabitants in the Baltic Basin was related to the appearance of positive feedbacks between the living and non-living components of this ecosystem. The existence of this positive feedback was due to cyanobacterial communities, the development of a biofilm on the substrate, and mineralization of an extracellular polymer substance, which led to the formation of hardgrounds and consolidation of the surface of the bioclastic substrates. The appearance in the Middle Ordovician of positive feedback between the expansion of the bioclastic substrates and an increase in carbonate production by their inhabitants, resulted in the Ordovician substrate revolution and explosive diversification of Ordovician benthic animals. Cyanobacterial films episodically appearing on the substrate, were an essential factor in the formation of this feedback.

Increases in benthic community production and metabolism in response to marine‐derived nutrients from spawning Atlantic salmon (Salmo salar)

Summary Atlantic salmon (Salmo salar) and other anadromous fishes represent a major vector for transporting marine‐derived nutrients (MDNs) to Atlantic rivers. Marine‐derived nutrient subsidies may be key for maintaining ecological processes and ecosystem function in river basins. Stream channels and mesocosms designed to approximate natural river systems were used to measure the response of stream productivity in two treatments, one with marine‐derived nutrients from spawning Atlantic salmon and one without marine‐nutrient subsidies (control). Biofilm biomass (measured as chlorophyll a) and benthic metabolism (measured as the net change in dissolved oxygen) were evaluated from artificial substrata encompassing pre‐spawning, spawning and post‐spawning periods. We calculated marine‐nutrient contributions from spawning salmon using a simple empirical process model. We found that biofilm accrual was significantly greater with MDN inputs, with mesocosms having higher biomass (34.8 ± 1.2 mg chl a m−2) and growth rates (0.071 ± 0.002 mg m−2 day−1) than the stream channels (24.4 ± 4.8 mg chl a m−2 and 0.052 ± 0.003 mg m−2 day−1, respectively). Both control mesocosms and stream channels had significantly lower biomass (10.4 ± 0.7 mg chl a m−2 and 6.3 ± 2.5 mg chl a m−2, respectively) and growth rates (0.042 ± 0.008 mg m−2 day−1 and 0.029 ± 0.009 mg m−2 day−1, respectively) than treatment channels. Despite having a lower biofilm biomass, stream channels yielded a significantly greater final gross primary production of 2343.5 mg C m−2 day−1. The presence of MDNs in the stream channels shifted biofilm metabolism from heterotrophy (P/R = 0.283) to autotrophy (P/R = 2.422) within 112 days. Spawning Atlantic salmon contributed a total of 20.98 g m−2 of nitrogen and 1.04 g m−2 of phosphorous to each stream channel, through excretion and gametes alone. There was a strong predictable positive relationship between the increase in productivity and the amount of marine‐derived nitrogen and phosphorous delivered. This study highlights the importance of marine‐derived nutrients from Atlantic salmon for driving and maintaining freshwater productivity. Marine‐nutrient subsidies relieve the ‘bottom‐up’ constraints on stream productivity by facilitating the production of enough energy to support the food web, lessoning the reliance on outside energy sources.

Assessment of Secondary Production and Efficiency of Different Mesh Sizes to Study Benthic Communities Associated to a Zostera marina Meadow

Aims: The problem addressed in this paper, was to reduce the number of sieves in order to propose appropriate methodologies for the estimations of abundance, secondary production, community composition and structure of benthic fauna associated to a Zostera marina meadow. Therefore we are aiming to calculate in an efficient way, secondary production of benthic communities in coastal areas associated to a Zostera marina meadow and examine the retention efficiency of different mesh sizes . Study Design: Bimonthly five randomly chosen cores of 15 cm of diameter and 18 cm length (area=176.7 cm≤), were collected. Place and Duration of Study: The samples were taken during one year period from June 2008 to June 2009 in a Zostera marina meadow at Punta Banda estuary, a shallow coastal

Effects of an oil spill on benthic community production and respiration on subtropical intertidal sandflats

This study determined effects of an oil spill on subtropical benthic community production and respiration by monitoring CO2 fluxes in benthic chambers on intertidal sandflats during emersion before and after an accidental spill. The oil spill decreased sediment chlorophyll a concentrations, altered benthic macrofaunal community, and affected ecological functioning by suppressing or even stopping microalgal production, increasing bacterial respiration, and causing a shift from an autotrophic system to a heterotrophic system. Effects of the oil spill on the macrofauna were more severe than on benthic microalgae, and affected sedentary infauna more than motile epifauna. Despite the oil spill’s impact on the benthic community and carbon metabolism, the affected area appeared to return to normal in about 23days. Our results suggest that the prompt response of benthic metabolism to exposure to petroleum hydrocarbons can serve as a useful indicator of the impact of an oil spill.

In situ production and respiration of the benthic community during emersion on subtropical intertidal sandflats

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 441:33-47 (2011) - DOI: https://doi.org/10.3354/meps09362 In situ production and respiration of the benthic community during emersion on subtropical intertidal sandflats Li-Hua Lee1,2, Li-Yung Hsieh1,2, Hsing-Juh Lin2,3,* 1Endemic Species Research Institute, Jiji, Nantou 552, Taiwan 2Department of Life Sciences, National Chung Hsing University, Taichung 402, Taiwan 3Biodiversity Research Center, Academia Sinica, Taipei 115, Taiwan *Email: hjlin@dragon.nchu.edu.tw ABSTRACT: In situ benthic community production and respiration during emersion were measured monthly in the course of a 19 mo survey from June 2008 to December 2009 by monitoring CO2 fluxes in benthic chambers on intertidal sandflats of a subtropical coastal wetland. Maximum gross community production (GCPm) and community respiration (CR) all exhibited higher values in summer and fall and lower values in spring and winter. GCPm and CR were positively correlated with air temperature. Temperature coefficients (Q10) showed that a rise of 10°C would increase the GCPm and CR by factors of 3.72 and 4.80, respectively. GCPm was also positively correlated with sediment grain size and negatively correlated with the silt/clay content. CR exhibited a strong positive correlation with sediment chlorophyll a concentration and macrofaunal biomass. To provide an accurate annual budget of benthic production during emersion, corrections were considered for cloudiness and the time lag between emersion and maximum production due to vertical migration of benthic diatoms and variations in CR during nighttime emersion periods. Annual net community production (NCP) during emersion on sandflats was estimated to be 2.87 g C m−2 yr−1, indicating an autotrophic system. However, taking into account the variation in benthic metabolism during immersion, the subtropical intertidal sandflats shifted to a heterotrophic system, and annual NCP was calculated to be −91.47 g C m−2 yr−1. KEY WORDS: Carbon sink · Gross community production · Community respiration · Net community production · Sediment granulometry · Kaomei Wetland · Taiwan Full text in pdf format PreviousNextCite this article as: Lee LH, Hsieh LY, Lin HJ (2011) In situ production and respiration of the benthic community during emersion on subtropical intertidal sandflats. Mar Ecol Prog Ser 441:33-47. https://doi.org/10.3354/meps09362 Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 441. Online publication date: November 15, 2011 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2011 Inter-Research.

Density, biomass, and production of selected benthic invertebrate taxa in two natural lakes and one fertilized lake in insular Newfoundland

Most studies of experimental perturbation of the benthiccommunity employ simple estimates of numerical abundancewhen making comparisons among treatments (Rosenberg& Resh 1993, Benke 1994). Although valid in manyinstances, numerical abundance is influenced by the balancebetween reproduction and death, each of which may respondindependently to the perturbation. Simple numerical esti-mates also cannot reflect differences in individual size thatmay result from growth rate enhancement. Secondary pro-duction estimates take reproduction, growth, and death intoaccount (Benke 1994) and thus may be more powerful indi-cators of ecosystem change and give us a better understand-ing of why changes are occurring. Secondary production esti-mates are infrequently reported, probably because theyrequire large sample sizes and labour-intensive weight deter-minations.Thus, benthic community production has usually beenneglected in mesocosm nutrient enrichment experiments andbenthic production estimates are almost non-existent inwhole-lake nutrient enrichment experiments. When benthicproduction estimates have been reported with respect toexperimental nutrient additions the results have been con-flicting. Peterson et al.(1993) observed initial growth rateincreases, but total secondary production did not increase dueto “top-down” processes (predation) in a tundra river system.Aagaard (1982) reported density increases for 2 chirono-mid species during a whole-lake enrichment experiment, butthese increases and the production estimates were reported asbeing within the limits expected by annual variation alone,and thus the effect due to the nutrient enrichment was notclear.Our study had 2 main objectives. First, to document thebenthic macroinvertbrate biomass and production of thedominate taxa in 3 small Newfoundland lakes and to put thisinformation in context with respect to other estimates foundin the literature. To our knowledge this is the first attempt atcalculating secondary production estimates for these habitatsin Newfoundland despite them being common and importantto the overall production of highly valued salmonid species(Dempson et al. 1996).Our second objective was to document the relationshipbetween whole-lake nutrient enrichment and its effect onbenthic secondary production. The working hypothesis forthis objective was that the increase in nutrient load to theenriched ecosystem would increase primary productivity,which in turn would increase the productivity of the benthos.Benthic responses could be manifested as numericalincreases (Clarke et al. 1997) and/or growth rate increases(larger size), both of which should be reflected in populationproduction estimates.

Annual budget of benthic production in Mont Saint-Michel Bay considering cloudiness, microphytobenthos migration, and variability of respiration rates with tidal conditions

In order to provide an accurate annual rate of net benthic community production, community photosynthetic response to incident irradiance and respiration were measured at different times of the year, at mid-tide level on the muddiest part of the Mont Saint-Michel Bay. As the water turbidity prevented any photosynthesis by the microphytobenthos during immersion periods, primary production was measured only during emersion periods. In contrast respiration was expected to vary according to the tidal cycle and was measured during both emersion and immersion periods. Primary production and respiration rates under emersion were assessed using in situ infra-red gas analysis of CO2 exchange measured in a benthic chamber. Respiration rates under immersion were assessed through total CO2 concentration variations in incubated cores.When respiration rate was considered constant over a day and equal to the rate measured under emerged conditions, the community respiration was 54.56gCm−2yr−1. Taking into account the variations of respiration during the emersion/immersion cycle, community respiration increased to 101.76gCm−2yr−1 (86% increase). Assuming that community primary production varied as a function of irradiance from the time of exposure until flooding, GCP was 53.22gCm−2yr−1 when calculated with theoretical irradiance and 45.86gCm−2yr−1 after correction for cloudiness (14% decrease). Then, by integrating the effect of vertical migration of microphytobenthos, the rate was adjusted to 23.49gCm−2yr−1 (49% decrease). The net community production budget, calculated as the difference between the GCP and the CR budgets taking into account the corrections described above, was −78.27gCm−2yr−1. This example of annual budget calculation highlights the need to integrate several processes occurring over various time scales to accurately reflect the metabolic balance of a system. The results also confirmed the heterotrophic status generally suggested for intertidal muddy sediments.

Dynamics of macrozoobenthos productivity characteristics on shelves of the Far Eastern seas in the 2000s

The trophic structure of benthic communities in the Sea of Okhotsk and Bering Sea was analyzed based on the results of macrobenthic survey catches conducted in the Far Eastern seas in the 2000s. The production of trophic levels and entire communities was determined. It was shown that production of benthic communities is still at a high level and has almost not changed since the 1980s. The arrangement of the communities of some shelf areas by productivity characteristics was made.

Low community photosynthetic quotient in coral reef sediments

Fluxes of dissolved inorganic carbon and oxygen at the water–sediment interface were measured at eight coral reef stations (Indian Ocean) in summer and winter. The dark fluxes provided the community respiratory quotient (CRQ = dissolved inorganic carbon release / oxygen uptake) and the diurnal fluxes corrected from the dark fluxes gave the community photosynthetic quotient (CPQ = oxygen gross release / dissolved inorganic carbon gross uptake). The CRQ and the winter CPQ were not significantly different from 1. Summer CPQ (0.79; SD 0.02) was significantly lower than 1 due to the combined effect of the daily evolution of the community respiration and the discrepancy between the daily evolution in community oxygen respiration and community carbon respiration. These results highlight the importance of measuring simultaneously the benthic community production and respiration for long term integrated data sets, instead of the traditional daily or seasonal budget calculations from limited measures of community respiration. To cite this article: D. Taddei et al., C. R. Biologies 331 (2008).

Indirect estimation of benthic secondary production in the Lagoon of Venice (Italy)

Five published indirect methods to estimate benthic secondary production of intertidal mudflats and a new proposed formulation based on quarter-power allometric scaling and the “Universal Temperature Dependence” of biological processes (UTD) were compared. For this purpose, a dataset consisting of an annual series of samples, taken from the Lagoon of Venice from March 1996 to March 1997, at sites characterised by different seagrass coverage was used. All methods resulted in that biomass and secondary production decreased progressively when moving from the seagrass meadow toward areas of unvegetated substrate, suggesting an influence of the available marine phanerogams on the neighbouring sites. The equation proposed in this paper gives results comparable with those obtained using empirical regression models from literature. The main conclusion from this study is that general equations proposed by the “metabolic theory of ecology” can be applied for indirect estimations of secondary production of benthic communities.

Role of the bacterial community in the annual benthic metabolism of two contrasted temperate intertidal sites (Roscoff Aber Bay, France)

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 344:39-48 (2007) - DOI: https://doi.org/10.3354/meps06947 Role of the bacterial community in the annual benthic metabolism of two contrasted temperate intertidal sites (Roscoff Aber Bay, France) Cédric Hubas1,2,*, Luis Felipe Artigas1, Dominique Davoult2 1FRE 2816 ELICO, Université du Littoral Côte d'Opale, Maison de la Recherche en Environnement Naturel, 32 av. Foch, Wimereux 62930, France 2UMR 7144 AD2M, Université Pierre et Marie Curie-Paris 6, Station Biologique de Roscoff, BP 74, Roscoff 29680, France *Email: hubas@sb-roscoff.fr ABSTRACT: The role of the bacterial community in the annual benthic metabolism of Roscoff Aber Bay, France, was estimated during low tide at 2 sampling sites of different trophic status, located at either end of a strong environmental gradient. The benthic gross primary production (GPP) and community respiration (BCR) were assessed in situ over 1 yr with a benthic chamber; simultaneously, bacterial production (BP) was estimated by radiotracer incorporation in slurries. BP appeared to be significantly controlled by temperature during low tide. On an annual scale, microphytobenthos gross primary production (GPPa), bacterial production (BPa), meiofauna production (MePa), macrofauna production (MaPa) and benthic community respiration (BCRa) were estimated. While the estimated annual processes were generally higher at the muddy station, our results indicated that (1) the contribution of BPa to the annual benthic community production (CPa = BPa + MePa + MaPa) increased with increasing grain size, and (2) the bacterial community can modulate its growth efficiency (BGEa) when exposed to an environmental gradient: in intertidal sediments, the production of new cells is enhanced when the organic matter concentration is lower, sustaining the development of the community on the annual scale. This behaviour was inferred to be the predominant factor affecting the trophic state of the system. KEY WORDS: Intertidal sediments · Benthic bacterial growth efficiency · Gross primary production · Community respiration Full text in pdf format PreviousNextCite this article as: Hubas C, Artigas LF, Davoult D (2007) Role of the bacterial community in the annual benthic metabolism of two contrasted temperate intertidal sites (Roscoff Aber Bay, France). Mar Ecol Prog Ser 344:39-48. https://doi.org/10.3354/meps06947 Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 344. Online publication date: August 23, 2007 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2007 Inter-Research.

Spatial and Temporal Variability in Dissolved Inorganic Nitrogen Fluxes at the Sediment–Water Interface in Lake Illawarra, Australia

In this study, benthic flux measurements of inorganic nitrogen (i.e., \( {\text{NH}}^{ + }_{4} \), \( {\text{NO}}^{ - }_{2} \) + \( {\text{NO}}^{ - }_{3} \)) were made using a batch incubation system at different stations (i.e., shallow sandy macrophyte and unvegetated beds, and deep central mud) over four seasons in Lake Illawarra, NSW, Australia, to study the influence of different primary producers (i.e., seagrasses, microphytobenthos (MPB) and macroalgae) and/or different sediment types (i.e., sand or mud) on the benthic fluxes. In general, nutrient fluxes displayed typical diel variations, with lower flux out of sediments (release) or enhanced uptake by the sediment in the light, due to the photosynthetic activities of the plant-MPB-sediment community in Lake Illawarra during photosynthetic periods. A distinct seasonal pattern of inorganic-N fluxes was also observed (e.g., the marked difference between summers 2002 and 2003). This may be explained by the seasonal variations in the biomass and activity (growing or decay phases) of MPB, seagrass and macroalgae, which may influence their nutrient assimilation and alter the chemical conditions of surface sediments that influence the benthic geochemical processes and thus benthic nutrient fluxes. On an annual basis, unvegetated sediments displayed net DIN effluxes, while seagrass beds showed a net DIN uptake, and the highest DIN uptakes coincided with the largest standing crop of seagrass and/or macroalgae and the highest levels of benthic community production. This may be due to the enhanced denitrification and/or assimilation activity by rooted plants and macroalgae, and the effect is most efficient during periods of net growth (e.g., in Spring 2002).

Closed-chamber System for Primary Production of Benthic Communities in Sub-tropical Lagoon

Closed-chamber System for Primary Production of Benthic Communities in Sub-tropical Lagoon

Short-term variability of intertidal benthic community production during emersion and the implication in annual budget calculation

Short-term variability in benthic community primary production was studied during the course of emersion on a study site located in the Bay of Somme (eastern English Channel, France). Primary production was estimated at the community level through in situ measurements of carbon dioxide fluxes (infra-red analysis) in benthic chambers. Throughout the emersion period, gross com- munity production (GCP) exhibited strong variations that were strongly correlated with natural vari- ations in light. Light response curves explained the variations in GCP during the greater part of the emersion period, and vertical migrations of the microphytobenthos were suggested to explain the remaining variations (i.e. just before or just after immersion of the study site). A time lag was observed between the start of emersion and the maximum GCP, which was positively correlated with the time lag between emersion and local noon. The introduction of this time lag within the annual budget calculation enhanced production variability at a 2 wk time scale (i.e. tidal cycle), but light variability at the small time scale (i.e. cloudiness) remained the major factor inducing production vari- ability. Results highlighted that omitting the time lag between emersion time and the maximum GCP within annual budget calculations led to large overestimations of annual GCP, since the annual bud- get for the study site was recalculated as being 67 g C m -2 yr -1 compared to 110 g C m -2 yr -1 when the short-term variability was not taken into account.