Microphytobenthic Biomass Research Articles

Mapping intertidal microphytobenthic biomass with very high-resolution remote sensing imagery in an estuarine system

Microphytobenthos (MPB) contributes significantly to estuarine primary production, so that quantifying its biomass is crucial for assessing their ecosystem functioning. Conventional sampling methods are labour-intensive, logistically challenging, and cannot provide a comprehensive spatial distribution map of MPB biomass. Satellite imagery has offered a feasible alternative for mapping large areas at various temporal and spatial resolutions. However, no imaging device with a spatial resolution consistent with the few square centimetres sampled in-situ has been used in the field. This makes it challenging to accurately relate field biomass measurements with remotely sensed radiometric observations. In this study, two similar multispectral sensors were mounted on an unmanned aerial vehicle (UAV) at different altitudes, as well as on a custom-built device specifically designed to acquire images at ∼1 m altitude, in order to collect very-high spatial resolution reflectance data of MPB biofilms at the Guadalquivir Estuary (Spain) mudflats. In addition, a hyperspectral spectroradiometer acquiring in-situ field reflectance was used for validation. Simultaneously, MPB samples were collected using a 2 mm depth contact corer method, which were analysed through high-performance liquid chromatography (HPLC) to measure the concentrations of major MPB pigments. To assess the relationship between the MPB pigments and different reflectance-based spectral indices, generalised linear mixed effects models (GLMMs) were used, achieving a significant positive relationship between chlorophylls and all spectral indices tested. These models were used to map microphytobenthic biomass, yielding a mean biomass in the range of 30–50 mg Chl-a m−2 in the Guadalquivir estuary during late winter. This study demonstrates the potential of low-altitude/high spatial resolution radiometric imaging as an efficient, rapid, and non-destructive addition to in-situ measurements of MPB biomass, providing exciting perspectives for the monitoring of estuarine systems on a millimetric scale of variability.

Influence of nutrient enrichment on colonisation and photosynthetic parameters of hard substrate marine microphytobenthos

This study aimed to assess the influence of nutrient enrichment on the development of microalgal biofilm on concrete and PVC cubes. Three mesocosms were utilized to create a nutrient gradient over a period of 28 days. Various parameters including biomass, photosynthetic activity, microtopography, and extracellular polymeric substances (EPS) were measured. Imaging PAM techniques were employed to obtain surface-wide data. Results revealed that nutrient availability had no significant impact on Chl a biomass and the maximum quantum efficiency of PSII (/). The photosynthetic capacity and efficiency were minimally affected by nutrient availability. Interestingly, the relationship between microphytobenthic (MPB) biomass and photosynthesis and surface rugosity exhibited distinct patterns. Negative reliefs showed a strong correlation with / while no clear pattern emerged for biomass on rough concrete structures. Overall, our findings demonstrate that under conditions of heightened eutrophication, biofilm photosynthesis thrives in the fissures and crevasses of colonized structures regardless of nutrient levels. This investigation provides valuable insights into the interplay between nutrient availability and surface rugosity.

Altered nitrogen transformation pathways and a legacy of sediment organic matter enrichment

Estuaries are ecologically valuable ecosystems that process nutrients through complex biogeochemical processes. Here we identify drivers and inhibitors of nitrogen removal in unvegetated intertidal sandflats at six sites in Manukau Harbour (37° 2.00′S 174° 42.00′E) to quantify the exchange of solutes across the sediment-water interface, with nitrogen removal rates (NRR) measured at two contrasting sites (PI and CB) near and far, respectively, from an historical wastewater treatment plant. Solute fluxes were paired with sediment and macrofauna community data to identify drivers of ecosystem function. Fluxes of oxygen, nitrogen and phosphorous were found to vary among sites, with differences attributed to variation in sediment characteristics (grain size, chlorophyll a, organic content) and macrofauna community structure. Mean NRR was found to vary between sites (PI = 32.2 vs CB = 217.9 μmol N2/m2/h), with bioturbating macrofauna (bivalves Austrovenus stutchburyi and Macomona liliana), microphytobenthic biomass, and exposure to nutrients likely key contributing drivers.

Influence of microphytobenthos on the sedimentary organic matter composition in two contrasting estuarine microhabitats.

The influence of microphytobenthic community on the composition of sedimentary organic matter was evaluated in two Bahía Blanca estuary microhabitats contrasting in vegetation and hydrodynamic conditions; namely, S1 located in a Sarcocornia perennis saltmarsh with macroscopic microbial mats and S2 in a mudflat without macroscopic microbial mats or vegetation. Moisture, organic matter, chlorophyll a, phaeopigments, carbohydrates (CH), proteins (PRT), and abundance and structure of microphytobenthic community were evaluated in surface sediments. Higher moisture was observed at S2 and was related to the proximity of this site to the subtidal zone and the effect of the environmental variables temperature and rain. No significant differences were found in organic matter content between sites; however, at S1, a higher concentration was registered during winter and early spring associated to the period of higher microphytobenthic biomass. Chlorophyll a and phaeopigments were higher at S1, attributed to the higher microphytobenthos abundance at this site. Differences in microphytobenthos were observed not only in quantity but also in community structure since at S1 filamentous cyanobacteria dominated the community, whereas at S2, higher abundance of centric diatoms and the absence of cyanobacteria were observed during most of the study. S1 showed higher concentration of proteins and carbohydrates which could be attributed to the higher production of fresh organic matter by microphytobenthos. The total protein and carbohydrate concentrations allowed us to classify both microhabitats into the meso-oligotrophic category, contrasting with the classification made by other authors using water column proxies.

Microphytobenthic primary production on exposed coastal sandy sediments of the Southern Baltic Sea using ex situ sediment cores and oxygen optodes

The shallow coastal water zone of the tide-less southern Baltic Sea is dominated by exposed sandy sediments which are typically inhabited by microphytobenthic communities, but their primary production is poorly studied, and hence four stations between 3.0 and 6.2 m depth were investigated. Sediment cores were carefully taken to keep the natural layering and exposed in a controlled self-constructed incubator. Respiratory oxygen consumption and photosynthetic oxygen production were recorded applying planar oxygen optode sensors. We hypothesized that with increasing water depths the effects of wind- and wave-induced erosion and mixing of the upper sediment layer are dampened and expected higher microphytobenthic biomass and primary production in the incubated cores.Our data partly confirm this hypothesis, as cores sampled at the most exposed stations contained only 50% chlorophyll a m−2 compared to the deeper stations. However, primary production was highly variable, probably due to fluctuating sediment-disturbing conditions before the cores were taken. Due to these physical forces sand grains were highly mobile and rounded, and small epipsamic benthic diatoms dominated, which preferentially occurred in some cracks and crevices as visualized by scanning electron microscopy. The data fill an important gap in reliable production data for sandy sediments of the southern Baltic Sea, and point to the ecological importance and relevant contribution of microphytobenthic communities to the total primary production of this marine ecosystem. Oxygen planar optode sensor spots proved to be a reliable, sensitive and fast detection system for ex situ oxygen exchange measurements in the overlying water of intact sediment cores.

The importance of weather and tides on the resuspension and deposition of microphytobenthos (MPB) on intertidal mudflats

Abiotic variables, such as weather and tidal forces, are potentially as important as biotic factors (growth, predation, competition) in driving the variability of microphytobenthic (MPB) biomass on intertidal flats. Patterns of spatial distribution and temporal variability in MPB Chl. a, sediment Extracellular Polymeric Substances (EPS) and benthic diatom species composition were investigated during daily sampling spanning neap to spring tide periods on intertidal mudflats in the Colne Estuary, U.K., in three different seasons, with a particular focus on the influence of wind, rainfall, sun hours in the days prior to sampling, and tidal range. Spatial distribution (at < 1 m and <5 m scales) made the greatest contribution to biomass variability, followed by temporal (inter-monthly) variability. MPB Chl. a and EPS concentrations were positively correlated with sun-hours and tidal range, and negatively with rainfall and wind speed. Higher benthic MPB biomass was associated with lower suspended solid and Chl a loads, indicating biostabilisation of surface sediment. Suspended sediment loads and suspended Chl. a concentrations were positively correlated, and were significantly higher during neap rather than spring tides. Sediment settlement rates were higher during neap tides and related to suspended sediment load. The percent similarity in the benthic and suspended diatom assemblages (species relative abundance, RA) increased linearly with suspended solid load, with highest similarity during neap tides, with pennate benthic diatom taxa (Gyrosigma balticum, G. scalproides and Pleurosigma angulatum) dominant, indicating local sediment resuspension. During Spring tides, species similarity was lower, with a higher RA of planktonic centric diatoms (Actinoptychus, Coscinodiscus and Odontella) and lower sediment loads. Despite greater volumes of water movement during high tidal range periods, the highest levels of localised resuspension and remobilisation of MPB biomass across the mudflats occurred during low tidal range neap tide periods, when wind-induced waves were a key factor, particularly with shallower water depths over the intertidal mudflats.

Contrasted impact of two macrofaunal species (Hediste diversicolor and Scrobicularia plana) on microphytobenthos spatial distribution and photosynthetic activity at microscale

Microphytobenthos is most often the primary source of carbon for coastal soft-sediment communities, especially in intertidal and shallow subtidal environments. The influence of benthic macrofaunal organisms on microphytobenthic biomass, spatial distribution and photosynthetic capacities is not only resulting from their feeding intensity but also indirectly from their bioturbation activity, which regulates nutrient fluxes and sediment mixing. This study compares the impact of two species (Hediste diversicolor and Scrobicularia plana) that dominate macrofaunal communities in estuarine intertidal mudflats on microphytobenthic biomass and photosynthetic activity. Imaging-PAM fluorescence was used to non-invasively map the development of microphytobenthic biomass and to assess its spatial extent. Our results showed that, due to intense deposit feeding, Scrobicularia plana quickly limited microphytobenthos growth and photosynthetic activity, even at low density (<250 ind m−2). In contrast, the negative impact of Hediste diversicolor on microphytobenthos development due to direct consumption was very low. Thereby, the stimulation of nutrient fluxes at the sediment-water interface resulting from bioirrigation seems to enhance microphytobenthos growth and photosynthesis.

Evidence for better microphytobenthos dynamics in mixed sand/mud zones than in pure sand or mud intertidal flats (Seine estuary, Normandy, France).

Understanding the dynamics of microphytobenthos biomass and photosynthetic performances in intertidal ecosystems will help advance our understanding of how trophic networks function in order to optimize ecological management and restoration projects. The main objective of this study was to investigate microphytobenthic biomass and photosynthetic performances as a function of the sedimentary and environmental variabilities in the range of intertidal habitats in the downstream Seine estuary (Normandy, France). Our results highlight higher biomass associated with more stratified biofilms and better photosynthetic performances in areas characterized by a sand/mud mixture (40–60% of mud) compared to pure sand or pure mud environments. This type of sediment probably offers an efficient trade-off between the favorable characteristics of the two types of sediments (sand and mud) with respect to light penetration and nutrient accessibility. Moreover, the large quantities of exopolysaccharides produced in sand/mud mixtures emphasizes the functional role played by microphytobenthos in promoting sediment stability against erosion. This allows us to show that despite the strong increase in sand content of the downstream Seine estuary, intertidal flats are still productive since microphytobenthic biomass, photosynthetic performances and exopolysaccharides secretion are highest in sand-mud mixtures. This study also underlines the impact of ecosystem modifications due to human disturbance and climate change on the dynamics of key primary producers in estuaries.

Feeding selectivity of Holothuria atra in different microhabitat in Panjang Island, Jepara (Java, Indonesia)

Abstract. Hartati R, Zainuri M, Ambariyanto A, Widianingsih W. 2020. Feeding selectivity of Holothuria atra in different microhabitat in Panjang Island, Jepara (Java, Indonesia). Biodiversitas 21: 2233-2239. Particle selectivity by deposit feeder sea cucumber Holothuria atra was an important concept in its feeding ecology. This species utilized the organic matter that coated sediment and detrital particles as food. Thus, particle size, organic matter, and microalgal biomass had been proposed as variables food resources along which niche separation could occur in optimal foraging strategy. This study was conducted in five microhabitats of different coverage of seagrass bed (P1-P4) up to the rubble area (P5) over a tidally variable depth range of 0,5-5m in Panjang island, Jepara. Twenty samples of sea cucumber H. atra were taken from defined microhabitat, along with samples of sediment underneath the sea cucumber. Granulometry of the particles ingested by sea cucumbers, total organic matter, and microphytobenthic biomass (as chlorophyll-a) found throughout their digestive tract (alimentary canal) and in the sediments was analyzed. Comparison of the contents and the rates of organic matter assimilation of the digestive tract with those of the microhabitat sediment were carried out. The results showed that H. atra fed on sediment underneath their body and it was revealed that there were strong (ƿ=0.833-0.876) to very strong (ƿ=0.945) positive relationship between grain size in the sediment and in their alimentary canal which showed their feeding selectivity of the sediment. H. atra also found to have efficiency in feeding by taking advantage of the high TOM content and high abundance of microphytobenthic organisms (presented as chlorophyll-a) in their natural microhabitats.

Effects of two estuarine intertidal polychaetes on infaunal assemblages and organic matter under contrasting crab bioturbation activity

Polychaetes and burrowing crabs are widely distributed in intertidal soft bottom environments, playing an important role in structuring infaunal assemblages through trophic and non-trophic interactions such as bioturbation. In southwestern Atlantic (SWA; 37°40′S, 57°23′W) intertidal mudflats, the polychaetes Laeonereis acuta and Neanthes succinea coexist with the burrowing crab Neohelice (Chasmagnathus) granulata. N. granulata and L. acuta strongly modify the sediment characteristics at different spatial scales, changing the infaunal assemblages and probably affecting feeding mode of N. succinea, which could prey upon L. acuta. Here, we experimentally evaluated the effects of constant densities of L. acuta and N. succinea on the benthic species assemblages and sediment organic matter (OM) content in two contrasting scenarios of crab bioturbation: inside and outside crab beds. We found that (1) both polychaetes did not affect the mean density of other macrofaunal organisms neither the meiofauna in general, but L. acuta modifies the abundance of specific groups such as foraminiferans; (2) polychaetes produced changes in meiofaunal spatial distribution probably by adding habitat heterogeneity; and (3) no evidence of predation of N. succinea on L. acuta were observed. Additionally, the variable effects of polychaetes on chlorophyll and OM content showed that they were species-specific and also modified by crab bioturbation. Moreover, effects of crab bioturbation on primary producers, quality and content of OM, and on some macro and meiofaunal organisms were found. Our results suggest that the effects of L. acuta and N. succinea on benthic species and OM content are mostly species-specific and, with regard to food sources (OM content and microphytobenthic biomass), strongly modified by larger scale crab bioturbation.

A model to assess microphytobenthic primary production in tidal systems using satellite remote sensing

Quantifying spatial variability in intertidal benthic productivity is necessary to guide management of estuaries and to understand estuarine ecological processes, including the amount of benthic organic carbon available for grazing, burial and transport to the pelagic zone.We developed a model to assess microphytobenthic (MPB) primary production using (1) remotely sensed information on MPB biomass and remotely sensed information on sediment mud content, (2) surface irradiance and ambient temperature (both from local meteorological observations), (3) directly-measured photosynthetic parameters and (4) a tidal model. MPB biomass was estimated using the normalized-difference vegetation index (NDVI) and mud content was predicted using surface reflectance in the blue and near-infrared, both from Landsat 8 satellite imagery. The photosynthetic capacity (maximum photosynthesis rate normalized to MPB chl-a) was estimated from ambient temperature, while photosynthetic efficiency and the light saturation parameter were derived from in situ fluorometry-based production measurements (PAM). The influence of tides (submergence by turbid water) on MPB production was accounted for in the model. The method was validated on several locations in two temperate tidal basins in the Netherlands (Oosterschelde and Westerschelde). Model based production rates (mg C m−2 h−1) matched well with an independent set of in situ (PAM) measurement based production rates (Oosterschelde: RMSE = 9.7, mean error = 1.5, χ = 0.57; Westerschelde: RMSE = 46.7, mean error = −17.6, χ = 0.9). The relationship between photosynthetic capacity and temperature shows considerable variation and may be improved by using sediment surface temperature instead of ambient temperature. A sensitivity analysis revealed that emersion duration and mud content determine most of the variability in MPB production. Our results demonstrate that it is possible to derive a satellite remote sensing-based overview of average hourly and daily MPB primary production rates at the macro scale. As the proposed model is generic, the model can be applied to other tidal systems to assess spatial variability in MPB primary production at the macro scale after calibration at the site of interest. Model calibration, results and possible applications for regular monitoring of MPB production are discussed below.

Spatio-temporal variability in Mediterranean rocky shore microphytobenthos

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 575:17-29 (2017) - DOI: https://doi.org/10.3354/meps12216 Spatio-temporal variability in Mediterranean rocky shore microphytobenthos E. Maggi1,2,*, L. Rindi1,2, M. Dal Bello1,2,5, D. Fontanini3, A. Capocchi3, L. Bongiorni4, L. Benedetti-Cecchi1,2 1Dipartimento di Biologia, Università di Pisa, Via Derna 1, 56126 Pisa, Italy 2CoNISMa, Consorzio Nazionale Interuniversitario per le Scienze del Mare, 00196 Rome, Italy 3Dipartimento di Biologia, Università di Pisa, Via L. Ghini 13, 56126 Pisa, Italy 4Istituto di Scienze Marine - Consiglio Nazionale delle Ricerche (ISMAR-CNR), Arsenale - Tesa 104, Castello 2737/F, 30122 Venezia, Italy 5Present address: Massachusetts Institute of Technology, 77 Massachusetts Avenue, Cambridge, MA 02139, USA *Corresponding author: emaggi@biologia.unipi.it ABSTRACT: Knowledge of spatio-temporal variability of assemblages is the first step in identifying key factors affecting the abundance and distribution of organisms. Despite a long history of ecological studies on rocky intertidal habitats, there is still a lack of basic knowledge about the microphytobenthic components. We investigated the spatio-temporal variability of microphytobenthos in the northwest Mediterranean at multiple scales, including both seasonal and daily observations, as well as its composition. Spatial variability of microphytobenthic biomass varied significantly with season, with an increase in small-scale variance from cold to warm periods. Furthermore, during warmer months, small-scale variances (tens to hundreds of centimeters) were larger than large-scale components (tens to thousands of meters). These results suggest large spatio-temporal variation in the processes driving variation in microphytobenthic assemblages, including interactive effects among stressful abiotic conditions, substratum topography and grazing. In addition, observed variability on a daily scale suggested that microphytobenthos at the study site (dominated by cyanobacteria) might cope with stressful environmental conditions through both physiological and behavioral strategies at micro-spatial scales, including small movements within the substratum. Additional research on ecological and physiological aspects of rocky shore microphytobenthos is needed to better understand its role within interaction webs and primary productivity processes. KEY WORDS: Spatio-temporal variability · Microphytobenthos · Daily variation · Bacterial diversity · Rocky shore · Mediterranean Sea Full text in pdf format PreviousNextCite this article as: Maggi E, Rindi L, Dal Bello M, Fontanini D, Capocchi A, Bongiorni L, Benedetti-Cecchi L (2017) Spatio-temporal variability in Mediterranean rocky shore microphytobenthos. Mar Ecol Prog Ser 575:17-29. https://doi.org/10.3354/meps12216 Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 575. Online publication date: July 20, 2017 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2017 Inter-Research.

Microphytobenthic biomass, species composition and environmental gradients in the mangrove intertidal region of the Andaman Archipelago, India.

Monthly sampling in mangrove intertidal sediments of Andaman Archipelago was carried out during a 1-year study (January to December, 2013) in order to analyse the spatial and temporal distribution of microphytobenthos (MPB) and MPB biomass (sediment chlorophyll-a (chl-a)) in the surficial layer 0-1cm. The MPB community was mainly composed of diatoms. The MPB biomass concentration in surface sediment (0-1cm) ranged from 0.7 to 16.98μgcm-3. Population density of benthic diatoms varied from 78 to 224 indcm-3. This study identified 41 diatom taxa (27 pennate diatoms, 14 centric diatoms) in the sediment, and among all the diatom taxa, we distinguished few true planktonic species-Coscinodiscus centralis, Coscinodiscus marginatus, Leptocylindricus danicus, Planktoniella sol, Thalassiosira decipiens, Thalassionema nitzschioides and Thalassiothrix longissima. Overall, a high percentage of diatoms were pennate (81%) as opposed to centric. Based on benthic diatom abundance, species composition and distribution, MPB assemblages of sampling stations were grouped into two distinct clusters: one with St. 1 and St. 3 and another one with St. 2 and St. 4. Canonical correspondence analysis (CCA) revealed seasonality as the most important factor determining variability in diatom species composition among sampling sites. There was a distinct seasonal pattern in MPB biomass distribution and benthic diatom cell density during monsoon and post-monsoon seasons. Our results suggest that among various physical and chemical variables studied, greater levels of overlying water nutrients and sediment textures significantly correlated and were conducive factors for MPB. This is the first detailed study on the MPB from these mangrove sediments, providing benchmark data for future studies about these remote groups of Andaman and Nicobar Islands.

Nitrogen Retention in Coastal Marine Sediments—a Field Study of the Relative Importance of Biological and Physical Removal in a Danish Estuary

The aim of this study was to elucidate the relative importance of physical versus biological loss processes for the removal of microphytobenthic (MPB) bound nitrogen in a coastal environment at different times of the year via a dual isotope labeling technique. We used 51Cr, binding to inorganic sediment particles but not participating in any biological processes, and 15N–NO3−, taken up by the MPB and turned over as part of the MPB nitrogen pool. Retention, down-mixing, and export of 15N were due to both biological and physical processes, so that by comparing retention of the two isotopes, we were able to discern the relative importance of physical and biological processes. The isotope marking was supplemented with measurements of sediment chlorophyll biomass and oxygen fluxes, allowing us to evaluate MPB biomass as well as primary production vs. respiration in the sediment. In spring/early summer, the system was characterized by tight N cycling and high N retention: any remineralized N was immediately taken up and retained in the MPB biomass. In late summer and autumn, the system was still physically stable, but high biological mediated N losses were observed. In early winter, the system was physically dominated due to low MPB biomasses and activity combined with a significant storm event. Our data support the hypothesis that the relative balance between physical and biological processes in determining retention and removal of MPB-bound nitrogen changes seasonally.

Declines in benthic macroinvertebrate community metrics and microphytobenthic biomass in an estuarine lake following enrichment by hippo dung.

Hippos transfer massive quantities of trophic resources from terrestrial to aquatic ecosystems through defecation. The ramifications of the latter for the functioning of benthic ecosystems are unknown, but are dependent ultimately on rates of utilisation relative to inputs. Low input and high utilisation can strengthen bottom-up pathways and enhance consumer biomass and abundance. However, if inputs exceed utilisation rates, dung can accumulate, leading to a decline in water quality, with important repercussions for resident assemblages. Here, we quantify the consequences of hippo dung inputs on benthic assemblages in an estuarine lake in South Africa. The system supports over a thousand hippos, and during recent drought periods (extending over a decade), hippo dung has been observed to form mats over benthic habitats. Enrichment of plots using exclusion/inclusion cages with dung at naturally occurring concentrations indicated a decline in benthic chl-a by roughly 50% and macrofaunal abundance, biomass and richness by up to 76, 56 and 27% respectively. Our findings suggest that persistent inputs of hippo dung can act as an important stressor of benthic systems, leading ultimately to a loss of productivity. Accumulation of hippo dung over benthic habitats is therefore an important mechanism by which hippos indirectly structure aquatic ecosystems.

Microbial-meiofaunal interrelationships in coastal sediments of the Red Sea.

Population density and biomass of bacteria and meiofauna were investigated seasonally in the sediments of the north-western bank of Red Sea. Samples of sediments were collected seasonally from three different stations to determine microphytobenthic biomass (chlorophyll a), protein, lipid, carbohydrate, and total organic matter concentrations. These investigations revealed that microbial components tended to increase their dominancy, whereas sensitive meiofauna were extremely reduced during the entire study period. Thus a very low density of the total meiofauna (with an annual average of 109 ± 26 ind./10 cm2) was recorded whilst the benthic microbial population densities exhibited higher values (ranging from 0.31 ± 0.02 × 108 to 43.67 ± 18.62 × 108/g dry sediment). These changes in the relative importance analysis of benthic microbial components versus meiofaunal ones seem to be based on the impact of organic matter accumulation on the function and structure of these benthic communities. Proteins, lipids and carbohydrates showed very low concentration values, and the organic matter mostly consisted of carbohydrates, reflecting lower nutritional values for benthic fauna in general and meiofauna in particular. The distribution of microbial and meiofaunal communities seems to be dependent on the quality of the organic matter rather than on its quantity. Total organic matter concentrations varied between 5.8 and 7.6 mg/g, with organic carbon accounting for only 32% of the total organic matter. Chlorophyll a attained very low values, fluctuating between 0.11 and 0.56 μg/g, indicating the oligotrophy of the studied area. The very low concentration of chlorophyll a in the Red Sea sediment suggests that the sedimentary organic matter, heterotrophic bacteria and/or protozoa constitute an alternative resource that is consumed by meiofauna when algae are less abundant. Protozoa, therefore, represent the “missing link in bacteria–meiofauna interaction in the Red Sea marine sediment ecosystem.

Combined engineering effects of clams and crabs on infaunal assemblages and food availability in intertidal systems

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 540:57-71 (2015) - DOI: https://doi.org/10.3354/meps11478 Combined engineering effects of clams and crabs on infaunal assemblages and food availability in intertidal systems M. Fernanda Alvarez1,2,*, Mariana Addino1,3, Oscar Iribarne1, Florencia Botto1 1Laboratorio de Ecología, Instituto de Investigaciones Marinas y Costeras (IIMyC), Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET), Universidad Nacional de Mar del Plata (UNMdP), Dean Funes 3350 - CP 7600, Argentina 2Present address: Laboratorio Cuenca del Salado, Instituto de Limnología “Dr. Raúl A. Ringuelet” (ILPLA-CONICET), Universidad Nacional de La Plata (UNLP), Boulevar 120 no. 1460- CP 1900, Argentina 3Present address: Grupo de Ecología y Paleoecología de Ambientes Acuáticos Continentales (IIMyC-CONICET-UNMdP), Dean Funes 3350 - CP 7600, Argentina *Corresponding author: feralvarez@ilpla.edu.ar ABSTRACT: In soft sediments, ecosystem engineers (EEs) may play key roles in modifying habitats and therefore affecting bottom-assemblage species. In the southwestern Atlantic mud flats, 2 EEs coexist: the stout razor clam Tagelus plebeius and the burrowing crab Neohelice (Chasmagnathus) granulata. Clams create small depressions (i.e. millimeters), while crabs build large burrows (i.e. centimeters) generating crab beds covering many hectares. We hypothesized that these differences in the bioturbation scale may have different consequences for infaunal assemblages. We found that (1) microscale sediment-surface heterogeneities created by clams (e.g. holes and surrounding depressions) were related to higher organic-matter content and microphytobenthic biomass (measured as chlorophyll a), (2) abundances of meiofaunal groups (copepods, ostracods, and nematodes) were higher in clam holes than outside at all tidal levels, and (3) habitats with a more heterogeneous structure—such as clam holes inside a crab bed—had a higher food availability and an abundance of several meiofaunal groups (e.g. ostracods, and principally nematodes). Large-scale bioturbation (crab-bed formation) also affected primary producers, infaunal assemblages, and clam distribution, because at the highest intertidal levels clams were absent outside the crab beds. Our results thus demonstrate the differential effects of 2 contrasting EEs on the organization of soft-bottom communities and the key role of microheterogeneities in adding specific structures to already modified systems on a larger scale. KEY WORDS: Ecosystem engineers · Habitat structure · Infaunal assemblages · Clams · Crabs Full text in pdf format PreviousNextCite this article as: Alvarez MF, Addino M, Iribarne O, Botto F (2015) Combined engineering effects of clams and crabs on infaunal assemblages and food availability in intertidal systems. Mar Ecol Prog Ser 540:57-71. https://doi.org/10.3354/meps11478 Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 540. Online publication date: November 26, 2015 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2015 Inter-Research.

Intertidal biofilm distribution underpins differential tide-following behavior of two sandpiper species (Calidris mauri and Calidris alpina) during northward migration

The discovery that some shorebird species graze heavily on biofilm adds importance to elucidating coastal processes controlling biofilm, as well as impetus to better understand patterns of shorebird use of intertidal flats. Western sandpipers (Calidris mauri) and dunlin (Calidris alpina) stopover in the hundreds of thousands on the Fraser River estuary, British Columbia, Canada, during northward migration to breeding areas. Western sandpipers show greater modification of tongue and bill morphology for biofilm feeding than dunlin, and their diet includes more biofilm. Therefore, we hypothesized that these congeners differentially use the intertidal area. A tide following index (TFI) was used to describe their distributions in the upper intertidal during ebbing tides. Also, we assessed sediment grain size, biofilm (= microphytobenthic or MPB) biomass and invertebrate abundance. Foraging dunlin closely followed the ebbing tide line, exploiting the upper intertidal only as the tide retreated through this area. In contrast, western sandpipers were less prone to follow the tide, and spent more time in the upper intertidal. Microphytobenthic biomass and sediment water content were highest in the upper intertidal, indicating greater biofilm availability for shorebirds in the first 350 m from shore. Invertebrate density did not differ between sections of the upper intertidal. Overall, western sandpiper behaviour and distribution more closely matched MPB biofilm availability than invertebrate availability. Conservation of sandpipers should consider physical processes, such as tides and currents, which maintain the availability of biofilm, a critical food source during global migration.

Spatial Distributions of Grazing Activity and Microphytobenthos Reveal Scale-Dependent Relationships Across a Sedimentary Gradient

The density, spatial structure and functional roles of macrofaunal and microphytobenthic (MPB) communities change across sedimentary gradients. Grazing by macrofauna can impose considerable top-down control on MPB biomass at the scale of the animal’s feeding ambit (cm scale), yet how relationships between deposit feeders and MPB scale up across such transitional environments (10’s m scale) is poorly understood. We determined the relationship between sediment chlorophyll-a concentration (a proxy of MPB biomass), distance to feeding traces (a proxy of recent deposit feeding activity) made by the tellinid bivalve Macomona liliana (at cm scale) and macrofaunal densities (at 10’s m scale) across a sediment mud content gradient. Correlative relationships, estimated by generalised least-squares regression, between recent deposit feeding activity and MPB biomass were scale dependent and significant only at the site (10’s m) scale. MPB biomass declined by 28 % as coverage of feeding traces increased from 2 to 28 %, with feeding trace area contributing significantly to variation in chlorophyll-a (std. coefficient = −0.24, p = 0.01). However, the interaction term between the density of the suspension-feeding clam Austrovenus stutchburyi and sediment mud content explained a larger amount of the variability (std. coefficient = 0.72, p < 0.001). Our results demonstrate that significant effects on MPB biomass can emerge across large, spatially heterogeneous areas of tidal flat, despite appearing stochastic at small scales. They also highlight the need to consider interactions between MPB and macrofauna across abiotic gradients and the potential roles of non-deposit feeding taxa.

Microalgal responses to physico-chemical variability in the small temporarily open/closed Seteni Estuary, South Africa

The Seteni Estuary is a small temporarily open/closed estuary (TOCE) in South Africa under the influence of agricultural practices. While the general significance of microalgae to estuarine production is widely recognised, the factors regulating microalgal biomass in these heterogeneous systems are less well understood, particularly when man-induced pressures are superimposed on natural variability. This study investigated microalgal responses to physico-chemical variability in the nutrient-enriched Seteni Estuary in 2008–2009. Microphytobenthic biomass ranged from 1.1 to 91.7 mg Chl a m-2, while phytoplankton biomass varied between 0.22 and 18 mg Chl a m-3. Despite the high dissolved inorganic nitrogen (DIN) concentrations recorded, salinity and rainfall were identified as the main environmental drivers, highlighting the importance of allochthonous inputs. While this system appears to function as a typical TOCE, the relatively low microalgal biomass recorded may be an artifact of several factors such as phosphorus limitation, herbicide treatment, etc., acting singly or together to depress biomass levels. However, should the balance be upset, the most probable result would be a dramatic increase in microalgal biomass, to the point where harmful algal blooms may ensue. The system therefore needs to be closely monitored to prevent further degradation.