300 research outputs found

    The comparison of macrobenthic recolonization patterns near and away from crab burrows on a sublittoral sand flat

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    This study assessed the influence of crab burrows (Macrophthalmus hirtipes) on localized patterns of macrobenthic colonization on a sand flat at 6 m depth in Otago Harbor, New Zealand. 150 m2 of surface sediments were artifically disturbed to simulate a storm and core samples were collected 2, 4, and 30 days later. At each time, samples were randomly collected near and away from crab burrows. A general pattern of high abundances away from burrows was apparent for most common taxa, number of taxa, number of individuals, and dominant polychaete feeding guilds. The differences in abundance near and away from burrows were evident over the three sampling occasions. On the basis of their potential for suspension and transport in the water column during a storm, individuals were allotted to two groups: movable and stationary. Significant trends of increasing abundance over time were found for the movable group, stationary group, and the total number of individuals in samples collected away from burrows. Samples collected near burrows showed a slight but nonsignificant decrease in abundance over time. Changes in the number of taxa over time were not significant, although a similar visual trend as observed for the total number of individuals was apparent. The same taxa were common near and away from burrows, but differences in abundance produced different patterns of colonization. The low abundances around burrows were attributed to the disturbance generated by crabs walking in and out of burrows. Generally the results reported in this study are similar to those which report the influence of ghost shrimps (Callianassa spp.) on macrofauna. This study also demonstrated that patterns of abundance near and away from burrows were maintained during recolonization after a simulated storm disturbance

    Effects of Polyester Microfibers on Microphytobenthos and Sediment-Dwelling Infauna

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    Microfibers often dominate sediment microplastic samples, but little is known about their ecological effects on benthic organisms and functions. Polyethylene terephthalate) (PET) microfibers were added to 36 sediment chambers at six concentrations (0-0.5 g kg-1 sediment) to assess the effects on microphytobenthos (MPB), a key deposit-feeding bivalve, Macomona liliana, and sediment nutrient pools. MPB photosynthesis was promoted in 18 chambers through a 12 h light/dark cycle. Another 18 chambers were maintained under dark conditions to inhibit photosynthesis. After 35 days of MPB growth and stabilization, four M. liliana were added to each chamber for a further 40 days. MPB biomass and composition were examined alongside M. liliana biochemical and behavioral properties and porewater dissolved inorganic nutrient concentrations. Increasing microfibers resulted in lower MPB biomass, fewer diatom-associated fatty acids (FAs), and an increase in cyanobacteria. The changes in MPB coincided with up to 75% lower energy reserves and reduced burrowing activity in M. liliana. In the light, nitrate + nitrate (NOx) was significantly elevated and related to M. liliana and MPB biochemical properties. Ammoniu (NH4+) concentrations increased but were variable in both the light and the dark. Our results suggest that increasing microfiber concentrations influence the interactions between M. liliana and MPB and affect biogeochemical processing in coastal marine sediments

    The role of microphytobenthos in soft‐sediment ecological networks and their contribution to the delivery of multiple ecosystem services

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    Sediment dwelling, microscopic primary producers, that occupy sediments in the photic zone, are commonly referred to as microphytobenthos (MPB). The MPB are essential components of soft-sediment systems, but are often overlooked when assessing coastal ecosystem functionality and service delivery. The MPB are involved in several complex interactions and feedback that underpin the delivery of vital ecosystem services. MPB profoundly influence the flow and cycling of carbon and nutrients, such as nitrogen, directly and indirectly underpinning highly productive shallow water marine food webs. The MPB can also stabilize sediments through the formation of biofilms, and significantly improve water quality by mediating the benthic–pelagic coupling of nutrients, sediment and pollutants. The functional role of the MPB is compromised by increasing anthropogenic pressures such as nutrient enrichment, sedimentation, herbicides and emerging contaminants such as microplastic pollution. However, MPB are extremely good at buffering the effects of these land-sourced stressors at the interface between land and sea. Synthesis. Society often appreciates the final provisioning of goods and services from our coastal marine environments. However, provisioning services are only possible due to the multitude of supporting and regulating services that underpin them. Microphytobenthos (MPB) are central to benthic ecological networks, and contribute to ecosystem service delivery through various pathways. Understanding the critical role of MPB in complex networks is therefore essential to appreciate their importance in ecosystem function and service delivery into the future

    Microplastics interact with benthic biostabilization processes

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    Funding: J A H would like to acknowledge funding from two anonymous philanthropic donors through the 'Oceans of Change' and the 'Microphytes & Microplastics' projects. G C was funded by MBIE Endeavour Research Programme; ID C03X1802; Impacts of microplastics on New Zealand. J A H and D R P would like to acknowledge partial funding from Horizon 2020 European Research Council Consolidator Award (GEOSTICK, Grant 725955).Marine microplastics (MPs) accumulate in sediments but impacts on ecosystem functions are poorly understood. MPs interactions with stabilizing benthic flora/fauna or biostabilization processes, have not been fully investigated, yet this is critical for unraveling MPs effects on ecosystem-scale processes and functions. This is also vital for understanding feedback processes that may moderate the stock and flow of MPs as they are transported through estuaries. The relationships between sedimentary MPs, biota, environmental properties and sediment stability from field sediments, were examined using variance partitioning (VP) and correlation analyses. VP was used to identify common and unique contributions of different groups of variables (environmental, fauna and microplastic variables) to sediment stability. The influence of microplastic presence (fragment/fiber abundances and microplastic diversity) on sediment stability (defined using erosion thresholds and erosion rates) was demonstrated. Furthermore, MPs appeared to mediate the biostabilizing effects of environmental properties (including microorganisms) and fauna. Environmental properties and sediment stability could also explain the variation in MPs across sites suggesting biostabilizing properties may mediate the abundance, type and diversity of MPs that accumulate in the bed. The potential for MPs to influence biota and biostabilization processes and mediate microplastic resuspension dynamics within estuaries is discussed.Publisher PDFPeer reviewe

    Seabed drag coefficient over natural beds of horse mussels (Atrina zelandica)

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    Measurements of seabed drag coefficient, C100, were made under tidal currents at four sites in Mahurangi Harbour, New Zealand. At the first three sites the dominant roughness element was the pinnid bivalve, Atrina zelandica (horse mussel). At the fourth site, which was devoid of horse mussels but covered in cockle shells, patches of seaweed and crab burrows, C100 was smallest (0.0055), but still twice as large as the value typically applied to abiotic, flat, cohesionless seabeds (0.0025). The mean drag coefficient plus-or-minus standard error at the three sites with horse mussels was: 0.0082 ± 0.0010 (site 1); 0.0096 ± 0.0009 (site 2); 0.0115 ± 0.0016 (site 3). There were no clear differences amongst sites 1, 2 and 3 in terms of the attributes of individual horse mussels (e.g. shell height, width or orientation), which could have been used to explain the ranking of the drag coefficients. There were, however, differences amongst the three sites in terms of spatial distribution of individual bivalves. The site with the highest density of horse mussels, site 1, had the lowest drag coefficient and an areal concentration (λ) of horse mussels higher than typical values cited for the critical concentration (λc) for the onset of skimming flow over various idealized, three-dimensional roughness elements. At sites 2 and 3, the drag coefficient was given by: C100=[Îș/1n (300/mkλ)]2 which was valid for λ \u3c λ c, where Îș is von Karman\u27s constant, k is the horse mussel height (i.e., protrusion above the seabed), m ≈ 100 and λc ≈ 0.2. The stable eddies that are hypothesized to lodge between roughness elements at concentrations greater than λc may influence benthic community dynamics

    Tipping Points in Coastal Ecosystems

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    Change can happen fast in our coastal ecosystems and we often do not know what has been lost until it’s too late. Once ecological ‘tipping points’ are passed, it is difficult to reverse the state of the ecosystem.1 Often these changes creep up on us because they are caused by the cumulative impact of multiple stressors. These changes in ecosystems mean we can lose important ecosystem functions that underpin many of the things we value about out coastal ecosystems. One of the key challenges of ecosystem-based management (EBM) is therefore to identify what combination of stressors are likely to cause threshold changes and what parts of the ecosystem are most likely to be affected. A multi-institutional team of scientists from across New Zealand is conducting the science to assess the risk of passing these ‘tipping points’ in estuaries before they happen

    Structure of the internal boundary layer over a patch of pinnid bivalves (Atrina zelandica) in an estuary

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    Measurements of tidal-current boundary-layer flow over an experimental 2-m by 2-m patch of pinnid bivalves (Atrina zelandica) in a northern New Zealand estuary are presented. Previous work demonstrated a link between mesoscale (order 100 m) patchiness of the benthic biota and time-averaged boundary-layer dynamics. The aim in this new experiment was to describe the three-dimensional structure of turbulence at the patch scale (order 1 m). Flow over three densities of Atrina was investigated: 340 individuals per 4 m2, 50 individuals per 4 m2 and zero individuals. An internal boundary layer (IBL) grows downstream from the leading edge of the patch at the base of the ambient boundary layer. One meter in from the leading edge, the top of the IBL was ~ 12 cm above the bed for the high-density patch and ~ 6 cm for the low-density patch. Flow in the IBL was three-dimensional in that vertical and transverse mean velocities were nonzero, secondary Reynolds stresses were nonzero and comparable with the primary stress, and velocity spectra deviated from scaling relationships for two-dimensional flow. Thus, the observed IBL was still in its infancy, i.e., it consisted of a roughness sublayer only as the distance from the leading edge of the patch was not enough for development of a second, overlying logarithmic layer. In summary, the IBL that envelops the Atrina patch is a region of lower mean longitudinal velocities but more energetic turbulence relative to the ambient boundary layer. The former translates into shelter, which some organisms might take advantage of, and the latter translates into increased vertical exchange across the top of the IBL, which might enhance fluxes of nutrients, colonists and suspended sediments, and might have implications for deposition and resuspension of organically rich biodeposits. The results extend our knowledge of turbulence over patches of suspension feeders at the 1-m scale and therefore provide information needed to improve depiction of flow in models of suspension-feeder-flow interactions

    ANALISIS PEMAHAMAN KONSEP MATEMATIKA SISWA DENGAN MODEL PEMBELAJARAN PROBLEM BASED LEARNING PADA POKOK BAHASAN SEGITIGA (Study deskriptif di Kelas VII SMP Negeri 2 Plered Kab. Cirebon)

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    Anggun Maya Sari. NIM 59451058. “Analisis Pemahaman Konsep Matematika Siswa dengan Model Pembelajaran Problem Based Learning pada Pokok Bahasan Segitiga”. (Studi Deskriptif di Kelas VII SMP Negeri 2 Plered). Pembelajaran yang efektif adalah pembelajaran yang menyediakan kesempatan kepada siswa untuk belajar mandiri, sehingga dalam prosesnya siswa dapat memperoleh pemahaman dan pengetahuan dengan lebih mendalam. Akan tetapi proses kegiatan pembelajaran matematika yang berlangsung disekolah, pada umumnya guru hanya sekedar penyampai informasi tanpa mempertimbangkan seberapa jauh pemahaman siswa terhadap konsep matematika dari pokok bahasan segitiga yang disampaikan. Tujuan penelitian ini adalah 1) mengetahui seberapa besar pemahaman konsep yang dimiliki peserta didik; 2) mengetahui factor pendukung dan penghambat peserta didik dalam memahami konsep yang diberikan; 3) mengetahui deskripsi aktivitas siswa dalam memahami konsep matematika melalui model pembelajaran Problem Based Learning; 4) mengetahui respon siswa setelah melaksanakan model pembelajaran Problem Based Learning; 5) mengetahui sejauhmana pemahaman konsep matematika siswa setelah mengikuti proses pembelajaran Problem Based Learning. Penerapan model pembelajaran Problem Based Learning (PBL) merupakan salah satu model pembelajaran yang dapat memberikan kondisi belajar aktif kepada siswa. Dengan diterapkannya pembelajaran matematika dengan model pembelajaran PBL, diharapkan dapat membantu siswa dalam memahami konsep matematika. Penelitian ini menggunakan pendekatan kualitatif dan kuantitatif dengan metode deskriptif. Pengumpulan data menggunakan lembar observasi, pedoman wawancara, angket dan tes. Informan dalam penelitian ini adalah kelas VII yang sudah dibentuk kelompok kelas, yaitu VII A, VII D dan VII F. dengan menggunakan proportionate stratified random sampling, maka dari masingmasing kelompok kelas didapat 18 siswa sebagai informan penelitian. Berdasarkan dari hasil wawancara tentang siswa dalam pemahaman konsep matematika, diperoleh siswa masih kurang dan masih perlu banyak bimbingan. Aktivitas siswa selama pembelajaran melalui model pembelajaran PBL diperoleh dari hasil lembar observasi dengan nilai rata-rata dari semua aspek sebesar 54,39% yang termasuk dalam kategori sedang. Berdasarkan angket respon siswa setelah dilaksanakan model pembelajaran PBL termasuk dalam kategori baik dengan nilai rata-rata 76,44%. Pemahaman konsep matematika siswa setelah mengikuti proses pembelajaran dengan model pembelajaran PBL diperoleh siswa lebih rajin dalam mencari bahan untuk menyelesaikan soal-soal yang diberikan dan menambah pemahaman siswa mengenai konsep matematika, meski masih belum 100% benar, dan hasil tes didapat nilai rata-rata 39% yang termasuk dalam kategori sangat kurang. Kata Kunci: Pemahaman konsep matematika, Problem Based Learning, Segitig

    Positive contribution of macrofaunal biodiversity to secondary production and seagrass carbon metabolism

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    Funding Information: We thank A. Toikkanen and N. Uotila for their valuable work in the laboratory, and I. McDonald for field assistance. We thank two anonymous reviewers for their very constructive comments that helped improve this paper. The study was funded by the Academy of Finland (Project ID 294853) and the University of Helsinki and Stockholm University strategic fund for collaborative research (The Baltic Bridge initiative). DL and ST were supported by a senior visiting research fellowship funded by the Walter and Andrée de Nottbeck Foundation. Publisher Copyright: © 2022 The Authors. Ecology published by Wiley Periodicals LLC on behalf of The Ecological Society of America.Coastal vegetated habitats such as seagrasses are known to play a critical role in carbon cycling and the potential to mitigate climate change, as blue carbon habitats have been repeatedly highlighted. However, little information is known about the role of associated macrofauna communities on the dynamics of critical processes of seagrass carbon metabolism (e.g., respiration, turnover, and production). We conducted a field study across a spatial gradient of seagrass meadows involving variable environmental conditions and macrobenthic diversity to investigate (1) the relationship between macrofauna biodiversity and secondary production (i.e., consumer incorporation of organic matter per time unit), and (2) the role of macrofauna communities in seagrass organic carbon metabolism (i.e., respiration and primary production). We show that, although several environmental factors influence secondary production, macrofauna biodiversity controls the range of local seagrass secondary production. We demonstrate that macrofauna respiration rates were responsible for almost 40% of the overall seafloor community respiration. Macrofauna represented on average >25% of the total benthic organic C stocks, high secondary production that is likely to become available to upper trophic levels of the coastal food web. Our findings support the role of macrofauna biodiversity in maintaining productive ecosystems, implying that biodiversity loss due to ongoing environmental change yields less productive seagrass ecosystems. Therefore, the assessment of carbon dynamics in coastal habitats should include associated macrofauna biodiversity elements if we aim to obtain robust estimates of global carbon budgets required to implement management actions for the sustainable functioning of the world's coasts.Peer reviewe
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