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13. The Effect of Sediment Mud Content on Primary Production in Seagrass and Unvegetated Intertidal Flats.

Author

Flowers, Georgina J. L., Needham, Hazel R., Bulmer, Richard H., Lohrer, Andrew M., and Pilditch, Conrad A.

Subjects
MUD, ESTUARINE sediments, EFFECT of human beings on climate change, SEAGRASSES, PRODUCTION losses, NUCLEAR power plants
Abstract

As a consequence of anthropogenic activities and climate change, accelerated terrestrial sediment runoff is causing the gradual mudification of soft sediment estuarine habitats worldwide. Increased sediment mud content (< 63 µm) has been recognised to alter seagrass morphology and cause declines in primary production in unvegetated habitats. However, the effect of increased mud content on primary production in seagrass meadows remains largely unknown. To address this, primary production in intertidal seagrass meadows (Zostera muelleri) and adjacent unvegetated habitats was measured in situ using benthic incubation chambers across an existing sedimentary gradient (nine sites spanning 5–33% mud content). An additional two unvegetated mudflat sites (39–49% mud content) were also sampled to expand the gradient. Seagrass net (NPP) and gross primary production (GPP) was greater than in the adjacent unvegetated habitat and did not vary with mud content, even after standardising GPP by photosynthesising biomass (i.e. photosynthetic efficiency). In contrast, in the adjacent unvegetated habitat, photosynthetic efficiency declined with increasing mud content. Inclusion of the additional mudflat sites negatively impacted NPP, GPP, and photosynthetic efficiency in the unvegetated habitat. Thus, while primary production in seagrass meadows may have some resilience to future increases in mud content (up to ~33%), further degradation and loss of seagrass habitats could result in the expansion of unvegetated habitats and ultimately lead to production losses, likely to be most acute in areas with high mud content (≥ 39%). [ABSTRACT FROM AUTHOR]

Published
2024
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15. Modelling spatial distributions of biogenic habitat‐forming taxa to inform marine spatial planning

Author

Bennion, Matthew, primary, Brough, Tom, additional, Leunissen, Eva, additional, Morrison, Mark, additional, Hillman, Jenny R., additional, Rowden, Ashley A., additional, Gordon, Dennis P., additional, Kelly, Michelle, additional, Nelson, Wendy, additional, Tracey, Dianne M., additional, Macpherson, Diana, additional, Neill, Kate, additional, Lohrer, Andrew M., additional, and Lundquist, Carolyn J., additional

Published
2024
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20. The effects of terrestrial sediment inputs on ecosystem functions in seagrass meadows and unvegetated sediments

Author

Pilditch, Conrad A., Needham, Hazel Rosemary, Lohrer, Andrew M., Bulmer, Richard H., Flowers, Georgina, Pilditch, Conrad A., Needham, Hazel Rosemary, Lohrer, Andrew M., Bulmer, Richard H., and Flowers, Georgina

Abstract

Ecological functions in estuarine seagrass and unvegetated soft sediment habitats underpin many valuable ecosystem services. However, changing land-use and climate are accelerating inputs of fine terrestrial sediments, threatening these habitats. The prolonged suspension of fine sediments can reduce seafloor light availability and long-term accumulations increase sediment mud content (particles < 63 µm), both of which could have significant consequences on ecosystem functioning. Understanding how ecosystem functioning may respond to environmental change is vital to estuary management. In this thesis, I investigated the short- and long-term effects of elevated terrestrial sediment inputs on benthic primary production and nutrient cycling in intertidal seagrass meadows (Zostera muelleri) and microphytobenthos-dominated unvegetated habitats. To investigate the effects of reduced seafloor light availability and prolonged submergence periods resulting from global heating induced sea-level rise, I conducted a two-year seasonal in situ assessment of photosynthesis-irradiance relationships during submerged and emerged conditions in an adjacent seagrass meadow and unvegetated sandflat. Submerged gross primary production (GPP) in both habitats and emerged GPP in the seagrass habitat were strongly controlled by light availability. Higher rates of light-saturated GPP were found during submerged periods compared to emerged periods in both habitats, but this difference was most pronounced in the unvegetated habitat. If the water-column remains clear, sea-level rise could therefore increase daily GPP in soft sediment habitats. However, declines in submerged GPP with increased water-column turbidity will be exacerbated with sea-level rise. Across a natural mud content gradient, I measured primary production in seagrass and unvegetated habitats to address the long-term implications of elevated sediment inputs. In sediments with ≤ 35 % mud content, net primary production (NPP) and GP

Published
2024

21. Variations in ecosystem service provision of two functionally similar bivalve habitats.

Author

Rullens, Vera, Lohrer, Andrew M., Townsend, Michael, and Pilditch, Conrad A.

Subjects
*BIVALVES, *HABITATS, *WATER quality, *NITROGEN in water, *ECOSYSTEM services, *QUALITY of service, *WATER quality monitoring
Abstract

The quantification of ecosystem services (ES) remains challenging and can result in biases towards data-rich ES in management. For infaunal bivalves, little quantitative in situ data are available on the ES they provide, and differences between functionally similar species in different habitats are rarely considered. Here, we aimed to measure and compare the ecosystem functions (primary production, nutrient processing, water clearance rates) underpinning water quality regulation in an estuarine intertidal and subtidal bivalve habitat (dominated by Austrovenus stutchburyi and Paphies australis respectively). In situ benthic chambers were used to measure sediment–water column solute fluxes (NH4+, N2, O2) and clearance rates which were scaled up (accounting for habitat differences; e.g. inundation period) to daily estimates of ES potential. Higher hourly microphytobenthic productivity, nitrogen recycling and water filtration were observed for the intertidal bivalve habitat. These differences were attributed to environmental differences rather than differences in bivalve biomass. However, scaling these rates to daily ES estimates showed that inundation period will restrict water quality regulating services in the intertidal. Measuring multiple ecosystem functions in situ provides an important step forward in ES quantification and accounts for ecological complexity, feedbacks and highlights habitat-specific differences in how functionally similar species contribute to ES. [ABSTRACT FROM AUTHOR]

Published
2024
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32. Loved to pieces: Toward the sustainable management of the Waitematā Harbour and Hauraki Gulf

Author

Aguirre, J. David, Bollard-Breen, Barbara, Cameron, Marcus, Constantine, Rochelle, Duffy, Clinton A.J., Dunphy, Brendon, Hart, Kyna, Hewitt, Judi E., Jarvis, Rebecca M., Jeffs, Andrew, Kahui-McConnell, Richelle, Kawharu, Margaret, Liggins, Libby, Lohrer, Andrew M., Middleton, Irene, Oldman, John, Sewell, Mary A., Smith, Adam N.H., Thomas, Daniel B., Tuckey, Ben, Vaughan, Mel, and Wilson, Ross

Published
2016
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