title: Marine-derived nitrogen and carbon in freshwater-riparian food webs of the Copper River Delta, southcentral Alaska

authors: Hicks, Brendan J.

subjects: stable isotopes

abstract: After rearing to adulthood at sea, coho salmon (Oncorhynchus kisutch) return to freshwater to spawn once and then die on or near their spawning grounds. We tested the hypothesis that spawning coho salmon return marine N and C to beaver (Castor canadensis) ponds of the Copper River Delta (CRD), Cordova, southcentral Alaska, thereby enhancing productivity of the aquatic food webs that support juvenile coho salmon. We sampled three types of pond treatment: (1) natural enrichment by spawning salmon, (2) artificial enrichment via addition of salmon carcasses and eggs, and (3) ponds with no salmon enrichment. All ponds supported juvenile coho salmon. Seasonal samples of stable isotopes revealed that juvenile coho salmon, threespine sticklebacks (Gasterosteus aculeatus), caddisfly larvae, leeches, and chironomid midge larvae were enriched with marine N and C. The aquatic vascular plants bur reed (Sparganium hyperboreum), pondweed (Potamogeton gramineus), and mare’s tail (Hippuris vulgaris) were enriched with marine N only. Riparian vegetation (Sitka alder Alnus viridis ssp. sinuata and willow Salix spp.) did not show enrichment. Artificial additions of adult carcasses and eggs of coho salmon increased the δ15N and δ13C values of juvenile coho salmon. In this dynamic and hydrologically complex coastal environment, spawning coho salmon contributed marine N and C comprising 10–50% of the dietary needs of juvenile coho salmon through direct consumption of eggs and carcass material. Invertebrates that have assimilated marine N and C yield a further indirect contribution. This perennial subsidy maintains the productivity of the ecosystem of the coho salmon on the CRD.

text: Marine-derived nitrogen and carbon in freshwater-riparian food webs of the Copper River Delta, southcentral Alaska After rearing to adulthood at sea, coho salmon (Oncorhynchus kisutch) return to freshwater to spawn once and then die on or near their spawning grounds. We tested the hypothesis that spawning coho salmon return marine N and C to beaver (Castor canadensis) ponds of the Copper River Delta (CRD), Cordova, southcentral Alaska, thereby enhancing productivity of the aquatic food webs that support juvenile coho salmon. We sampled three types of pond treatment: (1) natural enrichment by spawning salmon, (2) artificial enrichment via addition of salmon carcasses and eggs, and (3) ponds with no salmon enrichment. All ponds supported juvenile coho salmon. Seasonal samples of stable isotopes revealed that juvenile coho salmon, threespine sticklebacks (Gasterosteus aculeatus), caddisfly larvae, leeches, and chironomid midge larvae were enriched with marine N and C. The aquatic vascular plants bur reed (Sparganium hyperboreum), pondweed (Potamogeton gramineus), and mare’s tail (Hippuris vulgaris) were enriched with marine N only. Riparian vegetation (Sitka alder Alnus viridis ssp. sinuata and willow Salix spp.) did not show enrichment. Artificial additions of adult carcasses and eggs of coho salmon increased the δ15N and δ13C values of juvenile coho salmon. In this dynamic and hydrologically complex coastal environment, spawning coho salmon contributed marine N and C comprising 10–50% of the dietary needs of juvenile coho salmon through direct consumption of eggs and carcass material. Invertebrates that have assimilated marine N and C yield a further indirect contribution. This perennial subsidy maintains the productivity of the ecosystem of the coho salmon on the CRD.

year: 2005

title: A mass balance evaluation of the ecological significance of historical nitrogen fluxes in Lake Kinneret

authors: Nishri, A.

subjects: nitrate

abstract: Lake Kinneret (LK) is a monomictic lake that has undergone significant biological and chemical changes over the last three decades of the twentieth century. The transition between the 1970s and the 1980s attracted a lot of scientific attention as it was marked by significant changes in the ecology of the lake. In the early 1980s, phytoplankton biomass increased, apparently in response to an increase in the external soluble reactive phosphorus (SRP) load. This period was marked by a rise in hypolimnetic levels of ammonium (NH4) and SRP as well as surface water dissolved oxygen (DO) and pH. Cconcomitantly, in surface waters in winter levels of NH4 increased and NO₃ decreased. In this study interrelationships amongst these observations were examined with a mass balance modelling approach, including simulation of individual nutrient sources and sinks, focusing on nitrogen fluxes in winter. The step-like rise in phytoplankton biomass in 1981 may have been triggered by the increase in winter external loads of SRP, as P is likely to be the growth-limiting nutrient during this season. The additional P load led to a sequence of changes including greater summer phytoplankton biomass, followed by enhanced sedimentation of organic matter. Furthermore, higher organic matter mineralization fluxes within the hypolimnion resulted in elevated levels of NH4 and SRP in this layer through the 1980s, with a feedback to productivity in the trophogenic zone following seasonal destratification in early winter. In an apparent transition period (late 1970s to early 1980s), an increase in the modelled rate of nitrate (NO₃) production occurred via nitrification together with increased uptake of the additional nitrate by phytoplankton. These results are consistent with increased phytoplankton abundance and elevated levels of surface water NH4 and DO during this period. Through this period the increase in phytoplankton uptake of NO₃ predominated over the increase in nitrification, and NO₃ concentrations in the 1980s were reduced compared with the previous decade, with increased partitioning of N in biomass and NH₄.

text: A mass balance evaluation of the ecological significance of historical nitrogen fluxes in Lake Kinneret Lake Kinneret (LK) is a monomictic lake that has undergone significant biological and chemical changes over the last three decades of the twentieth century. The transition between the 1970s and the 1980s attracted a lot of scientific attention as it was marked by significant changes in the ecology of the lake. In the early 1980s, phytoplankton biomass increased, apparently in response to an increase in the external soluble reactive phosphorus (SRP) load. This period was marked by a rise in hypolimnetic levels of ammonium (NH4) and SRP as well as surface water dissolved oxygen (DO) and pH. Cconcomitantly, in surface waters in winter levels of NH4 increased and NO₃ decreased. In this study interrelationships amongst these observations were examined with a mass balance modelling approach, including simulation of individual nutrient sources and sinks, focusing on nitrogen fluxes in winter. The step-like rise in phytoplankton biomass in 1981 may have been triggered by the increase in winter external loads of SRP, as P is likely to be the growth-limiting nutrient during this season. The additional P load led to a sequence of changes including greater summer phytoplankton biomass, followed by enhanced sedimentation of organic matter. Furthermore, higher organic matter mineralization fluxes within the hypolimnion resulted in elevated levels of NH4 and SRP in this layer through the 1980s, with a feedback to productivity in the trophogenic zone following seasonal destratification in early winter. In an apparent transition period (late 1970s to early 1980s), an increase in the modelled rate of nitrate (NO₃) production occurred via nitrification together with increased uptake of the additional nitrate by phytoplankton. These results are consistent with increased phytoplankton abundance and elevated levels of surface water NH4 and DO during this period. Through this period the increase in phytoplankton uptake of NO₃ predominated over the increase in nitrification, and NO₃ concentrations in the 1980s were reduced compared with the previous decade, with increased partitioning of N in biomass and NH₄.

year: 2010

title: Mai uta ki tai: Cyclone-driven suspended sediment effects on early benthic juvenile kōura (Jasus edwardsii), Te Ākau o Tokomaru, Aotearoa

authors: Karaha-Paki, Vijuan

abstract: Kōura (Jasus edwardsii) are ecologically, culturally, and economically significant taonga species central to mahinga kai systems throughout Aotearoa New Zealand. In Te Tairāwhiti, particularly Te Ākau o Tokomaru, Cyclone Gabrielle (February 2023) resulted in unprecedented sediment loads being delivered to coastal waters, smothering inshore rocky reefs that serve as critical nursery habitats for settling puerulus and juvenile kōura. This research investigated how repeated suspended sediment exposure affects the body condition, survival, and physiological condition of early benthic juvenile kōura, integrating Western scientific methods with mātauranga Māori perspectives to support kaitiakitanga and ecosystem recovery. 

A 52-day pulse-based laboratory experiment exposed 81 early benthic juvenile kōura to three treatment levels: Control (0 mg/L), Tobserved (1,000 mg/L), and Tmaximised (5,000 mg/L) suspended sediment concentrations, alternating between exposure phases and recovery periods to simulate natural post-storm sedimentation dynamics. Sediment was sourced from the Mangahauini River mouth to reflect local conditions. Kōura were initially housed communally (Days 1-19), and then separated into individual tāruke following observed cannibalism. Across the experiment, body weight to carapace length (BW:CL) ratios, survival, blood refractive index, gill condition, and moult stage were assessed. 

All treatment groups began with statistically equivalent body condition (p = 0.135), but cumulative effects emerged over time. During communal housing, mortality was highest in the Tobserved treatment (51.9%) compared with Control and Tmaximised treatments (both 18.5%). After separation, Tmaximised individuals showed the greatest losses (45.5%), mostly during the recovery rather than exposure phases. Overall mortality reached 45.7%, with sediment-exposed treatments experiencing 55% (Tmaximised) to 59% (Tobserved) losses compared with 22.2% in the Controls (p = 0.001). 

By Day 52, sediment exposure significantly reduced body condition (p = 0.016), with the Controls maintaining higher BW:CL ratios than Tmaximised (p = 0.013). Gill assessments indicated universal and severe damage in sediment-exposed kōura (100%) but none in the Controls (0%). Quantitative image analysis confirmed strong sediment concentration- dependent effects across all damage metrics – particle lodgement, filament integrity, surface discolouration, and composite scores (all p < 0.001) – with structural deformities in 66.7% of Tobserved and 100% of Tmaximised individuals. Blood refractive index showed no treatment differences, and 84.1% of kōura remained in intermoult stage at Day 52, with no significant difference in moult stage distribution between treatments (p = 0.328). However, moult frequency during the individual phase was lower in sediment-exposed groups compared to the Controls (Control: n = 11, Tobserved: n = 4, Tmaximised: n = 5). 

These findings show that suspended sediment exposure poses population-level threats to kōura recruitment through irreversible gill damage and delayed mortality. Elevated cannibalism during communal holding, particularly observed in the Tobserved treatment, likely resulted from temporal clustering of moult events rather than sediment-induced behaviour. For Te Ākau o Tokomaru and the wider CRA 3 fishery, this highlights the need for integrated catchment-to- coast management addressing land-derived sediment inputs and protecting coastal nursery habitats. From a Te Ao Māori perspective, sedimentation represents a disruption to whakapapa relationships with Tangaroa and a weakening of mauri in coastal ecosystems. Restoring these connections requires co-governance frameworks that embed mātauranga Māori, empower kaitiaki-led monitoring and rāhui, and address the cumulative impacts of land-use intensification and repeated cyclone events on ecosystem resilience in Te Tairāwhiti.

text: Mai uta ki tai: Cyclone-driven suspended sediment effects on early benthic juvenile kōura (Jasus edwardsii), Te Ākau o Tokomaru, Aotearoa Kōura (Jasus edwardsii) are ecologically, culturally, and economically significant taonga species central to mahinga kai systems throughout Aotearoa New Zealand. In Te Tairāwhiti, particularly Te Ākau o Tokomaru, Cyclone Gabrielle (February 2023) resulted in unprecedented sediment loads being delivered to coastal waters, smothering inshore rocky reefs that serve as critical nursery habitats for settling puerulus and juvenile kōura. This research investigated how repeated suspended sediment exposure affects the body condition, survival, and physiological condition of early benthic juvenile kōura, integrating Western scientific methods with mātauranga Māori perspectives to support kaitiakitanga and ecosystem recovery. 

A 52-day pulse-based laboratory experiment exposed 81 early benthic juvenile kōura to three treatment levels: Control (0 mg/L), Tobserved (1,000 mg/L), and Tmaximised (5,000 mg/L) suspended sediment concentrations, alternating between exposure phases and recovery periods to simulate natural post-storm sedimentation dynamics. Sediment was sourced from the Mangahauini River mouth to reflect local conditions. Kōura were initially housed communally (Days 1-19), and then separated into individual tāruke following observed cannibalism. Across the experiment, body weight to carapace length (BW:CL) ratios, survival, blood refractive index, gill condition, and moult stage were assessed. 

All treatment groups began with statistically equivalent body condition (p = 0.135), but cumulative effects emerged over time. During communal housing, mortality was highest in the Tobserved treatment (51.9%) compared with Control and Tmaximised treatments (both 18.5%). After separation, Tmaximised individuals showed the greatest losses (45.5%), mostly during the recovery rather than exposure phases. Overall mortality reached 45.7%, with sediment-exposed treatments experiencing 55% (Tmaximised) to 59% (Tobserved) losses compared with 22.2% in the Controls (p = 0.001). 

By Day 52, sediment exposure significantly reduced body condition (p = 0.016), with the Controls maintaining higher BW:CL ratios than Tmaximised (p = 0.013). Gill assessments indicated universal and severe damage in sediment-exposed kōura (100%) but none in the Controls (0%). Quantitative image analysis confirmed strong sediment concentration- dependent effects across all damage metrics – particle lodgement, filament integrity, surface discolouration, and composite scores (all p < 0.001) – with structural deformities in 66.7% of Tobserved and 100% of Tmaximised individuals. Blood refractive index showed no treatment differences, and 84.1% of kōura remained in intermoult stage at Day 52, with no significant difference in moult stage distribution between treatments (p = 0.328). However, moult frequency during the individual phase was lower in sediment-exposed groups compared to the Controls (Control: n = 11, Tobserved: n = 4, Tmaximised: n = 5). 

These findings show that suspended sediment exposure poses population-level threats to kōura recruitment through irreversible gill damage and delayed mortality. Elevated cannibalism during communal holding, particularly observed in the Tobserved treatment, likely resulted from temporal clustering of moult events rather than sediment-induced behaviour. For Te Ākau o Tokomaru and the wider CRA 3 fishery, this highlights the need for integrated catchment-to- coast management addressing land-derived sediment inputs and protecting coastal nursery habitats. From a Te Ao Māori perspective, sedimentation represents a disruption to whakapapa relationships with Tangaroa and a weakening of mauri in coastal ecosystems. Restoring these connections requires co-governance frameworks that embed mātauranga Māori, empower kaitiaki-led monitoring and rāhui, and address the cumulative impacts of land-use intensification and repeated cyclone events on ecosystem resilience in Te Tairāwhiti.

year: 2025