title: The effects of terrigenous sediment on the behaviour of Macomona liliana (Bivalvia) in permeable sediments: Implications for porewater exchange

authors: McCartain, Lisa

subjects: Bivalve

abstract: Catastrophic sedimentation events create one off disturbances that can cause mass mortality events in receiving estuaries. In contrast, the deposition of small amounts of terrigenous sediment (TS) is on-going and likely to have long-term consequences for benthic communities who, play important roles in ecosystem functioning. The aim of this thesis was to look at the effects of small amounts of TS on the behaviour of an infaunal deposit-feeding bivalve (Macomona liliana), which may have implications for sediment porewater fluxes and ecosystem functioning. To determine the effect of TS on behaviour, mesocosm experiments in a recirculating flume tank were run. Time lapse imagery was used to capture surface activity, and high resolution pressure sensors were buried within the sediment and captured changes in hydraulic activity. The effect of three TS treatments were tested, low, high and mixed. The low and high treatments were surface additions of TS (0.09 g cm -2 and 0.20 g cm -2, respectively) and represented the initial deposition and build-up of TS. The mixed treatment, mixed 0.20 g cm -2 through the top 2 cm of sediment, to mimic the incorporation of TS into marine sediments over time. Behaviours were observed pre- and post-treatment addition, and were compared to determine the effect of TS on M. liliana behaviour. The surface (top 2 cm) sediment properties were measured to determine the degree of surface modification by the TS treatments.
TS significantly modified the properties of the sediment surface and the hydraulic conductivity. These caused subtle, but significant, changes in some of the behaviours observed in M. liliana, and on a whole, behaviour which bioturbated the sediment surface decreased. Two feeding modes were observed at the surface, deposit-feeding and suspension-feeding/ventilation. There was a switch in feeding modes, from deposit-feeding to suspension-feeding/ventilation, in the low and mixed treatments. The duration of suspension-feeding/ventilation was, on average, three times longer than deposit-feeding, across all treatments, therefore a switch in modes altered the temporal patterns of sediment pressurisation. The amplitude of sediment pressurisation during feeding was significantly increased in the mixed treatment (up to 5× higher) as a result of decreased hydraulic conductivity. Additionally, the pressure signal measured during deposit-feeding was twice that of suspension-feeding/ventilation in the mixed treatment. 
Collectively the short-term changes in M. liliana behaviour are likely to increase sediment stability and the persistence of TS in the environment, potentially causing long-term degradation to habitat and M. liliana condition. As a result of reduced hydraulic conductivity, larger porewater fluxes are likely to be generated in the mixed treatment, and this would be two fold larger during deposit-feeding than in suspension-feeding/ventilation. This paired with the different temporal scales of the two feeding modes, and the observed switches in feeding modes, would have important consequences for geochemical conditions. Rather than short periods of high pressurisation, there would be longer periods of smaller pressurisations, which would increase the duration of sediment oxygenation, but reduce the porewater flux. This is likely to promote more stable geochemical conditions, which when compared to oscillating conditions, has been shown to reduce nutrient recycling and estuarine productivity.

text: The effects of terrigenous sediment on the behaviour of Macomona liliana (Bivalvia) in permeable sediments: Implications for porewater exchange Catastrophic sedimentation events create one off disturbances that can cause mass mortality events in receiving estuaries. In contrast, the deposition of small amounts of terrigenous sediment (TS) is on-going and likely to have long-term consequences for benthic communities who, play important roles in ecosystem functioning. The aim of this thesis was to look at the effects of small amounts of TS on the behaviour of an infaunal deposit-feeding bivalve (Macomona liliana), which may have implications for sediment porewater fluxes and ecosystem functioning. To determine the effect of TS on behaviour, mesocosm experiments in a recirculating flume tank were run. Time lapse imagery was used to capture surface activity, and high resolution pressure sensors were buried within the sediment and captured changes in hydraulic activity. The effect of three TS treatments were tested, low, high and mixed. The low and high treatments were surface additions of TS (0.09 g cm -2 and 0.20 g cm -2, respectively) and represented the initial deposition and build-up of TS. The mixed treatment, mixed 0.20 g cm -2 through the top 2 cm of sediment, to mimic the incorporation of TS into marine sediments over time. Behaviours were observed pre- and post-treatment addition, and were compared to determine the effect of TS on M. liliana behaviour. The surface (top 2 cm) sediment properties were measured to determine the degree of surface modification by the TS treatments.
TS significantly modified the properties of the sediment surface and the hydraulic conductivity. These caused subtle, but significant, changes in some of the behaviours observed in M. liliana, and on a whole, behaviour which bioturbated the sediment surface decreased. Two feeding modes were observed at the surface, deposit-feeding and suspension-feeding/ventilation. There was a switch in feeding modes, from deposit-feeding to suspension-feeding/ventilation, in the low and mixed treatments. The duration of suspension-feeding/ventilation was, on average, three times longer than deposit-feeding, across all treatments, therefore a switch in modes altered the temporal patterns of sediment pressurisation. The amplitude of sediment pressurisation during feeding was significantly increased in the mixed treatment (up to 5× higher) as a result of decreased hydraulic conductivity. Additionally, the pressure signal measured during deposit-feeding was twice that of suspension-feeding/ventilation in the mixed treatment. 
Collectively the short-term changes in M. liliana behaviour are likely to increase sediment stability and the persistence of TS in the environment, potentially causing long-term degradation to habitat and M. liliana condition. As a result of reduced hydraulic conductivity, larger porewater fluxes are likely to be generated in the mixed treatment, and this would be two fold larger during deposit-feeding than in suspension-feeding/ventilation. This paired with the different temporal scales of the two feeding modes, and the observed switches in feeding modes, would have important consequences for geochemical conditions. Rather than short periods of high pressurisation, there would be longer periods of smaller pressurisations, which would increase the duration of sediment oxygenation, but reduce the porewater flux. This is likely to promote more stable geochemical conditions, which when compared to oscillating conditions, has been shown to reduce nutrient recycling and estuarine productivity.

year: 2013

title: Innovation and the local workforce

authors: Maré, David C.

subjects: O31

abstract: We combine firm-level innovation data with area-level Census data to examine the relationship between local workforce characteristics, especially the presence of immigrants and local skills, and the likelihood of innovation by firms. We examine a range of innovation outcomes, and test the relationship for selected subgroups of firms. We find a positive relationship between local workforce characteristics and average innovation outcomes in labour market areas, but this is accounted for by variation in firm characteristics such as firm size, industry, and research and development expenditure. Controlling for these influences, we find no systematic evidence of an independent link between local workforce characteristics and innovation.

text: Innovation and the local workforce We combine firm-level innovation data with area-level Census data to examine the relationship between local workforce characteristics, especially the presence of immigrants and local skills, and the likelihood of innovation by firms. We examine a range of innovation outcomes, and test the relationship for selected subgroups of firms. We find a positive relationship between local workforce characteristics and average innovation outcomes in labour market areas, but this is accounted for by variation in firm characteristics such as firm size, industry, and research and development expenditure. Controlling for these influences, we find no systematic evidence of an independent link between local workforce characteristics and innovation.

year: 2013

title: Evaluating the effects of invasive brown bullhead catfish (Ameiurus nebulosus) on kōura (freshwater crayfish, Paranephrops planifrons) in Lake Rotoiti

authors: Francis, Laura Beverley

subjects: catfish

abstract: Brown bullhead catfish (Ameiurus nebulosus) are opportunistic carnivores native to North America and were first detected in Te Weta Bay, Lake Rotoiti, in March 2016. A cordon was placed across the bay to try and contain catfish, but they had already established populations elsewhere. Spread of catfish in the lake raised concern for resident populations of freshwater crayfish or kōura (Paranephrops planifrons), which are of ecological and cultural significance to Māori. Given the limited knowledge of the potential impacts of catfish on native biota, this thesis aims to evaluate the effects of catfish on kōura in Lake Rotoiti. To do this, Bay of Plenty Regional Council (BOPRC) routine fyke netting data was used to explore species trends and relationships. A habitat survey was also conducted using whakaweku (bracken fern bundles) and fyke nets, to generate data on species’ habitat preferences and kōura metrics (e.g., sizes and sex ratios). In addition to fishing, kōura and catfish stomachs were dissected to determine diet. Potential food items of catfish were also collected for stable isotope analysis to estimate dietary overlap between catfish and kōura, and long-term resource acquisition. 

Routine BOPRC fyke netting results indicated that kōura catch per unit effort (CPUE) has declined in Lake Rotoiti, with mean catch rates dropping from 10.6 kōura net-1 night-1 in 2016 to 4.2 kōura net-1 night-1 in 2018. Over the same period, catfish CPUE has increased in the lake, with the highest catch rates in Te Weta Bay, where mean catch rates have increased from 1.1 catfish net-1 night-1 in 2016 to 63.7 catfish net-1 night-1 in 2018. Catfish catch rates were negatively associated with catch rates of kōura (r = −0.180). Mean catfish density also had a significant effect on kōura catch rates, with significantly more kōura being caught at sites without catfish. The negative association between catfish and kōura could be due to catfish eating or competing with kōura, or their differing habitat preferences. Catfish were positively associated with sites that are weedy or muddy and kōura were negatively associated with muddy habitats and were positively associated with rocky habitats. Whakaweku set at shallow depths <1 m in the lake littoral zone were ineffective at catching kōura during the habitat survey. 

Catfish diet consisted largely of chironomid larvae (Chironomidae), detritus, common bullies (Gobiomorphus cotidianus), and to a lesser extent kōura. Kōura were found in 12% of large catfish (>200 mm fork length; FL) stomachs analysed and contributed 5% volumetrically to large catfish diet. Unfortunately, the contribution of kōura to catfish diet could not be established using stable isotopes because isotopic signatures of kōura and bullies were too close to differentiate. Kōura diet consisted primarily of animal remains (common bullies and invertebrates) and detritus. Stable isotopes of carbon and nitrogen revealed that diets of kōura and catfish overlapped, with kōura sharing more of their diet with catfish than vice versa, likely reflecting catfish’s broad diet. This study suggests that catfish are responsible for the recent decline in kōura CPUE in Lake Rotoiti and that catfish are directly and indirectly affecting kōura through predation and competition for shared food resources.

text: Evaluating the effects of invasive brown bullhead catfish (Ameiurus nebulosus) on kōura (freshwater crayfish, Paranephrops planifrons) in Lake Rotoiti Brown bullhead catfish (Ameiurus nebulosus) are opportunistic carnivores native to North America and were first detected in Te Weta Bay, Lake Rotoiti, in March 2016. A cordon was placed across the bay to try and contain catfish, but they had already established populations elsewhere. Spread of catfish in the lake raised concern for resident populations of freshwater crayfish or kōura (Paranephrops planifrons), which are of ecological and cultural significance to Māori. Given the limited knowledge of the potential impacts of catfish on native biota, this thesis aims to evaluate the effects of catfish on kōura in Lake Rotoiti. To do this, Bay of Plenty Regional Council (BOPRC) routine fyke netting data was used to explore species trends and relationships. A habitat survey was also conducted using whakaweku (bracken fern bundles) and fyke nets, to generate data on species’ habitat preferences and kōura metrics (e.g., sizes and sex ratios). In addition to fishing, kōura and catfish stomachs were dissected to determine diet. Potential food items of catfish were also collected for stable isotope analysis to estimate dietary overlap between catfish and kōura, and long-term resource acquisition. 

Routine BOPRC fyke netting results indicated that kōura catch per unit effort (CPUE) has declined in Lake Rotoiti, with mean catch rates dropping from 10.6 kōura net-1 night-1 in 2016 to 4.2 kōura net-1 night-1 in 2018. Over the same period, catfish CPUE has increased in the lake, with the highest catch rates in Te Weta Bay, where mean catch rates have increased from 1.1 catfish net-1 night-1 in 2016 to 63.7 catfish net-1 night-1 in 2018. Catfish catch rates were negatively associated with catch rates of kōura (r = −0.180). Mean catfish density also had a significant effect on kōura catch rates, with significantly more kōura being caught at sites without catfish. The negative association between catfish and kōura could be due to catfish eating or competing with kōura, or their differing habitat preferences. Catfish were positively associated with sites that are weedy or muddy and kōura were negatively associated with muddy habitats and were positively associated with rocky habitats. Whakaweku set at shallow depths <1 m in the lake littoral zone were ineffective at catching kōura during the habitat survey. 

Catfish diet consisted largely of chironomid larvae (Chironomidae), detritus, common bullies (Gobiomorphus cotidianus), and to a lesser extent kōura. Kōura were found in 12% of large catfish (>200 mm fork length; FL) stomachs analysed and contributed 5% volumetrically to large catfish diet. Unfortunately, the contribution of kōura to catfish diet could not be established using stable isotopes because isotopic signatures of kōura and bullies were too close to differentiate. Kōura diet consisted primarily of animal remains (common bullies and invertebrates) and detritus. Stable isotopes of carbon and nitrogen revealed that diets of kōura and catfish overlapped, with kōura sharing more of their diet with catfish than vice versa, likely reflecting catfish’s broad diet. This study suggests that catfish are responsible for the recent decline in kōura CPUE in Lake Rotoiti and that catfish are directly and indirectly affecting kōura through predation and competition for shared food resources.

year: 2019