title: The role of Chaetopterus sp. in reshaping sediment characteristics and benthic communities in Queen Charlotte Sound

authors: Scott-Simmonds , Thomas

abstract: Soft-sediment habitats are critical to marine ecosystems, supporting diverse benthic communities and key processes such as nutrient cycling, sediment stabilisation, and energy transfer. Among these habitats, tube-building polychaetes like Chaetopterus act as ecosystem engineers, modifying sediment properties and influencing community structure and functioning. This study investigated the ecological impacts of Chaetopterus in East Bay, Queen Charlotte Sound, focusing on its role in sediment modification, macrofaunal biodiversity, and functional group composition. 

Field surveys were conducted across ten paired Chaetopterus and control sites, selected to capture a gradient in tube mat density and depth. At each site, five sediment and macrofaunal samples were collected using coring techniques, enabling a robust comparison of Chaetopterus-modified and unmodified habitats. 

Results showed significantly higher organic content (3.1% ± 0.2 vs. 2.0% ± 0.1) and mud content (19.8% ± 2.0 vs. 7.7% ± 0.5) in Chaetopterus habitats, highlighting its role in sediment enrichment and stabilisation. Macrofaunal communities exhibited significantly greater species richness (20.0 ± 0.8 vs. 14.5 ± 0.7 species per core) and diversity (Shannon diversity: 2.48 ± 0.05 vs. 2.16 ± 0.06), driven by increased structural complexity and organic matter retention. 

Functional group analysis revealed a shift towards surface-oriented taxa in Chaetopterus habitats, including increased surface-feeding deposit feeders (e.g., amphipods) and scavengers (e.g., Halicarcinus cookii), alongside a relative reduction in deeper-burrowing taxa such as bioturbating polychaetes (Prionospio multicristata) and burrowing bivalves (Tawera spissa). This suggests that Chaetopterus tube mats promote surface-associated processes like organic matter turnover and detritus retention, while potentially suppressing sediment-mixing and oxygenation functions. 

Chaetopterus habitats exhibited significantly lower dispersion (PERMDISP), indicating more functionally homogeneous assemblages compared to control sites, where greater within-group variability reflected a broader range of functional traits, including suspension feeders and opportunistic burrowers (e.g., Phoxocephalidae amphipods). Chaetopterus density was significantly correlated with macrofaunal community composition, reinforcing the role of tube mats as a key driver of functional trait distributions. However, the extent of these effects varied across sites, suggesting that local environmental factors, particularly sediment properties (mud content, organic matter) and Chaetopterus density, mediate its influence on benthic communities. 

These findings advance understanding of habitat-modifying polychaetes by demonstrating that Chaetopterus effects are highly context-dependent, shaped by habitat × site interactions and environmental conditions. While previous studies have identified Chaetopterus as a biodiversity enhancer, this study highlights its dual role as both a facilitator of surfacedominated processes and a potential suppressor of deeper sediment functions. These findings provide critical insights into its ecological role within New Zealand's coastal ecosystems and underscore the need for site-specific management strategies that balance local biodiversity benefits with broader ecosystem functions.

text: The role of Chaetopterus sp. in reshaping sediment characteristics and benthic communities in Queen Charlotte Sound Soft-sediment habitats are critical to marine ecosystems, supporting diverse benthic communities and key processes such as nutrient cycling, sediment stabilisation, and energy transfer. Among these habitats, tube-building polychaetes like Chaetopterus act as ecosystem engineers, modifying sediment properties and influencing community structure and functioning. This study investigated the ecological impacts of Chaetopterus in East Bay, Queen Charlotte Sound, focusing on its role in sediment modification, macrofaunal biodiversity, and functional group composition. 

Field surveys were conducted across ten paired Chaetopterus and control sites, selected to capture a gradient in tube mat density and depth. At each site, five sediment and macrofaunal samples were collected using coring techniques, enabling a robust comparison of Chaetopterus-modified and unmodified habitats. 

Results showed significantly higher organic content (3.1% ± 0.2 vs. 2.0% ± 0.1) and mud content (19.8% ± 2.0 vs. 7.7% ± 0.5) in Chaetopterus habitats, highlighting its role in sediment enrichment and stabilisation. Macrofaunal communities exhibited significantly greater species richness (20.0 ± 0.8 vs. 14.5 ± 0.7 species per core) and diversity (Shannon diversity: 2.48 ± 0.05 vs. 2.16 ± 0.06), driven by increased structural complexity and organic matter retention. 

Functional group analysis revealed a shift towards surface-oriented taxa in Chaetopterus habitats, including increased surface-feeding deposit feeders (e.g., amphipods) and scavengers (e.g., Halicarcinus cookii), alongside a relative reduction in deeper-burrowing taxa such as bioturbating polychaetes (Prionospio multicristata) and burrowing bivalves (Tawera spissa). This suggests that Chaetopterus tube mats promote surface-associated processes like organic matter turnover and detritus retention, while potentially suppressing sediment-mixing and oxygenation functions. 

Chaetopterus habitats exhibited significantly lower dispersion (PERMDISP), indicating more functionally homogeneous assemblages compared to control sites, where greater within-group variability reflected a broader range of functional traits, including suspension feeders and opportunistic burrowers (e.g., Phoxocephalidae amphipods). Chaetopterus density was significantly correlated with macrofaunal community composition, reinforcing the role of tube mats as a key driver of functional trait distributions. However, the extent of these effects varied across sites, suggesting that local environmental factors, particularly sediment properties (mud content, organic matter) and Chaetopterus density, mediate its influence on benthic communities. 

These findings advance understanding of habitat-modifying polychaetes by demonstrating that Chaetopterus effects are highly context-dependent, shaped by habitat × site interactions and environmental conditions. While previous studies have identified Chaetopterus as a biodiversity enhancer, this study highlights its dual role as both a facilitator of surfacedominated processes and a potential suppressor of deeper sediment functions. These findings provide critical insights into its ecological role within New Zealand's coastal ecosystems and underscore the need for site-specific management strategies that balance local biodiversity benefits with broader ecosystem functions.

year: 2025

title: The impact of router outages on the AS-level internet

authors: Luckie, Matthew John

subjects: computer science

abstract: We propose and evaluate a new metric for understanding the dependence of the AS-level Internet on individual routers. Whereas prior work uses large volumes of reachability probes to infer outages, we design an efficient active probing technique that directly and unambiguously reveals router restarts. We use our technique to survey 149,560 routers across the Internet for 2.5 years. 59,175 of the surveyed routers (40%) experience at least one reboot, and we quantify the resulting impact of each router outage on global IPv4 and IPv6 BGP reachability.

Our technique complements existing data and control plane outage analysis methods by providing a causal link from BGP reachability failures to the responsible router(s) and multi-homing configurations. While we found the Internet core to be largely robust, we identified specific routers that were single points of failure for the prefixes they advertised. In total, 2,385 routers -- 4.0% of the routers that restarted over the course of 2.5 years of probing -- were single points of failure for 3,396 IPv6 prefixes announced by 1,708 ASes. We inferred 59% of these routers were the customer-edge border router. 2,374 (70%) of the withdrawn prefixes were not covered by a less specific prefix, so 1,726 routers (2.9%) of those that restarted were single points of failure for at least one network. However, a covering route did not imply reachability during a router outage, as no previously-responsive address in a withdrawn more specific prefix responded during a one-week sample. We validate our reboot and single point of failure inference techniques with four networks, finding no false positive or false negative reboots, but find some false negatives in our single point of failure inferences.

text: The impact of router outages on the AS-level internet We propose and evaluate a new metric for understanding the dependence of the AS-level Internet on individual routers. Whereas prior work uses large volumes of reachability probes to infer outages, we design an efficient active probing technique that directly and unambiguously reveals router restarts. We use our technique to survey 149,560 routers across the Internet for 2.5 years. 59,175 of the surveyed routers (40%) experience at least one reboot, and we quantify the resulting impact of each router outage on global IPv4 and IPv6 BGP reachability.

Our technique complements existing data and control plane outage analysis methods by providing a causal link from BGP reachability failures to the responsible router(s) and multi-homing configurations. While we found the Internet core to be largely robust, we identified specific routers that were single points of failure for the prefixes they advertised. In total, 2,385 routers -- 4.0% of the routers that restarted over the course of 2.5 years of probing -- were single points of failure for 3,396 IPv6 prefixes announced by 1,708 ASes. We inferred 59% of these routers were the customer-edge border router. 2,374 (70%) of the withdrawn prefixes were not covered by a less specific prefix, so 1,726 routers (2.9%) of those that restarted were single points of failure for at least one network. However, a covering route did not imply reachability during a router outage, as no previously-responsive address in a withdrawn more specific prefix responded during a one-week sample. We validate our reboot and single point of failure inference techniques with four networks, finding no false positive or false negative reboots, but find some false negatives in our single point of failure inferences.

year: 2017

title: Assessment of effects of proposed treated wastewater discharge to the Te Arikiroa Thermal Channel and Sulphur Bay (Lake Rotorua)

authors: Dada, Ayokunle Christopher

abstract: After 2019, irrigation operations at the Land Treatment System (LTS) in the Whakarewarewa Forest are scheduled to cease. A number of options and locations have been considered for the discharge of the treated wastewater when the current discharge consent ceases. Following consultations and technical assessments, the preferred option of Rotorua Lakes Council is to upgrade the existing plant to a full Membrane Bioreactor Plant with the addition of an Ultraviolet Disinfection System (or alternative treatment to achieve an equivalent performance in terms of treated wastewater quality). Under this arrangement, wastewater would be subjected to biological, chemical and physical treatment processes, and the treated wastewater discharged through Te Arikiroa Thermal Channel to Sulphur Bay. Rotorua Lakes Council is thus undertaking an environmental impact assessment study to determine the effects of discharging treated wastewater to the thermal channel and Puarenga Bay (Lake Rotorua), with particular reference to aesthetic, water quality and ecological considerations. These considerations include potential effects related to faecal indicator bacteria, nutrient concentrations, metals, dissolved oxygen, and taonga species (native species of cultural significance).
The assessment focused on:
(i)	The projected treated wastewater characteristics;

(ii)	Existing conditions of the receiving water;

(iii)	The sensitivity of the receiving water and the impact of the proposed discharge on water quality and taonga species (native species of cultural significance) in Te Arikiroa Thermal Channel and Sulphur Bay.

The main techniques used to inform the assessment in this study were:
1) Analysis of historical water quality data, 2011-2014;
2) Collection of additional water quality data at Te Arikiroa Thermal Channel and Sulphur Bay and along a transect to quantify spatial variability (sampling in 2016 and 2017);
3) Mass balance dilution modelling to predict water quality in the Te Arikiroa Thermal Channel and Sulphur Bay (Lake Rotorua), at a site outside of the assumed mixing zone;
4) Lake ecosystem modelling conducted by Abell et al. (2015) to assess effects related to eutrophication;
5) Background review of biological information and field investigations for taonga species at Sulphur Bay and Te Arikiroa Thermal Channel (2017).

text: Assessment of effects of proposed treated wastewater discharge to the Te Arikiroa Thermal Channel and Sulphur Bay (Lake Rotorua) After 2019, irrigation operations at the Land Treatment System (LTS) in the Whakarewarewa Forest are scheduled to cease. A number of options and locations have been considered for the discharge of the treated wastewater when the current discharge consent ceases. Following consultations and technical assessments, the preferred option of Rotorua Lakes Council is to upgrade the existing plant to a full Membrane Bioreactor Plant with the addition of an Ultraviolet Disinfection System (or alternative treatment to achieve an equivalent performance in terms of treated wastewater quality). Under this arrangement, wastewater would be subjected to biological, chemical and physical treatment processes, and the treated wastewater discharged through Te Arikiroa Thermal Channel to Sulphur Bay. Rotorua Lakes Council is thus undertaking an environmental impact assessment study to determine the effects of discharging treated wastewater to the thermal channel and Puarenga Bay (Lake Rotorua), with particular reference to aesthetic, water quality and ecological considerations. These considerations include potential effects related to faecal indicator bacteria, nutrient concentrations, metals, dissolved oxygen, and taonga species (native species of cultural significance).
The assessment focused on:
(i)	The projected treated wastewater characteristics;

(ii)	Existing conditions of the receiving water;

(iii)	The sensitivity of the receiving water and the impact of the proposed discharge on water quality and taonga species (native species of cultural significance) in Te Arikiroa Thermal Channel and Sulphur Bay.

The main techniques used to inform the assessment in this study were:
1) Analysis of historical water quality data, 2011-2014;
2) Collection of additional water quality data at Te Arikiroa Thermal Channel and Sulphur Bay and along a transect to quantify spatial variability (sampling in 2016 and 2017);
3) Mass balance dilution modelling to predict water quality in the Te Arikiroa Thermal Channel and Sulphur Bay (Lake Rotorua), at a site outside of the assumed mixing zone;
4) Lake ecosystem modelling conducted by Abell et al. (2015) to assess effects related to eutrophication;
5) Background review of biological information and field investigations for taonga species at Sulphur Bay and Te Arikiroa Thermal Channel (2017).

year: 2018