Kevin J. Collier

Context: Phenology plays a key role in shaping population dynamics, community structure and evolutionary adaptations. For freshwater mussels that rely on a parasitic larval (glochidia) phase on fish, shifts in reproductive phenology driven by environmental conditions may result in mismatches between glochidia release and host fish availability. Aims: We investigated intra- and interspecific reproductive timing variations in sympatric Echyridella aucklandica and E. menziesii, and identified thermal cues (accumulated degree days, ADD) associated with brooding and glochidia maturation. Methods: Brooding activity and glochidia maturation were assessed fortnightly–monthly over 1 year within four New Zealand streams. Results: The previously unknown phenology of E. aucklandica showed earlier brooding (May–July) and longer gravidity (9–11 months) than for E. menziesii (August; 6–7 months). Both species exhibited peak brooding in late austral spring–summer (November–December). ADD played a key role in regulating the timing of brooding onset in both species, as evidenced by the narrow ADD range observed across sites, and the relationship between ADD and brooding onset in both species. Conclusion: The demonstrated link between ADD and reproductive phenology has broad implications in the context of climate change. Specifically, it raises concerns about potential timing mismatches in glochidia release and host-fish availability, which could affect the survival and reproductive success of freshwater mussels.

Floodplain ecosystems are focal points for human settlement, and consequently are often subjected to extensive modification and infrastructure development. Establishment of non‐native species in floodscapes presents a range of challenges when they become problematic and drive changes in native aquatic communities and ecosystems. These non‐native species are often tolerant of reduced water and habitat quality, conferring a competitive advantage over native species. The coupled effects of invasive alien species, landscape modification and floodscape hydrological control collectively reduce ecological resilience, creating feedback loops that reinforce negative effects on native fish. The regulated lower Waikato River floodplain is a New Zealand hotspot for fish introductions, with their proliferation exacerbating the effects of agricultural development, urban expansion, and flood control infrastructure. We argue that the resilience of native fish assemblages to these pressures can be improved through utilizing a series of complementary measures, including enhanced catchment management, strategic alterations to the location, design, and operation of floodplain infrastructure (e.g., gates, pumpstations, and stopbanks), habitat restoration for native fish, and targeted management of invasive species. These measures will need to consider the likely persistence of invasive alien fish, however, to limit their expansion in the face of a changing climate. Although knowledge and implementation gaps exist, tying these strands together presents an opportunity to enhance the resilience of native fisheries into the future. Key to success will be re‐thinking floodplain management to include ecosystem services, and this will require ongoing commitment and cooperation amongst all stakeholders to address knowledge gaps and enable effective implementation.

Larvae (glochidia) of Unionida mussels form obligate symbiotic associations with host fish to complete their life‐cycle. To identify previously unknown host fish associations for the threatened New Zealand Echyridella aucklandica , glochidia infestation on fish by two mussel species was quantified in four Waikato streams. A host for E. aucklandica was identified for the first time, with glochidia found to attach and encyst on the common smelt Retropinna retropinna but not on other fish species caught. In contrast, E. menziesii was found on a range of fish species but not on the two R. retropinna caught. Encysted E. aucklandica glochidia showed evidence of growth on the gills of host fish. These preliminary results provide critical knowledge of host–glochidia interactions in sympatric New Zealand unionid species to support integrated conservation management targeting both unionid communities and host fish populations.

We measured δ ¹⁵ N, δ ¹³ C, and percent carbon (C) and nitrogen (N) on foot and remaining soft tissue of the two native freshwater mussel species Echyridella aucklandica and E. menziesii (Hyriidae: Unionida) from three Waikato, northern New Zealand, streams to investigate differences among sites, sexes and species. Mean differences in δ ¹⁵ N and δ ¹³ C between foot and remaining soft tissue (mainly guts, gills and gonads) were 15 N and δ ¹³ C displayed marked differences among sites for both species, with δ ¹⁵ N variations consistent with the level of catchment land‐use intensification. Variation in δ ¹³ C and δ ¹⁵ N among replicate mussels was low indicating few individuals are required to precisely characterise isotope signatures of local populations. The lack of evidence of trophic resource partitioning among species, and consistent differences in isotope ratios between sites, suggests that the more widespread and abundant E. menziesii may provide an effective baseline integrator of catchment activities that alter carbon supplies and nitrogen sources.

Ponds are increasingly being constructed to enhance amenity values in human‐dominated lowland landscapes, but little is known of design features that influence macroinvertebrates which can provide important food resources for fish and waterbirds. We quantified pond characteristics, sampled benthic and water‐column macroinvertebrates in winter, and related abundance, biomass and community composition to characteristics of 34 ponds on the lower Waikato River floodplain, northern New Zealand. Compositionally different macroinvertebrate communities occupied water‐column and benthic habitats. Landscape setting had a significant effect on benthic composition in terms of biomass, while the independent effects of frequency of pond drying or flooding, respectively, influenced benthic (abundance, biomass) or water‐column (abundance) communities. Distance‐based linear models highlighted physicochemical conditions, water depth regimes and riparian vegetation composition as key variables accounting for dissimilarity in total macroinvertebrate biomass between ponds. Our results indicate that managing hydrological stability of ponds in terms of permanence and flooding influences the composition and biomass of invertebrate communities. Within this hydrological template, design of appropriate depth regimes and riparian conditions can enhance accrual of macroinvertebrate biomass, thereby increasing food resources for fish and waterbirds.

Ponds can provide important refuges for aquatic biota on developed floodplains and are increasingly being constructed in an effort to enhance native biodiversity and ecosystem services in degraded landscapes. This study examined 34 constructed ponds to investigate the influence of design features on community composition, native biodiversity, and the biomass or abundance of common fish and waterbirds on the lower Waikato River floodplain, northern New Zealand. Inundation frequency appeared to be a key factor affecting biomass of the native shortfin eel Anguilla australis and three invasive fish species (common carp [Cyprinus carpio], brown bullhead [Ameiurus nebulosus], and goldfish [Carassius auratus]), suggesting that colonisation occurred during flooding by adjacent waterbodies. Linear models indicated that shortfin eel abundance and total eel biomass were positively associated with the biomass of potential fish prey, the area occupied by islands and cover by trees in the riparian zone. Native waterbird species richness was strongly related to water area, edge length (including islands) and area:perimeter ratio, with little increase in richness for ponds >1 ha in area, perimeters longer than 800 m, and ratios over 20. The protected grey teal (Anas gracilis), and the recreationally hunted species phenotypically assigned as mallard (Anas platyrhynchos + hybrids) and grey duck (Anas superciliosa + hybrids) appeared most strongly influenced, respectively, by perimeter length, water depth, and biomass of potential macroinvertebrate food supplies, suggesting variable effects of pond design attributes among waterfowl species. Overall, these results indicate that constructed ponds can be designed to promote native waterbird diversity, enhance eel fishery and waterfowl gamebird services, and also limit the proliferation of some non‐native invasive fish species in degraded floodplain landscapes. A hierarchy of constructed pond design attributes was identified, involving landscape position and connectivity, pond morphology and complexity, and riparian maturity and buffering, which were associated with direct (habitat) and indirect (food supply, physicochemistry) effects on biodiversity and provisioning services.

Dense macrophyte beds are known to produce extreme diurnal oxygen and temperature conditions in shallow lakes. However their influences in managed hydropeaking reservoirs has received limited attention. We measured dissolved oxygen, pH and water temperature in the Lake Karāpiro hydroreservoir, northern New Zealand, across a gradient of proportional water‐column height occupied by the invasive macrophytes Egeria densa and Ceratophyllum demersum, which dominated in the upper‐riverine (variable water inflow) and lower‐lacustrine (variable water level) sections, respectively. Hypoxia and anoxia events that occurred inside invasive macrophyte beds during their summer peak biomass accumulation period were more pronounced for C. demersum than for E. densa, and within the bottom 20% of the water column. In contrast, pH and temperature changed little in relation to proportional macrophyte height. Macrophyte species differences in the production of hypoxia and anoxia events increased when site‐specific hydropeaking management covariates (depth, inflows, water level) were accounted for. This association with hydropeaking likely resulted from contrasting hydrodynamics in the lower‐lacustrine and upper‐riverine lake sections, where oxygen can decrease with higher water levels and lower water inflow rates, respectively. During the course of our study, some macrophyte beds were treated with herbicide, enabling us to document prolonged and sustained hypoxic/anoxic conditions near the bottom following spraying. These results underscore the adverse effects of invasive macrophytes on water physicochemical attributes that sustain aquatic biota, and highlight the context‐dependent nature of these effects moderated by reservoir management for hydropeaking and macrophyte control.

(2020). Preface: land-use impacts on aquatic ecosystems - tribute to John Quinn. New Zealand Journal of Marine and Freshwater Research: Vol. 54, Special issue: Land-use impacts on aquatic ecosystems: evidence and solutions —Tribute to John Quinn, pp. 305-307.

The 2018 conservation status assessment of freshwater invertebrate taxa was the most comprehensive to date. Of the Threatened and At Risk taxa in 2018 (177 taxa), 48 were listed as Nationally Critical , 14 as Nationally Endangered , 16 as Nationally Vulnerable , 10 as Declining , and 89 as Naturally Uncommon . Most taxa were listed as either Not Threatened (315 taxa) or required more information for assessment ( Data Deficient ; 178 taxa). Analyses of temporal changes in conservation status since 2002 revealed that the majority of changes were due to greater understanding of taxa distributions, rather than gains or losses in population sizes or area of occupancy. Insufficient data on taxa distributions, along with a lack of autecological information, are two of the major knowledge gaps facing freshwater invertebrate conservation in New Zealand. Further impediments to conservation include (i) a lack of systematics research, (ii) a large number of species remain undiscovered and undescribed, and (iii) the status and trend of populations is unknown for most taxa. We also provide an analysis of the habitats that harbour many of the rarer taxa. Finally, we conclude by recommending a number of actions that should, collectively, help fill these knowledge gaps and address these issues.