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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. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

We characterised the quantity (mass per unit area or volume), quality (cabon:nitrogen ratio) and enrichment (δ15N) of basal food resources and benthic macroinvertebrates in six shallow lakes in the Waikato region, New Zealand, to elucidate patterns related to lake type (peat, riverine), habitat (littoral, mid-lake) and enrichment status (Trophic Level Index >6 or ≤5). Total seston dry mass was dominated by fine material that was correlated with chlorophyll a concentration. Seston was a higher quality food resource than benthic particulate organic matter which had higher biomass overall in littoral than in mid-lake habitats. Biomass of Chironomidae was highest in the less-enriched peat lakes, possibly due to clearer water supporting benthic algae in shallow littoral areas. Our results highlight the potential role of multiple bottom-up influences on shallow lake food webs. The more abundant and higher quality pelagic food resources in highly enriched lakes may have implications for resilience to non-indigenous fish invasion. [ABSTRACT FROM AUTHOR]