Ian C. Duggan

Constructed treatment wetlands provide habitat for zooplankton communities in agricultural peat lake catchments

Zooplankton are an essential component of healthy functioning lake and wetland ecosystems. Despite this, zooplankton communities within constructed treatment wetlands (CTWs) in agricultural landscapes remain unstudied. Taxa richness, total abundances and community composition were evaluated for zooplankton assemblages from three habitat types (lakes, CTWs and drainage ditches) within five intensive agricultural peat lake catchments in New Zealand. Relationships to water quality, physicochemical and biotic habitat variables were examined. Zooplankton were dominated by cladocerans, copepods, ostracods and rotifer taxa, representing a range of communities typical of lake and pond habitats. CTWs supported species otherwise absent from lake and drain habitats, increasing the overall biodiversity of the highly-modified peat lake catchments. Taxa richness of CTWs was higher than that of drains, and a few CTWs had greater diversity than several lakes. The morphological variables area and depth contributed to the greatest differences between habitats, followed by pH, inorganic nitrogen, conductivity and temperature. Correspondingly, zooplankton communities were significantly influenced by habitat area, depth and pH, as well as ammonium, phosphate, water temperature, dissolved oxygen, and macrophyte cover. Opportunities were explored for refining CTW designs to enhance zooplankton biodiversity and potentially improve treatment efficiency through increasing the complexity and diversity of CTW habitat niches.

Assessment of chemical and physical treatments to selectively kill non-indigenous freshwater zooplankton species

ABSTRACT Non-indigenous zooplankton species pose a biosecurity threat to New Zealand’s freshwater native taxa. Nine species are known to have established in New Zealand lakes to date. The spread of some zooplankton taxa is linked to the translocation of farmed fish, principally grass carp (Ctenopharyngodon idella), and recreational vessel movements. The aims of this study were to assess the effectiveness of a range of chemical and physical treatments for transport water and associated equipment to kill freshwater cladoceran, copepod, and rotifer zooplankton species, and their risk to non-target fish. Sodium chloride was the most effective and applicable chemical treatment tested at length in the cladoceran and, combined with physical treatment via mechanical filtration of water or hot water immersion of equipment (to also manage the risk of diapausing eggs), represents an effective option for the control of non-indigenous zooplankton, with limited impact on stenohaline fish.

The role of mobile consumers in lake nutrient cycles: a brief review

We summarise current understanding of consumer recycling in lake nutrient cycles and expand on it by integrating emerging knowledge from food web ecology. The role of consumer nutrient recycling (CNR) is initially framed in the wider context of lake nutrient cycling, which includes hydrodynamic and biogeochemical processes, and their responses to global environmental change. Case studies are used to demonstrate that effects of CNR on lake ecosystems range widely, from reduced nutrient cycling rates to exacerbation of eutrophication. CNR depends on consumer biomass, body size and diet, remaining relatively consistent through the year and becoming important as other fluxes seasonally ebb. Universal patterns in food web structure, for example, consumer–resource biomass ratios, body size scaling and relationships between trophic level and diet breadth, are used to demonstrate the predictability of CNR effects. Larger, mobile, top predators excrete nutrients at a lower rate but over a wider range, linking nutrient cycles across habitats. Smaller-bodied, lower trophic level consumers have strong localised nutrient cycling effects associated with their limited mobility. Global environmental-change drivers that alter food web structure are likely to have the greatest impact on CNR rates and should direct future studies.

Invertebrates associated with aquatic plants bought from aquarium stores in Canada and New Zealand

Invertebrate species carried incidentally (i.e., ‘hitchhikers’) in the aquarium trade have gained increasing attention in recent years, but factors affecting the movement of species from stores to homes are poorly understood. We aimed to determine how macrophytes bought from stores act as vectors for transport of non-indigenous invertebrate species. We tested whether incidental invertebrate faunas carried on macrophytes vary internationally by comparing the New Zealand and Canadian trades, and if macrophyte species with different morphologies carry different risks. We recorded a large variety of invertebrate species associated with Vallisneria spp., Sword plants (Echinodorus spp.) and Elodea canadensis bought from stores, including species non-indigenous to both countries. Community composition of incidental fauna differed significantly between New Zealand (primarily domestically cultivated) and Canadian (primarily imported) bought macrophytes. Differences in composition between different macrophyte species were only statistically significant between wild-collected E. canadensis and the cultured species in New Zealand. Behaviours observed in stores, such as the amount of time macrophytes were removed from water before being placed in plastic bags for transport, did not affect the abundances or richness of incidental invertebrates transported, and thus did not appear to be effective in reducing invasion risk. We therefore recommend chemical treatment for removal of invertebrates from macrophytes at or pre-border, and from tanks containing plants at culture facilities and in stores. Such management will reduce the probability of introduction of hitchhikers to home aquaria, from which risk of release to natural waters is greatest.

A new, subalpine species of Daphnia (Cladocera, Anomopoda) in the D. carinata species complex, in the South Island, New Zealand

Until recently, only one native and three apparently introduced Daphnia species were known from New Zealand. We demonstrate that (1) Daphnia in subalpine habitats in southern New Zealand differ morphologically and genetically from the native taxon previously labelled Daphnia carinata to merit species nova status and (2) the name of the latter should revert to D. thomsoni, used by Sars (1894) for Daphnia described from New Zealand mud. We compare some key characteristics and cytochrome c oxidase subunit 1 (CO1) sequences of the New Zealand native and other morphologically similar species. Distinctive characteristics of subalpine populations, described as Daphnia tewaipounamu sp. nov., are a wide cephalic shield with lateral flanges curving dorsally via rounded fornices, dorsal cervical depression variably expressed as a ‘step’ in the cephalic shield exuviae and retention of ephippia within shed carapace exoskeletons long after ecdysis. CO1 sequences revealed that D. tewaipounamu sp. nov. belongs to the D. carinata complex but is highly divergent (>14%) from other known members of this complex. New Zealand D. thomsoni is divergent (>15%) from D. carinata s.s. However, it is not endemic to New Zealand, as we confirmed its presence in Tasmania, and some Australian populations are closely related to it.

Mitochondrial DNA indicates different North American east coast origins for New Zealand and German invasions of Skistodiaptomus pallidus (Copepoda: Calanoida)

The freshwater calanoid copepod Skistodiaptomus pallidus (Herrick, 1879), native to the Mississippi basin of North America, has recently established non-indigenous populations in New Zealand, Germany and Mexico. We used the mitochondrial cytochrome c oxidase subunit I (COI) gene to more precisely identify the origins of S. pallidus populations within New Zealand and Germany. The S. pallidus COI sequences suggested that both New Zealand and German populations were most similar to those from the most easterly regions of the USA (e.g., New York, Virginia and Georgia). However, several haplotypes were found to be divergent between the New Zealand and German populations, indicating the exact sources of the introductions were likely different for each country. German sequences possessed two of the major haplotypes known from the east coast of USA, while New Zealand had one, indicating a shipping related vector of introduction with greater propagule supplies to Germany is plausible. Although both German and New Zealand populations contained haplotypes identical to common east coast North American sequence records, both non-indigenous populations had haplotypes not yet recorded in the USA. Further sampling of the native range will be required to determine the exact origin of the non-indigenous S. pallidus populations and may also help to identify more precisely the vectors and pathways of the translocations.