Tasman Bay Research Articles

Structural evolution, segmentation and activity of the onshore-offshore Waimea-Flaxmore Fault System in south-eastern Tasman Bay, South Island, New Zealand

ABSTRACT The Waimea-Flaxmore Fault System (W-FFS) from the Nelson-Richmond urban area to D’Urville Island is analysed through six regional transects that join depth-converted seismic lines in Tasman Bay to onshore cross sections. Reverse reactivation of basement faults of the W-FFS by mechanisms of fault-propagation folding at c. 19-10 Ma occurred along the entire length of the fault system. However, the W-FFS remained Quaternary active only from the vicinity of Cape Soucis southwards into onshore Nelson, in contrast with cessation of activity along eastern Tasman Bay since 7 Ma. The inactive western faults of the W-FFS are buried below Plio-Quaternary marine sediments and segmented by the newly identified, c. E-W, Croisilles Fault Zone, Cross Point and D’Urville faults, with cumulative dextral offset of c. 27 km. The c. E-W faults extend from the onshore into Tasman Bay and are interpreted as the northernmost Late Miocene strands of the Marlborough Fault System that have accommodated incipient distributed shear in the crustal block north of the Queen Charlotte Fault Zone. Segmentation and along-strike changes of the W-FFS occur at the transition from the contractional domain of onshore Nelson to the northern Marlborough strike-slip domain, driven by large-scale kinematics of the Australia-Pacific plate boundary.

Sedimentation since 140 ka in Te Tai-o-Aorere Tasman Bay, Aotearoa New Zealand

ABSTRACT Late Pleistocene and Holocene sedimentation records changes in glacio-eustatic cycles, oceanography, active tectonics, and sediment supply. Here, we use high-resolution seismic-reflection profiles in Te Tai-o-Aorere Tasman Bay to investigate sedimentary deposit distributions associated with sea-level cyclicity over ∼140 ka. We identify nine seismic stratigraphic units below the inner continental shelf, interpret their character based on stratal relationships and acoustic properties, and infer ages using global sea level. The sequence includes stacked deposits and unconformities associated with the shifting shoreline over glacial cycles. Prominent erosional features include a lowstand ravinement surface and two transgressive surfaces formed during sea-level rise following the last two glacial maxima of ∼20 ka and ∼140 ka. The youngest surface marks the base of post-glacial sediment accumulated since ∼12 ka in the study area. Post-glacial sediment includes five seismically mappable units, covering an area of ∼1400 km2 and deposit volume of ∼9 km3. Time-averaged sediment accumulation rates are estimated to range from a maximum of ∼1.6–2.8 m/kyr to ∼0.5–0.9 m/kyr. Sequence stratigraphy interpreted in Te Tai-o-Aorere Tasman Bay is representative of accumulation in a relatively wide-shelf, sheltered inner bay setting supplied by mountainous catchments, and provides stratigraphic context necessary for future stratigraphic and tectonics studies.

Catchment modifications influence the composition of basal organic matter supporting suspension-feeding bivalves

Marine primary production is sensitive to multiple environmental stressors from land-based and maritime anthropogenic activities. Stressors may alter the distribution, abundance and composition of primary producers and thereby directly influence the fluxes of organic matter into marine food webs. To investigate these effects, we measured the relative contributions of basal organic matter derived from macroalgae and phytoplankton to five suspension-feeding bivalve species (Pecten novaezelandiae, Atrina zelandica, Tucetona laticostata, Perna canaliculus and Mytilus galloprovincialis) along a gradient in catchment modification and marine farming activity in the Marlborough Sounds, Tasman Bay and Fiordland, on the South Island of New Zealand. Stable isotope analyses (δ15N and δ13C) were conducted on samples of basal organic matter and muscle tissue of bivalves collected from multiple sites within each region during 2018 and 2019. Mass balance mixing models revealed significant differences in the composition of basal organic matter supporting individual bivalve species among sites and regions. The proportion of macroalgal-derived organic matter supporting the subtidal bivalve community was negatively associated with the area of modified land use in the surrounding catchments. These results support strong linkages between land use in catchments and the composition of basal organic matter sources supporting bivalve communities. Values of δ15N among four of the bivalve species were consistently higher at sites associated with salmon farming, indicating inputs of allochthonous nitrogen from the farms. These findings highlight the intimate connection between anthropogenic stressors and the trophic dynamics of shellfish in the coastal zone.

An evaluation of strategies for restoring a degraded New Zealand scallop fishery using stochastic dynamic simulation modelling

A decision-theoretical approach was used to evaluate strategies to rebuild a severely depleted scallop (Pecten novaezelandiae) populations in the Tasman Bay and Golden Bay of New Zealand. These strategies were: no intervention, cessation of seabed bottom contact fishing, and reduction of sediment and nutrient runoff from surrounding land through on-farm practices. Our approach combined outputs of estimated effects of on-farm practices on erosion and nutrient reduction with a stochastic dynamic model of the scallop populations. The most effective individual intervention is eliminating bottom contact fishing through dredging and trawling which increased scallop biomass on average by 73% compared to the no intervention scenario. Although on-farm practices have reduced sedimentation and nutrient runoff significantly (28–36% and 2%, respectively), they have no effect on scallop biomass if implemented individually and led to only marginal improvements in scallop biomass if implemented alongside cessation of bottom contact fishing (2–4%). Although our results showed, on average, substantial recovery in the scallop population when reducing seabed bottom contact and water pollution, the large uncertainty boundaries makes it unclear whether these improvements would be realized. The long-term success of such strategies will depend on the available habitat being able to sustain high densities of healthy scallop adults and recruits, a situation that has been posited in our analysis. Where scallop juvenile survival is compromised by sedimentation, nutrient pollution, or other exogenous influences, proposed interventions may be insufficient to aid recovery.

Geographic variation in life-history traits of the long-lived monacanthid Meuschenia scaber (Monacanthidae)

Demography and life-history characteristics of reef fishes may vary as a consequence of ecological and environmental factors that lead to changes among populations. We evaluated variation in life-history traits in the leatherjacket Meuschenia scaber (Monacanthidae) through age-based analysis of 2112 fish collected from three locations in New Zealand distributed along an 8° latitudinal and 5 °C SST gradients. Meuschenia scaber showed distinct differences in age structure, growth patterns, maximum size and age, sex ratio and mortality across this latitudinal gradient. At warmer lower latitudes (Hauraki Gulf) the population displayed significantly greater mean adult body size (Lmax) and asymptotic length (L∞) in comparison with the other two locations. Fish from Tasman Bay (mid-range latitude) had a longer life span (Tmax) and a maximum age of 19 years, which represents the longest-lived monacanthid documented to date. Fish from Pegasus Bay (cooler higher latitude) showed a slower initial growth than lower latitude counterparts. The difference in maximum age between the sexes declined clinally from 7 years in the Hauraki Gulf to 3 years in Tasman Bay and 1 year in Pegasus Bay. Meuschenia scaber females tended to display heavier and larger body size than males at all three locations. Sex ratios varied among populations and with depth, suggesting females in the Hauraki Gulf and Tasman Bay may move into deeper water with age. Given the increasing global exploitation of monacanthids in multispecies fisheries and their long-living nature, our results provide valuable age-based demographic information essential for future conservation, monitoring and management programs.

Creating functional groups of marine fish from categorical traits.

BackgroundFunctional groups serve two important functions in ecology: they allow for simplification of ecosystem models and can aid in understanding diversity. Despite their important applications, there has not been a universally accepted method of how to define them. A common approach is to cluster species on a set of traits, validated through visual confirmation of resulting groups based primarily on expert opinion. The goal of this research is to determine a suitable procedure for creating and evaluating functional groups that arise from clustering nominal traits.MethodsTo do so, we produced a species by trait matrix of 22 traits from 116 fish species from Tasman Bay and Golden Bay, New Zealand. Data collected from photographs and published literature were predominantly nominal, and a small number of continuous traits were discretized. Some data were missing, so the benefit of imputing data was assessed using four approaches on data with known missing values. Hierarchical clustering is utilised to search for underlying data structure in the data that may represent functional groups. Within this clustering paradigm there are a number of distance matrices and linkage methods available, several combinations of which we test. The resulting clusters are evaluated using internal metrics developed specifically for nominal clustering. This revealed the choice of number of clusters, distance matrix and linkage method greatly affected the overall within- and between- cluster variability. We visualise the clustering in two dimensions and the stability of clusters is assessed through bootstrapping.ResultsMissing data imputation showed up to 90% accuracy using polytomous imputation, so was used to impute the real missing data. A division of the species information into three functional groups was the most separated, compact and stable result. Increasing the number of clusters increased the inconsistency of group membership, and selection of the appropriate distance matrix and linkage method improved the fit.DiscussionWe show that the commonly used methodologies used for the creation of functional groups are fraught with subjectivity, ultimately causing significant variation in the composition of resulting groups. Depending on the research goal dictates the appropriate strategy for selecting number of groups, distance matrix and clustering algorithm combination.

Comparative population genetic study of an important marine parasite from New Zealand flat oysters

The comparative genetic structure of hosts and parasites can reveal constraints acting on parasite dispersal among host populations and the evolution of local adaptation. We sampled New Zealand flat oysters Ostrea chilensis from 12 sites throughout New Zealand to (1) determine the distribution and prevalence of the haplosporidian parasites Bonamia exitiosa and B. ostreae, and (2) test for congruent patterns of host and parasite genetic structure. B. exitiosa was detected at three sites: Hauraki Gulf (5% prevalence), Marlborough Sounds (30%), and Foveaux Strait (7%), whereas B. ostreae was only detected in the Marlborough Sounds (37%). Using nuclear internal transcribed spacer (ITS) rDNA sequences of B. exitiosa, as well as mitochondrial cytochrome c oxidase subunit 1 gene (CO1) sequences of O. chilensis from the same sites plus other key O. chilensis growing areas (Tasman Bay and Chatham Islands), we compared the genetic structure of host and parasite. B. exitiosa displayed genetic structure across all three sites which were reflected in populations of O. chilensis except for gene flow between Tasman Bay-Marlborough Sounds-Chatham Islands. The observed patterns reflect the host specificity of Bonamia parasites and the limited dispersal capability of oysters. O. chilensis may experience long distance dispersal which is likely influenced by oceanographic factors. Nonetheless, a failure to detect Bonamia parasites among genetically connected O. chilensis populations suggests natural long distance co-dispersal of Bonamia parasites with O. chilensis is unlikely. Instead, the dispersal of Bonamia parasites is likely influenced by anthropogenic factors.

5 Key Challenges and Solutions for Governing Complex Adaptive (Food) Systems

There is increasing recognition in academic circles of the importance of adaptive governance for the sustainability of social-ecological systems, but little examination of specific implications for the 34% of land-use where human activities are pervasive but potentially commensurate with functioning ecosystems: agricultural production systems. In this paper, we argue for the need to view food systems and agro-ecosystems as multi-scalar complex adaptive systems and identify five key challenging characteristics of such systems: multi-causality; cumulative impacts; regime shifts; teleconnections and mismatch of scales. These characteristics are necessary features of multi-scalar adaptive systems, and apply equally to social and natural subsystems. We discuss the implications of these characteristics for agricultural production systems and consider how governance can rise to these challenges. We present five case studies that highlight these issues: pollinator declines; payments for ecosystem services; pest control and pesticide resistance; downstream aquatic systems in Tasman Bay, New Zealand; and riparian buffers in Puget Sound, USA. From these case studies we derive recommendations for managing agricultural systems, both specific and general. Ultimately, adaptive governance of agro-ecosystems will likely hinge upon three paradigm shifts: viewing farmers and ranchers not only as food producers but also as land and water managers; seeking not yield maximization but rather resilient management of food ecosystems; and critically, as it transcends the production-system literature, engaging broad audiences not only as consumers but also citizens.

Tapeworm bolus expelled from New Zealand variable oystercatchers (Haematopus unicolor) during handling: first record of this phenomenon in wild birds, and a global checklist of Haematopus cestode parasites

On two occasions in November and December 2009, whilst being captured and handled for banding in Tasman Bay, New Zealand, two variable oystercatchers (Haematopus unicolor Forster, 1844) voided a number of cestode strobilae from their cloaca. Their morphology indicates that they belong to the family Hymenolepididae, confirmed by BLASTn searches of large and small subunits of ribosomal DNA partial sequences (18S and 28S, respectively). However, they cannot currently be assigned to any species reported for any oystercatcher species from New Zealand nor from oystercatchers worldwide. We present a checklist of all cestode parasites reported in the literature for Haematopus species, along with their sources and synonyms. While the taxonomy of New Zealand oystercatchers is currently uncertain, more detailed knowledge of the parasite fauna of this bird group may help to elucidate the historical biogeography of the oystercatchers. The means of collection of these tapeworms is unusual and does not appear to have been reported in the literature previously.

Fish−habitat associations in New Zealand: geographical contrasts

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 450:131-145 (2012) - DOI: https://doi.org/10.3354/meps09566 Fish−habitat associations in New Zealand: geographical contrasts Russell G. Cole1,*, Niki K. Davey1, Glen D. Carbines2,4, Rob Stewart3 1National Institute of Water and Atmospheric Research Ltd., PO Box 893, Nelson 7040, New Zealand 2National Institute of Water and Atmospheric Research Ltd., PO Box 6414, Dunedin 9016, New Zealand 3National Institute of Water and Atmospheric Research Ltd., PO Box 14-901, Wellington 14901, New Zealand 4Present address: Saltwater Science Ltd., PO Box 89234, Torbay, North Shore, Auckland 0742, New Zealand *Email: r.cole@niwa.co.nz ABSTRACT: Relationships between fishes and habitat variables were assessed by transect counts and manipulative experiments on subtidal rocky reefs in 3 poorly known regions of New Zealand (eastern Bay of Plenty, western Cook Strait, and eastern Stewart Island). Canonical correspondence analysis successfully described associations between fishes and habitat features. Depth, topographic complexity, and macroalgal canopy cover were most consistently identified as influencing fish abundance. Experimental macroalgal clearances at eastern Bay of Plenty (short term) and western Cook Strait (longer term) indicated that Notolabrus celidotus used areas comprising macroalgal canopy more than cleared areas, whereas Parapercis colias and N. fucicola were more active in cleared areas. Effects of canopy clearance on fish activity were most obvious in summer at Cook Strait. Orthogonal manipulations of canopy and topographic complexity at a distant site (Tasman Bay) produced similar results for 2 species, indicating geographic generality of habitat models for N. celidotus and P. colias. KEY WORDS: Temperate reef fishes · Macroalgae · New Zealand · Experiments · Topographic complexity Full text in pdf format PreviousNextCite this article as: Cole RG, Davey NK, Carbines GD, Stewart R (2012) Fish−habitat associations in New Zealand: geographical contrasts. Mar Ecol Prog Ser 450:131-145. https://doi.org/10.3354/meps09566 Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 450. Online publication date: March 29, 2012 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2012 Inter-Research.

Dispersal of Oyster (Ostrea chilensis) Larvae in Tasman Bay Inferred using a Verified Particle Tracking Model that Incorporates Larval Behavior

ABSTRACT We present a particle tracking model that simulates the dispersal of the oyster Ostrea chilensis Philippi in Tasman Bay, New Zealand. The model was calibrated to reproduce observed vertical distributions of larvae, and was verified against an independent data set of such distributions. The seabed in Tasman Bay contains little hard substrate other than shell hash. By comparing simulated and observed settlement, we infer that larvae must either be able to sense shell hash at a distance and orient onto it, such that settlement success is higher than indicated by the 1-km2 resolution relative density (square meter of exposed shell per square meter of seabed), or be settling on material other than shell hash. The modeling indicates that only a very small proportion of those larvae that do settle travel more than 1 km from their natal location. There are plans to endeavor to restore the oyster fishery by provision of new shell hash to the bed. Our simulations suggest that these new beds will be coloniz...

Motueka River plume facilitates transport of ruminant faecal contaminants into shellfish growing waters, Tasman Bay, New Zealand

Hydrographic and water quality surveys of the Motueka River and its river plume were conducted during a moderate flood event (peak flow of 420 m3/s) to assess the source and fate of faecal contaminants transported into Tasman Bay. Escherichia coli (E. coli) and enterococci concentrations in the river were up to 10000 and 7300 Most Probable Number (MPN)/100 ml during peak flow, respectively. A coastal survey revealed a shallow low-salinity plume that extended at least 6 km into Tasman Bay and the region's largest aquaculture management areas (AMAs). Mussels within the influence of the river plume, including those collected within an AMA, had E. coli and enterococci concentrations as high as 1300 and 2200 MPN/100 g tissue, respectively. Application of microbial source tracking markers using end-point PCR assays identified the presence of faecal contamination from ruminant animals (cows, sheep) in water and mussel samples. The detection of ruminant faecal contamination within shellfish located 6 km offshore highlights the close connection between land use and the quality of New Zealand's highly valued coastal resources.

Variation in nutrient loading from the Motueka River into Tasman Bay, New Zealand, 2005–2009: implications for the river plume ecosystem

The monthly mass transport of nitrate nitrogen (NO3-N), ammonium nitrogen (NH4-N), total nitrogen (TN), dissolved reactive phosphorus (DRP), total phosphorus (TP) and dissolved reactive silica (DRSi) from the Motueka River catchment into Tasman Bay (South Island, New Zealand) was estimated for the period 2005–2009 based on observed historical relationships between recorded river flows and the associated measured concentrations of each nutrient. The resulting average annual loading estimates for TN, TP and DRSi ranged from 397–829, 25–72 and 4053–6576 tonnes, respectively, over the 5-year period. Large seasonal variations in nutrient loadings were also estimated with the highest rates generally, but not always, occurring during winter. The observed patterns suggest that phytoplankton biomass within the river outwelling plume may also vary in response to seasonal and inter-annual variations in catchment nutrient loading rates with potential follow-on food web effects including the growth of cultured GreenshellTM mussels. The estimated average annual TN loading rate (2005–2009) from the Motueka River catchment (613 tonnes) is only c. 20% of the annual loss of nitrogen based on extrapolated literature values for denitrification rates in Tasman Bay. We therefore suggest that, under the present land use scenario in the Motueka catchment, there is little potential for resulting dysfunctional river plume ecosystem enrichment effects to occur.

Spatial delineation of the depositional footprint of the Motueka River outwelling plume in Tasman Bay, New Zealand

Progress towards development of a river plume ecosystem basis for management of coastal resources requires a thorough understanding of the nature and spatial extent of terrestrial influences on receiving water and seabed characteristics. As a case study, we estimate suspended sediment (SS) loading rates from the Motueka River catchment into Tasman Bay, New Zealand and describe benthic characteristics along a series of transects encompassing the coastal river plume. A mineral-rich geological formation in the headwaters of the river was identified as a storm-generated source of highly elevated concentrations of nickel and chromium in river margin sediments, and coastal sediments extending >5 km offshore. A major storm in 2005, focused in the upper catchment, resulted in an estimated SS discharge of 161,000 tonnes into the Bay. Spatial gradients of a suite of sediment trace metal signatures, organic content and infauna community structure were used to define a river plume depositional footprint of c. 180 km2. We suggest that the boundaries of the Motueka catchment be redefined to include this area in order to facilitate engagement of marine stakeholders in management decisions that may affect coastal biological resources.

Modelling storm-event E. coli pulses from the Motueka and Sherry Rivers in the South Island, New Zealand

Storm-induced Escherichia coli pulses in the Motueka River (2074 km2) and the Sherry River (78.4 km2) are modelled. The model focuses on the catchment outlets, representing key processes, including E. coli transfer to and from the river bed, with account taken of the hysteresis in, and non-linear, non-stationary, response of E. coli concentrations to river stormflows. The model fits the Motueka River observations well, but less well in the Sherry River. A greatly simplified description of headwater and riparian inputs is satisfactory at the larger catchment scale where near-field, in-channel processes dominate the response. Spatial heterogeneity in rainfall-run-off and faecal sources probably contribute to the poorer fit in the smaller catchment. Despite using a relatively small number of driving variables and parameters, the model has the potential to predict real-time E. coli input to Tasman Bay in river plumes causing shellfish and bathing beach contamination.

Sediment yield response to large storm events and forest harvesting, Motueka River, New Zealand

Suspended sediment yields (SY) were measured at seven sites in the Motueka catchment to characterise major influences on sediment yield variation and estimate sediment delivery to Tasman Bay. Relationships between storm event SY and peak flow were used with long-term flow records to calculate SY. At large catchment scale, there were clear differences in SY related to geology and rainfall, but the major influence on SY was the impact of a >50-year return period storm that caused an increase in event SY ranging from 10–20 times in the headwaters to 2–3 times at the coast. Forest harvesting was an important influence at small catchment scale, producing a five-fold increase in event SY. The magnitude of the SY increase, the time to recover and the total area affected were all smaller than the impact of large storms. Annual SY at the coast was extremely variable, ranging from 49,000 t to 1.7 Mt.

Annual pattern of brooding and settlement in a population of the flat oyster Ostrea chilensis from central New Zealand

Temporal patterns of larval brooding and settlement were investigated in a flat oyster (Ostrea chilensis) population in Tasman Bay, central New Zealand. The proportion of the population brooding larvae and larval settlement rates were monitored over 26 months. A peak period of brooding activity began in late spring and continued through summer. Maximum rates of 17% and 23% of adult oysters brooding larvae occurred in November and December, and an estimated 55–78% of adult oysters incubated larvae over the entire summer breeding period. These proportions of brooders are higher than those previously reported for Tasman Bay. A very low level of brooding activity (1%) occurred during winter. Temporal trends in larval settlement closely tracked brooding patterns. Settlement was greatest between November and January, and there were very low rates in winter. The seasonal breeding pattern in the population was intermediate between northern and southern populations, confirming a latitudinal gradient of reproductive behaviour for O. chilensis in New Zealand. Results are useful in optimising the timing of substrate deployment in an enhancement programme for the oyster fishery.

Tidal circulation in Tasman and Golden Bays: Implications for river plume behaviour

An investigation into the tidal residual circulation in the Tasman/Golden Bays system was performed. This investigation involved collecting hydrographic and current meter data, and configuring a numerical circulation model. The model was able to reproduce the gross features of the major tidal flows within the system revealed by the data. The simulated tidal residual circulation conformed to that previously suggested, except along the western side of Tasman Bay where this investigation suggests that residual flows move northwards. The validated model was then used to produce simulations of the fate of the plumes from the major rivers. Salinity field simulations describing different river flow and wind direction/velocity scenarios suggest that the Motueka River plume can cover considerable proportions of western side Tasman Bay, extending into Golden Bay during flood conditions. The embedded sediment transport model was also used to investigate the fate of fine sediments entering the bays. Simulated distribution patterns of fine sediments entering the bays from the four major tributaries were found to be consistent with existing bathymetric and seabed substrate characteristics.

Wave energy and clast transport in eastern Tasman Bay, New Zealand

AbstractCoarse‐gravel beaches are common features along the eastern margin of Tasman Bay, at the north end of South Island, New Zealand. Although these features have traditionally been interpreted as spits, contemporary incident wave energy appears too small to transport boulders and cobbles persistently along the beaches and platforms by longshore drift. An alternative explanation suggests that boulder beaches are essentially derived in situ from resistant bedrock, which lies seaward and was buried by gravel during the Holocene sea level rise. Wind, wave and clast size data from Cable Bay and the Nelson Boulder Bank were used to resolve this problem. Wave and wind data indicate that waves reaching these areas are derived locally in Tasman Bay, and are limited in size and energy. Hindcasting predicts a 4·7 m wave could propagate from Tasman Bay. However, during Cyclone Yalli, the most intense storm in nearly 40 years of wind records, the largest wave measured in the nearby area of Cable Bay was only 2·7 m high. Maximum orbital velocity on the seabed beneath a 4·7 m is calculated to be 2·9 m s−1, which cannot initiate transport of clasts greater than 0·15 m in diameter. Clasts on the gravel platforms have average diameters greater than this, but some clasts may be as large as 1·0 m in diameter. By comparison, a swash run‐up method predicts that a wave 4·7 m high can transport clasts no larger than 0·3 m in diameter. These data and approximate calculations strongly suggest that the present wave environment in eastern Tasman Bay is not capable of consistently transporting clasts on the boulder platforms by longshore drift. Reduced sea levels in the pre‐Holocene period would further reduce wave energies available in Tasman Bay. Copyright © 2006 John Wiley & Sons, Ltd.

Geographic distribution of Pfiesteria spp. (Pfiesteriaceae) in Tasman Bay and Canterbury, New Zealand (2002–03)

The fish‐killing heterotrophic dino‐flagellate species Pfiesteria piscicida and P. shumwayae (also Pseudopfiesteria shumwayae) were present throughout New Zealand and were residents of Tasman Bay's well‐flushed estuaries and Canterbury's brackish lakes, as determined by polymerase chain reaction‐based detection assays. The two species occurred in a wide range of salinities and temperatures, although detection was restricted seasonally from spring through to autumn, except for one incidence in the shallow waters of Wairewa/ Lake Forsyth, Canterbury, in the winter of 2003. The DNA sequencing data indicated that P. shumwayae may encompass a suite of genetically closely related species. The presence of Pfiesteria in New Zealand is not considered an immediate risk to fish or human health given the current low‐to‐moderate nutrient concentrations in New Zealand's estuaries and brackish lakes. However, increases in nutrient loadings could pose a risk, as has occurred in eastern United States estuaries.