Ocean temperature climate off North‐East New Zealand

The ocean temperature field off the north‐east coast of New Zealand is studied to quantify the annual cycle and reveal the intra‐ and inter‐annual variability. The data used are repeat expendable bathythermograph (XBT) sections between Auckland and either Suva or Honolulu which have been collected quarterly since 1986. These sections give temperature measurements between the surface and 800 m and Auckland and 30°S from 1986 to August 1999. The mean and annual cycle are compared with those from the NOAA World Ocean Atlas (WOA98). The results are similar; however WOA98 lacks the horizontal resolution to fully discern the East Auckland Current and North Cape Eddy, while the XBT analysis lacks the temporal resolution to discern higher frequency intra‐annual signals. The temperature variability in the mixed layer is dominated by the annual cycle, which accounts for 80–90% of the variance. The amplitude of the annual cycle diminishes rapidly with depth, from 2.8°C at the surface, to c. 0.1°C at 180 m. The phase of the annual cycle is retarded with depth, with peak temperatures occurring in February at the surface and in June/July at 180 m. Removing the annual cycle from the time series reveals the more subtle inter‐ and intra‐annual variability. This variability is of the order of 1°C in the upper 50 m, decreasing to 0.3°C at 400–500 m. The surface layer was cold between 1991 and 1994 (c. 0.7°C cooler than average), and 0.7°C warmer than average in 1999. The deeper ocean shows a different signal, being up to 0.3°C cooler in 1990–92, 0.3°C warmer in 1998, and c. 0.2°C warmer than average in 1999. The inter‐annual mixed layer variability is highly correlated with the Southern Oscillation Index and also with inter‐annual terrestrial air temperature and wind measurements from northern New Zealand. In contrast, at higher intra‐annual frequencies, the mixed layer variability is not correlated with air and wind measurements. At these higher frequencies, the air temperature is better correlated with the sea surface temperature (SST) than with the bulk mixed layer temperature.     

Physico‐chemical features of lake Ototoa,a sand‐dune lake in northern New Zealand

Lake Ototoa is a warm monomictic lake at 36° 31’ S, 174° 14'E. During a year's study (March 1969‐March 1970), the lake became thermally stratified in November, the metalimnion being between depths of 12 m and 16 m. Surface temperatures ranged between 10.2°c (in August) and 25.2°c (in late January), and bottom temperatures between 9.7°c and 17.5°c. The annual heat budget was calculated to be 642 354 KJ.m^‐2 (15 500 cal.cm^‐2) and the work of the wind in distributing the heat income 1.730 KJ.m^‐2 (1766 g.cm.cm^‐2). Secchi disc transparencies ranged between 5 m and 9.2 m (mean 7.07 m) and were greatest in the summer. Light transmission per metre was also high, ranging between 61% and 87%. Surface waters were normally supersaturated with oxygen, but during summer stratification oxygen concentrations in the bottom waters dropped to a minimum of 2.3 mg.litre^‐2 and a positive heterograde distribution of oxygen with depth was found. The oxygen deficit was 0.015 mg.cm^‐2.day^‐1 and showed the lake to be oligotrophic. Mean surface pH was 7.82, and the ionic composition of the waters was similar to that of other small New Zealand and Australian lakes located near the sea. Compared with other New Zealand lakes PO4‐P concentrations (range 1.00–10.20 μg.litre^‐1) were low and NO3—N concentrations (range 0.12–0.60 mg.litre^‐1) high.     

Land‐use impacts and water quality targets in the intensive dairying catchment of the Toenepi Stream,New Zealand

Water quality monitoring in Toenepi Stream, New Zealand, started in 1995 in a study of dairy farming influences on lowland stream quality and has continued since then with brief interruptions. Surveys have provided information about changes in farm and soil management practices as they relate to environmental sustainability. Although average water quality in Toenepi Stream has changed little during 1995–2004, there have been some notable improvements. Water clarity measured by black disc has improved from 0.6m to 1.5m, and median ammonia‐N and nitrate‐N concentrations have declined by 70% and 57%, respectively. The frequency and magnitude of extreme concentrations have declined—most notably for nitrogen (N) forms, which also had decreased mean values. Specific yields for suspended solids (SS) and phosphorus (P) forms in 2002–04 were 47–67% of 1995–97 values, mainly because of lower water yields. Reduced specific yields for N forms in 2002–04 (34–37% of 1995–97 yields) were also attributable to lower mean concentrations in stream water. Faecal bacteria concentrations have not abated and are on average 2–3 times recommended guideline values for contact recreation. Fewer dairy farms and an increased proportion irrigating dairyshed effluent to land, rather than discharging it to the stream via two‐pond systems, were likely causes of improvement in water quality. Water quality targets were developed for Toenepi Stream to achieve contact recreation criteria for the Piako River (downstream) and for intrinsic habitat values for Toenepi Stream. A range of mitigation measures has been formulated to meet these targets, but substantial uptake of sustainable farming practices is needed to improve water quality in Toenepi Stream.     

Albacore off the north‐west coast of New Zealand,February 1972

During two trolling surveys in February 1972, albacore, Thunnus alalunga (Bonnaterre), were located between Cape Reinga and Cape Egmont, but were more abundant between Kaipara Harbour and Albatross Point. Fish catches and associated hydrological data are presented. Albacore were caught only in areas where the sea surface temperatures were between 18.5°c and 21.3°c, and usually in areas where the water was blue and the bottom depth between 45 m and 80 m. The albacore were mainly of the 2‐ and 3‐year age‐groups. Of the 665 fish landed, 449 were tagged and released, but no recoveries have been made.

Commercial vessels located albacore within 20 km of New Plymouth during the summers of 1970 and 1971 when sea surface temperatures were 1.5–2.5°c higher than in February 1972, probably because of a more southward extension of the West Auckland Current in 1970 and 1971.     

Modelling the effect of climate change on the wave climate of the world’s oceans

This paper analyses the trends and the future projections of significant wave height in several ocean areas at different parts of the world. It uses a stochastic Bayesian hierarchical space-time model, with a regression component with atmospheric levels of CO₂ as covariates in order to estimate the expected long-term trends and make future projections towards the year 2100. The model was initially developed for an area in the North Atlantic ocean, and has been found to perform reasonably well there, and it is now investigated how the model performs for other ocean areas. 11 new ocean areas have been analysed with the model, and this paper presents the results pertaining to the estimated long-term trends and future projections of monthly maximum significant wave height for each of the 12 ocean areas.     

First identification of the cylindrospermopsin‐producing cyanobacterium Cylindrospermopsis raciborskii in New Zealand

Cylindrospermopsis raciborskii is a planktonic freshwater cyanobacterium that is becoming increasingly prevalent in water bodies worldwide. During a survey of toxic cyanobacteria in New Zealand, C. raciborskii was identified in a sample collected from Lake Waahi (Waikato). This is the first identification of this species in New Zealand. Liquid chromatography‐mass spectrometry and liquid chromatography‐tandem mass spectrometry were used to confirm the presence of the cyanotoxins cylindrospermopsin (CYN) and deoxy‐cylindrospermopsin (do‐CYN). Detection of CYN and do‐CYN demonstrates that C. raciborskii is a now a species of concern in recreational, stock drinking, and potable water supplies in New Zealand.     

A model of the formation and development of ocean shear wave

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Seasonal hydrology of waters off the Otago peninsula,South‐Eastern New Zealand

Variations of temperature and salinity were observed off the Otago Peninsula from October 1966 to December 1967. In‐shore temperatures were more variable than those seawards and variability decreased with increasing depth. Temperatures over the continental shelf and down to 200 m in the open sea varied seasonally. Below 200 m temperature variations were small and non‐seasonal. Salinities were depressed in the shallow coastal waters by land run‐off, this tendency being more pronounced in autumn and winter. Seawards of this coastal zone seasonal variations of salinity were small. Over the outer shelf a zone of higher salinities was always present. Beyond this zone salinities decreased with increasing distance from shore and with increasing depth. A salinity minimum was sometimes present between 500 and 1,000 m.

Although the upper 200 m were seasonally stratified, the same water masses could always be recognised. Two water masses were present near the surface, the Southland Current, here interpreted as being subtropical in origin, being located in shore of Subantarctic Surface Water. These two water masses are separated by the clearly defined Southland Front. Along the shore, neritic conditions develop through modification of Southland Current water by coastal and climatic effects. Seawards, beneath Subantarctic Surface Water, the core of Antarctic Intermediate Water could sometimes be recognised as a salinity minimum.     

Soft‐bottom macrobenthic communities of Manukau Harbour,New Zealand

A survey of the macrobenthos at 42 stations in the channels and subtidal sandflats in Manukau Harbour, Auckland, revealed four biotic associations; although referred to as communities, they are not equivalent to Peterson‐type communities since they are not particularly discrete and there is some overlap in species composition. The similarity in species between stations was measured by percentage similarity coefficients using Jaccard's coefficient for presence‐absence data and Czekanowski's coefficient for log‐transformed quantitative data. Stations were grouped in dendrograms by group‐average sorting which allowed re‐arrangement of the similarity matrices into trellis diagrams.

Dominant species in each of the four groups of stations were ranked by calculating a ‘community score’ for each, based on its abundance, fidelity, and bioindex value within the group. Each of the four groups was found to support a unique group of species and these are considered as representing four communities. Two indicator species in each community were identified from the highest community scores: Group 1, the Microcosmus/Nolomithrax community — associated with a coarse sediment of dead bivalve shells and small rocks in shallow water. It has high species diversity indices; Group 2, the Halicarcinus/Bugula community— associated with a relatively coarse sediment of dead shells, grit, and little sand in deep water in the main channels; Group 3, the Amalda/Myadora community—associated with fine sand with mud or shell grit in shallow parts of the channels; and Group 4, the Fellaster/Pagurus community — associated with ironsand in shallow water in the outer harbour. It has low species diversity indices.     

Dimensions of long‐nosed Chimaera Harriotta Raleighana from New Zealand

The proportional dimensions of 66 adult specimens of Harriotta raleighana Goode & Bean, 1895 (Holocephali: Rhinochimacridae) from New Zealand are summarised; in both sexes there is considerable variation in proportions. Within the size range of the sample, the snout region of males is proportionately longer than that of females, and growth of the snout is negatively allometric in both sexes. Meagre data suggest that similar sexual dimorphism and allometry occur in North Atlantic specimens, though very large and very small specimens do not fit an extrapolation of the New Zealand data. None of the New Zealand males has the snout tip upturned and armed with large rounded knobs as described for North Atlantic males.     

Structure of a mudflat diatom community in the Avon‐Heathcote Estuary,New Zealand

Parameters of community structure (species composition and relative abundance, number of taxa, diversity, evenness, and cell density) were measured for a mudflat diatom community in the Avon‐Heathcote estuary, New Zealand. Fifty three diatom species were identified: 25 taxa (species and varieties) are new New Zealand records. The Shannon‐Wiener information index (H') was 3.46, indicating high diversity. Evenness (J') ranged from 0.57–0.67. The association between the biomass of the pulmonate gastropod, Amphibola crenata, and benthic diatom community structure was studied using large open enclosures (4.0 m²) to manipulate snail biomass. Community structure was compared at 0, 5 (natural biomass), and 10 g A. crenata dry weight per m. A similarity index (SIMI=0.88–0.95), as well as H’ and J’ indicated close similarity between the diatom assemblages within all enclosures, but number of taxa increased from 33 to 49 with increasing snail biomass. Cell densities were significantly lower at high snail biomass (6088 valves per mm²) compared to enclosures with no snails (10 110 valves per mm ). A. crenata had a higher ratio of diatom fragments to whole diatom valves in its faeces (2.42) than in its crop (0.55), indicating that it is capable of fragmenting diatoms.     

Differential UVB‐sensitivities of five New Zealand freshwater zooplankton species

Abstract

The ultraviolet (UV) sensitivity of five species of freshwater zooplankton (three Cladocera, two Copepoda) were investigated. The animals were exposed to varying levels of UV‐radiation in a sunshine‐simulator and the UV doses for 10 and 50% mortality (LD₁₀, LD₅₀) were estimated using a dose‐response model. To place these doses in context they were compared with modelled clear‐sky surface UV irradiances in New Zealand. The cladocerans Daphnia carinata and Ceriodaphnia dubia were sensitive to levels of UVB irradiance of LD₁₀ = 18–25 kJ m^?2 and LD₅₀ = 35–37 kJ m^?2. These sensitivities are consistent with published values for other cladocera. In contrast a third cladoceran, Bosmina meridionalis, exhibited no higher mortality over the full range of the cumulative UVB‐doses used (3–40 kJ m^?2) than controls receiving no UV exposure. The copepod Boeckella delicata showed the highest UV‐sensitivity of all organisms tested (LD10 = 7 kJ m^?2, LD50 = 33 kJ m^?2) whereas for Boeckella triarticulata, which was more heavily pigmented than B. delicata, no UV‐induced mortality was observed. Under natural conditions UV irradiances of up to 100 kJ m^?2 day^?1 can fall on the surface of New Zealand lakes. Although this is attenuated in natural waters, these data suggest that UVB irradiance may be a significant ecological variable to some zooplankton species.     

Occurrence of gravel in the stomachs of two New Zealand stream‐dwelling fish (note)

Gravel occurred in. the stomachs of 17.8% of 924 Galaxias vulgaris and 2.8% of 430 Philypnodon breviceps taken from the Glentui River, Canterbury, between June 1970 and November 1971. It is suggested that differences in feeding habits and feeding locality are responsible for the difference in occurrence of gravel in the stomachs of the two fish species. Galaxias vulgaris feeds in the water column in riffles and, being a drift feeder, is more likely to ingest inedible material by accident than is P. breviceps, which feeds on the bottom in sheltered or quiet stretches of the river.     

Life‐history studies on New Zealand Brachyura

Abbreviated or direct development is described in Pilumnus novaezealandiae Filhol, 1886 and P. lumpinus Bennett, 1964 from New Zealand. Embryonic development is separated into Nauplius, Metanauplius and embryonic zoeal stages. The ontogenetic position of the pre‐zoeal cuticle suggests that it represents the Metanauplius stage, and the absence of plumose pre‐zoeal aesthaetes in P. novaezealandiae implies relationship with the more recently evolved brachyuran families. The significance of the pre‐zoeal cuticle in brachyuran phylogeny is discussed. In P. noveazealandiae four embryonic zoeal phases are recognised as approximately equivalent to the four Zoea larval stages occurring in the majority of xanthid Brachyura. It was not possible to distinguish similar phases in embryonic zoeal development of P. lumpinus because of advanced anachronism which is normally associated with abbreviated development. The appearance of relatively advanced structures very early in ontogeny is attributed to the absence of the need for successive developmental stages to be adapted for free life. In the embryonic Zoea, carapace spines considered to assist with flotation and orientation, and natatory setae, are together reduced or absent in abbreviated development where such structures would be of no use within the egg.

In P. novaezealandiae and P. lumpinus increase in egg size during incubation is probably due to absorption of water by the embryo during development, and eclosion is initiated by rupture of the chorion through internal pressure thus created. Larvae of P. noveazealandiae hatch at a Megalopa larval stage and are retained beneath the pleon of the female crab. Those of P. lumpinus hatch as advanced, much‐modified, and non‐natatory Zoeae which are not retained by the parent. Simultaneous moulting of the pre‐zoeal and zoeal skins occurs in both species.

The Megalopa larva and first five juvenile crab stages of P. novaezealandiae are described and compared with equivalent stages of P. vestitus from Australia recorded by Hale (1931). The Megalopa larva of P. lumpinus is described. P. lumpinus is considered as the least evolved of the three species of Pilumnus possessing abbreviated development, while P. vestitus suggests a second stage, and the third and most advanced stage is shown by P. novaezealandiae Ecology of these three species is correlated with abbreviated development. Retention of potentially free‐swimming Megalopa larvae by the parent explains gregariousness among juvenile crabs and adults of both P. novaezealandiae and P. vestitus

It is probable that abbreviated development has evolved among marine and freshwater Brachyura as a response to habitat requirements of the adult crabs. Partial or complete abbreviation of the planktonic phase and retention of larvae would assist with retaining the stock within a restricted locality or ecological niche. Abbreviated development among Brachyura therefore has little phylogenetic significance.     

Life‐history studies on New Zealand Brachyura

A brief account is given of the systematics and distribution of Heterozius rotundifrons A. Milne Edwards, Ozius truncatus H. Milne Edwards, and Heteropanope (Pilumnopeus) serratijrons (Kinahan). Keys are given for the separation of Zoea larvae of New Zealand xanthid Brachyura and to the Megalopa larvae of Heterozius rotundifrons and Ozius truncatus

Notes are given on the seasonal breeding cycle of Heterozius rotundifrons, and the pre‐Zoea larva, two Zoea larval stages, and Megalopa larva reared in the laboratory are described. Larval characters of H. rotundifrons are specialised and do not support its recently suggested classification in the family Atelecyclidae. The larvae show no relationships with those of the Cancridae or of the Corystidae, and affinities with described larvae of the Xanthidae or even the Brachyrhyncha are obscure. Larval development is incompletely abbreviated possibly to reduce dispersal in response to restricted intertidal habitat requirements of the adult crabs.

The pre‐Zoea larva, four Zoea larval stages, and the Megalopa larva of Ozius truncatus reared in the laboratory are described. A key to the Zoea larval stages is given. Larvae of this species are distinct both at the generic and specific levels, but are generally similar to those known of xanthid crabs. It is difficult to relate the genus Ozius to other xanthid genera on the basis of larval characters alone.

The pre‐Zoea larva and stage one Zoea larva of Heteropanope (Pilumnopeus) serratifrons are described. There are probably four Zoea larval stages in the development of this species. Zoea larval characters suggest that in the family Xanthidae, Heteropanope and Pilumnopeus should be separated from other genera in the subfamily Pilumninae with which they are currently classified.     

Velocity measurements in the East Auckland Current north‐east of North Cape,New Zealand

Flow in the East Auckland Current (EAUC) system to the north‐east of North Cape, New Zealand is examined using data from two current meter mooring arrays, with supporting data from conductivity/temperature/depth (CTD) and satellite altimetry. Variable currents up to 45 cm s_–1 were observed. The variability was partly attributable to changes in position and strength of the North Cape Eddy whose centre lies some 150 km offshore. The observed flows across the mooring line correlate well with those estimated from satellite altimetry. This gives confidence in the use of the satellite data to estimate the transport variability in the EAUC in the 1992–2001 period. No seasonal cycle was found in the volume transports but rather broadband variability at periods longer than 100 days.     

Wind‐wave development across a large shallow intertidal estuary: A case study of Manukau Harbour,New Zealand

Locally generated wind‐waves in estuaries play an important role in the sediment dynamics and the transport of biota. Wave growth in estuaries is complicated by tidally varying depth, fetch, and currents. Wave development was studied at six sites along a transect across Manukau Harbour, New Zealand, which is a large intertidal estuary with a tidal range of up to 4 m. Three meteorological masts were also deployed across the measurement transect to measure wave forcing by the wind. A spatial variation in wind speed by up to a factor of 2 was observed which has a significant effect on wave development at short fetches. The wind variation can be explained by the extreme change in surface roughness at the upwind land‐water boundary. The tidally varying depth results in non‐stationary wave development. At the long fetch sites wave development is dictated by the tidally varying depth with peak frequencies continuing to decrease after high water, whereas wave height is attenuated by bottom friction. The non‐dimensional energy and peak frequency parameters commonly used to describe wave growth, clearly exhibit depth limiting effects, but with wider scatter than in previous studies in simpler environments. The peak frequency predictions of Young & Verhagen (1996a) fit our data well. However, the wide variability of energy limits the usefulness of standard growth prediction curves in such situations, and highlights the requirement for a validated, shallow‐water numerical model.     

Algal blooms and climate anomalies in north‐east New Zealand,August ‐December 1992

A raphidophyte‐dominated phytoplankton bloom extended discontinuously along the northeastern coastline of New Zealand, from Bream Tail, north of Leigh, to the western coast of the Coromandel Peninsula from late August until December 1992. The bloom was associated with an “El‐Niño” phase of the Southern Oscillation, resulting in unusually cold sea temperatures. The dominant bloom species in the north was Fibrocapsa japonica and in the south Heterosigma akashiwo. Associated species included the coccolithophorid Gephyrocapsa oceanica and the naked form of the silicoflagellate Dictyocha speculum. By December, numbers of the armoured form of D. speculum had increased, as those of raphidophytes and coccolithophorids declined. Bioassays to test for shellfish biotoxins were negative and Artemia salina bioassays, indicators of ichthyotoxicity, were negative except for Heterosigma akashiwo cultures, isolated from Coromandel water samples.