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.     

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.     

Feeding ecology of whelks on an intertidal sand flat in north‐eastern New Zealand

The dispersion patterns and feeding behaviour of intertidal whelks were investigated in north‐eastern New Zealand. Aggregations of whelks feeding on clams occurred regularly, with an average of 15–20 individuals per aggregation. Death of clams was attributable to predation in up to 50% of the aggregations, although scavenging of dead and moribund animals was the main activity of whelks. Laboratory and field studies showed that Lepsiella scobina (generally not considered a soft shore species) was the main whelk predator at Lews Bay, Whangateau Harbour, drilling a small neat hole through the clam shell. The distinction between Cominella spp. as predators or scavengers is not so clear. Reseeding of intertidal clams, Austrovenus stutchburyi, has been proposed as a technique for reestablishing populations in some degraded New Zealand estuaries. The impact of whelk predation has many implications for A. stutchburyi reseeding. Both L. scobina and Cominella adspersa may potentially prey on newly reseeded clams as they preferentially attacked small clams in the laboratory. On‐growing to a larger size before reseeding may be advantageous although large size was not found to protect prey from predation. Additionally, no seasonal trend in whelk activity was found.     

Water clarity records from twenty‐two New Zealand lakes

Water clarity values from 22 New Zealand lakes show that the largest and deepest have the highest values, except those affected by glacial silt or humic coloration. Smaller and shallower lakes have lower water clarity values.     

Laboratory studies on zooplankton‐cyanobacteria interactions

Laboratory studies on cyanobacteria‐zooplankton interactions have largely focused on the inadequacy of cyanobacteria as a food source. Some features of cyanobacteria can be regarded as anti‐herbivore defences. Large colonies of Aphanizomenon, Anabaena and Microcystis cannot be handled by zooplankton, but do not interfere seriously with the filtering process. Small colonies and filaments, however, may cause severe inhibition of the feeding process by mechanical interference. This reduces zooplankton growth, reproduction, and survival. Copepods, rotifers, and Bosmina are less affected by mechanical disturbance than cladocerans. If ingested, some cyanobacteria may be poorly digested or may not provide essential nutrients. Some cyanobacteria are reported to be toxic to zooplankton. Several strains of Microcystis produce an endotoxin, but the amount of toxin produced differs among strains and with the condition of Microcystis. Zooplankton encountering toxic cells cease feeding. Some evidence of an extra‐cellular herbivore deterrent was found for Anabaena. Thus, cyanobacteria may either be individually protected or may create an environment that is unfavourable for efficient grazers (e.g., Daphnia).     

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.     

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.     

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.     

Land‐use effects on the hyporheic ecology of five small streams near Hamilton,New Zealand

Although the importance of the subsurface saturated interstitial zone (hyporheic zone) to the ecological functioning and maintenance of water quality of stream ecosystems is well known, there is little information on the impacts of different forms of land use upon this zone. Hyporheic physico‐chemistry and invertebrates were compared among small streams draining hill‐country catchments under pasture, exotic pine forest, and native forest near Hamilton, New Zealand. In streams draining native forest, the hyporheic zone harboured a relatively diverse invertebrate fauna comprising mostly taxa common in the surface benthos, although a few apparently obligate hyporheic taxa (ostracods, blind amphipods) were collected. Few individuals and taxa occupied the hyporheic zones of streams draining pasture with some groups such as water mites conspicuously absent. The hyporheos of the stream in exotic pine forest was similar in richness and abundance to that of the pasture streams. Hyporheic water temperatures were significantly higher in the pasture streams than those in pine or native forest. There were strong positive correlations between percentage saturation of dissolved oxygen in the hyporheic zones of all streams and both species richness and total invertebrate abundance. We suggest that land clearance for pasture leads to hill slumping and siltation that bury the lateral bars along the stream channels, rendering this habitat unsuitable for hyporheic invertebrates. Channel narrowing and incision may physically remove further hyporheic habitat, and the reduction of flushing flows to remove interstitial silt and clay leads to low hyporheic dissolved oxygen concentrations and reduced colonisation by surface benthos.     

Tagging experiments on trawl‐caught trevally,Caranx georgianus,off north‐east New Zealand, 1973–79

A total of 2676 trevally, Caranx georgianus Cuvier, was tagged in the Hauraki Gulf and Bay of Plenty during 1973 and 1974. Fish were caught by research trawler, anaesthetised, and tagged with spaghetti tags. During the following 5 years, 130 tags (4.9%) were returned. Most recaptures came from set nets (42%), followed by commercial trawlers (22%), Danish seiners (11%), research trawl (9%), other methods (7%), and method unknown (9%). Excluding tagged fish taken by research trawl, 85% of tag returns were made by commercial fishermen and 15% by amateurs. Initial tagging mortality was low, but was probably significant over an extended period. Movements of trevally were limited; 88% moved less than 30 nautical miles (55 km) from the release site. However, there was sufficient movement to regard trevally from the Bay of Plenty and probably also the Hauraki Gulf as one stock.     

Spectral features of the New Zealand deep‐water ocean wave climate

The wave climate at the Maui site off the west coast of the North Island and off the east coast of Great Barrier Island to the east of the North Island are examined. This is done by means of average wave spectra derived from a 2‐year database, acquired from Waverider buoy measurements made over 1980 and 1981. The average spectra provide information about the individual sea states which characterise the wave climate, and show that on average the sea state on the east coast is less energetic than it is on the west coast. Further, it is seen that this difference results largely from a dominant and persistent long‐period south‐westerly swell of 12.4 s period which is present at the Maui location but absent from the Great Barrier Island seas.     

Icebergs south‐East of New Zealand in 1967 (note)

Sightings of 85 icebergs south‐east of New Zealand in February and March 1967 are reported, with associated sea surface temperatures.     

Succession of a wharf‐pile fauna at Lyttelton,New Zealand

A 31/2‐year succession of wharf‐pile fauna is described from communities of different known ages on piles at Lyttelton, New Zealand. Intertidal regions of the piles were initially colonised by the barnacle Elminius modestus; these populations developed to form a subclimax community which was subsequently replaced by a climax community of the mussel Modiolus neozelanicus after 21/2 years. The stability of this climax is discussed. In the infratidal region initial settlement of the tubicolous amphipod Corophium acherusicum and an erect bryozoan Bugula sp. was followed after 5 months by colonisation by solitary tunicates. These tunicates became dominant only after H years and provided numerous niches for superficial foulers, crevice dwellers, and motile organisms. This succession is compared and contrasted with a terrestrial succession of plants. Four vertical zones were recognised: supralittoral zone, midlittoral zone, in‐fralittoral fringe, and infralittoral zone. Species additional to those recorded by Skerman (1958) are appended.     

Intertidal sand‐dwelling Peracarid fauna of North Island,New Zealand

Abstract

Substrate and infauna samples were taken at four tidal levels (mean high water springs, high mid beach, low mid beach, and mean low water neaps) with a 0.0625 m² quadrat at 14 North Island beaches in New Zealand. The distributions of Peracarida (Crustacea) were correlated with sediment type, tidal height, and degree of exposure; sampling began in March 1972 and was completed in November 1973.

Substrate samples were sieved and median diameter of the particles ranged from very coarse sand of — 0.60? to very fine sand of + 3.259?. Substrates were variously sorted: ? quartile deviation ranged from 0.14? to 0.66?, skewness from ‐ 0.08? to + 0.07?.

Peracarid fauna was moderately abundant; the maximum value was 720 animals per square metre on a fully exposed beach. Highest average abundance (303 per square metre) for the 14 beaches was recorded from the mean low water neap station. Amphipoda was the dominant group (54% of all Peracarida recorded), followed by Isopoda (33%) and Cumacea (13%). Frequency of occurrence at the 56 stations was headed by Amphipoda (64%), followed by Isopoda (46%), and Cumacea (20%).

The results are compared with data from Stewart Island beaches, and the biogeographical distributions of recorded Peracarida are discussed. An unexpectedly high degree of endemism exists for a warm‐temperate region, caused by the isolation of New Zealand, which has no direct shallow water contact with tropical or cold temperate regions.     

Lake‐shore spawning of rainbow trout at Lake Rotoma,New Zealand

The presence of suitable gravel size alone can stimulate female rainbow trout (Salmo gairdneri) to excavate nests for spawning on the shores of Lake Rotoma. Emergent fry result from lake‐shore spawning, and could contribute significantly to the trout fishery in Lake Rotoma. Lake‐shore spawning could be enhanced by the use of stable artificial spawning beds that have adequate depth and appropriate sizes of gravel.     

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.     

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.     

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.