摘要:

We carried out a benthic survey and two experiments in runs at eight sites down the Kakanui River (South Island, New Zealand) during summer low flows, to investigate the interaction between nutrients, periphyton, and macro‐grazers. Benthic periphytic biomass was generally low (< 20 mg m‐2chlorophylla) at most sites, but high densities of macro‐grazers (mainly snails) were observed at six of the eight sites. Chlorophyllaand cellular P concentrations were generally higher on artificial substrates in the first‐ to third‐order tributaries, compared with downstream. Macro‐grazer densities (mainly snails) were also highest in the second‐ and third‐order tributaries. Enrichment of patches with N and P did not translate into significant increases in chlorophyllaconcentrations. Instead there was a general increase in macro‐grazers, and an increase in the relative abundance ofCocconeis placentula. In a second experiment, the chlorophyllalevel was five‐fold higher on the substrates where macro‐grazers were excluded and there was no significant response of chlorophyllato nutrient addition on these substrates. On the grazed substrates, densities of snails and caddis‐larvae were two‐fold higher with N+P enrichment. These experiments provided evidence for a tight coupling between first and second trophic levels, and strong grazer control of periphyton, in this river.

ISSN:0028-8330    

DOI:10.1080/00288330.1994.9516601

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

摘要:

The impact of small (fork length < 100 mm) and large (≥ 100 mm) brown trout (Salmo truttaL.) on the distribution of the common river galaxias (Galaxias vulgarisStokell) was investigated in the Shag River (South Island, New Zealand). Riffle reaches were sampled by electrofishing and their macrohabitat was described in terms of substratum, flow, elevation, and vegetation characteristics. Galaxias densities in reaches containing large trout were lower than reaches with only small trout or no trout and trout size was the most important variable determining galaxias density. Densities of galaxias < 80 mm were reduced in the presence of large trout, but not galaxias > 80 mm. Reaches with large, small, or no trout varied in terms of water depth, percentage cobble, and elevation. However, these differences were unlikely to account for variations in galaxias densities because selection for these particular habitat features accounted for only a small proportion of the observed variation in galaxias density. A change in macrohabitat use by galaxias from fast current velocities in sites without trout to slower velocities in sites with large trout may be explained by competition for areas of high velocity (potentially the better feeding areas). However, a combination of interspecific competition and predation by large brown trout is likely to be responsible for the observed reductions in the density of smaller galaxias.

ISSN:0028-8330    

DOI:10.1080/00288330.1994.9516602

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

摘要:

Different proportions of component species of faecal streptococci were found in New Zealand sewage, animal processing effluents, and animal faeces.Enterococcus faeciumwas the major species in raw sewage (43–65%), followed byE.faecalis(19–40%) orE. durans(14–23%). Meat processing effluent usually had a higher proportion off. durans(37–73%) than sewage. Enterococci, mainlyE. durans(34%), dominated in sheep faeces, butStreptococcus boviscomprised 53% of the faecal streptococci in cattle faeces. In sewage‐contaminated groundwater, a survival pattern ofE. faecalis > E. faecium > E. durans > S. equinus > S. boviswas predicted. The proportion ofE.duranswas low in rivers impacted by animal wastes, and decreased during treatment of sewage and meatworks effluent and after both effluents were mixed with sea water. Thus, superior survival ofE. faeciumandE. faecalismeans that they are likely to be the dominant species in receiving waters, irrespective of whether the pollution is of human or animal origin. Faecal coliform: faecal streptococci/ enterococci ratios were similar in raw sewage and meat processing effluents (generally > 3), but superior enterococcus survival caused a decrease in ratios in groundwater and sea water. Thus, these ratios are probably not useful in distinguishing between human and animal pollution sources in New Zealand receiving waters.

ISSN:0028-8330    

DOI:10.1080/00288330.1994.9516603

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

摘要:

Regression equations are presented for the estimation of dry weight from head width and body length for 20 common New Zealand stream‐dwelling macroinvertebrate taxa. Equations for taxa grouped at order level are also provided. A power equation, y = a xbis used to express the relationship between dry weight and body size. For the majority of taxa, dry weight could be estimated with more precision from body length than from head width.

ISSN:0028-8330    

DOI:10.1080/00288330.1994.9516604

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

摘要:

In September 1991, several north‐south transects were made across the Chatham Rise along 179°E, using a ship equipped with a 150 kHz Acoustic Doppler Current Profiler (ADCP). Current meters were deployed near the crest of the rise. There is good agreement between the ADCP and current meter measurements. Zonal (along‐rise) currents are dominated by diurnal tides, whereas meridian (cross‐rise) currents are dominated by semi‐diurnal tides. An estimate of the mean currents over 4 days of intensive observations over the northern flank of the Chatham Rise shows currents of up to 0.15 m s‐1, probably associated with meanders of the Subtropical Convergence.

ISSN:0028-8330    

DOI:10.1080/00288330.1994.9516605

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

摘要:

Multi‐channel Advanced Very‐High Resolution Radiometer (AVHRR) images of sea surface temperature (SST) in the New Zealand region have been archived since 1989. The first 2 years of data are used to investigate the variability in sea surface temperature (SST) and its gradients around New Zealand. Empirical orthogonal function (EOF) analyses show that the annual cycle accounts for 92% of the variance of SST, but for less of the variance in SST gradient. The Southland and Subantarctic Fronts have an annual modulation in their strengths, accounting for about 20% of their variance; these modulations are out of phase, with the Southland Front being strongest in winter. The Subtropical Convergence shows variability that cannot be easily described by one mode, but appears to migrate meridionally with an annual period, being furthest north in March.

ISSN:0028-8330    

DOI:10.1080/00288330.1994.9516606

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

摘要:

Fecundity estimates were made from late‐vitellogenic ovaries of orange roughy sampled from five spawning grounds in New Zealand waters: Challenger Plateau (1987, 1988, 1989, 1990), Cook Canyon (1988, 1989), Chatham Rise (1990), Ritchie Banks (1990), and Puysegur Bank (1991). Total fecundity of fish from the different areas ranged from 11 000 to 180 000 eggs per fish, with mean relative fecundity ranging between 26 000 and 49 000 eggs per kg body weight. Total fecundity was positively related to length in all samples except from the Ritchie Banks. Comparisons of size‐fecundity relationships were made between years from Challenger Plateau samples, and between Challenger Plateau, Cook Canyon, Chatham Rise, and Puysegur Bank samples. There was no apparent trend in fecundity over time on the Challenger Plateau. There were significant differences revealed by analysis of covariance between areas, with fecundity of orange roughy from the Puysegur Bank being greater than on the Chatham Rise, which was in turn greater than that of fish from Cook Canyon and Challenger Plateau regions.

ISSN:0028-8330    

DOI:10.1080/00288330.1994.9516607

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

摘要:

Growth rates were estimated for juvenile (0+, 1+, and 2+ age classes) New Zealand snapper using length‐frequency data, and length‐at‐age data based on otolith daily increment counts. Growth rates were also estimated for early juvenile snapper reared in Australia. Published estimates of snapper growth rates were reviewed, and the growth history of snapper up to 3 years old discussed. Growth rates were highest during spring‐autumn, and lowest during winter. This seasonal cycle was correlated with changes in water temperature. Wild and reared juvenile snapper grew linearly after metamorphosis at rates ranging from 0.35 to 1.53 mm day‐1(typically 0.5–0.9 mm day‐1). Growth of wild juveniles slowed dramatically during the first winter, and virtually ceased in subsequent winters. Growth rates during the second and third spring‐summer growth periods were typically 0.2–0.4 mm day‐1. Within a year class, large snapper were large because they were older, rather than because they were faster growers, than small snapper. Bimodal length‐frequency distributions were common, and probably resulted from variability in spawning and recruitment success. Growth rates did not differ among snapper samples collected over an 8–12 km spatial scale.

ISSN:0028-8330    

DOI:10.1080/00288330.1994.9516608

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

摘要:

The chemical composition of recent marine sediments and pore waters in areas of shallow underwater volcanic vents in the Bay of Plenty, New Zealand, was studied. Values of pH in the sediments in active sites were higher than in control sites, and concentrations of Fe, Cu, and Ni were elevated; however, the general chemical composition of the sediments and pore waters was rather similar to that of common shelf sediments. The chemical composition of pore waters agrees well with the usual diagenesis of these sediments; the increase in temperature might influence the rates of diagenetic processes. No signs of uniform seeping of volcanic waters through the sediments were detected. Hydrothermal waters and gases are preferentially transported through sulfur tubes. These tubes and sulfide concretions replacing magnetite were collected at and near the hydrothermal vents.

ISSN:0028-8330    

DOI:10.1080/00288330.1994.9516609

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

摘要:

Very little is known about calcification rates of bryozoans, despite their importance in modern temperate‐latitude shelf carbonate sediments and in temperate limestones. Here we report the carbonate production rates for 19 species of bryozoans over 3, 9, and 12‐month periods from a settling experiment in 14 m water depth at Cape Rodney, Hauraki Gulf. Based on the larger bryozoan colonies, estimates of calcification rate range from 25 to 740 mg CaCO3 y‐1. Extrapolation of calcification rate to overall bryozoan sediment production is not straightforward, but a value of 24–240 g CaCO3m‐2y‐1for the sample site has been determined, equivalent to a sediment accumulation rate of 4–40 cm per 1000 years (ky). In reality, over a large shelf region both dilution by other organisms and a patchy areal distribution of living bryozoans would reduce these values to only a few cm ky‐1. The relatively low rates of accumulation deduced here are mainly consistent with the few other studies of bryozoan sedimentation in temperate waters, and also with those typically reported (1–3 cm ky‐1) for many occurrences of temperate bryozoan‐rich limestones from the rock record.

ISSN:0028-8330    

DOI:10.1080/00288330.1994.9516610

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor