摘要:

The growth response of the PSP‐producing dinoflagellateAlexandrium minutum, cultured from a shellfish poisoning outbreak in 1993 in the Bay of Plenty, was studied in semi‐continuous cultures, using 54 combinations of irradiance and different nitrogen (N) sources (nitrate (NO3−), ammonium (NH+4), urea) and concentrations. Irradiance had more influence on growthof A. minutumcultures enriched with NO3−than on cultures enriched with either NH4 or urea. At the high irradiance level (100 μmol m−2s−1), the greatest growth (0.5 doubling d−1) was recorded in cultures enriched with NO3−, followed by cultures enriched with NH4+and urea, respectively. For cultures enriched with either NH4+or urea, nutrient concentrations contributed to greater variations in growth than irradiance. At high irradiance, growth ofA. minutumpeaked in cultures enriched with about 25μMof either NH4+‐N or urea‐N. Growthof A. minutumwas substantially reduced when grown at 50 μM of either form of “recycled” N, and growth ceased at concentrations ≥ 100 and ≥ 200 μMof NH4+‐N and urea‐N, respectively. Growth ofA. minutumappeared to saturate at relatively low irradiance (Ik< 40 μmol m−2s−1). These results imply thatA. minutumis able to substain reasonably good growth rates, even in poorly illuminated depths within the water column.

ISSN:0028-8330    

DOI:10.1080/00288330.1997.9516740

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

Growth rate estimates were obtained for elephantfish using length‐frequency and tag‐recapture data from the east coast of South Island during 1966–88. Elephantfish hatch from egg cases at about 10 cm fork length (FL) during May‐July. Females grow faster than males after their first year and growth is fastest in summer. In 1966–68, elephantfish in Pegasus Bay grew faster than in Canterbury Bight, resulting in modal length differences that were maintained for the first 3 years of life. This suggests there are at least two distinct juvenile nurseries. Maximum observed lengths were 76 cm FL for males and 97 cm FL for females. Length‐frequency analyses identified 5–8 male age classes and 8–9 female age classes, but longevity probably exceeds these values. Growth rates of 0+ elephantfish in Pegasus Bay in 1983—84 and Canterbury Bight in 1988 were 33–56% greater than in 1966–68. The faster growth rate meant male age at maturity was 4+ in the 1960s and 2+ to 3+ in the 1980s. If female length at maturity was the same in the 1980s as in the 1960s, then female age at maturity would have been 5+ to 6+ in the 1960s and 4+ to 5+ in the 1980s. The increased growth rates and earlier maturity may have led to an increase in elephantfish stock productivity between the 1960s and 1980s.

ISSN:0028-8330    

DOI:10.1080/00288330.1997.9516741

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

The relationship between photosynthesis(P)and light(E)was determined for phytoplankton from the mixed layer and the deep chlorophyll maximum (DCM) at 23 stations off the east coast of New Zealand during February‐March 1995. The stations encompassed three water masses, Sub‐tropical, Sub‐antarctic and the Sub‐tropical Convergence Zone. The light‐saturated rate of photosynthesis(Pmax)and slope of the light‐limited portion of the curve (a) were determined using a light gradient incubator. The absorption spectra of the phytoplankton assemblages were used to calculate the maximum quantum efficiency of photosynthesis (ϕmax)‐ A higher mixed‐layerPmaxin Sub‐tropical water over Sub‐antarctic water (4.26 compared to 5.85 mg C (mg Chl.a)−1h−1) was consistent with the temperature difference of 4°C, although there was also a taxonomic composition difference between these waters. The highest variability ofPmaxand α, as well as the highestPmaxvalues, were seen within the STC, but ranges for all water masses overlapped. Physical conditions in the water masses were similar and no correlations between any measured physical or chemical feature of the stations and anyP‐Eparameter could be identified.

ISSN:0028-8330    

DOI:10.1080/00288330.1997.9516742

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

Tag shedding rates of Hallprint dart and loop tags, and tag‐related mortality in the snapperPagrus auratuswere experimentally determined on fish held in captivity for periods up to 18 months. An artefact of the experimental process appeared to exacerbate dart tag shedding in one treatment. However, for other treatments, the instantaneous shedding rates for the first 7 months was 0.0006 day−1. Shedding rates were not linear for periods beyond 7 months and were described by a logistic function. The instantaneous shedding rate for the loop tags was much lower at 0.00016 day−1. Overall mortality during the experiment was only 1.9% and the causes of death could not be related to tagging. The relative return rates of the two different tag‐types from a field tagging programme were compared after analysis of fish size, spatial, temporal, and tagger‐type distribution. In all direct comparisons within each stratum, loop tag return rates were higher. It was concluded that the retention capabilities are better for loop tags than for dart tags inP. auratus.

ISSN:0028-8330    

DOI:10.1080/00288330.1997.9516743

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

The aim of this study was to measure nanoflagellate abundance in New Zealand waters, and identify the key factors which both influence, and are influenced by, nanoflagellate abundance. Nanoflagellate populations were sampled in winter and spring 1993 from a series of sites representing different water masses around the South Island of New Zealand. Both numbers and biomass of heterotrophic (HNF) and autotrophic nanoflagellate (ANF) populations were larger in spring by a factor of four. ANF were about three times as abundant as HNF in both seasons. The physiochemical variables, temperature, NH4‐N, and urea combined with bacteria and picophytoplankton numbers explained between 67 and 94% of the variation in nanoflagellate abundance. In addition, there was evidence that variation in abundances between seasons and water masses was influenced by food availability, predation, and changes in species composition represented by large differences in cell biovolume.

ISSN:0028-8330    

DOI:10.1080/00288330.1997.9516744

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

The avoidance response of the migratory juvenile stage of six species of diadromous fish to different levels of suspended solid (SS) was determined in the laboratory using a two‐choice avoidance tank. Trials were mostly conducted with resuspended sediment from the outlet of Lake Waahi, New Zealand, but a series of tests was also conducted with kaolin for comparison. Banded kokopu(Galaxias fasciatus)was the most sensitive species, displaying a 50% avoidance response to kaolin and Waahi silt at 17 and 25 NTU, respectively. Koaro(Galaxias brevipinnis)and inanga(Galaxias maculatus)were found to be less sensitive than banded kokopu, with a 50% avoidance response to Waahi silt at 70 and 420 NTU, respectively. Shortfinned and longfinned elvers(Anguilla australisand/1,dieffenbachii), and redfinned bullies(Gobiomorphus huttoni)showed no avoidance behaviour, even at the highest turbidities (1100 NTU) tested. Based on these laboratory results, and until field testing is undertaken, a limit of about 15 NTU in otherwise clear waterways should ensure that the upstream migration of some of the most common New Zealand native freshwater species will not be affected.

ISSN:0028-8330    

DOI:10.1080/00288330.1997.9516745

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

Data on seven lakes in the Rotorua District were examined to determine trophic state changes in these lakes. The method of data analysis was specifically designed to find small changes in the trophic state of lakes. For each variable, theP‐value from 12 monthly paired sample Studentt‐test comparisons was calculated and a change of trophic state value (CTS) was assigned, based on the P‐value. The CTS values for all the variables examined for a single lake were averaged (C) with a standard error (CV). The resulting Change/ Confidence Value index (C/CV) indicated the nature of the trophic change observed and the degree of confidence that could be placed in the stated change. This study finds that in recent years Lakes Rotorua and Rotoiti have become less eutrophic; Lakes Okareka and Rotoma may have become less eutrophic; Lakes Okataina and Rotokakahi have not changed in trophic state in the last 22 years, and Lake Tikitapu may have become more eutrophic.

ISSN:0028-8330    

DOI:10.1080/00288330.1997.9516746

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

In the Bay of Plenty, New Zealand, 32 coastal beach sites, 23 lake beach sites, and 31 river swimming hole sites were sampled for enterococci as indicators of bathing suitability over 3 summers (from 1991 to 1995). The median enterococcal numbers of 5 samples collected from each site over each season were compared to the guideline medians: 35 and 33 enterococci per 100 ml for marine and fresh waters, respectively. The “5‐sample median” values generally agreed with longer‐term medians (n = 24, 28) from river and estuary sites sampled between 1990 and 1994. During the summers of 1991 and 1993, high enterococcal numbers at marine and lake swimming sites were assumed to be derived primarily from sewage effluent and farm run‐off, either directly or from freshwater inflows. Enterococcal numbers dropped significantly in these waters when effluents were either treated or removed from the waters. In 1995, all marine bathing waters complied with the guideline value of 35 enterococci per 100 ml. Evidence from long‐term monitoring of estuary sites indicated that most marine bathing sites have high‐quality bathing water with short‐term variability caused by winds, tides, and outfall discharges. In 1995, all but one lake site complied with the freshwater median guideline of 33 enterococci per 100 ml. Most upstream river sites also complied with the freshwater guideline.

ISSN:0028-8330    

DOI:10.1080/00288330.1997.9516747

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

The fish community of the Kakanui River estuary on the east coast of the South Island, New Zealand, was studied seasonally over 1 year by diel seine netting and nocturnal fyke (trap) netting. Twenty species were recorded, although nine of these together constituted 0.2% of the total number of fish caught. Marine species were represented by single individuals of four species. Brown trout (Salmo trutta)and rainbow trout(Oncorhynchus mykiss)were the only species without an obligatory marine life‐history phase. Small benthic fishes, cockabullies(Tripterygion nigripenne), and common bullies{Gobiomorphus cotidianus)were the numerically dominant species and, together with a further nine species, were resident year‐round. Winter was the season of lowest abundance of most species. Spatial patterns of distribution were apparent with common bullies, giant bullies(G. gobioides), and longfinned eels(Anguilla dieffenbachii)occurring mainly in the upper estuary; common smelt(Retropinnna retropinna)mainly in the lower estuary; and cockabullies, yelloweyed mullet{Aldrichetta forsteri), and shortfinned eels{Anguilla australis)present throughout the estuary.

ISSN:0028-8330    

DOI:10.1080/00288330.1997.9516748

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

Phytoplankton biomass and productivity at two sites in the newly impounded Lake Dunstan and, upriver, in Lake Wakatipu (Frankton Arm) showed ranges throughout 1 year of 0.2–2.0 mg chlorophyllam−3and 0.9–6.0 mg C m−3h−1(maximum rate of carbon fixation). Peaks in phytoplankton abundance occurred in spring and summer in both lakes, but relationships of biomass and productivity vs light and nutrients differed between the lakes. In Lake Dunstan, P‐vs‐I parameters indicated that phytoplankton were photo‐acclimated to prevailing light conditions. In the Frankton Arm, P‐vs‐I parameters indicated that phytoplankton were poorly adapted to light conditions. Phytoplankton biomass and productivity were only depressed at the shortest observed hydraulic residence times (< 3 days). Phytoplankton biomass and productivity in Lake Dunstan were predicted from dissolved and particulate nitrogen concentrations and mean mixed‐layer light intensity. Annual mean chlorophyllalevel was predicted satisfactorily using a published empirical model based on total phosphorus and inorganic suspended solids; a published deterministic model developed for reservoirs was tested and did not predict chlorophyllaconcentrations accurately. The results are discussed in the context of the paradigm of trophic upsurge which is commonly observed in newly impounded reservoirs.

ISSN:0028-8330    

DOI:10.1080/00288330.1997.9516749

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor