摘要:

Most chinook salmon in the Rakaia River spawn in upland tributaries. In spring very large numbers of fry emigrate from side streams to the main river. It has been thought that most of these fry do not survive, and thus do not contribute to the adult population. In contrast, we found that many fry take up residence in the river and, after a period of growth, proceed slowly seawards, reaching the coast in late spring to early summer. By the time fry recruitment to the upper river ceases (November), juvenile salmon are abundant throughout the river, ranging in fork length (FL) from 35 mm in the upper reaches to 80 mm near the river mouth. Most fingerlings enter the sea at 60–90 mm FL. From November the residual population in the upland tributaries enters the river as fingerlings 50–60 mm FL. In the absence of severe flooding, these “stream residents” are probably outnumbered by “river residents”.

ISSN:0028-8330    

DOI:10.1080/00288330.1987.9516213

出版商:Taylor & Francis Group    

年代:1987

数据来源: Taylor

摘要:

New Zealand rivers were surveyed for filamentous algal proliferations following prolonged periods of low flows to define their extent, standing crop, and composition. Significant growths were found at 167 of the 423 sites surveyed. The geometric mean river bed cover of filamentous algae was 26% in summer and 22% in winter. Proliferations of >40% cover occurred at 16% of the sites. The geometric mean standing crop was 15.3 g/m2(ash‐free dry weight) in summer and 1.87 g/m2in winter. Proliferations of >50 g/m2(AFDW) occurred at 8% of the sites. A taxonomic classification analysis of the summer data identified nine main clusters of sites which appeared to correspond to different catchment land uses. One, or a combination, of the following taxa dominated these clusters:Ulothrix zonata, Phormidiumspp.,Sti‐geocloniumsp.,Spirogyraspp.,Compsopogon coe‐ruleus, Oedogoniumspp.,Cladophorasp.,Cladophora glomerata, Rhizocloniumsp., andMelosira varians. Ulothrix zonataandDiatoma hiemalevar.mesodondominated the sites sampled in winter. There was a close positive relationship between the average standing crop and the average water conductivity of the nine site clusters.

ISSN:0028-8330    

DOI:10.1080/00288330.1987.9516214

出版商:Taylor & Francis Group    

年代:1987

数据来源: Taylor

摘要:

Lake Pupuke is unique in New Zealand in that all four obligate submerged members of the adventive Hydrocharitaceae,Vallis‐neria giganteaGraebn., and the “oxygen weeds”Lagarosiphon major(Ridl.) Moss ex Wagner,Elo‐dea canadensisMichx., andEgeria densaPlanch, co‐exist there. Dense stands ofVallisneria, up to 5 m tall, dominated the mid‐littoral zone (2–7 m depth) through to 1985.Egeriawas first recorded as present in Lake Pupuke in 1980. It occurred in the mid‐littoral zone and in 1982 it was estimated to occupy 2%, in 1983 10%, and by 1985, 25% of total macrophyte volume in Lake Pupuke. This trend suggests thatEgeriais the potential dominant of this community.

ISSN:0028-8330    

DOI:10.1080/00288330.1987.9516215

出版商:Taylor & Francis Group    

年代:1987

数据来源: Taylor

摘要:

Macroinvertebrates from six macro‐phyte communities and from an intermittently vegetated sublittoral community were collected from Lake Alexandrina during a period of 2.5 years. Each of the six communities was dominated by one native species (Myriophyllum triphyllum, Isoetes alpinus, Chara fibrosavar.acanthopitysorChara globularis)or by the adventiveElodea canadensis. Thirteen of the 21 macroinvertebrate taxa associated with these communities were herbivores and/or detritivores and these contributed at least 90% to total abundance; the remaining eight were predators. The gastropodPotamopyrgus antipoda‐rumwas dominant in all communities; overall, gastropods (four species) contributed between 66 and 90% to total abundance. A few species showed a marked preference for certain communities. Seasonal changes in macroinvertebrate abundance and biomass are discussed and the results compared with those from other New Zealand lakes. Biomass data for all communities and the extent of the oscillations in biomass between years are consistent with the designation of mesotrophic status for Lake Alexandrina.

ISSN:0028-8330    

DOI:10.1080/00288330.1987.9516216

出版商:Taylor & Francis Group    

年代:1987

数据来源: Taylor

摘要:

Values for aboveground biomass (standing crop) from December 1982 to December 1985 at two sites in Lake Alexandrina (South Island, New Zealand) are reported. Weak seasonality was apparent forChara fibrosaat 1.8 m,Elodea can‐adensis, Isoetes alpinus, andChara globularis. The biomass of other species did not appear to be directly related to annual changes in solar radiation and water temperature. Annual growth for six species was estimated from annual changes in above‐ground biomass and ranged from 296 mg C m‐2day‐1(forE. canadensis)to 17 mg Cm‐2day‐1(forChara corallina). The growth of two species was also determined using short‐term measurements of stem and branch length and gave estimates of 177 and 545 mg C m‐2day‐1forE. canadensisat two sites and 97 mg Cm‐2day‐1forMyriophyllum triphyllum.

ISSN:0028-8330    

DOI:10.1080/00288330.1987.9516217

出版商:Taylor & Francis Group    

年代:1987

数据来源: Taylor

摘要:

The distribution of temperature, salinity, dissolved inorganic nutrients, and chlorophyllais described along a transect in Pelorus Sound, as are phytoplankton populations and zoo‐plankton biomass. River water contributed dissolved inorganic nutrients to Pelorus Sound; silicon was a conservative property. Pelorus Sound was a sink, and the open sea a source for nitrate‐nitrogen. Havelock Arm and Cook Strait water appeared to be a source for ammonium‐nitrogen. Winter cooling at the head of Kenepuru Sound produced high‐density water which sank at the confluence with Pelorus Sound; this is a mechanism (in addition to internal tides) whereby low‐salinity high‐nutrient water is mixed downwards. Phytoplankton biomass was dominated by diatoms in July 1981. Zoo‐plankton biomass in outer Pelorus Sound in May 1982 was dominated byAmelia aurita. The distribution of chlorophyllais discussed in relation to the input of river water, inorganic nutrients, and variations in zooplankton grazing pressure. The proposition that more mussel farms would result in long‐term food limitation of cultured mussel production is discussed.

ISSN:0028-8330    

DOI:10.1080/00288330.1987.9516218

出版商:Taylor & Francis Group    

年代:1987

数据来源: Taylor

摘要:

Short‐term effects of deposit feeding on benthic micro‐organisms are known from several marine environments, but longer‐term influences of deposit feeders have not been extensively investigated. The long‐term microbial response to deposit feeding by the gastropodAmphibola crenatawas monitored in a 10‐month field study where deposit feeding intensity was controlled in artificial enclosures. The presence of the snail resulted in a minor decrease in bacterial numbers and a slight increase in heterotrophic activity relative to bacterial cell numbers. This effect may have been the long‐term signature of a previously reported pulse in bacterial production during the recolonisation ofAmphibolafaeces. Normal snail density had a strong inhibitory effect on primary productivity by the benthic microalgae, reducing CO2fixation to 29–47% of levels that could be attained when snails were excluded. Variations in the effect of deposit feeding on micro‐organisms over the experimental period suggest that it may be modified by seasonal factors acting on benthic communities. In a similar interaction of influences, seasonal changes in microbial biomass and activity appeared to vary with snail density.

ISSN:0028-8330    

DOI:10.1080/00288330.1987.9516219

出版商:Taylor & Francis Group    

年代:1987

数据来源: Taylor

摘要:

Several recent studies have indicated that deposit feeder nutrition is more complex than depicted in traditional models of detrital food webs. Micro‐organisms may be less important as sources of carbon than as sources of nitrogen, and the microbial contribution to deposit feeder diets appears to vary from site to site. The carbon requirements for respiration of two populations of the gastropodAmphibola crenatawere compared with carbon available from assimilation of sediment bacteria and microalgae. The calculated total microbial contributions were 23.5 and 50.3% of the snails’ estimated carbon requirements for respiration. The contribution of microalgae is probably subject to more local variability than that of sediment bacteria. These results suggest that several living and non‐living food sources collectively contribute to the nutritionof Amphibola crenata, with non‐living sources possibly supplying the major portion of the snail's carbon requirement.

ISSN:0028-8330    

DOI:10.1080/00288330.1987.9516220

出版商:Taylor & Francis Group    

年代:1987

数据来源: Taylor

摘要:

The surface distribution and metabolic uptake of nitrate and ammonium were investigated as they related to the movements of water in the upwelling zone off the north‐west coast of South Island, New Zealand. Analyses were also made of chlorophyllaand paniculate nitrogen as indicators of phytoplankton biomass.

ISSN:0028-8330    

DOI:10.1080/00288330.1987.9516221

出版商:Taylor & Francis Group    

年代:1987

数据来源: Taylor

摘要:

Heating otoliths of the orange roughy(Hoplostethus atlanticus;Trachichthyidae) by the break‐and‐burn method causes a crystal transformation from aragonite to calcite. However, the change does not affect the legibility of the check rings. Orange roughy otolith check rings fall into two classes: a diffuse deposit (that is not visible in the break‐and‐burn method, but may have an annual periodicity) and structural check rings (which appear as fine lines on the surface, but as dark bands in the body of the otolith). Structural check ring deposition is irregular, but fortuitous aggregations of structural check rings might be mistaken for conventional annual check rings.

ISSN:0028-8330    

DOI:10.1080/00288330.1987.9516222

出版商:Taylor & Francis Group    

年代:1987

数据来源: Taylor