Possible biological significance of contaminated sediments in Port Jackson,Sydney, Australia

Comprehensive investigations of estuaries incentral New South Wales has identified Port Jackson as themost contaminated waterway on the eastern seaboard ofAustralia. Extensive areas of the estuary are mantled insediment containing high concentrations of a large range ofmetallic and organic contaminants. Although extensive, thisdatabase does not provide an effective basis for determiningthe potential adverse effects of chemicals on livingresources. In the absence of any ecotoxicologicalinformation, the recently published (1999) draft Australianand New Zealand Environmental and Conservation Council(ANZECC) sediment quality guidelines have been used toassess possible adverse biological effects of thesetoxicants. The ANZECC guidelines use the lower effects range of thewidely used U. S. National Oceanic and AtmosphericAdministration (NOAA) scheme to identify potentiallycontaminated sediment and as a threshold to trigger foradditional investigative work. This guideline level has beenused in the current study to assess possible toxicity ofcontaminated sediments in Port Jackson. It is estimated thatsediments in approximately 26% of the estuary, mainly theupper parts of the harbour and much of the central harbour,have a 67% probability of being toxic. Sediments in thecentral harbour and a major tributary, the Middle Harbour,comprising about 40% of the estuary, have a 13 to 25%probability of toxicity. All sediments in the harbour,except at the mouth of the estuary, would require additionalenvironmental assessment based on the proposed draft ANZECCsediment quality guidelines.     

RIPARIAN ZONE CLASSIFICATION FOR MANAGEMENT OF STREAM WATER QUALITY AND ECOSYSTEM HEALTH1

ABSTRACT: Riparian zones perform a variety of biophysical functions that can be managed to reduce the effects of land use on instream habitat and water quality. However, the functions and human uses of riparian zones vary with biophysical factors such as landform, vegetation, and position along the stream continuum. These variations mean that “one size fits all” approaches to riparian management can be ineffective for reducing land use impacts. Thus riparian management planning at the watershed scale requires a framework that can consider spatial differences in riparian functions and human uses We describe a pilot riparian zone classification developed to provide such a framework for riparian management in two diverse river systems in the Waikato region of New Zealand. Ten classes of riparian zones were identified that differed sufficiently in their biophysical features to require different management. Generic “first steps” and “best practical” riparian management recommendations and associated costs were developed for each riparian class. The classification aims to not only improve our understanding of the effectiveness of riparian zone management as a watershed management tool among water managers and land owners, but to also provide a basis for deciding on management actions.     

Assessing conservation status with extensive but low-resolution data: Application of frequentist and Bayesian models to endangered Athabasca River rainbow trout

Use of extensive but low-resolution abundance data is common in the assessment of species at-risk status based on quantitative decline criteria under International Union for Conservation of Nature (IUCN) and national endangered species legislation. Such data can be problematic for 3 reasons. First, statistical power to reject the null hypothesis of no change is often low because of small sample size and high sampling uncertainty leading to a high frequency of type II errors. Second, range-wide assessments composed of multiple site-specific observations do not effectively weight site-specific trends into global trends. Third, uncertainty in site-specific temporal trends and relative abundance are not propagated at the appropriate spatial scale. A common result is the propensity to underestimate the magnitude of declines and therefore fail to identify the appropriate at-risk status for a species. We used 3 statistical approaches, from simple to more complex, to estimate temporal decline rates for a designatable unit (DU) of rainbow trout in the Athabasca River watershed in western Canada. This DU is considered a native species for purposes of listing because of its genetic composition characterized as >0.95 indigenous origin in the face of continuing introgressive hybridization with introduced populations in the watershed. Analysis of abundance trends from 57 time series with a fixed-effects model identified 33 sites with negative trends, but only 2 were statistically significant. By contrast, a hierarchical linear mixed model weighted by site-specific abundance provided a DU-wide decline estimate of 16.4% per year and a 3-generation decline of 93.2%. A hierarchical Bayesian mixed model yielded a similar 3-generation decline trend of 91.3% and the posterior distribution showed that the estimate had a >99% probability of exceeding thresholds for an endangered listing. We conclude that the Bayesian approach was the most useful because it provided a probabilistic statement of threshold exceedance in support of an at-risk status recommendation.     

Nitrogen fixation (acetylene reduction) in the phyllosphere of Thalassia testudinum

N₂ fixation (C₂H₂ reduction) associated with the leaves of the sea grass Thalassia testudinum was investigated at 5 sites in South Florida (Biscayne Bay) and one site in the Bahamas (Bimini Harbor). Significant activities were correlated with the occurrence of a heterocystous blue-green alga (Calothrix sp.) on the leaves. C₂H₂ reduction was not stimulated by organic compounds, either aerobically or anaerobically in the light or dark. Therefore, other physiological types of microbes were not important in N₂ fixation. Diurnal and seasonal variations in N₂ fixation occurred, with maximal rates during the daytime and in the late spring and early summer. N₂ fixation was negligible at four stations in Biscayne Bay. At the fifth station, near Fowey Rock, about 5 kg N ha^-1 year^-1 was fixed. In the summer, the N₂ fixed per day (4–5 mg N m^-2) could provide 4 to 23% of the foliar productivity demands of T. testudinum at this site and the station in Bimini Harbor. N₂ fixation at the periphery of a sea-grass patch, near Fowey Rock, could provide 8 to 38% of the daily nitrogen requirement for leaf production, and thereby might compensate for a less effective trapping and recycling of nitrogen from dead leaves in such regions.     

The annual cycle of heterotrophic planktonic ciliates in the waters surrounding the Isles of Shoals,Gulf of Maine: an assessment of their trophic role

Macrofauna living on subtidal rocks reefs in southern California excrete ammonium, a potentially important nutrient for benthic algae. Ammonium excretion rates of eleven macroinvertebrate and five fish taxa were determined from a total of 324 in situ incubations conducted between October 1984 and August 1985 at 14 to 17 m depths off Santa Catalina Island, California. Total ammonium excretion ranged from over 100 mol h^-1 by the kelp bass Paralabrax clathratus to less than 0.1 mol h^-1 by the gastropod Conus californicus. Weight-specific ammonium excretion generally ranged from 0.5 to 4 mol g^-1 h^-1 in invertebrates and from 3 to 7 mol g^-1 h^-1 in fishes. Intraspecific excretion rates varied substantially. Coefficient of variation of excretion rates were higher than reported for laboratory studies and multiple regression indicated that 50 to 90% of the variation in ammonium excretion rates of five species studied in detail could not be explained by the combined variation in dry weight, water temperature, time of day, and incubation dates. The excretion data, along with estimates of population densities and size-frequency distributions, indicate that benthic macrofauna release a total of 25 to 30 mol NH ₄ ⁺ m^-2 h^-1 both day and night. The species that generally make the largest contributions are a gobiid fish (Lythrypnus dalli), followed by three gastropods (Astraea undosa, Tegula eiseni, and T. aureotincta) and a sea urchin (Centrostephanus coronatus). The amount of ammonium excreted by these macrofauna on rocky reefs is insignificant compared to our previously published data on the nighttime excretion of blacksmith (Chromis punctipinnis), a pomacentrid fish that feeds in the water column during the day and shelters on the reef at night. Including blacksmiths, we estimate that the amount released by rocky-reef macrofauna at night is >280 mol m^-2 h^-1, a rate that is similar to that for many other marine communities. Additional studies are required to determine if benthic algae utilize ammonium released by these macrofauna, especially at night.Contribution No. 58 of the Ocean Studies Institute; Contribution No. 123 of the Catalina Marine Science Center     

Species-specific influence of group composition on collective behaviors in ants

The success of a social group is often driven by its collective characteristics and the traits of its individuals. Thus, understanding how collective behavior is influenced by the behavioral composition of group members is an important first step to understand the ecology of collective personalities. Here, we investigated how the efficiency of several group behaviors is influenced by the aggressiveness of its members in two species of Temnothorax ants. In our manipulation of group composition, we created two experimentally reconstituted groups in a split-colony design, i.e., each colony was split into an aggressive and a docile group of equal sizes. We found strong species-specific differences in how collective behaviors were influenced by its group members. In Temnothorax longispinosus, having more aggressive individuals improved colony defense and nest relocation efficiency. In addition, source colony identity strongly influenced group behavior in T. longispinosus, highlighting that manipulations of group compositions must control for the origin of the chosen individuals. In contrast, group composition and source colony did not influence collective behaviors in Temnothorax curvispinosus. This suggests that the mechanisms regulating collective behaviors via individual differences in behavior might differ among even closely related species.