Spring bloom sedimentation in a subarctic ecosystem

A 5-yr study (1985 to 1989) of spring bloom sedimentation in Auke Bay, Alaska, indicates that the sinking response of diatoms to ambient nutrients influences both species succession during the spring bloom and the subsequent sedimentation of new production. Diatoms from the genera Thalassiosira, Chaetoceros and Skeletonema formed the bulk of the spring bloom each year. Growth of Thalassiosira spp. consistently initiated the primary bloom, while Skeletonema costatum tended to grow later in, or after, the primary bloom. We postulate that this successional pattern is driven by interspecific nutrient competition. Overall, sedimentation flux of the dominant species of bloom diatoms was correlated with surface concentrations of cells integrated over the bloom period. In fact, different linear relationships existed when Thalassiosira and Chaetoceros spp. were considered separately, but not for Skeletonema sp., indicating that marked differences exist between the sedimentation tendencies of these genera. The observed inter-generic differences are explicable by the different overall sinking rates, as well as different nutrient-sensitivities of the sinking rates of each genus. Thalassiosira spp., the fastestsinking and most nutrient-sensitive species, contributed up to 10 x more carbon to the benthos in all years of the study, reaching a maximum of 11.1 gCm^-2 over a single spring bloom event in 1988. This study indicates that the tendency to sink to the benthos during and/or after a bloom is highly dependent on species-specific cell physiology, and supports the idea that it is the fast-sinking, nutrient-sensitive diatoms, such as Thalassiosira species, that constitute the major source of vertical carbon flux in this embayment and other such coastal ecosystems during the spring bloom.     

Population Variability and Extinction Risk

Abstract: Population models generally predict increased extinction risk (ER) with increased population variability (  PV  ), yet some empirical tests have provided contradictory findings. We resolve this conflict by attributing negative measured relationships to a statistical artifact that arises because PV tends to be underestimated for populations with short persistence. Such populations do not go extinct quickly as a consequence of low intrinsic variability; instead, the measured variability is low because they go extinct so quickly. Consequently, any underlying positive relationship between PV and ER tends to be obscured. We conducted a series of analyses to evaluate this claim. Simulations showed that negative measured relationships are to be expected, despite an underlying positive relationship. Simulations also identified properties of data, minimizing this bias and thereby permitting meaningful analysis. Experimental data on laboratory populations of a bruchid beetle (Callosobruchus maculatus) supported the simulation results. Likewise, with an appropriate statistical approach (Cox regression on untransformed data), reanalysis of a controversial data set on British island bird populations revealed a significant positive association between PV and ER (p = 0.03). Finally, a similar analysis of time series for naturally regulated animal populations revealed a positive association between PV and quasiextinction risk (p < 0.01). Without exception, our simulation results, experimental findings, reanalysis of published data, and analysis of quasiextinction risk all contradict previous reports of negative or equivocal relationships. Valid analysis of meaningful data provides strong evidence that increased population variability leads to increased extinction risk.     

Expression of multiple forms of an adhesive plaque protein in an individual mussel, Mytilus edulis

Individual blue mussels, Mytilus edulis L., can express at least 20 variants of a small protein known as M. edulis foot protein 3 or Mefp3. Mefp3 has been shown to be a component of the adhesive plaque of the byssus, the structure securing mussels to solid substrata. The cDNAs and deduced fp3 protein sequences display more variation at the carboxy-terminus than at the N-terminus, although there is some variation present throughout the protein. This indicates that there most likely are multiple copies of the gene encoding this protein. Each protein sequence contains a signal peptide, 24 to 25 residues in length, and a mature protein sequence of 44 to 54 residues. Gly is the most common amino acid in the mature protein at 20 to 25 mol%. Tyr and Arg follow closely at 20 to 23 and 16 to 21 mol%, respectively. Both of these amino acids were previously shown to be post-translationally modified to 3,4-dihydroxyphenylalanine (Dopa) and 4-hydroxyarginine, respectively, in this protein. MALDI-TOF (matrix-assisted laser desorption ionization with time-of-flight) mass spectrometric analysis of the underside of adhesive plaques reveals the presence of Mefp3-like proteins. Curiously, only four or five out of 20 possible fp3 variants are detectable in plaques deposited on glass or plastic. This would suggest that selection of protein variants for deposition onto surfaces is determined at the level of translation. Received: 11 August 1998 / Accepted: 15 April 1999     

An evaluation of the use of individual grass species in retaining polluted soil and dust particulates in vegetated sustainable drainage devices

A sustainable means of preventing polluted particulates carried in urban storm water entering rivers, groundwater and lakes is by employing vegetated sustainable drainage system (SUDS) devices, or best management practices to trap or biodegrade them. In the UK, a mixture of grass species is recommended for use in devices such as swales or filter strips. However, there is little evidence in support of the efficiency of the individual grasses or mixtures to deal with such contaminated material. A pot-based pollutant retention study was conducted using processed street dust from central Coventry, UK, as a simulated pollutant to be applied in different quantities to a variety of recommended grasses for vegetated SUDS devices. Analysis was conducted on compost cores, roots and shoots for heavy metals (Cd, Cu, Ni, Pb and Zn). Street dust mainly concentrated in the top compost layer for all grasses with only the finer material migrating down the profile. Analysis of roots indicated little accumulation, with ANOVA statistical tests indicating significant differences in heavy metal concentrations, with less in the compost and more in the shoots. Development of root systems on or near the surface possibly explains increased uptake of heavy metals by some species. Overall Agrostis canina and Poa pratensis showed the greatest accumulations compared to their controls although Agrostis capillaris syn.tenuis and Agrostis stolonifera also demonstrated accumulation potential. On ranking, Agrostis canina and Poa pratensis were highest overall. These rankings will assist in selecting the best grasses to address pollution of the urban environment by contaminated particulates.     

What currency do scatter-hoarding gray jays maximize?

Gray jays (Perisoreus canadensis) cache thousands of food items during each summer for use during the subsequent winter. Previous work on the economics of gray jay scatter-hoarding behavior was based on the assumption that the jays maximize the rate at which they store food energy; alternative currencies were not considered. Here we develop and test models based on two currencies, net rate (net recoverable energy stored per unit time) and efficiency (recoverable energy stored per unit energy expended). Our experiment involved providing gray jays with two options. After collecting a single food item upon arrival at a feeding apparatus, a jay could wait for two additional food items to become (simultaneously) available and then transport all three items for storage in scattered arboreal sites. Alternatively, the jay could immediately transport the single item to a storage site and return to the source repeatedly for additional single-item loads. By incrementally increasing the amount of time jays were required to wait for multipleitem loads, we were able to determine how long jays would wait before switching from multiple- to single-item caching trips. In contrast with the finding in a variety of species that efficiency-maximization models provide a better account of foraging behavior, the net rate-maximization model was a better predictor of the jays' switching point than was the efficiency-maximization model (Figs. 2 and 3). We discuss these conflicting results in the context of recent theory that describes the conditions favoring rate- versus efficiency-maximizing behavior (Ydenberg et al. 1994). Offprint requests to: T.A. Waite     

ASsessment Of Alcohol Ethoxylate Surfactants And Fatty Alcohols Mixtures In River Sediments And Prospective Risk Assessment

A feasible and relatively readily available analytical method was adapted for the assessment of alcohol ethoxylates (AE) and fatty alcohols (FA) in sediments. This study illustrates the simultaneous measurement of 38 of 114 possible alcohol ethoxylate ethoxymers (AE) and fatty alcohols (FA) found in commercially important AE products. We predicted toxicity for all identified fractions, as well as the total mixture toxicity, relative to three exposure scenarios via sewage treatment plants (STP) for these widely used chemicals in consumer products and hence generate a preliminary environmental risk screening for AE and FA in sediments. The method is based on derivatization of solvent or solid-phase extracts with 2-fluoro-N-methylpyridinium p-toluenesulfonate (Pyr+). The derivatized extracts were analyzed with liquid chromatography/mass spectrometry (LC/MS) operating in the positive ion electrospray mode. The extraction efficiency of AE and FA in three different sediments of varying composition was evaluated with spike-recovery studies, ranging from 64% to 80%. The detection limits for individual ethoxymers typically ranged from 1 to 5ngg⁻¹on a dry weight basis. The mean limit of detection (LOD) was 6ngg⁻¹and the median LOD was 3ngg⁻¹. AE and FA in sediments were found to be stable for two weeks if preserved with 3% (v/v) formalin and stored at 4–6^∘C. Based on equilibrium partitioning, background concentrations of AE and FA were predicted to be below concentrations known to elicit chronically toxic effects. Total worst case mixture toxicities for all AE ethoxymers combined with FA were predicted to result in a risk quotient less than 0.6. Activated sludge treatment (STP) significantly reduced the release of total AE and FA by four-fold, suggesting that the total mixture risk quotient would be < 0.15 for sediment dependent organisms.     

Comparison of Streambed Sediment and Aquatic Biota as Media for Characterizing Trace Elements and Organochlorine Compounds in the Willamette Basin, Oregon

During 1992–93, 27 organochlorine compounds (pesticides plus total PCB) and 17 trace elements were analyzed in bed sediment and aquatic biota from 20 stream sites in the Willamette Basin as part of the U.S. Geological Survey's National Water-Quality Assessment Program. Data from each medium were compared to evaluate their relative effectiveness for assessing occurrence (broadly defined as documentation of important concentrations) of these constituents. Except for Cd, Hg, Se, and Ag, trace element concentrations generally were higher in bed sediment than in biota. Conversely, although frequencies of detection for organochlorine compounds in biota were only slightly greater than in bed sediment, actual concentrations in biota (normalized to lipid) were as much as 19 times those in sediment (normalized to organic carbon). Sculpin (Cottus spp.) and Asiatic clams (Corbicula fluminea), found at 14 and 7 sites, respectively, were the most widespread taxa collected during the study. Concentrations of trace elements, particularly As and Cu, were typically greater in Asiatic clams than in sculpin. In contrast, almost half of the organochlorine compounds analyzed were found in sculpin, but only DDT and its degradation products were detected in Asiatic clams; this may be related to the lipid content of sculpin, which was about three times higher than for clams. Thus, the medium of choice for assessing occurrence depends largely on the constituent(s) of interest.     

Uptake of atmospheric mercury by deionized water and aqueous solutions of inorganic salts at acidic,neutral and alkaline pH

Mercury (Hg) is well known as a toxic environmental pollutant that is among the most highly bioconcentrated trace metals in the human food chain. The atmosphere is one of the most important media for the environmental cycling of mercury, since it not only receives mercury emitted from natural sources such as volcanoes and soil and water surfaces but also from anthropogenic sources such as fossil fuel combustion, mining and metal smelting. Although atmospheric mercury exists in different physical and chemical forms, as much as 90% can occur as elemental vapour Hg0, depending on the geographic location and time of year. Atmospheric mercury can be deposited to aquatic ecosystems through both wet (rain or snow) and dry (vapour adsorption and particulate deposition) processes. The purpose of the present study was to measure, under laboratory conditions, the rate of deposition of gaseous, elemental mercury (Hg0) to deionized water and to solutions of inorganic salt species of varying ionic strengths with a pH range of 2-12. In deionized water the highest deposition rates occurred at both low (pH 2) and high (pH 12). The addition of different species of salt of various concentrations for the most part had only slight effects on the absorption and retention of atmospheric Hg0. The low pH solutions of various salt concentrations and the high pH solutions of high salt concentrations tested in this study generally showed a greater tendency to absorb and retain atmospheric Hg0 than those at a pH closer to neutral.