Thin layers of bioluminescent copepods found at density discontinuities in the water column

To learn how organisms apportion space in the open ocean, biological oceanographers have sought to improve temporal and spatial resolution of ocean sampling systems. Their objectives are to simultaneously measure physical, chemical and biological structure in the water column in order to find significant correlations that may reveal underlying processes. Here we report one such correlation between intense peaks of bioluminescence and density discontinuities in the water column. Intensified video recordings made in these bioluminescent “hot spots” were analyzed with a computer image-recognition program that identifies organisms based on the temporal and spatial characteristics of their luminescent displays. Based on this analysis, the source of the “hot spots” was found to be very thin layers (0.5 m) of the bioluminescent copepod Metridia lucens present at from 5 to 100 times average background concentrations. Given the recent discovery that the vertical distribution of marine snow is also strongly correlated with density discontinuities in the water column, we suggest that this finding may provide a possible explanation for the disparity between estimated energy requirements of marine copepods and measurements of average in situ food concentrations. The energy costs associated with locating food-rich micro-patches is greatly reduced if those patches are spread out into very thin layers, because the search strategy can be reduced from three dimensions to one. Received: 28 December 1998 / Accepted: 12 April 1999     

Oviposition height increases parasitism success by the robber fly Mallophora ruficauda (Diptera: Asilidae)

For parasitoids, host finding is a central problem that has been solved through a variety of behavioural mechanisms. Among species in which females do not make direct contact with hosts, as is the case for many dipteran parasitoids, eggs must be laid in an appropriate part of the host habitat. The asilid fly Mallophora ruficauda lays eggs in clusters on tall vegetation. Upon eclosion, pollen-sized larvae fall and parasitize soil-dwelling scarab beetle larvae. We hypothesized that wind dissemination of M. ruficauda larvae is important in the host-finding process and that females lay eggs at heights that maximize parasitism of its concealed host. Through numerical and analytical models resembling those used to describe seed and pollen wind dispersal, we estimated an optimal oviposition height in the 1.25- to 1.50-m range above the ground. Our models take into account host distribution, plant availability and the range over which parasitic larvae search for hosts. Supporting our findings, we found that the results of the models match heights at which egg clusters of M. ruficauda are found in the field. Generally, work on facilitation of host finding using plants focuses on plants as indicators of host presence. We present a case where plants are used in a different way, as a means of offspring dispersal. For parasitoids that carry out host searching at immature stages rather than as adults, plants are part of a dissemination mechanism of larvae that, as with minute seeds, uses wind and a set of simple rules of physics to increase offspring success.     

Southern California's marine monitoring system ten years after the National Research Council evaluation

In 1990, the National Research Council (NRC) published two in-depth assessments of marine environmental monitoring effectiveness. The first of these, Managing Troubled Waters: The Role of Marine Environmental Monitoring, provided a national perspective and the second, Monitoring Southern California's Coastal Waters, examined the specifics of monitoring design and implementation in a densely populated, highly urbanized coastal region. The reports include explicit recommendations about the need for greater regionalization of monitoring efforts, supported by greater standardization of field, laboratory, and data analysis methods. They also identified the need for centralized data management and for greater flexibility in the language of standard discharge permits, flexibility that would permit discharge agencies to more readily participate in regional monitoring and research programs. Other recommendations identified a need for EPA and NOAA to focus on creating a national monitoring program structured as a network of coordinated local and regional efforts. Finally, the NRC emphasized the need for better reporting and for periodic review of monitoring's relevance to management concerns. In this paper, we use southern California as a test case to assess progress made in implementing the NRC's recommendations. We review progress made on each recommendation and discuss the features of the regulatory and management climate that contributed to or impeded this progress. We also consider whether, and to what extent, the NRC's recommendations remain relevant in the present context.     

Local mate competition and precise sex ratios in Telenomus fariai (Hymenoptera: Scelionidae), a parasitoid of triatomine eggs

Telenomus fariai is a gregarious endoparasitoid of the eggs of several species of Triatominae (Hemiptera) with a high degree of sibmating: males fertilize their sisters inside the host egg before emergence or emerge first and copulate with their sisters as these emerge. Our results show that, when laying alone, T. fariai behaves adaptively, minimizing offspring mortality and conforming to the prediction of local mate competition (LMC) theory by laying a single male, which is sufficient to fertilize all the sisters. When more than one wasp was placed with one host, sex ratios still conformed to LMC predictions but, despite the decreasing number of eggs laid per wasp, clutch size could not be completely adjusted to avoid mortality. This is not surprising, as superparasitism is rare in the field. Offspring production was independent of the contacts between conspecifics but was affected by the number of mothers laying on a single host egg. The sex of the progeny was precisely determined: a female produced one male per clutch when laying on both unparasitized or previously parasitized hosts. On the other hand, a mother produced less daughters when superparasitizing. Under crowded conditions, the number of eggs laid per female wasp and per host decreased as the number of mothers increased. Developmental mortality also increased with the number of T. fariai eggs per host, determining a maximum of approximately 14 emerged adults. Host resources per individual affected male and female adult size with similar intensity, and male adult mortality was slightly higher than that for females. These results, and previous findings, suggest that T. fariai attains Hamiltonian sex ratios by laying one male and a variable number of females, and that the detection of chemical marks left by conspecifics provides information on the number of foundresses sharing a patch. Received: 4 February 2000 / Received in revised form: 19 April 2000 / Accepted: 20 May 2000     

Assessing urban runoff program progress through a dry weather hybrid reconnaissance monitoring design

Characterizing dry weather conditions in urban Municipal Separate Storm Sewer Systems (MS4s), and then prioritizing and addressing problems due to urban pollutants, is a daunting challenge. The size and complexity of most MS4s and the ephemeral nature of many dry weather problems hamper efforts to identify and eliminate pollutant sources, and to track trends in condition. As a result, assessing overall program progress has proven difficult. We describe a hybrid dry weather urban monitoring design from southern California that combines probabilistic and targeted sampling to rigorously identify and prioritize problems and track program progress. Data from probabilistic sites define the urban background and establish tolerance intervals, which identify sites that persistently exceed the overall urban background. Targeted sites focus on locations where nearby activities and/or past history suggest that pollutant levels will be elevated. Embedding targeted monitoring within a probabilistic design enables data from targeted sites to be interpreted in a more meaningful regional context. Data from all sites are also used to construct site- and pollutant-specific control charts. These charts quickly identify instances where a site's behavior significantly changes, compared to its past behavior, suggesting an active source in the upstream drainage area. The hybrid design, and the use of formal statistical tools (tolerance intervals and control charts), permit the program to systematically prioritize problematic sites, compare conditions to the regional urban background, and track trends over time. In addition, the program's design allows several measures of program progress to be defined and thus consistently followed over time. Such hybrid designs can provide substantial advantages compared to more traditional monitoring approaches.     

Integrating probabalistic and targeted compliance monitoring for comprehensive watershed assessment

Environmental monitoring typically falls into one of two broad categories. Targeted designs, utilizing fixed stations, focus on describing and quantifying impacts, tracking trends, and assessing compliance with regulatory guidelines or limits. Probabilistic designs, in contrast, draw sampling stations at random from an area or region, and the stations are used to describe conditions in the region of interest based on a subpopulation of sites. These two design approaches are usually viewed as mutually exclusive, with randomized designs used for broader regional assessments of overall ambient condition and targeted designs for demonstrating regulatory compliance and/or characterizing specific, localized impacts. Combining elements of both approaches into a single design provides benefits not available from either design alone. Embedding targeted monitoring within the framework of a probabilistic design enables data from targeted stations to be viewed in a more accurate regional context and provides a consistent background against which to identify characteristic regional patterns of contamination and impact. We use the San Gabriel River Regional Monitoring Program, recently implemented in southern California, to illustrate the structure of a hybrid design and how it enables data analyses and assessments that provide a more complete picture of conditions in the watershed. For example, the hybrid design showed that approximately 80% of the metals levels at compliance sites were below the 25th percentile of the overall watershed condition as indicated by the probabilistic sampling.     

Simple digestion procedure followed by the azomethine-H method for accurate boron analysis and discrimination between its fractions in wastewater and soils

Excess boron is a growing environmental problem. It often affects agricultural yields, where reuse of wastewater for irrigation is practiced. This problem raises the need for reliable, simple and economical methods to monitor boron concentrations in wastewater and soil extracts. One such method, the commonly used azomethine-H spectrophotometric method, suffers from color interference, originating from high concentrations of dissolved organic matter, when applied to many wastewater and agricultural soil extracts. Moreover, this method only quantifies free dissolved boron and lacks the ability to quantify boron that is adsorbed to either the dissolved organic matter or suspended solids that are present in the sample. This work suggests a modification of the standard azomethine-H method, in which the solution is digested with potassium persulfate prior to the standard procedure. We show that this pretreatment can overcome the color interference and lead to highly accurate and precise boron analyses in wastewater. In soil extracts, the boron concentrations obtained using the suggested procedure were better correlated to inductively coupled plasma (ICP) spectrometry results than those measured by the standard method, because whereas the standard method quantifies the free dissolved boron only, the modified method, like the ICP method, quantifies the total dissolved boron in the sample. Thus, the suggested modification can be used to quantify the respective distributions of free dissolved boron, boron adsorbed to dissolved organic matter and boron adsorbed to suspended solids in soil extracts and water samples.