Predation,recruitment and the dynamics of communities of coral-reef fishes

I investigated the ability of predators to influence the patterns of species richness and abundance of non-piscivorous fishes on small, artificial reefs replenished by natural recruitment. Periodic removal of predators effectively reduced the species richness and abundance of predators on removal reefs. The difference between the number of predators on control and removal reefs was greatest immediately following the removal of predators and attenuated between removals. During periods of recruitment, species richness and total abundance of recently-recruited, non-piscivorous fishes were generally greater on predator-removal reefs than on control reefs. Species richness and total abundance of resident non-piscivorous fishes were not affected by the removal of predators in the first year of the experiment. Both abundance and species richness of residents, however, were greater on the removal reefs during the second year of the experiment. The difference in the responses of the two age classes to the removal of predators suggests that predators may affect community patterns of older age classes through time-lagged effects on the survivorship of younger age classes. At the end of the experiment, species richness was positively related to abundance for recruits and residents. The effects of removing piscivorous fishes on the abundance of non-piscivorous fishes were similar for species considered separately. A greater number of species of recruit and resident fishes were more abundant on reefs from which predators had been removed. These data suggest that predators can play an important role in structuring communities of fishes on coral reefs.     

Microbial RNA and DNA synthesis in marine sediments

A technique for measuring rates of RNA and DNA synthesis in sedimentary microbial communities has been adapted from methods developed for marine and freshwater microplankton research. The procedure measures the uptake, incorporation and turnover of exogenous [2, ³H]-adenine by benthic microbial populations. With minor modification, it is applicable to a wide range of sediment types. Measurement of nucleic acid synthesis rates are reported from selected benthic marine environments, including coral reef sediments (Kaneohe Bay, Oahu, Hawaii), intertidal beach sands (Oahu and southern California) and California borderland basin sediment (San Pedro Basin), and comparisons are made to selected water-column microbial communities. Biomass-specific rates of nucleic acid synthesis in sediment microbial communities were comparable to those observed in water-column assemblages (i.e., 0.02 to 2.0 pmol deoxyadenine incorporated into DNA [ng ATP]^-1 h^-1 and 0.2 to 8.9 pmol adenine incorporated into RNA [ng ATP]^-1 h^-1). DNA synthesis rates were used to calculate carbon production estimates ranging from 2 g C cm^-3 h^-1 in San Pedro Basin sediment (880 m water depth) to 807 g C cm^-3 h^-1 in coral reef sediment from the Kaneohe Bay. Microbial community specific growth rate, (d^-1), estimated from DNA synthesis rates in surface sediments ranged from 0.1 in San Pedro Basin to 4.2 in Scripps Beach (La Jolla, California) intertidal sand.     

New methods for identification of disinfection byproducts of toxicological relevance: Progress and future directions

Disinfection byproducts (DBPs) represent a ubiquitous source of chemical exposure in disinfected water. While over 700 DBPs have been identified, the drivers of toxicity remain poorly understood. Additionally, ever evolving water treatment practices have led to a continually growing list of DBPs. Advancement of analytical technologies have enabled the identification of new classes of DBPs and the quantification of these chemically diverse sets of DBPs. Here we summarize advances in new workflows for DBP analysis, including sample preparation, chromatographic separation with mass spectrometry (MS) detection, and data processing. To aid in the selection of techniques for future studies, we discuss necessary considerations for each step in the strategy. This review focuses on how each step of a workflow can be optimized to capture diverse classes of DBPs within a single method. Additionally, we highlight new MS-based approaches that can be powerful for identifying novel DBPs of toxicological relevance. We discuss current challenges and provide perspectives on future research directions with respect to studying new DBPs of toxicological relevance. As analytical technologies continue to advance, new strategies will be increasingly used to analyze complex DBPs produced in different treatment processes with the aim to identify potential drivers of toxicity.     

Modeling the Relations Between Flow Regime Components,Species Traits,and Spawning Success of Fishes in Warmwater Streams

Modifications to stream hydrologic regimes can have a profound influence on the dynamics of their fish populations. Using hierarchical linear models, we examined the relations between flow regime and young-of-year fish density using fish sampling and discharge data from three different warmwater streams in Illinois, Alabama, and Georgia. We used an information theoretic approach to evaluate the relative support for models describing hypothesized influences of five flow regime components representing: short-term high and low flows; short-term flow stability; and long-term mean flows and flow stability on fish reproductive success during fish spawning and rearing periods. We also evaluated the influence of ten fish species traits on fish reproductive success. Species traits included spawning duration, reproductive strategy, egg incubation rate, swimming locomotion morphology, general habitat preference, and food habits. Model selection results indicated that young-of-year fish density was positively related to short-term high flows during the spawning period and negatively related to flow variability during the rearing period. However, the effect of the flow regime components varied substantially among species, but was related to species traits. The effect of short-term high flows on the reproductive success was lower for species that broadcast their eggs during spawning. Species with cruiser swimming locomotion morphologies (e.g., Micropterus) also were more vulnerable to variable flows during the rearing period. Our models provide insight into the conditions and timing of flows that influence the reproductive success of warmwater stream fishes and may guide decisions related to stream regulation and management.     

Surface-film microheterotrophs: amino acid metabolism and solar radiation effects on their activities

Rates of microheterotrophic utilization (incorporation+respiration) of ³H-leucine and ³H-glutamic acid were measured in seawater surface films from oligotrophic, eutrophic and mesotrophic waters incubated in situ off Baja California in July 1981 and off Southern California in November 1982. Neither visible nor ultraviolet radiation had a marked detrimental effect on microbial heterotrophy, although solar radiation sometimes appeared to be stimulatory. Film microheterotrophs utilized glutamic acid at rates between 0.07 and 0.13 nM h^-1 for oligotrophic waters and between 0.43 and 2.1 nM h^-1 for eutrophic waters; the respective turnover times ranged between 101 and 313 h and between 8.6 and 21.5 h. Film microheterotrophs from oligotrophic waters utilized leucine at rates comparable to those observed for glutamic acid, but turnover times were shorter. Leucine metabolism rates of film microheterotrophs in eutrophic waters were slower than glutamic acid rates, but turnover times were similar. Naturally varying amino acid concentrations accounted, in part, for differences in turnover times. In oligotrophic waters, higher utilization rates were observed for surface-film microheterotrophs than for subsurface (10 cm) microheterotrophs, whereas in eutrophic waters, utilization rates were similar for surface-film microheterotrophs and subsurface microheterotrophs. Surface-film microheterotrophs, in most cases, had an average of 63% amino acid carbon assimilation efficiency, similar to euphotic-zone heterotrophs. Surface-film microheterotrophs are actively involved in the metabolism and turnover of amino acids.     

Microbial populations in surface films and subsurface waters: Amino acid metabolism and growth

Sea surface microlayer (film) and subsurface microbial populations (biomass and activities) were studied in the Damariscotta (Maine) estuary in May and September, 1987. Dissolved free and combined amino acids (DFAA, DCAA), bacterial numbers, microbial ATP, bacterial and microbial DNA synthesis (via³H-thymidine and³H-adenine), and amino acid (³H-glutamic acid) metabolism were measured. DFAA and DCAA were typically enriched in the surface microlayers relative to surface waters, although utilization of glutamic acid was usually more rapid in subsurface waters, as was incorporation of thymidine. Bacteria represented 12 to 40% of the microbial biomass as determined by ATP, except during microalgal blooms in the microlayer. Bacteria were generally not enriched in the surface films, although ATP usually was enriched. Rain input appeared to deplete population densities but stimulated population activities. Two stations which contained similar microbial populations (as estimated by bacterial counts, chlorophylla and ATP) showed very different microbial activities, apparently due to the effects of a substantial rainstorm on one of the stations. The bacterially-dominated processes utilizing thymidine and glutamic acid were enhanced approx five-fold after the rain. Autotrophic carbon production increased approx two-fold, while total microbal community DNA synthesis (as estimated by adenine incorporation into DNA) increased nearly tenfold. The observations of this study indicate that surface microlayers in the temperate waters off the coast of Maine contain highly active heterotrophic and autotrophic populations. The microbial community responds rapidly to changes in nutrient and dissolved organic matter concentrations resulting from both seasonal and temporal effects, including rain and runoff.     

Bound residues of organic compounds in the soil: the significance of pesticide persistence in soil and water: a European regulatory view

The paper discusses key aspects of the European Union (EU) regulatory policy for persistence of agricultural pesticide active substances (a.s.) in soil, which is examined in the context of the EU Authorisations Directive (91/414/EEC). For agricultural pesticide regulation within EU Member States (MS), the Authorisations Directive will gradually replace existing national systems. Discussion is concentrated on this directive, looking in particular at the Uniform Principles therein and the possible ways that these decision-making guidelines could be developed into a regulatory framework. The aim in this process of negotiated development is to identify any questions or data requirements that will be needed for persistent pesticides, over and above those generally required for all compounds. The present European regulatory position on soil non-extractable or bound residues is discussed. Finally, a brief mention of pesticide persistence in water and sediment is made.     

Bi-directional sex change in a coral-dwelling goby

Bi-directional sex change has recently been reported among obligate coral-dwelling gobies of the genus Gobiodon. However, neither the functional role of this pattern of sex change nor the frequency of sex change in either direction in natural populations is known. We investigated the social structure and pattern of sex change of Gobiodon histrio at Lizard Island on the Great Barrier Reef. The social structure of G. histrio within coral colonies usually consisted of a single juvenile or a heterosexual adult pair. The size of adult social groups was not constrained by coral colony size. In contrast to expectations for pair-forming species, G.␣histrio was primarily a protogynous hermaphrodite. All immature G. histrio were females and sex change from female to male occurred readily when two mature females were placed in a coral colony. In addition, male G. histrio were able to change back to females when two mature males were placed in a coral. Sex change from female to male, however, occurred with over twice the frequency of sex change from male to female. Where two males were placed in a coral colony, heterosexual pairs were most frequently re-established by immigration of females from outside the treatment population. This pattern might be predicted if sex change from male to female is more expensive than sex change from female to male for G. histrio. Where sex change is expensive, movement may be favoured over sex change, particularly where coral densities are high and movement among corals incurs little mortality risk. Received: 10 November 1997 / Accepted after revision: 16 May 1998     

There are many ways to be a mutualist: endophytic fungus reduces plant survival but increases population growth

One of the challenges to quantifying the costs and benefits of symbiosis is that symbionts can influence different components of host fitness. To improve understanding of the ecology of inherited symbionts, we developed general theory for a perennial host-hereditary symbiont interaction, in which symbionts can have independent and potentially opposing effects on host regeneration and survival. The model showed that negative effects on one component of fitness may be outweighed by positive effects on another, leading to a net positive impact of symbiosis on population growth. Model predictions depended on the availability of suitable patches, which influenced the relative contributions of survival vs. regeneration to host fitness. We then used experimental symbiont removal to quantify effects of a hereditary, fungal endophyte on a grass host. Endophyte presence strongly reduced host survival but increased regeneration. Application of the model revealed that negative effects on plant survival were overwhelmed by beneficial effects on regeneration, resulting in stable endophyte persistence at 100% frequency, consistent with field observations. Our work demonstrates the utility of a demographic perspective for predicting the dynamics of symbioses and supports the hypothesis that symbionts function as mutualists when host and symbiont fitness are coupled through vertical transmission.     

Periphyton and Sediment Bioassessment in North Florida Bay

Periphyton colonization and sediment bioassessment were used ina survey to compare the relative environmental condition ofsampling sites located in Florida Bay and four peripheral sloughareas during the summer of 1995. Periphyton biomass, pigmentcontent, tissue quality and community composition weredetermined. In addition, benthic community composition and thetoxicities of whole sediments and associated pore waters weredetermined for two species of rooted macrophytes, an epibenthicinvertebrate and bioluminescent bacteria. Several locational differences were observed for the response parameters.Periphyton biomass was significantly greater in the Taylor Riverand the least in Shell Creek (P < 0.05). Most sediments were notacutely toxic to mysid shrimp nor phytotoxic. However, sedimentsfrom the Taylor River were more phytostimulatory than others (P< 0.05). Contaminant bioresidues were similar at most sites,however, mercury, chromium and nickel concentrations weregreater for periphyton colonized in the Taylor River and TroutCreek areas. Structural characteristics of the periphytic algalcommunity usually were statistically similar but a consistenttrend of lower density and diversity was evident for ShellCreek. The benthic community was the least diverse and dense inthe Canal C-111. The results of this study provide an initialindication of differences in the role of several slough areas aspossible sources of bioavailable contaminants to Florida Baywhich warrants additional investigation.