Evidence of in situ diel vertical migration of a red-tide microplankton species in Ría de Vigo (NW Spain)

The migration capacity of red-tide species in the natural environment was studied at a station in the Ría de Vigo (Rías Bajas, NW Spain) over a 24 h period in September 1991. The Ría de Vigo, where red tides are frequent, normally shows a positive estuarine circulation and is subjected to seasonal upwelling and downwelling phenomena. A marked diel pattern was observed for five species that are capable of causing red tides (Ceratium furca, Scrippsiella trochoidea, Dinophysis acuminata, Mesodinium rubrum, and Eutreptiella sp.). Such diel behaviour could be clearly advantageous in a stratified environment where light and nutrients are often in two separate layers. Active movement enables species such as dinoflagellates and some ciliates to exploit high levels of irradiance at the surface during the day and to take up nutrients in deeper layers at night. Patchy distribution of phytoplankton, shear-induced horizontal dispersion and density variations were considered, but none of them accounted for the vertical changes observed. Vertical migration is thought to be one of the mechanisms that could promote blooms in nutrient-depleted surface layers.     

Society for Environmental Geochemistry and Health 14th European Conference

Society for Environmental Geochemistry and Health 14th European Conference     

Sibling recognition in spiny mice (Acomys cahirinus)

Summary Sibling recognition by spiny mice (Acomys cahirinus) was investigated by housing groups consisting of two pairs of littermates together and recording frequency of dyadic pairing. A total of 136 animals (68 pairs of siblings) were tested in three experiments. Sibling pairs were observed more often than pairings between nonsiblings; however, such preferences were no longer evident if the nonsiblings were exposed to one another prior to testing. Animals made anosmic through zinc sulfate treatment did not differ on their frequencies of sibling vs. nonsibling pairing and showed a higher incidence of group huddling (by all four animals) than did intact controls. Weanling A. cahirinus appear to be able to recognize (i.e., are attracted to) their littermate siblings through olfactory cues, which seems to be a modifiable attraction to odors to which the littermates were exposed rather than an irreversible imprinting-like process.The research project reported herein was supported by grant # 00973 from NICHD     

Collection and analysis of baseline vegetation data

Vegetation baseline studies are dependent on the use of an adequate classification of vegetation, which structures all further study. The reliable and careful execution of sampling techniques is as important as choosing a sound sampling scheme. In order for vegetation mapping to represent the vegetation accurately, significant community gradation and anomalous communities should be portrayed. Data analysis should distinguish between precision and accuracy, include an indication of the statistical reliability of estimates, and explain and interpret findings.     

Methodology of light response curves: application of chlorophyll fluorescence to microphytobenthic biofilms

The light response curve methodology for microphytobenthic biofilms was studied by comparing the two most usual approaches used in pulse amplitude modulated (PAM) fluorometry. The non-sequential light curve (N-SLC) method is characterized by independent measures of the photosynthetic activity across a light gradient whereas the rapid light curve (RLC) method consists of successive measures on the same sample exposed to a stepwise increase of light intensities. Experiments were carried out on experimental microphytobenthic biofilms prepared from natural assemblages and acclimated to dark conditions. In preliminary experiments, N-SLCs were constructed from fluorescence induction curves performed at 12 different photon flux densities (PFDs). A minimum of 50 s of illumination was necessary to reach a stable light response curve; shorter illumination times resulted in underestimating the physiological parameters (α the light utilization coefficient in light-limited conditions and rETR_max the maximum rate of photosynthesis efficiency) of the light response curve. For the comparison between N-SLCs and RLCs, the same time of illumination (50 s) was used for each light step of RLCs so that N-SLCs differed from RLCs only by the way the amount of light was delivered, i.e., a light dose accumulation for RLC. The experimental results showed the difference between the two photobiological response curves. In the lower range of PFDs, RLCs exhibited a larger value of α; in this light-limited part of the response curve the incremental increase of PFDs limited the development of NPQ and resulted in a better optimization of electron transport rate for RLC. In the higher range of PFDs, the trend was reversed and the RLC showed a lower value of rETR_max than the N-SLC did; this is attributed to the light dose accumulation which likely led to a more efficient dispersion of energy, as illustrated by a higher non-photochemical quenching (NPQ). In conclusion, these results confirm that parameters derived from both methods differ in their value and do not bear the same physiological information.     

Age-specific social dominance affects habitat use by breeding American redstarts (Setophaga ruticilla): a removal experiment

Summary By removing older males from their breeding territories, we tested the hypothesis that age-related dominance behavior influenced the pattern of habitat selection by breeding American redstarts Setophaga ruticilla (Aves: Parulinae). Fifteen older male redstarts removed in five experimental replicates during three breeding seasons were replaced by ten yearling and five older males; no redstart males of either age colonized the control sites during the same time periods, although two yearlings disappeared. Significantly more yearling males (67%, n=9) colonized the vacated areas than were present in the redstart population at large (26.8%, n=209). We reject the alternative hypothesis that yearling male redstarts occupy different habitats from older males because of age-related (innate) habitat preferences. Redstarts that colonized the territories made vacant by our removals (i.e., floaters) were a behaviorally heterogeneous group of animals. The presence of both yearling and older male floaters indicates that suitable habitat is limiting for this species and that intraspecific competitive interactions are important in habitat distribution, and potentially in population regulation.     

Environmental periodicity and ecosystem stability

Simple ecosystem models involving a primary producer, nutrients, and a herbivore are developed with metabolic dependence on periodic functions representing solar radiation and temperature. Simulation results suggests that the models yield generally stable output provided that equilibrium values for the state variables are positive in the nonperiodic analog. Linear dependence of plant growth on nutrient supply leads to a larger stability domain than that produced by hyperbolic dependence.