Does the spawning of Calanus finmarchicus in high latitudes follow a reproducible pattern?

In the spring of 1989, an experimental study of the spawning behaviour of Calanus finmarchicus was carried out in Malangen, northern Norway. Here, a single cohort of females reproduce from mid-March to May, approximately coinciding with the wax and wane of the spring phytoplankton bloom. An evaluation of population characteristics such as the proportion of adults, sex ratio, as well as gonad maturation and daily productivity of the females clearly reveals three phases within the population's reproductive period. In between incline and decline, the highest spawning rates (on average >20 eggs female^-1 d^-1, equivalent to 5.7% body C d^-1) occur after the males have disappeared from the population and almost all females have mature gonads. During this period, the ratio of adults to copepodid Stage Vs changes from dominance of adults to that of CVs. Although first egg production was observed prior to the phytoplankton increase, it is suggested that the onset of the phytoplankton spring bloom in the first few days of April enhances the final maturation of ovaries in the females and therefore triggers the onset of the main spawning period. The clutch sizes (max. 95 eggs clutch^-1) vary with the age of the females, while the spawning frequencies depend on the available food quantities. The overlap of an estimated minimal 4 wk spawning period for the individuals leads to a main reproductive phase for the population of ca. 3 wk, during which time mean clutch sizes and spawning frequencies are maximal (highest average clutch size: 70 eggs female^-1 clutch^-1, 100 to 60% of the females spawning). This period ends before the end of the phytoplankton bloom. Calculated by stepwise interpolation and summation of the mean daily egg production in the population, an average female produced ca. 600 eggs during the spring bloom in Malangen 1989. We suggest that reproduction and population development of C. finmarchicus in spring follows a reproducible pattern for a given temperature regime and non-limiting food conditions. In the case of clearly identifiable cohorts, it seems possible to trace the state of reproduction by evaluating population parameters.     

Assessing reference conditions according to the European Water Framework Directive using modelling and analysis of historical data: an example from Randers Fjord,Denmark

The European Water Framework Directive (WFD) requires the definition of reference conditions, i.e. pristine conditions, for all surface waters. As the present state of Danish coastal waters cannot be referred to as pristine, reference conditions have to be assessed by analysis of historical data or by the use of models. Using Randers Fjord as an example, the aim of this work was i) to demonstrate possibilities and restrictions of assessing reference conditions by historical data and by modelling; and ii) to demonstrate how ecological conditions have changed along with eutrophication. The ample historical data from Randers Fjord allowed us to assess reference conditions with respect to benthic macrophytes and benthic fauna. Models of varying complexity enabled us to assess reference conditions for nutrients, chlorophyll a, Secchi depth, and eelgrass. We conclude that models can be a useful supplement to assess reference conditions, though they are presently restricted by the lack of quantitative links between eutrophication and species composition.     

Toxicity of boron to the duckweed,Spirodella polyrrhiza

Boron is an essential nutrient for plants and the potential exists for efficient removal of this element by wetland treatment systems due to accumulation by plants. To evaluate the efficacy of using Spirodella polyrrhiza to treat boron-contaminated wastewater or to be a suitable species for removing other nutrients from boron-containing wastewater the toxicity of this micronutrient was determined using standard methods. Frond production is apparently a more sensitive endpoint than either growth rate or the presence of abnormal fronds. Frond production in S. polyrrhiza was significantly reduced at 3.55 mg B/l. Significant reductions in growth rate and the percentage of abnormal (chlorotic, necrotic, and dead) fronds were observed at 18.9 and 22.4 mg B/l, respectively. The EC50 for frond production, frond growth rate, and abnormal fronds were 14.3, 11.7, and 17.7 mg B/l, respectively. S. polyrrhiza did not remove significant amounts of boron from the treatment solutions under the conditions and concentrations existing in this study. The inability of S. polyrrhiza to remove even small amounts of boron from the test solutions indicates this species is not suitable for treating boron-containing wastewater, even those with low boron concentrations.     

Can initial intraspecific spatial aggregation increase multi-year coexistence by creating temporal priority?

Both intraspecific spatial aggregation and temporal priority effects have the potential to increase long-term species coexistence. Theory and models suggest that intraspecific aggregation can facilitate coexistence via limited dispersal or asymmetric interaction distances. During community assembly, intraspecific aggregation may also delay interactions between more and less competitive species, thus creating opportunities for priority effects to facilitate longer-term coexistence. Few empirical studies have tested predictions about aggregation and coexistence, especially in the context of community assembly or ecological restoration. We investigated (1) impacts of intraspecific aggregation on the assembly of eight-species communities over three years, (2) the scale dependence of these impacts, and (3) implications for California prairie restoration. We planted eight native species in each of 19, 5 m wide, octagonal plots. Species were either interspersed throughout the plot or aggregated into eight, 2.2-m(2), wedge-shaped, monospecific sectors. Over three years, species diversity declined more quickly in interspersed plots than in aggregated plots. Two species had higher cover or increased more in interspersed than aggregated plots and were identified as "aggressives." Four species had higher cover or increased more in aggregated than interspersed plots and were identified as "subordinates." Within aggregated plots, aggressive species expanded beyond the sector in which they were originally seeded. Cover of aggressive species increased faster and reached higher values in sectors that were adjacent to the originally planted sector, compared to nonadjacent sectors. Cover of aggressive species also increased more and faster near plot centers, compared to plot edges. Areas near plot centers were representative of smaller aggregation patches since species were planted closer to heterospecific neighbors. Two subordinate species maintained higher cover near plot edges than near plot centers. Moreover, two subordinate species maintained higher cover when seeded in sectors farther away from aggressive species. These results suggest that initial intraspecific aggregation can facilitate species coexistence for at least three years, and larger aggregation patches may be more effective than smaller ones in the face of dispersing dominants. The creation of temporal priority effects may represent an underappreciated pathway by which intraspecific aggregation can increase coexistence. Restorationists may be able to maintain more diverse communities by planting in a mosaic of monospecific patches.