The wax and wane of Phaeocystis globosa blooms

Phaeocystís globoso spring blooms start when daily irradiance exceeds 100 W h m 2 day t and diploid flagellates in a non-turbulent environment transform into non-flagellate cells and produce the first colony stage. In the colonies the nonflagellate cells grow rapidly under ample nutrient (N, P, 81, C) conditions, are not grazed, and compete with diatoms by raising the seawater pH. Once a nutrient is depleted the colony structure weakens and the non-flagellate cells disappear through grazing, lysis or by transforming into two morphologicaliy different haploid flagellates. The latter occurs when daily irradiance is less then 100 W h m 2 dayt, the result of sinking towards the seabed. The haploid microand mesoflagellates leave behind a ghost colony. The fusion of the micro- and the mesoflagellate produces a diploid macroflagellate, the inoculum for the next bloom. ... Zie: Summar

A comparison of six different ballast water treatment systems based on UV radiation, electrochlorination and chlorine dioxide

The spread of aquatic invasive species through ballast water is a major ecological and economical threat. Because of this, the International Maritime Organization (IMO) set limits to the concentrations of organisms allowed in ballast water. To meet these limits, ballast water treatment systems (BWTSs) were developed. The main techniques used for ballast water treatment are ultraviolet (UV) radiation and electrochlorination (EC). In this study, phytoplankton regrowth after treatment was followed for six BWTSs. Natural plankton communities were treated and incubated for 20 days. Growth, photosystem II efficiency and species composition were followed. The three UV systems all showed similar patterns of decrease in phytoplankton concentrations followed by regrowth. The two EC and the chlorine dioxide systems showed comparable results. However, UV- and chlorine-based treatment systems showed significantly different responses. Overall, all BWTSs reduced phytoplankton concentrations to below the IMO limits, which represents a reduced risk of aquatic invasions through ballast water

Identification of a domoic acid-producing Pseudo-nitzschia species (Bacillariophyceae) in the Dutch Wadden Sea with electron microscopy and molecular probes

Biological monitoring in the Dutch Wadden Sea between November 1993 and July 1994 revealed Pseudo-nitzschia-like pennate chain-forming diatom species with cell numbers ranging from 10^2 to 10^5 per litre. Cultured isolates and field samples were examined by electron microscopy, which revealed the majority to be Pseudo-nitzschia pungens. This species dominated over other diatoms in the phytoplankton population during November 1993 and at the end of June 1994. At the beginning of June 1994, P. fraldulenta was also present; occasionally, P. delicatissima was observed. One isolate showed the characteristic morphology of P. multiseries. Species-specific polyclonal antibodies and large-subunit (LSU) rRNA-targeted oligonucleotides for North American strains of P. multiseries and P. pungens applied to the European isolates, confirmed species designations based on electron microscopy. The isolate of P. multiseries from the Dutch Wadden Sea produced domoic acid; after 55 days of growth about 19 pg per cell was measured. This is the first report of a domoic acid-producing P. multiseries isolated from European coastal waters.

Structure of sediment-associated bacterial communities along a hydrocarbon contamination gradient in coastal sediment

The bacterial diversity of a chronically oil-polluted retention basin sediment located in the Berre lagoon (Etang-de-Berre, France) was investigated. This study combines chemical and molecular approaches in order to define how the in situ petroleum hydrocarbon contamination level affects the bacterial community structure of a subsurface sediment. Hydrocarbon content analysis clearly revealed a gradient of hydrocarbon contamination in both the water and the sediment following the basin periphery from the pollution input to the lagoon water. The nC17 and pristane concentrations suggested alkane biodegradation in the sediments. These results, combined with those of terminal-restriction fragment length polymorphism analysis of the 16S rRNA genes, indicated that bacterial community structure was obviously associated with the gradient of oil contamination. The analysis of bacterial community composition revealed dominance of bacteria related to the Proteobacteria phylum (Gamma-, Delta-, Alpha-, Epsilon- and Betaproteobacteria), Bacteroidetes and Verrucomicrobium groups and Spirochaetes, Actinobacteria and Cyanobacteria phyla. The adaptation of the bacterial community to oil contamination was not characterized by dominance of known oildegrading bacteria, because a predominance of populations associated to the sulphur cycle was observed. The input station presented particular bacterial community composition associated with a low oil concentration in the sediment, indicating the adaptation of this community to the oil contamination

Central role of dynamic tidal biofilms dominated by aerobic hydrocarbonoclastic bacteria and diatoms in the biodegradation of hydrocarbons in coastal mudflats

Mudflats and salt marshes are habitats at the interface of aquatic and terrestrial systems that provide valuable services to ecosys- tems. Therefore, it is important to determine how catastrophic incidents, such as oil spills, influence the microbial communities in sediment that are pivotal to the function of the ecosystem and to identify the oil-degrading microbes that mitigate damage to the ecosystem. In this study, an oil spill was simulated by use of a tidal chamber containing intact diatom-dominated sediment cores from a temperate mudflat. Changes in the composition of bacteria and diatoms from both the sediment and tidal biofilms that had detached from the sediment surface were monitored as a function of hydrocarbon removal. The hydrocarbon concen- tration in the upper 1.5 cm of sediments decreased by 78% over 21 days, with at least 60% being attributed to biodegradation. Most phylotypes were minimally perturbed by the addition of oil, but at day 21, there was a 10-fold increase in the amount of cyanobacteria in the oiled sediment. Throughout the experiment, phylotypes associated with the aerobic degradation of hydro- carbons, including polycyclic aromatic hydrocarbons (PAHs) (Cycloclasticus) and alkanes (Alcanivorax, Oleibacter, and Oceano- spirillales strain ME113), substantively increased in oiled mesocosms, collectively representing 2% of the pyrosequences in the oiled sediments at day 21. Tidal biofilms from oiled cores at day 22, however, consisted mostly of phylotypes related to Alcaniv- orax borkumensis (49% of clones), Oceanospirillales strain ME113 (11% of clones), and diatoms (14% of clones). Thus, aerobic hydrocarbon biodegradation is most likely to be the main mechanism of attenuation of crude oil in the early weeks of an oil spill, with tidal biofilms representing zones of high hydrocarbon-degrading activity