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An annual study of the bacterioplankton community structure was carried out at Stn L4 (50°15' N, 04°13' W) in the western English Channel between August 2003 and July 2004. Bacterioplankton abundance and community structure were assessed using flow cytometry and fluorescence in situ hybridization (FISH) with rRNA-targeted oligonucleotide probes, respectively. The Eubacteria domain dominated over the Archaea domain (<15%) at the highest phylogenetic level. The Sphingobacteria-Flavobacteria group of the Bacteroidetes phylum (SFB) numerically dominated in spring and early summer. The α-Proteobacteria dominated from late summer to winter. The SAR11 clade represented ~13% of the microbial community throughout the year and accounted for up to 69% of α-Proteobacteria in late spring. Annually, γ-Proteobacteria were 2 or 3 times less abundant than the other groups and showed no obvious seasonal trend. The SAR86 cluster accounted for up to half of γ-Proteobacteria when it peaked in summer. Consequently, we found that community structure at higher taxonomic level did not change dramatically with season but lower level phylogenetic groups showed pronounced seasonal peaks.KEY WORDS: Bacterioplankton · Seasonal variability · Community structure · English Channel · Fluorescence in situ hybridization Resale or republication not permitted without written consent of the publisherAquat Microb Ecol 42: [119][120][121][122][123][124][125][126] 2006 munity biomass, function, structure, and diversity are known to change between winter and summer (Pernthaler et al. 1998, Zaccone et al. 2002. Schauer et al. (2003) showed the overall stability in time of the taxonomic composition of the bacterioplankton in coastal marine system, with gradual changes throughout the year revealing a substitution of closely related phylotypes during the seasonal cycle. Crump et al. (2003) demonstrated that shifts in bacterioplankton community composition were related to seasonal cycles in the source and lability of dissolved organic matter. Similarly, succession in marine bacterioplankton assemblages occurred in response to seasonal shifts in water column stability and water temperature, suggesting that bacterioplankton community composition may demonstrate an annual pattern of variability (Murray et al. 1998). Other studies have demonstrated relationships between bacterioplankton community composition and seasonal dynamics of other members of the aquatic food web (Hofle et al. 1999, Fandino et al. 2001, Hahn & Hofle 2001, Arrieta & Herndl 2002.A typical seasonal dynamic in temporal coastal waters still remains to be established. Previous mesocosm experiments showed dramatic changes in the composition of the bacterial assemblage on daily to weekly time scales (van Hannen et al. 1999, Schäfer et al. 2001. However, it is not clear whether these changes are frequent in the field, although in some situations, such as during phytoplankton blooms, strong changes in numbers and phylogenetic shifts of the bacterial assemblage have been observed (Fandin...

The solar radiation regime on differently oriented surfaces of the shallow-water coral Goniastrea aspera is markedly different Field experiments involving rotation of small (20 cm diameter) hemispherical colonies exposed hitherto protected surfaces of the colonies to high levels of photosynthetically active radiation (PAR) whilst reducing PAR on the opposite surface. Photodamage and recovery, respectively, were recorded in the symbiotic algae using non-invasive chlorophyll fluorescence techniques. Measurements of photochemical efficiency (FJF,) indicated that the Photosystem I1 (PSII) reaction centres of algae in previously protected surfaces suffered 'chronic' photoinhibition, probably on a timescale of 3 h, as a result of exposure to elevated solar PAR. Furthermore, evidence from this study corroborates earlier findings that this photodamage is a function of high PAR irradiance for short periods rather than a similar dose accumulated more slowly. Sin~ultaneously, algae on the opposite surfaces were observed to recover their photochemical efficiency, but this recovery was at a much slower rate involving several days at reduced PAR. The photodamage was sufficiently severe to lead to the formation of visible lesions (bleached areas). Observations of coral polyp retraction and nleasurements of the protective xanthophyll pigments in the algae showed behavioural and photoprotective mechanisms being deployed to mitigate the photodamage.

Phytoplankton and microzooplankton community structure and the impact of microzooplankton grazing were investigated during a one-day study of an Emiliania huxleyi bloom off the coast of Devon during July 1999. Vertical profiles were undertaken at four stations, along a transect which crossed from a low reflectance to a high reflectance area as seen by satellite imagery. Microzooplankton dilution grazing experiments, coupled with pigment analysis to determine class specific grazing rates, were performed at two of these stations.Highest concentrations of chlorophyll-a (5·3 mg m−3) and accessory pigments were measured inside the area of high reflectance. Phytoplankton standing stocks ranged between 1588 and 5460 mg C m−2 and were also highest in the area of high reflectance. The phytoplankton community was dominated by coccolithophores and diatoms in low reflectance waters and by photosynthetic dinoflagellates in high reflectance areas. Microzooplankton standing stocks ranged between 905 and 2498 mg C m−2. Protozoa dominated the microzooplankton community. The protozoan community comprised a relatively even mixture of heterotrophic dinoflagellates, non-choreotrich and choreotrich ciliates in low reflectance waters. However, non-choreotrich ciliates dominated the communities inside the high reflectance area. Of the heterotrophic ciliates, a predatory ciliate Askenasia sp. dominated both non-choreotrich abundance and biomass.Results from grazing experiments showed that 60–64% of the chlorophyll-a biomass was consumed daily by the microzooplankton. Highest grazing mortality was associated with peridinin (dinoflagellates) and alloxanthin (cryptophytes). Lower grazing rates were found on fucoxanthin (diatoms and prymnesiophytes). Our results indicate that grazing on E. huxleyi in the area of remotely sensed high reflectance was low and highest grazing was on photosynthetic dinoflagellates and cryptophytes.