Insights into community-based bioassessment of environmental quality status using microphytobenthos in estuarine intertidal ecosystems

The feasibility of community-based bioassessment of environmental quality status was studied using microphytobenthos（MPB） in estuarine intertidal ecosystems.The sediment samples of MPB were collected monthly during a 1-year cycle（September 2006-August 2007） at four sampling stations in the Nakdong River Estuary,Korea.Environmental variables,such as salinity,radiation,grain size of sediment,Si（OH）4（Si）,nitrate（NO3^-）,nitrite（NO2^-）,ammonium（NH4~＋） and phosphates（PO4^（3-））,were measured synchronously for comparison with biotic parameters.The statistical analyses were carried out for assessment the relationship between biotic and environmental parameters.The results showed that：（1） the MPB community structures were significant differences among four sampling stations;（2） spatial variation in the MPB communities were significantly correlated with environmental variables,especially the nutrient NH4＋ in combination with salinity and grain size;（3） three species（Navicula lacustris,Pleurosigma anglulatum and Fragilaria sp.1） were significantly correlated with nutrients and/or Si;and（4） the species richness and diversity were significantly correlated with the grain size.It is suggested that MPB communities may be used as a potentially robust bioindicator for assessing environmental quality status in estuarine intertidal ecosystems.

Temporal and vertical distribution of microphytobenthos biomass in mangrove sediments of Zhujiang (Pearl River) Estuary

Being a primary producer, Microphytobenthos （MPB） play an important role in the benthic ecosystem of mangrove swamps. The temporal and vertical distribution of MPB biomass, expressed as chlorophyll a （Chl a）, was investigated in mangrove swamps on the Qi＇ao island and the Futian Mangrove Nature Reserve, Guangdong Province, South China. Both locations are situated in the Zhujiang （Pearl River） Estuary. For each location, bi-monthly sampling was carried out at four sites during low tide period. Except one site on the Qi＇ao Island, which was in Phragrnites australis marsh, all sites were in mangrove swamps. The Chl a concentration in surface （0-1 cm） sediment ranged from 0.2/2g/cm3 to 8.3 #g/cm3 in the Qi＇ao Island and from 2.1/zg/cm3 to 15.6/2g/cm3 in the Futian Mangrove Reserve. The peak Chl a concentration occurred in winter or early spring, while the lowest Chl a concentration, with a value of about one quarter of the peak, was observed in summer or early autumn. The vertical distribution of Chl a concentration exhibited an exponential decline with depth, which indicated a muddy sediment with high organic matter, and the slope of the curve was positively related to Chl a concentration in the surface sediment. The MPB biomass of the Qi＇ao Island was significantly lower than that of the Futian Mangrove Reserve. Our results suggest that the overlaying water quality might influence the MPB biomass in surface sediments.

Behavioral and physiological photoresponses to light intensity by intertidal microphytobenthos

Behavioral and physiological responses to light are the two major mechanisms by which natural microphytobenthic assemblages adapt to the intertidal environment and protect themselves from light stress. The present study investigated these photoresponses with diff erent light intensities over 8 h of illumination, and used a specific inhibitor(Latrunculin A, Lat A) for migration to compare migratory and non-migratory microphytobenthos(MPB). Photosynthetic activity was detected using rapid light curves and induction curves by chlorophyll fluorescence. It showed distinct variation in migratory responses to diff erent light intensities; high light induced downward migration to avoid photoinhibition, and low and medium light(50–250 μmol/(m^2 ·s)) promoted upward migration followed by downward migration after certain period of light exposure. No significant difference in non-photochemical quenching(NPQ) or PSII maximal quantum yield(F v/F m) was detected between low and medium light irradiance, possibly indicating that only high light influences the photosynthetic capability of MPB. Decreased photosynthetic activity, indicated by three parameters, the maximum relative electron transport rate(r ETR_(max)), minimum saturating irradiance(E _k) and light utilization coefficient(α), was observed in MPB after exposure to prolonged illumination under low and medium light. Lat A ef fectively inhibited the migration of MPB in all light treatments and induced lower F v/F _m under high light(500 and 100 μmol/(m^2 ·s)) and prolonged illumination at 250 μmol/(m^2 ·s), but did not significantly influence F _v/F m under low light(0–100 μmol/(m^2 ·s)) or NPQ. The increase of NPQ in Lat A treatments with time implied that the MPB assemblages can recover their physiological photoprotection capacity to adapt to light stress. Non-migratory MPB exhibited lower light use efficiency(lower α) and lower maximum photosynthetic capacity(lower r ETR_(max)) than migratory MPB under light intensities above 250 μmol/(m ~2 ·s) after 4.0 h illumination.

Minireview: The role of viruses in marine photosynthetic biofilms

Microphytobenthos and sea ice algae comprise globally significant photosynthetic biofilms.While their microalgal and bacterial constituents are well characterized,there is very little information on their viral communities or on the virus-bacteria and virus-algae interactions within them.While high levels of interaction might be expected because of the high density of cells,infection rates,particularly of microalgae,have been found to be low.It remains unclear whether this is a result of environment characteristics,developed resistance or because of the small number of studies.