Microphytobenthos spatio-temporal dynamics across an intertidal gradient using Random Forest classification and Sentinel-2 imagery

Microphytobenthos (MPB) provides important ecosystem functions and services, contributing significantly to the total primary production in shallow coastal ecosystems. However, determining the factors that regulate the seasonal changes of MPB and its distribution patterns at larger scales is hindered by the considerable spatial and temporal variability in these environments. Here, we studied the dynamics of intertidal MPB biomass, cover, and net growth rates in a south European tidal flat (Cadiz Bay, Spain) over a four-year period using the Normalized Difference Vegetation Index (NDVI) calculated from Sentinel-2 satellite images. Pixels dominated by different benthic communities (MPB, Zostera sp., Caulerpa sp. and green macroalgae) were identified at a 10-m resolution using a Random Forest (RF) machine learning classification algorithm. MPB dominated the intertidal zone. MPB cover did not show a clear seasonal pattern and was clearly higher in the middle of the intertidal range of sea level. Despite interannual variability, MPB biomass was always higher during winter, coinciding with observations from other low latitude intertidal flats with temperate climate, and in the upper-middle intertidal. Net rates of MPB biomass change, calculated from the differences in MPB NDVI over time, showed maximal net growth rates from autumn to winter and maximum loss rates during spring and summer, although with high variability. Our study demonstrates that RF algorithms allow mapping MPB and other intertidal communities from Sentinel-2 multispectral satellite imagery accurately obtaining invaluable information from large areas at very high spatio-temporal resolution. The dissimilarities observed in the patterns of MPB variables over time or sea level, indicate differences in their ecological regulation, still largely unknown both here and in other temperate climate intertidal flats. High resolution remote sensing can aid in their detailed and systematic study producing a more integrated view of these systems and contributing to their science-based management and conservation.

Diel patterns of microphytobenthic primary production in intertidal sediments: the role of photoperiod on the vertical migration circadian rhythm

Diel primary production patterns of intertidal microphytobenthos (MPB) have been attributed to short-term physiological changes in the photosynthetic apparatus or to diel changes in the photoautotrophic biomass in the sediment photic layer due to vertical migration. Diel changes in primary production and vertical migration are entrained by external factors like photoperiod and tides. However, the role of photoperiod and tides has not been experimentally separated to date. Here, we performed laboratory experiments with sediment cores kept in immersion, in the absence of tides, with photoperiod or under continuous light. Measurements of net production, made with O₂ microsensors, and of spectral reflectance at the sediment surface showed that, in intertidal sediments, the photoperiod signal was the major driver of the diel patterns of net primary production and sediment oxygen availability through the vertical migration of the MPB photoautotrophic biomass. Vertical migration was controlled by an endogenous circadian rhythm entrained by photoperiod in the absence of tides. The pattern progressively disappeared after 3 days in continuous light but was immediately reset by photoperiod. Even though a potential contribution of a subjective in situ tidal signal cannot be completely discarded, Fourier and cross spectral analysis of temporal patterns indicated that the photosynthetic circadian rhythm was mainly characterized by light/dark migratory cycles.

Radiative Energy Budgets in a Microbial Mat Under Different Irradiance and Tidal Conditions

Irradiance and temperature variations during tidal cycles modulate microphytobenthic primary production potentially by changing the radiative energy balance of photosynthetic mats between immersion and emersion and thus sediment daily net metabolism. To test the effect of tidal stages on the radiative energy budget, we used microsensor measurements of oxygen, temperature, and scalar irradiance to estimate the radiative energy budget in a coastal photosynthetic microbial mat during immersion (constant water column of 2 cm) and emersion under increasing irradiance. Total absorbed light energy was higher in immersion than emersion, due to a lower reflectance of the microbial mat, while most (> 97%) of the absorbed light energy was dissipated as heat irrespective of tidal conditions. During immersion, the upward heat flux was higher than the downward one, whereas the opposite occurred during emersion. At highest photon irradiance (800 μmol photon m^-2 s^-1), the sediment temperature increased ~ 2.5 °C after changing the conditions from immersion to emersion. The radiative energy balance showed that less than 1% of the incident light energy (PAR, 400-700 nm) was conserved by photosynthesis under both tidal conditions. At low to moderate incident irradiances, the light use efficiency was similar during the tidal stages. In contrast, we found an ~ 30% reduction in the light use efficiency during emersion as compared to immersion under the highest irradiance likely due to the rapid warming of the sediment during emersion and increased non-photochemical quenching. These changes in the photosynthetic efficiency and radiative energy budget could affect both primary producers and temperature-dependent bacterial activity and consequently daily net metabolism rates having important ecological consequences.

Effects of green macroalgal blooms on the meiofauna community structure in the Bay of Cádiz

The effect of macroalgal blooms on the abundance and community structure of intertidal sediment meiofauna was studied using an in situ enclosure experiments (Bay of Cádiz, Spain). Meiofaunal abundance (3500-41,000 ind 10 cm⁻²) was three to sevenfold higher in the presence of macroalgae. Nematoda were the dominant taxon both in Control (52-82%) and Macroalgae plots (92-96%), followed by Harpacticoida Copepoda and Ostracoda. Non-metric Multi-Dimensional Scaling (MDS) analysis clearly separated the meiofaunal community from Control and Macroalgae plots. Organic matter, organic carbon, total nitrogen, chlorophyll a and freeze-lysable inorganic nutrients were higher in Macroalgae plots, and were highly correlated with the horizontal MDS axis separating Control and Macroalgae meiofaunal communities. Meiofaunal abundance and taxonomic composition in the Bay of Cádiz seem to be bottom-up controlled either through a grazer system based on microphytobenthos in bare sediments or through a decomposer system in macroalgae affected sediments.

Epistaxis of patients admitted in the emergency department is not indicative of underlying arterial hypertension

OBJECTIVE

To assess the association between epistaxis and arterial hypertension.

METHODS

A prospective study was conducted in 80 patients admitted in the emergency department, 42 with epistaxis and 38 well-matched controls. Blood pressure was measured upon admission and by continuous 24-hour ambulatory monitoring on the following days.

RESULTS

Estimated values upon admission did not differ between groups. A definitive diagnosis of hypertension was set in 18 patients admitted for epistaxis (42.9%) and in 11 controls (28.9%, p = NS). Systolic pressures during the 24-hour recording period, systolic pressures during day and diastolic pressures during night were significantly higher among patients admitted for epistaxis than among controls.

CONCLUSIONS

Although studies with larger series of patients are mandatory, epistaxis does not seem to result from underlying arterial hypertension.

Radiation therapy and concurrent cisplatin administration in locally advanced head and neck cancer. A Hellenic Co-operative Oncology Group study

In an attempt to improve local control of locally advanced head and neck cancer, radiation therapy was combined with cisplatin. Forty-eight patients entered into this study. All patients were irradiated with a 60Co unit and according to the protocol they should receive 70 Gy in the tumor area and 45 Gy in the rest of neck. Cisplatin was administered at a dose of 100 mg/m2 on days 2, 22 and 42. Thirty-seven (80%) patients received the total radiation dose as initially planned. Thirty-four (72%) patients achieved complete and 5 (10%) partial response. Grade 3-4 toxicities included vomiting (14%), stomatitis (4%), diarrhea (2%), myelotoxicity (14%), hoarseness (4%), dysphagia (30%), weight loss (32%), nephrotoxicity (4%) and dermatitis (2%). After a median follow-up of 26 (range, 18-33) months, 16 patients have died. Among the 35 complete responders 6 later on relapsed. Median relapse-free survival has not yet been reached. Combined radiation therapy and cisplatin appears to be a highly active treatment in patients with advanced head and neck cancer as far as primary locoregional response is concerned.

Primary extranodal non-Hodgkin's lymphoma of the head and neck

Among 387 cases of non-Hodgkin's lymphoma (NHL) treated in our units between January 1977 and December 1990, 52 (13.4%) had primary extranodal (PE) NHL of the head and neck. The median age was 55 years with a M:F ratio of 1.9:1. The most frequent primary site was the tonsil (28 cases), followed by oral cavity, parotid gland, orbit and other sites. The aggressive histological subtypes predominate. 55.2% of the patients were in stage I and 44.8% in stage II of disease. The CR rate was high (94.2%). The 5 years' overall survival rate was 65% and it was influenced mainly by stage (stage I 82.5% vs. 48.7% in stage II). Sex, age and histology did not significantly affect survival rate. Patients with primary Waldeyer's ring involvement (WR group) did not differ significantly from the other primary sites analyzed as a group (non-WR group) in respect to median age, sex distribution, histology and CR rates. They differed, however, in: (1) stage distribution with stage II disease more frequent in the WR group; (2) overall survival and disease-free survival both of which were significantly better in the non-WR group; and (3) the high incidence of GI tract involvement as initial manifestation of relapse in the WR group. It is concluded that the behaviour of the Waldeyer's ring PE-NHL is rather distinctive and should be considered separately from the other PE-NHL of the head and neck.