Climate change is affecting the trophic ecology of reef fishes through changes in reef-associated food availability and fish feeding behavior. The southern Arabian Gulf is a thermally extreme environment, providing an opportunity to study fish diets on reefs with summer temperatures representative of next-century conditions elsewhere. Using 18S metagenomic analyses of stomach contents, we provide the first description of the dietary composition of three abundant reef fishes (Pomacanthus maculosus, Pomacentrus aquilus, and Pomacentrus trichrourus) from the thermally extreme southern Arabian Gulf, with five sampling periods across 1 year used to assess seasonal variation in diet. In total, 146 stomach content samples were sequenced, resulting in 9.6 million filtered reads that aligned to 17 classes in 14 phyla. Corals (Cnidaria, Anthozoa) dominated stomach contents of all three fishes (overall mean: 74.6, 40.6, and 21.2% of stomach reads, respectively), suggesting coral consumption to be characteristic of reef fish diet in the region. Sanger sequencing validated the presence of corals in the stomach contents and identified two common genera in the region, Porites and Platygyra, as part of the diet. Other common phyla included sponges and annelid worms (P. maculosus: 14.9%, 4.1%; P. aquilus: 5.9%, 16.7%; P. trichrourus: 8.2%, 14.7%, respectively), with the remainder comprised of 11 other phyla. Algae were virtually absent in diets of all three species. The P. maculosus diet was consistently coral/sponge dominated across the year, but there was substantial seasonal variation in the damselfishes, with diets dominated by coral in the hottest month (August; P. aquilus: 89.4%, P. trichrourus: 51.5%) but broadest in spring (March, May) when corals became less common (<19.8% each) and bivalves, free living ascidians, and various arthropods increased; parasitic cestodes were also abundant in damselfish stomachs in spring (mean: >16.4%). These results suggest that these fishes have developed a feeding ecology responsive to the fluctuating and extreme environmental conditions of their region. These results broaden our understanding of the diets of these three species and document the nature, complexity and temporal dynamics of reef fish diets in the most thermally extreme coral reef environment on earth.

Dermal synthesis, following sun exposure, is the main source of vitamin D. This study characterizes ambient UVB radiation relevant for vitamin D production in Europe. A biological weighing function was applied to data from the Tropospheric Emissions Monitoring Internet Service (TEMIS) for 46 capital cities over an 18-year period (2004–2021) to isolate wavelengths relevant for vitamin D production (D-UVB). Cumulative and weighted D-UVB (CW-D-UVB) were calculated to approximate seasonal vitamin D accumulation and diminution. Monthly 25(OH)D concentration measurements were extracted from published reports. All data were analyzed by location and time. Despite a moderate latitudinal range (35–64° N), we observed large—up to five-fold—regional differences: the highest mean diurnal D-UVB dose of 5.57 kJ/m2 (SD = 3.55 kJ/m2) was observed in Nicosia (Cyprus) and the lowest in Reykjavik (Iceland, 1.16 ± 1.29 kJ/m2). Seasonal differences in diurnal D-UVB dose were even more pronounced, with a median 36-fold difference between annual peak and trough depending on a location (range: 10- to 525-fold). The mean duration of “vitamin D winter” was 126 days but varied widely (4 to 215 days). Monthly CW-D-UVB and 25(OH)D changes were very strongly correlated: the changes in 25(OH)D concentration increased by 12.6 nmol/L for every 100 kJ/m2 increment of CW-D-UVB in population-based studies (r2 = 0.79, p-value = 1.16 × 10−37). Understanding the differences in D-UVB radiation can help understand determinants of vitamin D status and guide region- and season-specific safe and effective sunlight exposure recommendations and vitamin D supplementation guidelines.

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Vitamin D is essential for good health. Dermal vitamin D production is dependent on environmental factors such as season and latitude, and personal factors such as time spent outdoors and genetics. Varying heritability of vitamin D status by season has been reported, suggesting that gene-environment interactions (GxE) may play a key role. Thus, understanding GxE might significantly improve our understanding of determinants of vitamin D status. The objective of this review was to survey the existing methods in GxE on vitamin D studies and report on GxE effect estimates. We searched the Embase, Medline (Ovid), and Web of Science (Core Collection) databases. We included only primary research that reported on GxE effects on vitamin D status using 25-hydroxyvitamin D as a biomarker. Sun exposure was the only environmental exposure identified in these studies. The quality assessment followed the Newcastle–Ottawa Scale for cohort studies. Seven studies were included in the final narrative synthesis. We evaluate the limitations and findings of the available GxE in vitamin D research and provide recommendations for future GxE research. The systematic review was registered on PROSPERO (CRD42021238081).