Bahía San Quintín is a coastal lagoon with large Ulva biomass and upwelling influence. Previous observations suggest that Ulva has increased recently as a result of oyster cultivation. To evaluate the possible role of Ulva as a temporary nutrient sink, biomass and tissue C, N, and P were determined seasonally. Maximum biomass was present during spring and early summer (1,413-1,160 t (dry)) covering about 400 ha. However, the biomass decreased to 35 t (dry) by winter. The mean annual percentage of Ulva C, N, and P was 28%, 2%, and 0.14%, respectively. This study shows that Ulva can store up to 28 t of N and 2 t of P in Bahía San Quintín during spring-summer. Ulva may be displacing the seagrass Zostera marina subtidal beds. A partial removal of the seaweed would reduce the risk of eutrophication and the displacement of eelgrass beds.

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[1] The Ballenas-Salsipuedes Channel (BSC) is considered an oceanographic province on its own within the Gulf of California. In this region, tidal mixing is modulated by quarterdiurnal, semidiurnal, diurnal, and fortnightly frequencies, producing a strong outcropping of cold and nutrient-rich waters. In this work we analyze the temporal and spatial variability of sea surface temperature (SST) data recorded simultaneously over a period of 1 year in six bays along the BSC. Minimum mean SST differences (< 0.5°C) among bays were observed in December, while maximum differences (> 2.5°C) were recorded in June. The monthly SST anomaly showed that from late October to late January, the channel behaved as a very well mixed region. In contrast, SST anomalies of up to 2.2°C among bays were observed from May to September, indicating intense heat gain in summer and highlighting spatial heterogeneity in the intensity of vertical mixing. Besides the seasonal temperature cycle, influenced by solar irradiation, four main periods (0.25, 0.5, 1, and 15 days) were identified, corresponding to the main timescales of variability induced by the tides. This work demonstrates that the main source of temporal SST variability in BSC is the tide-induced fortnightly modulation, suggesting the possibility of a pulsation mechanism in the outcropping of nutrient-rich waters reaching the surface layer throughout the channel; this could play a crucial role in explaining the exceptionally high biological production of this region.Citation: Martínez-Díaz-de-León, A., I.

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The many nutritional benefits reported in seaweeds have increased their demand in the western world for human consumption. In order to supply this demand, it is necessary to cultivate seaweeds both offshore and onshore. Offshore cultivation is highly vulnerable to climate variation. Cultures on land can be operated while essential variables can be controlled (nutrient supply) or partially regulated (light and temperature) providing a more uniform quality and continuous production. In this study, we present the results of pondculture in a commercial pilot-facility on the Pacific, temperate coast of Mexico, which has been continuously running for 2½ years. Ponds of 100 m 3 were seeded with 3 kg/m 2 of a previously selected strain of Ulva. Pulse fertilization and a full water exchange were made twice a week. Ponds were fully harvested every 3 weeks and re-seeded with the initial density. Seaweed production showed a bimodal distribution with a strong peak in spring (258-290 g m −2 day −1 ), a minor peak in autumn, and lower production in summer and much lower in winter (40-85 g m −2 day −1 ). Highest growth