February 1st to 5th 2016
Olhão, Portugal
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Contrasting timing of life stages across latitudes – a case of a marine forests forming species

Oral Presentation
Natural Resources
Wednesday, February 3, 2016 -
15:00 to 15:15

Pereira, T.R. 1 Engelen, A.H. 2 Pearson, G.A. 3 Valero, M. 4 Serrão, E.A. 5

1Centre of Marine Sciences (CCMAR), University of Algarve, Campus de Gambelas, 8005-139 Faro, Portugal
2Centre of Marine Sciences (CCMAR), University of Algarve, Campus de Gambelas, 8005-139 Faro, Portugal
3Centre of Marine Sciences (CCMAR), University of Algarve, Campus de Gambelas, 8005-139 Faro, Portugal

At low latitudes, Saccorhiza polyschides forests are highly seasonal, with macroscopic sporophytes present only between spring and autumn. At high latitudes, however, these are able to overwinter and survive for longer than a year. This seasonality at lower latitudes is commonly attributed to temperature. To test if this might be the factor leading to such differences across latitudinal ranges, field demographic surveys were combined with controlled culture experiments in two populations with contrasting timing of life stages: a central population in Brittany, France and a southern one in Northern Portugal.Our results did not support the initial hypothesis that such differences were caused by temperature. In the field, we found recruitment to be limited to spring in the south while further north sporophytes recruited year-round. Culture experiments showed that zoospores were able to develop under temperatures between 5 and 20°C, with optimum at 10-15°C, placing Portuguese winter temperatures within the optimum range, and thus indicating that seasonal recruitment is not caused by winter temperatures. Furthermore, zoospores took a maximum of 62 days, at 5°C, to develop into visible sporophytes, and only 20 days at 10°C, excluding the possibility that the absence of recruits through winter was a consequence of synchronized release of zoospores in autumn.While temperature doesn’t offer an explanation for the differences between populations at different latitudes, the presence of macroscopic sporophytes in southern populations coincides with the typical upwelling season, which is accompanied by increased nutrient levels. This seasonality of nutrient availability in the south, in contrast with more constant levels in north-central range, led to the alternative hypothesis that nutrient availability, and not temperature, might explain the differences in life stage timing across latitudes. This hypothesis was, however, not initially considered and requires testing.
keywords: 
Saccorhiza polyschides , seasonality, upwelling

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