During the European GBIF meeting Bioblitz/excursion the larva of Larvas of Large White Butterfly (Pieris brassicae) was identified feeding on this plant on the Meco beach. (Many thanks to @duarte for help with the plant species).

Portugal flora:
http://www.flora-on.pt/index.php#/1cakile+maritima

For the observation of the butterfly larva see: http://www.inaturalist.org/observations/3031052 and http://www.inaturalist.org/observations/3029206 (by @wouterkoch)

See also: https://dagendresen.wordpress.com/2016/04/29/european-gbif-nodes-meeting-bioblitz/