Flotsam

From a distance I thought these were spiderwebs or possibly moth larvae cocoons. On closer viewing I found they were neither. My assumption is that this is a thin layer of algae that formed on the surface of an ephemeral pond. As the water seeped away the algae was left high and dry, strung out like washing on a line. I've seen this before but my recollection is that its usually been pale brown or green in colour rather than this stark white. Does it have a name and does anyone out there know how its formed?

Bonus butterfly today was the small tortoiseshell - the first of its kind this year and bringing my species list to six, which is not bad for March. Still hoping for an Orange Tip, I know the first was seen a couple of days ago.