Kelp parts discarded from the sea

These kelp leftovers on the beach near Vermont, locally also called sea bamboo, are pieces of alga. The species is scientifically known as Ecklonia maxima. The large, brownish black, fibrous bodies grow erect in the seawater, forming the dominant kelp beds or kelp forests on rocks and sand in shallow seas. Kelp is not a plant but any one of a group of brown algae without vascular tissue or leaves.

The straps at the top are fronds. Each hollow stipe of 4 m to 10 m long has a gas-filled bulb near its tip, from which the flat, strap-like blades or fronds arise. The stipe is anchored at the base by means of a fibrous holdfast, not a root. The tough, branched, root‑like structure wraps around rock, gripping or wedging into crevices. The bulb or pneumatocyst at the top holds the kelp body upright, allowing the frond blades to remain in upper sunlit water. The alga relies on dissolved nutrients in seawater, not getting food from sand or rock. Up top the photosynthesising fronds contain brown pigment, and absorb the light penetrating the seawater.

The stipe stays tensioned, resisting the continual surges in the waves. Easy to understand that the compelling wave forces loosen pieces of kelp all the time! The broken-off bits drift, ending up on beaches and among rocks all over the place.

Kelp is economically important, as it is harvested for alginate used commercially in food, medicine, biotechnology, cosmetics, and in agriculture as animal feed, including for farmed abalone (iNaturalist; Wikipedia; https://www.kelpforestfoundation.org).