Life on a Kelp Blade

A closeup of a mature kelp blade shows bryozoan and nudibranch eggs.

Older blades of kelp often show white spots, like the ones in the image above. If you examine this Giant Kelp blade close-up, the white spots form intricate networks that look like alien cities. Here, the white network-like structures are bryozoans. Each cell is one individual. The individual that started the colony is at the middle of the net; that individual reproduces asexually to expand the net. The nets grow until, in this case, they meet their neighbors. The white spirals are the eggs of nudibranchs. A few species of nudibranchs dine on the bryozoans on kelp, so these eggs will hatch amidst a food source. Most nudibranchs lay eggs in spirals like these, and the spirals usually wind counter-clockwise. Links:

https://dedide.info/ecosystemservices/giant-kelp/

https://themarinedetective.com/tag/bull-kelp/

http://www.seaslugforum.net/showall/eggspir