Bryozoan Colony on a Kelp Frond

A colony of bryozoans (Membranipora membranacea) on a kelp blade

Kelp fronds often carry white spots. Darwin mentioned them, on kelp off Chile, in his bestseller Voyage of the Beagle. This white spot is composed of many cells, grouped around a center. Each cell contains an individual bryozoan, a Lacy Crust Bryozoan or Membranipora membranacea. A single individual is known as a zooid (which is a great scrabble word). Here you can see that the zooids are a filter-feeders, sieving the ocean for nutrients. They reproduce sexually in the spring and summer, to produce free-swimming larvae. They also reproduce asexually, by budding. The individual at the center of the colony is the oldest: the father and mother of those further out. On the east coast of the US, the lacy crust bryozoan is regarded as an invasive species, believed to weaken kelp. Off the west coast of the US, as well as Europe and Asia, they've been around for a long time.

A zoomed-out view of the same bryozoan colony.