It seems somehow ironic that I wrote last week about discovering a seaweed species that I happily found out was not invasive, but was merely unfamiliar to me, as I am now writing about a seaweed species that is invasive. When a friend who was visiting pulled up a glistening sample of dead man’s fingers, we both remarked that, while it was both invasive and had a less than sparkling name, Codium fragile is actually quite beautiful. Its thick, furry fronds, the texture of which are likely the reason it is known as dead man’s fingers, are a verdant green and catch the light easily under the water.
Codium has been here since the 1960s and is native to the Pacific, not the Atlantic. It is thought to have been introduced in the ballast water of ships, a common means of introducing species to new locations. Before we put the little sample back into the water, my friend noticed some tiny white dots moving around in its holdfast.
Being the nerdy scientist that I am, I pulled out my hand lens, which lives in my bag at all times, and looked more closely to find that these dots were perfect baby horseshoe crabs. I could see what is known as the prosoma, the front part of the shell that gives the crab its name as it is shaped like a horseshoe, moving on its hinge with the opisthosoma, the back portion of the shell, in a tell-tale motion. On closer look, I could even see the tiny eye spots on either side of the prosoma.
Horseshoe crabs are one of the most amazing creatures that are eas.