Note: This program first aired July 4, 2015.
A few weeks ago, I got a call from my nearly 4 year old nephew during dinner. I could hear the excitement in his voice as he shouted into the phone about seeing worms in the water at the town dock. I asked him what color they were and he said they were all colors. This brought back a memory from my own childhood, a memory until this moment I wasn’t even sure was real. I remember seeing huge iridescent blue green worms swimming at the surface of the water, and then seeing them washed up dead on the beach the next day. I saw them that one time, and never again, causing me to think I had either imagined it or witnessed something very rare. Hearing my nephew’s excitement a couple fo things became clear, what I saw was indeed real, and that now my family has an official childhood rite of passage: witnessing the spawning swim of the sand worms.
Sand worm, rag worm, clam worm, these common names all refer
to various species of polychaete worms found in coastal areas throughout the
north Atlantic. Polychaetes are marine segmented worms, meaning their bodies
are divided up into hundreds of discrete segments. Believe it or not this body
structure represented a big leap forward in terms of evolutionary complexity.
Polychaete worms are an incredibly diverse and successful group of organisms,
there are over 100 species listed for the Gulf of Maine alone.
The worms I saw as a child, and my nephew saw this spring
are Alitta virens, sometimes known as
the king rag worm, or sand worm. They live in burrows in low intertidal or sub
tidal sand or mud. The burrows are U shaped, with each end of the U an
opening at the surface of the sand. The
worms spend most of their lives in these burrows, pumping oxygenated water
through them so they can breathe (and a neat side effect is the diffusion of
oxygen into otherwise anoxic sediment. The oxygen burrowing worms draw down
into the sediment fuels an entire microscopic ecosystem). They stick their fearsome
heads and sharp black teeth out of the burrow to feed on various small benthic
sea creatures, and are said to sometimes scavenge omnivorously. Rag worms are
among the most long lived of polychaetes, some are thought to reach the ripe
old age of as much as 7 years. In the end though, regardless of how old they
get, their fate is the same. This group of polychaetes practices what is called
“semelparity”, meaning they reproduce once, and then they die.
As I said, these worms spend their lives in their burrows, only occasionally leaving to crawl along the bottom to find better digs, otherwise they are in the sediment. Things change however, when it is time to mate. The males undergo epitoky, their bodies change shape and structure in preparation for mating. They turn shimmery blue green and learn to swim, and around the new moon, they swim to the surface at high tide and release their sperm into the water column. That sperm makes its way down to the females who have remained in their burrows. They fertilize the eggs they have spent nearly a year developing in their bodies. Once the eggs are fertilized, the female excretes them on the surface of the sediment outside her burrow, where they develop, hatch and start a new generation of sand worms. After shedding sperm, the males die. After laying the eggs, the females die. Such is the life of a sand worm.
The moon is involved because the worms, both male and female are highly sensitive to photoperiod, and the development of the eggs begins a year before mating in response to changes in day length. Something about the combination of warming water in the spring, lengthening days, and darkness at night tells the males that the females are ready, but as far as I can tell, we can’t know for sure when the magic will happen. That is why it is such a good idea to be outside as much as you are able. You never know when you will stumble upon a certain flower blooming, a case of tiny spiders hatching, baby birds fledging, a lynx track in the snow, or hundreds of two foot long blue green worms swirling in the water doing their once in a life time dance.
References:
Alitta virens on
EOL http://eol.org/pages/458737/overview
Everything you want to know about clam and blood worms:
All about Annelids, from the Tree of Life: http://tolweb.org/Annelida
Actually, even more that you might want to know about
polychaets, from and OLD Woods Hole guide: http://hermes.mbl.edu/publications/biobull/keys/pdf/9.pdf
On lunar impact of breeding (but not of worms specifically) http://siderealtimes.blogspot.com/2011/12/effects-of-lunar-cycle-on-marine-animal.html
