One-Way Romance on the Full Moon

July 05, 2018

Bayside-Orchard Beach Lowtide Walk-Clamworm-20180428

Photographer: Rob Sheridan 
Summary Author: Rob Sheridan 

During full Moon nights in late spring, marine polychete Atlantic Clamworms (Alitta succinea) are compelled to rise from their shallow, silty burrows and swarm in the water column, releasing sperm and eggs, then dropping to the bottom, dead. This process of reproduction, called epigamy, improves the efficiency of fertilization and results in clouds of fertilized eggs that go on to become planktonic larvae. The few larvae not consumed by other marine organisms grow to become adult polychete worms, then sink to the bottom, feed on and within coastal muds, and await their own full Moon night as their progenitors have done for the past 500 million years.

This photo, taken through a few inches of water during incoming low tide on a Massachusetts tidal flat, shows an adult Atlantic Clamworm emerging from its burrow late in the afternoon on a day when the Moon was nearly full -- the waxing gibbous Moon had already risen. Its parapodia (mobile segmental excrescences that facilitate ground movement, burrowing, and also act as gills) have hypertrophied to enable its swarming in the water column, perhaps during this night's nearly full Moon. Photo taken on April 28, 2018.

Photo Details: Camera: Apple iPhone 5s; Software: Adobe Photoshop Elements 14.0 (Windows); Exposure Time: 0.0037s (1/272); Aperture: ƒ/2.2; ISO equivalent: 32; Focal Length (35mm): 29