Old Friends Stick Together

April 18, 2017

Bayside-sea slippers and barnacles

April 2017 Viewers' ChoicePhotographer: Rob Sheridan
Summary Author: Rob Sheridan

A number of invasive invertebrates have disrupted New England’s intertidal ecosystems in recent decades, but three old stalwart natives remain common. All three form amazing but different marine adhesives. The Blue Mussel (Mytilus edulis), shown in my hand, is a bivalve mollusk that adheres to rocks and to each other with strong slightly elastic byssal threads. These fine filaments are secreted by byssal glands along the foot of the mussel, forming as soon as the final planktonic stage finds a resting place and anchoring the maturing mussel for life.

The Atlantic Slipper Limpet (Crepidula fornicata) is a gastropod mollusk that has evolved a mucous based glue that prevents vertical removal (by predators) while permitting lateral motion, allowing the mobile animal to graze on algae. They're the whitish, rounded objects on the of the mussel's shell. Interestingly, the New England native Atlantic Slipper Limpet has become a difficult invasive in European waters, interfering with oyster production.

The Northern Rock Barnacle (Balanus balanoides), the objects with holes at the center of their shells, is a crustacean, like lobsters and crabs, rather than a mollusk. It's oriented with its head glued down by cement, excreted by glands at the base of its first antennae. After this cementing process, the barnacle then forms a calcium carbonate enclosure. It's the only crustacean that remains fixed in one spot for life. When covered with water, barnacles open their enclosure and extend feathery modified leg appendages (cirri) that filter nutritional organic matter from the water and function as gills.

All three species share a somewhat similar reproductive strategy. They adhere to hard substrates, including boat hulls and larger animals and to each other. Having female and male animals in proximity promotes reproduction; timing release of their gametes to facilitate commingling in the water. Fertilized eggs in all three species are initially planktonic before fixing on a stable surface for life, with their amazing adhesives. Scientists are actively pursuing these adhesives for a variety of medical uses. Photo taken on September 22, 2008.

Photo Details: Camera Model: Canon PowerShot SD1000; Focal Length: 5.8mm; Aperture: ƒ/2.8; Exposure Time: 0.0031 s (1/320); ISO equiv: 80.