Feeding at Argyle

     Some feeding behaviors observed at Argyle Creek are more obvious than others, because many of the animals are sessile and/or benthic.  The majority of the animals observed were herbivores, carnivores, deposit feeders or suspension feeders. Because many of the organisms are sessile, they rely on transport of food by water currents.  Many of the sessile organisms are filter feeders, feeding on plankton and other suspended material, while deposit feeders feed on detritus, herbivores on algae, and carnivores on other animals living in the creek.
 

Herbivores

The most abundant herbivores are chitons, which feed primarily on microscopic algae. These molluscs crawl with the aid of mucus over rocks or bivalves, feeding on the algal film growing on the surfaces.  A chiton feeds by scraping the surface with a radula, a structure with hard chitinous teeth that rasps food into the mouth. The radula is a defining characteristic of molluscs, although it has been lost evolutionarily in certain groups. Limpets, which feed a similar way, were also commonly found on all surfaces of the uppermost rocks in the creek.
 

A chiton of the genus Mopalia attached to a rock eating its way through
a strip of red algae by use of its tooth-like structure, the radula.

Suspension Feeders

    Suspension feeders rely on detritus and plankton.  The appendages and mechanisms used to capture food vary among organisms.  Filter feeding is one type of suspension feeding where small particles are removed from the water current and sorted by a filter.  Bivalves such as mussels, clams, scallops and oysters are filter feeders. Clams that burrow, and are therefore out of reach of most suspended material, use a siphon that protrudes out of the ground and brings water down to a set of filters within the shell.
 

A scallop feeding with its shells apart
A clam feeding with the help of its 
siphon coming out between its shells
 
    Annelid worms found at Argyle, such as serpulids, spirorbids, and terebellids, are also suspension feeders. Serpulids and spirorbids are worms that live inside hard, calcium carbonate tubes. The tubes are attached to the surface of rocks, shells or algae that remain submerged underwater. When feeding, these animals project tentacled structures out of the tube to catch food particles in the flowing water. By using cilia on their tentacles, these worms select particles based on size.
 
The feather duster worm in the family Serpulidae shown with its tentacles projected outside
of its calcareous tube for feeding on food material that may pass by.
 
    Barnacles are also extremely abundant at Argyle creek, found on rocks and on the shells of bivalves. Barnacles use their six pairs of articulated legs, known as cirri, for food capture.  The cirri, which collect particles using a waving and gripping motion, are protruded and retracted through two movable plates at the top of the shell.  Each branch of the legs has many setae to aid in food capture. Barnacles are not particularly selective filter feeders and are considered scavengers because they feed on dead matter as well.
 
   A barnacle using its cirri to feed.

Deposit Feeders

    Deposit feeders usually feed by consuming sediment and digesting the organic material from the surfaces of the sediment.  Terebellids, known as spaghetti worms, are sedentary burrowers that have specialized tentacles on their head used for feeding. The tentacles snake out over a surface to collect sediment particles, which are transported along ciliated grooves back to the mouth.
 

Carnivores

    Carnivorous animals feed on other animals. This was the least common method of feeding at Argyle.  Whelks and oysters, with the use of their radula and secretions from a gland in their foot, bore holes through the shells of their mollusc prey and eat the viscera.  Though not very common at Argyle, a few nudibranchs (sea slugs) were found, specifically the small nudibranch Aeolidia papillosa, which feeds on sea anemones (see Floats project).
 

The crab Cancer productus exhibiting its chelae,
specialized appendages used in feeding..

Multiple Feeding Methods

    Crustaceans use a combination of feeding methods, including detritivory, filter feeding, and predation. Crabs have a pair of appendages modified into "pincher like" structures called chelae used to capture and seize their food.  By the use of setae on certain appendages, food is captured and then brought to the mouth by other appendages.   Crabs also have specialized mouth parts to help with ingesting food.  Because their claws are modified with chelae, they can be predatory animals feeding mostly on chordates.  Crabs are also suspension feeders that eat floating detritus.  At Argyle we observed instances where more than one crab was competing for the same bivalve.  Thus, chelae may be involved in feeding, competition, and protection.
 
References: