These are year round inhabitants of the mudflats in Corophium volutator nearby areas.
Class: Malacosstraca Order: Amphipoda Family: Corophiidae Genus: Corophium
A female Corophium shown in its protective U-shaped burrow. Photo: Jim Wolford Distribution They occupy both sides of In North America, this specific species Corophium volutator occurs the North Atlantic on the only in the Bay of Fundy and the Gulf of Maine. In Europe they American and European occur from Scandinavia to the Mediterranean. coasts.
This amphipod (not a true shrimp) occupies semi-permanent Habitat U-shaped burrows in the fine sediments of mud flats, salt marsh They tolerate a wide range pools and brackish ditches. When present in high densities the of salinities from nearly openings of the burrows are clearly visible on the surface of fully saline to almost fresh their habitat. water.
They have different methods of feeding. Two methods may Food occur simultaneously; deposit and suspension feeding. Sediment They ingest particulate particles are retained and passed into mouth parts. Another matter, organic detritus and method is scraping organic material off the surface of sediment. diatoms. They feed at all Food must be of an appropriate size. There are seasonal stages of the tidal cycle. variations in what they consume. Diatoms (single-celled plants) flourish in the summer months.
Reproduction Males initiate courtship. Males may visit as few as two burrows or as many as 18 before The timing of this is very choosing one. Conflict may occur between males when a burrow important. They emerge is entered already occupied by another single male or a paired from their burrows on female and male. The male occupant will push the intruder away ebbing tides. During this from the entrance by interlocking his second antennae with the window of opportunity other male’s antennae. Females often station themselves at the they search for mates. mouths of their burrows for assessment by visiting males. Males Females by far outnumber run their long antennae back and forth along the undersides of males and several of their females; this may help determine their reproductive condition. burrows are investigated He makes his decision and enters her burrow. before a choice is made.
Development The number of eggs the female produces varies with her size. The bearing of young by The average is 38 but can reach 172. Most females don’t become amphipods in general is gravid until they are larger than 6 mm in length. The round eggs somewhat similar to are a creamy white and surrounded by a thin, flexible membrane. marsupials. The eggs are Over a period of two weeks the eggs divide repeatedly to form deposited into a pouch-like embryos in which limbs and eyes become visible. Amphipods go brood sac. Sperm released through “direct development”, the egg hatches out a miniature by the male enters this sac version of the adult. Once fully developed they break free from and the eggs contained the protective membrane. Newly hatched animals are 1.0 mm within become fertile. long. Male and female Characteristics The male and female antennae differ The mud shrimp has a long significantly. There are seven pairs of slender body that is whitish segmented legs with the top segment with brown markings. It has of each being typically small and separate from that of the next segment. a clearly segmented, dorso- ventrally flattened body. The head is small with two pairs of forward pointing antennae. As with all amphipods they have a stiff, chitinous exoskeleton. They can grow to 11 mm.
Adaptations Burrows The entire body is divided Small limbs towards the front are used in capture, handling and into a series of short ingestion of food. Attached at the base of these feeding limbs tubular segments. Each are small flaps which absorb oxygen from water flowing over segment has a pair of them. Some of the feeding limbs have long, fine bristles or jointed limbs. Small groups "setae" which overlap to form a filtering basket. Particles are of these perform a variety trapped on the mesh; desirable ones are moved forwards to the of functions. Sturdy, mouth. Here they are crushed between the grinding mandibles. flexible joints between Further along the thorax (body) are several long, flexible walking segments allow them to legs. Towards the rear or abdomen are small, feather-like limbs straighten or bend into a used when swimming. These also create a current of oxygenated ball. The head bears two water over the flaps or “gills”. The broad, flat tail segment pairs of long, flexible, (telson) and small uropdos form a broad tail fan used to provide sensory antennae. backward movement away from predators.
Status/Threats Severe weather conditions (storms and ice build up) kill off large Over a six week period numbers. By far the greatest threat is disruption of habitat. They huge numbers of these are are vulnerable to toxic materials washing into their marine consumed every year by environment. Organic wastes, pesticides, crude oil, heavy metals, migrating shorebirds. etc. contaminate the sediments these animals feed on. Mud flats Fish also are predators. in estuaries near urban areas are affected. Any form of commercial harvesting on the mudflats has negative impact. Sightings in Nova Scotia Bay of Fundy mudflats Also the mudflats of the Minas Basin.