New Jersey’s At-Risk Populations; Episode 7: The Yellow Lampmussel
The shell, well worn, of the Yellow Lampmussel.
Source: Daderot at Wikimedia Commons
Yellow Lampmussels (Lampsilis cariosa) are medium-sized freshwater mussels that have bivalve shells, meaning their two shells are hinged together. The males have a more elliptical and elongated shell while the females have a more egg–shaped shell. The shells are moderately inflated and thick. The outer shell is smooth, usually yellow with some brown patches while the inner shell, or the nacre, is a white to bluish-white color. Yellow Lampmussels can be found from Georgia up to the Lower Ottawa River in Canada, but in New Jersey, they are only found in the Delaware River from Mercer County to Sussex County.
The adults filter feed off of plankton, bacteria, and other particles straight from the water. This is actually a tremendous benefit to the ecosystem as freshwater mussels are one of the only species that filter the water and improve the quality of it. Yellow Lampmussels are also a part of the diets of many other animals including raccoons, muskrats, otters, bears, herons, some waterfowl, some turtles and large fish like sturgeon. In addition, the glochidia (larval Yellow Lampmussels) are eaten by many small aquatic animals.
Unlike many mollusks that are hermaphrodites (possessing both male and female genitalia), freshwater mussels typically have separate sexes; and the Yellow Lampmussel is no exception. The males, during spawning, release sperm into the water. If a mature female happens to draw the sperm into her shell, her eggs will be fertilized. The eggs will develop within her gills until they fully mature into the larval stage known as glochidia. This development phase could last anywhere from just a few days all the way to several months. Upon full development, millions of glochidia are released into the water through the female’s external siphon.
Still microscopic, the glochidia have a thin shell with two valves. To survive, they must find a host to feed off. Yellow Lampmussel larvae prefer Yellow and White Perch. They will attach to the body, gills, or even the eyes. While adhering to the fish, the glochidia undergo metamorphosis into juvenile mussels, which happen to resemble miniature versions of the adults. This conversion may take anywhere from 6 to 160 days. Once complete, the juvenile mussel will release itself from the host fish. Hopefully it will land in a suitable substrate, although they are capable of moving some short distances using their powerful foot. Then the juvenile mussel will burrow into the bottom sediment and spend its first year there.
Young Yellow Lampmussels grow fast and reach sexual maturity around six years of age and may live for about a century. During the winter, they will, again, burrow into the substrate and lay dormant.
A well preserved example of the Yellow Lampmussel shell.
Source: Conserve Wildlife Foundation of New Jersey at ConserveWildlifeNJ.org
Already one-tenth of all North American freshwater mussel species have gone extinct, just in the past 100 years. Of the remaining species, 75 percent are currently in peril. Habitat loss and invasive species, such as Zebra Mussels and Asian Clams, are the biggest threats to freshwater mussel survival. Overall, the Yellow Lampmussel is listed as endangered, however, in New Jersey, the current Yellow Lampmussel population is merely considered threatened, and has been since 2002, which is slightly better than endangered. The ultimate reasoning behind the threatened status is that, despite having a sufficient population size, the Yellow Lampmussel is solely endemic to the Delaware River in New Jersey, which makes them incredibly vulnerable as a species.
The primary causes of lost habitat are dam construction, other in-stream channelization projects, and dredging through sediment and contaminants. Dams impact the environment of the entire waterway, including physically, chemically, and biologically. Occasionally, the mussel populations are diminished by 30-60 percent, both upstream and downstream from the construction of dams. Perhaps the most damaging effect from the dams is the elimination of host species. This disrupts the breeding cycles of the mussels, as the glochidia cannot develop into mature individuals. Erosion causing the stream bottoms to shift and increased silt loads alter the environment, too, thus hindering the mussels’ persistence in the region. Heavy metals, pesticides, and sewage discharge from treatment plants, as well as other contaminants, also harm the environment for the mussels. Zebra Mussels are the primary invasive species threatening the existence of the Yellow Lampmussel population, as they compete for the same food and space.
Currently, surveys are still being conducted every spring, summer, and fall to determine special distributions, population sizes, and age distributions. Recent surveys indicate that more surveying should continue. Additionally physical barriers preventing the movement of host fish and glochidia need to be explored and noted, so that the reproductive cycles can be completed and the species can persist. Measures to prevent unnecessary habitat loss and environmental contamination are already in place under federal and state Clean Water acts, stream encroachment rules, environmental reviews of proposed development projects, and the New Jersey Endangered Species Act. Right now, there is even a Freshwater Invertebrate Project being conducted in New Jersey to gather data about invertebrates, including mussels, and to enact protective efforts. Stream bank restoration projects and barriers along streams are being built to negate any habitat loss as well as to prevent any more of it. Lastly, it is being urged that the protection classification of streams with endangered and threatened mussel species be upgraded so that the water quality could be better protected. So long as this course is continued, the proper response to ensure that the Yellow Lampmussel remains a part of the New Jersey fauna can be determined and enforced.