Allele – one of the variant forms of a gene.  Variation in inherited traits (e.g., eye color) results from different alleles.

Bathymetry – measurement of water depth.

Bivalve - animal that has two shells (ex. clams and oysters).

Culture – a method for growing and maintaining microorganisms in the laboratory by providing them with appropriate nutrients.

Disease - damage to cells sufficient to cause dysfunction of the organism.  Can be caused by nutritional deficiencies, contaminants, heredity or and infectious agent.

Epizootic – a disease having an unusually large prevalence in a nonhuman population (=epidemic in human populations).

Enzootic – a disease that is low in prevalence and constantly present in a nonhuman population (=endemic in human populations).

Genetic drift – random variation in allele frequency from generation to generation.

Genotype – the genetic composition of an organism that is not displayed as outward characteristics.

Phenotype – the result of the interaction of genotype with environment – the observable traits of an organism.

Hardy-Weinberg equilibrium - The stable frequency distribution of genotypes, AA, Aa, and aa, in the proportions p2, 2pq, and q2 respectively (where p and q are the frequencies of the alleles, A and a) that is a consequence of random mating in the absence of mutation, migration, natural selection, or random drift.

Histology – the study of tissues, usually done by the microscopic examination of thin sections of tissue that have been stained.
 
Host - organism infected by another organism (ex. eastern oyster).

Infection - the presence of an infectious or foreign organism in tissues of a host.  An infection does not necessarily produce disease.

Isobath – a contour line connecting point of equal depth.

Lagrangian particle – a particle that follows the fluid motion (i.e., in the Bay), possibly with the addition of behavior.

Mollusc - very diversified group of animals that belong to the Phylum Mollusca and live in a variety of habitats from the deep-sea to moist land areas (ex. snails, clams, oysters, squid, octopus).

Mutation – a permanent change in an organism’s DNA, which may be beneficial, detrimental, or have no effect.

Natural selection – the process whereby individuals with a particular genotype leave disproportionately more offspring because of superior traits such as survival or fecundity.

Null allele - an allele whose effect is either an absence of normal gene product at the molecular level or an absence of normal function at the phenotypic level.
 
Parasite - organism that lives on or in another (termed the host) and negatively impacts the host (ex. Perkinsus marinus).

PCR – Polymerase Chain Reaction – a molecular method that permits detection of very small amount of DNA.  If the DNA being detected is that of a parasite, the presence of the parasite can be inferred, even if it cannot be observed by traditional detection methods such as histology or culture.

Protozoa - single-celled animals (ex. Haplosporidium nelsoni and Perkinsus marinus).

Refugia – in this case, we specifically refer to a location that serves as a “refuge” from disease-caused selective pressure.  That is, the host is neither killed nor is reproduction impaired by the parasite.

Salinity – salt (sodium chloride) content, by weight, of water, usually measured as parts per thousand (ppt) or practical salinity units (psu).    Full-strength ocean water is about 35 ppt or psu, which is 3.5%.  In estuaries such as Delaware Bay, salt and fresh water mix along a gradient.  Oysters can be found in salinities as low as about 5 psu, but typically live in waters of about 10 to 30 psu.

Spat – newly set oyster, up to one year of age.

Wahlund effect – a subdivided population contains fewer heterozygotes than predicted despite the fact that all subdivisions are in Hardy-Weinberg equilibrium.