Marine parasite diversity and environmental gradients

A brief review of our knowledge of marine biodiversity, including parasite diversity, shows that we know little, due in particular to the scarcity of studies of deep-sea and meiofaunal organisms. This chapter, after a brief discussion of older studies which established the existence of zoogeographical regions and some patterns in the geographical distribution of marine parasites, describes latitudinal gradients in parasite diversity, reproductive strategies and host ranges, longitudinal gradients in diversity (centres of diversity and oceanic barriers between them), and depth gradients. The marine environment is less heterogeneous than terrestrial and freshwater habitats, and therefore more suitable for evaluating the causes of gradients. An attempt at such an evaluation is made. Important gaps in our knowledge are discussed and suggestions are made for future studies.