Terrestrial epiphytes are most diverse and abundant in neotropical forests that experience year-round humidity and no frosts. Diversity is lower in the palaeotropics (possibly due to historical aridity), and decreases at higher altitudes and latitudes, but epiphytes can still be important in temperate forests with oceanic climates. Aquatic epiflora are found virtually everywhere their host macro-phytes exist, that is, on sunlit surfaces free of sessile animals or destructive grazers. Epiflora are often abundant in eutrophic waters.
Epifauna occur in all aquatic environments: in lakes and rivers, from the intertidal to ocean trenches, and from tropical to polar latitudes. Densities are usually highest where there is strong net water movement supplying food for filter-feeders. Strong light supports algal growth, which benefits mobile epifauna that eat periphyton, but not sessile epifauna, which are often susceptible to being overgrown. On soft sediments, epifaunal densities tend to decline with increasing depth due to the reduction in food input from the sunlit surface waters, though densities can be locally high where detritus accumulates. Sessile epifauna are often delicate and long-lived, so are vulnerable to physical disturbances like dredging and trawling.
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