This study examined the emergence behavior of Pseudodiaptomus cokeri, a demersal copepod species found in Phosphorescent Bay, Puerto Rico. Surface plankton net tows, sledge-net tows, emergence traps and hand-net tows were used to examine day/night variations in vertical distribution
associated with substratum type and lunar periodicity. Greater emergence of adult and copepodite instars of P. cokeri predominately occurred at full moon (one-way ANOVA, Fisher's PLSD, P < 0.05). Copepodites of P. cokeri emerge in greater numbers to the surface than adults
during moonlit nights, which suggests that the degree of vertical migration becomes less pronounced with age (one-way ANOVA, P < 0.05). This copepod was more common in samples from seagrass and sand + macroalgae, the two most structurally complex substrata (one-way ANOVA, Fisher's PLSD,
P < 0,05), indicating that substratum heterogeneity enhances densities of animals on the bottom.
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