The Effect of Tidal Cycles on the Community Structure of Plankton (with Emphasis on Copepods) at Afmed Marina in Winter (A Preliminary Study)

Abstract

Tidal cycles had no significant effect on the abundance or community structure of plankton at AFMED (Aquaculture, Fisheries and Marine Environment Department) Marina, nor had any physicochemical factor, except salinity, on the density of copepods (p < 0.05), although variation in the physichochemical data measured was small. The major components of the plankton community throughout the study were copepods, Noctiluca spp. (mostly N. scintillans (Macartney) Kofoid & Swezy), and cirripede nauplii. Their abundance differed between high and low tides throughout the study. Variation between high and low tides was also observed among the various groups and species of copepods. MDPs (Mean Density Percentages) of calanoids, copepod nauplii, and poecilostomatoids were higher at high tide (45%, 20.09%, and 2.81%, respectively), while cyclopoid and harpacticoid MDPs were higher at low tide (30.63% and 9.95%, respectively). The most dominant copepods were Parvocalanus crassirostris (F. Dahl, 1894), Paracalanus spp., Oithona simplex Farran, 1913, Euterpina acutifrons (Dana, 1847), Oncaea spp., and Corycaeus spp. The copepods with the highest MDPs at high tide were Parvocalanus crassirostris (14.19%), Paracalanus spp. (10.79%), Oncaea spp. (1.75%) and Corycaeus spp. (1.06%), respectively, while Oithona simplex and Euterpina acutifrons had a higher MDP at low tide (14.97% and 9.12%, respectively). The highest MDP at low tide was that of Oithona simplex. Neither tide nor any other factor measured had a significant effect on any of the copepods. Other, related factors (mainly biological and anthropogenic) may thus have accounted for the differences in abundance and biodiversity observed.