Abstract
A qualitative and quantitative study on the epiphytic microalgae and epiphytic zooplankton were conducted in order to follow up their community structures on seaweeds in relation to some physico-chemical variables in the coastal waters of the Eastern Harbor of Alexandria. Water and macroalgal samples were collected seasonally during two years successively: Winter, summer, autumn (2012) and spring (2013). The collected seaweeds were Ulva fasciata (green alga), Corallina mediterranea, Corallina officinalis, Gelidium sp., Pterocladiella capillacea, Hypnea musciformis and Grateloupia doryphora (red algae). The studied water quality parameters were pH, salinity, dissolved oxygen, oxidizable organic matter and nutrient salts. The abundance of epiphytes were significantly different between morphotypes (two-way ANOVA), p≤0.05; ranking the branched thalli as the first preference for microalgal epihytes, sheet-like thalli with a smooth surface as the second one, while the lowest rank was for the mucilaginous species. The same result was found for epiphytic zooplankton. The results of the statistics revealed insignificant seasonal variations in the epiphytic microalgae and very weak correlations between the abundance of microalgae and the physico-chemical parameters. In contrast, there were significant differences for epiphytic zooplanktonic seasonal variations. Whereas, the zooplankton count was correlated preferably with environmental water salinity, followed by nutrients.
Highlights
Epiphytism is a widespread phenomenon in marine benthic communities, especially in the rocky intertidal zone (Kraberg and Norton, 2007)
Free living nematodes were dominant on C. officinalis (62%) but retrograded on C. mediterranea (30%) and co-dominated with the copepod Euterpina acutifrons and its larvae to form the main bulk of epiphytic zooplankton community (Table 6 and Fig. 6)
The abundance of epiphytes were significantly different between morphotypes, p≤ 0.05; ranking the branched thalli (C. mediterranea, C. officinalis, Gelidium sp., H. musciformis and P. capillacea) as the first preference for microalgal epihytes, sheet-like thalli with smooth surface (U. fasciata) as the second one, while the lowest rank was for the mucilaginous species G. doryphora, which was based on the average of the total count of each group
Summary
Epiphytism is a widespread phenomenon in marine benthic communities, especially in the rocky intertidal zone (Kraberg and Norton, 2007). Algal epiphytes play an important role in coastal benthic communities. They provide potential for mutualistic interspecific associations (Stachowicz and Whitlatch, 2005), as well as food and habitats for animals and they are considered as primary producers in the food chain (Danilov and Ekelund, 2000). They enter the second level of the food chain when they are grazed by invertebrates (Navarro, 1987). They enter the second level of the food chain when they are grazed by invertebrates (Navarro, 1987). Moncreiff et al (1992) reported that the production of epiphytic algae often exceeded that of macroalgae and seagrass itself
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