Biota Interactions for Ecological Assessment of a Deteriorated Coastal Lake following a Brief Period of Restoration

Abstract

The coastal lake, Maruit, was one of the most productive coastal ecosystems in Egypt until the 1960s. It experienced long-term deterioration due to continuous discharge of pollutants from Alexandria city into its basins. The Egyptian government started a restoration program in 2010 to divert pollution sources away from the lake. Samples were collected in November 2012 to assess the biological condition of Lake Maruit using parasitism and predation as biological linkages between pelagic and benthic communities. A preliminary survey of ectoparasites infesting tilapia fish was carried out during this study. Ectoparasites that were retained from 300 sampled tilapia fish were identified. Two groups of platyhelminth ectoparasites, Monogenea, Cichlidogyrus sp., and the parasitic-copepod, Ergasilus lizae, were detected. Ectoparasite Platyhelminthes infected the fish Oreochromis niloticus and O. aureus, whereas the crustacean parasitized Coptodon zillii. The parasitic prevalence was 15% and 3% for Cichlidogyrus sp., and Ergasilus lizae, respectively. Benthic biotas were similar among basins, which could indicate successful restoration. The lack of response of fish abundance to benthic biotic components indicates few direct trophic links. Phytoplankton and benthic microalgae were not the main fish diet. It was found that Halacaridae and fish data clustered, suggesting either Halacaridae are simply responding like fish or that fish are preying on them because they have a relatively large size. Unexpectedly, linear connections between the populations of biota and the parasite-infected fish were found, suggesting that parasites may control the behavior of their hosts. Organic matter concentration was the main driver of the lake ecosystem biota. While the low parasitism rate and lack of eutrophication is evidence of recovery, the low biota abundance, lack of fish and faunal diversity, and limited linkage among food web components indicate the restoration was incomplete or Lake Maruit was still suffering from degradation in 2012.