Assessing benthic ecological status of urban sandy beaches (Northeast Atlantic, Morocco) using M-AMBI

Abstract

Rapid coastal development in recent decades has resulted in littoral environmental degradation in Morocco. Casablanca, considered as the economic metropolis driver of the country, is highly impacted by the excess of pollution rejected directly on its shores. The present study aimed at assessing, for the first time, the ecological status (ES) of urban sandy beaches using the Multivariate AZTI Marine Biotic Index (M-AMBI). Five sampling urban beaches around Casablanca [Petite Zenata (PZ), Grande Zenata (GZ), Ain Diab (AD), Sidi Abderrahmane (SD) and Sidi Rahal (SR)] were chosen so as to include a variety of stresses. They were monitored from May 2009 to April 2010 for water and sediment physico-chemical characteristics as well as for their benthic macrofauna in the saturation zone.According to water and sediment analyses, the overall pattern of environmental quality status revealed that wastewater and sewage are significant sources of urban sandy beaches pollution around Casablanca. In the first place, the PZ beach, and, secondarily, the GZ beach were evidenced as the most impacted locations. Both beaches presented high organic matter levels and faecal contamination in the water column that exceeded the human health standards. Furthermore, the total organic carbon (TOC) concentrations in sediment highlighted an evident organic enrichment, mainly at PZ beach (TOC>20%). However, metal contamination was more evident in sediment than in the water column and exceeded rarely the Severe Effect Level.The benthic macrofauna was composed of a total of 28 taxa and revealed intra- and inter-beaches variations. Reference Conditions for the M-AMBI were selected according to historical reference condition combined to expert judgment based on historical data. Globally, M-AMBI worked well on assessing the ES under eutrophication stress due to excess nutrients input. The worst ES was recorded at PZ beach with most of time in bad ES. However, the spatio-temporal changes in the ES were not usually related to the various stressors despite the significant correlations observed between the M-AMBI and some physicochemical features of water and sediment. Sandy beaches are regarded as naturally stressed environments. The wide variations in their environmental conditions make it difficult to discern natural from human-induced changes. Therefore, the “Sandy Beach Quality Paradox” concept is proposed and will certainly be evolved concurrently with the assessment of the ES of sandy beaches. This first attempt on assessing the status of urban sandy beaches of Northeastern Atlantic (Morocco) should be considered as a first step towards more comprehensive and robust evaluation of the impact of human pressures on sandy beaches.