Assessing potential recovery of shore biotic assemblages following cessation of raw sewage input

Abstract

The presence of the raw sewage outfall at Wied Ghammieq resulted in a pollution gradient along the coast on moving away from the discharge point towards Zonqor Point (Marsascala). Such nutrient enrichment impacted the rocky shore biotic assemblages. Following cessation of discharge of raw sewage in 2011, recovery of the biotic assemblages is expected, whereby the impacted site, Wied Ghammieq, would exhibit environmental characteristics similar to those of unpolluted sites. In 2015, Attard (2016), indicated partial but not complete recovery of the mediolittoral zone biotic assemblages. The aim of the present study was to establish potential further recovery of rocky shore intertidal assemblages at the same four locations studied by Attard (2016). Apart from the same four locations used in Attard (2016)’s study, a further location was used in the present study to assess potential nutrient enrichment that may be resulting from the underwater pipeline that extends 1 km out to sea and carries effluent that originates at the Ta’ Barkat STP. Sampling was carried out using a 20 cm x 20 cm quadrat within the Lower Mediolittoral Zone (LMZ) and Upper Mediolittoral Zone (UMZ) at two sites allocated to each of the five study locations. The results of univariate PERMANOVA tests from the present study indicated that values of the four biological attributes under study: total abundance, number of faunal families, Shannon-Wiener and Pilou’s Evenness, were significantly different between some locations for biota in the LMZ. Mean values for number of faunal families at Location 1 were slightly lower than at the other locations but no significant differences were indicated. Significant differences were detected for mean total algal biomass and mean number of algal species amongst the study locations. An increase in the number of faunal families and total faunal abundance for UMZ biota was detected on moving away from the former discharge point; the results of statistical analyses indicated a significant difference for the mean number of families between the five study locations. The results of multivariate PERMANOVA showed no significant differences in the four attributes of biota within the LMZ between the five study locations. Overall, the results of the present study indicated partial recovery in LMZ biotic assemblages and possible complete recovery in UMZ biotic assemblages, which seems to indicate that the sewage outfall may have affected the LMZ biota more than the UMZ biota. Furthermore, localized potential nutrient enrichment may be present at Location 5, which may possibly be due to the influence of the effluent originating from the STP at Ta’ Barkat.