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Status of macrobenthic communities in the Manifa-Tanajib Bay System (Saudi Arabia), fifteen years after the 1991 oil spill. T.V. Joydas 1* , Mohammed Qurban 1 , P.K. Krishnakumar 1 , Abdulaziz Al-Suwailem 2 , Khalid Al-Abdulkader 3 1 Center for Environment and Water, Research Institute,
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Status of macrobenthic communities in the Manifa-Tanajib Bay System (Saudi Arabia), fifteen years after the 1991 oil spill T.V. Joydas1*, Mohammed Qurban1, P.K. Krishnakumar1, Abdulaziz Al-Suwailem2, Khalid Al-Abdulkader3 1Center for Environment and Water, Research Institute, King Fahd University of Petroleum and Minerals, Dhahran, Saudi Arabia. 2Marine Core Lab, King Abdulla University of Science and Technology, Thuwal, Saudi Arabia. 3Environmental Protection Department, Saudi Aramco, Dhahran, Saudi Arabia. Email: tvjoydas@kfupm.edu.sa
Introduction • 1991 oil spill heavily affected the shallow waters of the Saudi coast. • Long term effects on the shallow coastal bays. • Manifa – Tanajib Bay System (MTBS) is one among that. • In 1992: up to 6,900 µg g-1 of TPH from the surface sediment in Manifa Bay (Readman et al., 1996). • A consistent reduction in contamination of the bays in the subsequent years. • A study (year 2005) showed moderately polluted (78 µg g-1 of TPH) (de Mora et al., 2010) status in MTBS (de Mora et al., 2010).
Introduction continued.. Importance of benthos • An important role in nutrient recycling and secondary production. • Macrobenthos are good indicators of ecosystem health as: • they have limited mobility and thus are unable to avoid adverse conditions; • their life span are long enough to reflect the effects of environmental stressors; and • their communities are taxonomically diverse enough to respond to multiple types of stress. • Thus, changes in the taxonomic composition, abundance and biomass of macrobenthic organisms can be used to determine the response to several kinds of anthropogenic disturbances.
Introduction continued.. Inner bays • Hyper salinity (over 55 psu) • Extreme temperature variation (18 – 36 oC) • Weak water circulations • Shallow water (<3 m) • Outer bays • Seagrass and coral reefs • Deeper (>3 m) Spawning and nursery ground
Objectives • To assess the status of the macrobenthos from MTBS • To test whether any distinction in macrobenthos exists in the inner bays from the rest of the bay area, and • To identify the impact of principal environmental variables and the residual impact of 1991 oil spill , if any, on the macrobenthic communities.
Materials and Methods Sampling: April 2006 • 25 stations • Macrobenthos • Polychaetes down to species level • Sediment texture • TPH • Hydrography
Materials and Methods continued.. Data Analyses • Univariate, multivariate and graphical methods of PRIMER 6 for Windows. • Canonical Correspondence Analysis (CCA, ter Braak and Verdonschot, 1995) using XLStat (Version 2009.6.01, Addinsoft). To assess the health of the benthic community: • Abundance Biomass Curve (ABC). • Benthicopportunistic polychaetes amphipods index (BOPA) (Dauvin and Rullet, 2007). BOPA index where, fP is the ratio of the total number of opportunistic polychaetes individuals to the total number of individuals in the sample; fA is the ratio of the total number of amphipod individuals excluding the opportunistic Jassa amphipods to the total number of individuals in the sample.
Results and Discussion Hydrographical Parameters
Results and Discussion continued.. Sediment Characteristics • Inner bays: sandy at their openings; tends to finer inwards. • Outer bay: sandy in the shallow while silt/clay in the deeper offshore (>5m). • Coarser in the Manifa; finer towards Tanajib.
Results and Discussion continued.. Macrobenthic community • Polychaetes – the dominant taxa • There was inner bay – outer bay differences in densities
Results and Discussion continued.. Polychaete Community Structure • 118 polychaete species (Inner bay- 54; Outer bay 105) • Shannon – Wiener (H')(Log2) ≥3 in 64% of the stations
Results and Discussion continued.. Polychaete Community Structure continued.. • Distinct polychaete communities as per nMDS. • ANOSIM showed inner bays–outer bay dissimilarity (Global R = 0.62; P<0.001).
Results and Discussion continued.. Polychaete Community Structure continued.. Canonical correspondence analysis (CCA)
Results and Discussion continued.. ABC plots • Unpolluted: Stable community - biomass dominant • Polluted: opportunistic - numerically dominant • Biomass K-dominance curve lies above the abundance curve indicates a healthy community condition.
Results and Discussion continued.. BOPA index • 80% of the stations have high ecological status – unpolluted status • 20% of the stations have good ecological status – slightly polluted status (stations 4, 8, 11, 14 and 23). • In the slightly impacted sites …. • Low colonization of oil sensitive amphipods (0 – 80 ind. m-2). • Abundance of opportunistic polychaetes, Dasybranchus sp. (580 ind. m-2 at station 8) and Tharyx marioni (250 ind. m-2 at station 23) were observed.
Macrobenthos comparison Results and Discussion continued..
62.5 µg g-1 84.3 µg g-1 Results and Discussion continued.. TPH distribution
Results and Discussion continued.. TPH result comparison
Conclusion • Healthy status of the polychaete communities. • Due to hyper salinity the inner bay benthic communities were distinct. • This effect is different from the residual impact of 1991 oil spill. • Slightly polluted status (BOPA index) was noticed both in the inner bays and the outer bays. • There is not sufficient evidence to prove that the residual impact of 1991 oil spill is more pronounced in the inner bays. • The oil sensitive amphipods were not completely re-colonized in 20% of the stations, even after 15 years of the 1991 oil spill.
