Sukumaran Etal.2014.Impact of Oil Spill on Tidal Pool Macrobenthic Communities of a Tropical Rocky Shore - InDIA
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Impact of Chitra Oil Spill on Tidal Pool MacrobenthicCommunities of a Tropical Rocky Shore (Mumbai, India)
Soniya Sukumaran & Jyoti Mulik & M. A. Rokade &Archana Kamble
Received: 1 August 2013 /Revised: 11 February 2014 /Accepted: 15 February 2014# Coastal and Estuarine Research Federation 2014
Abstract A collision between the ships MSC Chitra andMV Khalijia 3 in the mouth region of Mumbai Harbourled to a leakage of around 800 t of fuel oil in August2010, affecting the rocky intertidal region of Colaba. Toevaluate the impact of this catastrophic event on theresident biota, a 15-month-long sampling programmewas initiated in the oil-affected area immediately afterthe spill. Petroleum hydrocarbons in water and sedimentorganic carbon values were high just after the oil spillbut subsequently decreased in the following months. Intotal, 70 macrobenthic taxa were identified. Univariatediversity indices indicated that while the ecological sta-tus of the site, albeit briefly, was affected during August2010, a healthy environment prevailed subsequently.Cluster and multi-dimensional scale (MDS) analysesdistinctly segregated the oil impacted monsoon monthsfrom the other sampling months. BIOENV analysesindicated that petroleum hydrocarbons and organic car-bon were the anthropogenic parameters influencingmacrobenthic community structure. Benthic Opportunis-tic Polychaetes Amphipods (BOPA) index was used toevaluate the ecological quality of the study area as theindex is sensitive to oil pollution. Low BOPA valuesthroughout the study period indicated that the environ-ment was good with few opportunistic species. Compar-ison with past data revealed that the oil spill did nothave long-term deleterious effects on the macrobenthicspecies diversity of this rocky beach, and reasons there-of are discussed.
Keywords Oil spill . Rocky shore . Tropical . Benthos . Tidalpools
Notwithstanding the tremendous strides made in shiptechnology and international regulatory initiatives, oilspills keep occurring more so in the developing world(Islam and Tanaka 2004; Sivadas et al. 2008) especiallyon shores along major shipping routes (Thompson et al.2002). Indian west coast, in particular, is vulnerablyexposed to oil accidentally or clandestinely released inthe Arabian Sea largely during the southwest monsoonmonths (JuneSeptember) when the alongshore surfacecurrent develops an easterly shoreward component(Gouveia and Kurup 1977). Mumbai, a major commer-cial hub, is located on the western coast of India andhas been vulnerable to oil pollution due to the presenceof a harbour and major oil terminal. A collision oc-curred between the ships MSC Chitra and MV Khalijia3 in the mouth region of Mumbai Harbour (18 51 99N 72 49 03 E) on 7 August 2010. Subsequently, therough sea conditions resulted in the drifting of MSCChitra which then ran aground on the Prongs reef offColaba (Fig. 1), leading to a leakage of around 800 t offuel oil (NIO 2011). Despite the efforts of the IndianCoast Guard to contain the spill, it quickly covered vastareas in the Mumbai Bay and sites along the open coastsouth of the Bay aided by a combination of strongsouthwest winds and monsoonal onshore currents. Theoil spill covered an area of 20 km2 up to Vashi in theinner Mumbai Bay. An initial survey conducted by theNational Institute of Oceanography indicated that con-centration of oil in water at some subtidal stations inthe Bay reached as high as 16,902 g l1. These values,
Communicated by Marianne Holmer
S. Sukumaran (*) : J. Mulik :M. A. Rokade :A. KambleRegional Centre Mumbai, CSIR-National Institute of Oceanography,Mumbai 400 053, Indiae-mail: firstname.lastname@example.org
Estuaries and CoastsDOI 10.1007/s12237-014-9791-8
however, reduced to lower levels within a short periodafter the oil spill (NIO 2011).
Due to its proximity with the accident site, Colaba coastwas one of the earliest segments to be significantly coated bythe oil spill (Fig. 1). Colaba, situated on the southernmosttip of Mumbai, has a rocky beach which supports di-verse marine biota including well-developed corals. De-spite being a part of Mumbai Metropolitan Region(MMR) which is the largest coastal urban settlement inIndia, the biodiversity of the Colaba zone is preservedprimarily due to its non-accessibility owing to its uniquelocation (Fig. 1). Previous biological studies in therocky intertidal of Colaba include descriptions ofmacroalgae (Dhargalkar and Komarpant 2003) and epi-fauna (Datta et al. 2010). Both accounts indicate thediverse nature of ecological communities of the area.
Marine macrobenthos has been widely employed to studythe impact of environmental perturbations including oil spills(Guidetti et al. 2000), as they are the species-rich, ubiquitousgroup consisting of both sensitive and hardy organisms withrelatively long life span. Being predominantly sessile, theyare exposed to sediment contamination and have variedresponse to stress depending on the species hardiness(Gesteira and Dauvin 2005). While many ecologicalhealth status indicators and indices based on variationsin macrobenthic community have been proposed(Dauvin et al. 2010), the Benthic Opportunistic Poly-chaetes Amphipods (BOPA) index is widely used for
determining the impact of oil spill on benthic commu-nities in coastal waters (Dauvin and Ruellet 2007;Joydas et al. 2012).
Given that intertidal zones are under greatest threat from oilpollution, studies galore have been conducted on the adverseeffects of oil spills on intertidal macrobenthic communities intemperate latitudes (Hir and Hily 2002; Yamamoto et al. 2003;Junoy et al. 2005; Lv et al. 2011). Reported impacts of an oilspill on rocky intertidal macrofauna include smothering oforganisms by oil (Shriadah 1998), disruption of settlementof juveniles (Nelson 1982), change in recruitment, growthand community structure, reduction in species diversity (Hirand Hily 2002; Crowe et al. 2000) and annihilation of sensi-tive species (Yamamoto et al. 2003; Stevens et al. 2012).However, only limited information on the immediate-to medium-term effect of an oil spill on macrobenthosof rocky intertidal area in the tropics is available (butsee Jones et al. 1998; Edgar et al. 2003; Stevens et al.2012). Also, few oil spill-related impact assessmentstudies on macrobenthos (Ingole et al. 2006; Sivadaset al. 2008) are available for the 5,700 km long Indiancoastline. Biological diversity is higher in tropical zones(Wafar et al. 2011), and therefore the impact of oilpollution on such regions may be higher as comparedto other areas (NAS 1985; Agard et al. 1993).
The Chitra oil spill presents an opportunity to study theimpact of oil pollution on the benthic ecology of sedimentedintertidal rocky pools in a tropical clime. The objective of the
Fig. 1 Location of the study site at Colaba, west coast of India
Estuaries and Coasts
present investigation was to evaluate the impact of the oil spillon the resident macrobenthos of a relatively clean rockybeach subsequent to the oil spill using a suite of uni-variate and multivariate analyses. As impacts of oil spillmay manifest over a few months after the episode(Stevens et al. 2012) and to account for seasonal im-pact, monitoring of the selected site was conducted forover 15 months. Also, we compare the present macro-faunal data with that obtained in the same study areaprior to the oil spill (Datta et al. 2010) to comprehendthe extent of ecological damage caused by the spill.
Material and Methods
Colaba is located near the southernmost tip of Mumbai. Thestudy area (18 54 19.6 N 72 48 12.2 E) is located in arocky intertidal area known as Prongs reef (Fig. 1). Theirregular rocky area of 0.5 km2 which gently slopes towardsthe sea entraps several water pools during ebb. These tidalpools with sandy bottoms provide an ideal environment formarine organisms. The climate of the study area is typicalof that of the central west coast of India with plentifuland regular rainfall occurring during JuneSeptember,oppressive summer (MarchMay) and a mild winter(DecemberFebruary). General coastal circulation offColaba is dominated by the annual cycle of monsoonwinds. Near shore waters of Colaba are subjected main-ly to semi-diurnal tides, and there exists an asymmetryin both period and range. The flood tidal front advancesin a northeasterly direction and ebbs towards the south-west. Mean tide ranges at Mumbai are 1.6 and 3.9 mduring neap and spring, respectively.
The Colaba site was entirely covered by oil in August 2010.The study site is unique as it is the only coralline intertidal areaalong the Mumbai coast. Being a restricted area, there is onlylimited access to the shore; therefore, human interference ispractically nil. Other rocky shores of Mumbai which were notimpacted (North Mumbai) are not coralline and are heavilyfrequented by people and therefore polluted to various levels.Therefore, no reference station could be established. Samplingat Colaba commenced on 13 August 2010 by which time thespill had covered the upper and middle intertidal zones to asignificant extent while the lower intertidal zones had little orno traces of oil contamination. Upper intertidal zone wascovered by concrete tripods for protection against seaerosion, while the lower intertidal area was inaccessibledue to the strong monsoonal waves. Sampling locations
preferred were the sedimented tidal pools in the heavilyoiled middle intertidal areas as it was observed duringthe initial sampling (August 2010) that oil was mostprevalent in these areas. For macrobenthic analyses,monthly, four sediment samples were collected fromfour different rocky tidal pools situated within a radius~300 m. All rocky pools were shallow (water depth~1020 cm) with sandy sediments (thickness ~510 cm). The co-ordinates were fixed using