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:

1. they have limited mobility and thus are unable to avoid adverse conditions;

2. their life span are long enough to reflect the effects of environmental stressors; and

3. 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.

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

Introduction continued..

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

o 25 stationso Macrobenthoso Polychaetes down

to species level o Sediment textureo TPHo 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). Benthic opportunistic 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.

1

1log

fA

fP

Results and Discussion

Hydrographical Parameters

48.8 48.85 48.9 48.95 49 49.0527.55

27.6

27.65

27.7

27.75

27.8

M anifa

Tanajib

2 0

2 1

2 2

2 3

2 4

2 5

2 6

2 7

Temperature (C)48.8 48.85 48.9 48.95 49 49.05

27.55

27.6

27.65

27.7

27.75

27.8

M anifa

Tanajib

4 14 24 34 44 54 64 74 84 95 05 15 25 35 4

Sallinity (psu)

48.8 48.85 48.9 48.95 49 49.0527.55

27.6

27.65

27.7

27.75

27.8

M anifa

Tanajib

5

5.2

5.4

5.6

5.8

6

6.2

6.4

6.6

6.8

7

DO (mg/L)

48.8 48.85 48.9 48.95 49 49.0527.55

27.6

27.65

27.7

27.75

27.8

M anifa

Tanajib

22.533.544.555.566.577.588.5

Turbidity (ntu)

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.

48.8 48.85 48.9 48.95 49 49.0527.55

27.6

27.65

27.7

27.75

27.8

M anifa

Tanajib

M edium sand

F ine sand

Very fine sand

C oarse silt

M edium silt

F ine silt

Very fine silt

C lay

Macrobenthic community Polychaetes – the dominant taxa

There was inner bay – outer bay differences in densities

Polychaetes(39%)

Crustaceans(22%)

Molluscs(29%) Others

(10%)

0

500

1000

1500

2000

2500

3000

Polychaetes Crustaceans Molluscs Others Total Macrobenthos

Inner bay Outer bay

Den

sity

(ind

. m-2

)

Taxa

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

0.00.51.01.52.02.53.03.54.0

Polychaete Species diversity

Polychaete species evenness

Polychaete Species dominance

Inner bay Outer bay

Com

mun

ity

Stru

ctur

e in

dice

s

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)

12

34

68

9

10

1112

13

15

16

17

1920

21

22

23

24

25

26

Plat iso

Exo cla

Arm int

Anc par

Das sp.

Nep dibPhy cap

Lum lat

Thar mar

Nep tul

Eun sp.1Pri pin

Ter str

Mag cin

Syl lon

Depth

Temperature

Salinity

Turbidity

MGS

-2

-1.5

-1

-0.5

0

0.5

1

1.5

-1.5 -1 -0.5 0 0.5 1 1.5

Axi

s 2

(32.

15 %

)

Axis 1 (45.60 %)

Sites Species

The inner bay stations

The outer bay stations

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).

0.00

0.04

0.08

0.12

0.16

0.20

0.24

0.28

0.32

Region

Bad

Poor

Moderate

Good

High

EcologicalStatus

Outer bay

BO

PA

inde

x

Inner bay

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.

Results and Discussion continued..

Macrobenthos comparison

Region ReferenceMean macrobenthic

density (ind. m-2)Polychaete

species richness

Bandar Mishab - Manifa

McCain (1984) 2,022 217

Safaniya - ManifaKFUPM/RI (1986)

1,989  

Safaniya - SalwahColes and McCain (1990)

4,710 271

Saudi Gulf open waters

KFUPM/RI (2003)

4,571 216

Kuwait watersAl-Yamani et al. (2009)

795 83

MTBS Present study 1,670 118

Results and Discussion continued..

TPH distribution

62.5 µg g-1

84.3 µg g-1

Results and Discussion continued..

TPH result comparison

Year ReferenceDepth in the

sediment (cm)TPH (µg g-1)

1991 Readman et al. (1996) 0-5 130

1992 Readman et al. (1996) 0-5 6900

1993 Readman et al. (1996) 0-5 460

2003 KFUPM/RI (2003) 10-20 10,000 

2005 de Mora et al. (2010) Surface 78

2006 Present study Surface up to 84

Results and Discussion continued..

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.

Thank You

King Fahd University of Petroleum and Minerals