Transcript Status of macrobenthic communities in the Manifa

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: [email protected]
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.
2.
3.
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
o 25 stations
o Macrobenthos
o Polychaetes down
to species level
o Sediment texture
o TPH
o 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
 fP

 log 
 1
 fA  1 
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
Tanajib
Tanajib
54
53
52
51
50
49
48
47
46
45
44
43
42
41
27.8
27.75
27.7
27.65
27.6
Manifa
Sallinity (psu)
27.55
48.8
48.85
48.9
48.95
49
27.8
27
26
27.75
25
27.7
24
23
27.65
22
27.6
27.55
21
Temperature (C)
48.8
49.05
Tanajib
48.85
48.9
Manifa
20
48.95
49
49.05
Tanajib
7
27.8
8.5
8
7.5
7
6.5
6
5.5
5
4.5
4
3.5
3
2.5
2
27.8
6.8
6.6
27.75
27.75
6.4
6.2
27.7
27.7
6
5.8
27.65
27.65
5.6
5.4
27.6
Manifa
DO (mg/L)
5
48.85
48.9
48.95
Manifa
5.2
27.55
48.8
27.6
49
49.05
Turbidity (ntu)
27.55
48.8
48.85
48.9
48.95
49
49.05
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.
Tanajib
27.8
27.75
27.7
Clay
Very fine silt
Fine silt
27.65
Medium silt
Coarse silt
27.6
Very fine sand
Manifa
Fine sand
Medium sand
27.55
48.8
48.85
48.9
48.95
49
49.05
Results and Discussion continued..
Macrobenthic community
 Polychaetes – the dominant taxa
Molluscs
(29%)
Others
(10%)
Crustaceans
(22%)
 There was inner bay – outer bay
differences in densities
Polychaetes
(39%)
Density (ind. m-2)
3000
Inner bay
2500
Outer bay
2000
1500
1000
500
0
Polychaetes
Crustaceans
Molluscs
Taxa
Others
Total
Macrobenthos
Results and Discussion continued..
Polychaete Community Structure
Community
Structure indices
 118 polychaete species (Inner bay- 54; Outer bay 105)
 Shannon – Wiener (H') (Log2) ≥3 in 64% of the stations
4.0
3.5
3.0
2.5
2.0
1.5
1.0
0.5
0.0
Inner bay
Polychaete Species
diversity
Outer bay
Polychaete species
evenness
Polychaete Species
dominance
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)
1.5
1
Axis 2 (32.15 %)
25
Phy cap
Nep dib
Anc par
26
0.5
6
The inner bay
stations
MGS
Temperature Das sp.
8
Depth
0
Pri pin Eun sp.117
21 Ter str 19
Nep tul
24 Exo cla 20
3
1
4
22
2
Lum lat
10
Mag cin
Thar mar 23
-0.5
-1
-1.5
Arm int
-1.5
-1
-0.5
9
16
Turbidity
13
0
0.5
Axis 1 (45.60 %)
Sites
Salinity
12
11
Syl lon
The outer bay
stations
-2
Plat iso
15
Species
1
1.5
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).
Ecological
Status
0.32
Bad
0.28
0.24
BOPA index
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.
Poor
0.20
Moderate
0.16
0.12
Good
0.08
0.04
High
0.00
Inner bay
Outer bay
Region
Results and Discussion continued..
Macrobenthos comparison
Mean macrobenthic
density (ind. m-2)
Polychaete
species richness
McCain (1984)
2,022
217
Safaniya - Manifa
KFUPM/RI
(1986)
1,989
Safaniya - Salwah
Coles and
McCain (1990)
4,710
271
Saudi Gulf open
waters
KFUPM/RI
(2003)
4,571
216
Kuwait waters
Al-Yamani et al.
(2009)
795
83
MTBS
Present study
1,670
118
Region
Reference
Bandar Mishab Manifa
Results and Discussion continued..
TPH distribution
62.5 µg g-1
84.3 µg g-1
Results and Discussion continued..
TPH result comparison
Depth in the
sediment (cm)
TPH (µg g-1)
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
Year
Reference
1991
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.
King Fahd University of Petroleum and Minerals
Thank You