Four sites following the salinity gradient of the Incomati River Estuary E1 (0-3NST), E2 (3-5NST), E3 (6-18NST) and E4 (19-27NST) were selected for the study. The aim of the study was to use free-living marine nematodes as pollution indicators in an area strongly affected by anthropogenic activities. Multivariate statistical analyses were used to determine the relationship between different environmental factors and with free-living marine nematodes. Metals such Cadmium, Colbat, Chromium, Copper, Iron, Manganese, Nickel, Vadium, Zinc and Aluminium influenced the diversity and density of free-living nematodes. Shannon-Wiener Diversity, Maturity Index and colonize-persisters percentage (c% - p%) were found to be good tools for use as pollution indicators in the study. Nematode genera such as Terschellingia, Theristus and Halalaimus were found to be dominant at a site strongly impacted by both metals concentration and organic matters. The three genera are believed to be good indicators of pollution in the Incomati River Estuary. It is recommended that further studies are done along the Mozambican Coast to identify nematodes that can be used as pollution indicators.
The Incomati River Estuary is prone to anthropogenic activities such as agricultural and industrial effluents from the upper catchments of the Incomati Basin. The presence of impoundments and abstraction taking place in the upper catchment reduces the flow regime, therefore, resulting in sediments fluxes. These activities affect the estuarine environment by changing the habitat structure and dynamics of living communities [
To understand the environmental quality of estuaries, free-living nematodes provide advantages as biological indicators because of their morphological structures such as mouth structure, tail shape and length-width ratio which relate to ecological functions [
The distribution and environmental factors affecting free-living nematodes are the main information in understanding the ecology of their communities and the role in dynamics of the ecosystems. There is no enough evidence of the availability of a specific factor such as grain size or organic content of sediment that contributed to the distribution patterns of nematodes [
The Incomati River Estuary is about 40 - 50 km long and meanders within the coastal plain. It is located on the east coast of Africa, Southern Mozambique (
The study was conducted from June 2017 to April 2018. Sampling was done during low tide in the subtidal region using a hand held perspex corer which was 1 m long and 3.6 cm diameter down to a depth of 10 cm. Most nematodes are
Site Names | Salinity Ranges | Estuarine Zone | Co-ordinates | |
---|---|---|---|---|
Latitude | Longitude | |||
E1 | 0 - 3 NST | Oligohaline | −25.7198611 | 32.6982694 |
E2 | 3 - 5 NST | Euhaline | −25.733775 | 32.680644 |
E3 | 5 - 18 NST | Mesohaline | −25.7622361 | 32.729275 |
E4 | 18 - 27 NST | Polyhaline | −25.8324361 | 32.73435 |
mostly found between 4 cm to 10 cm of the sediment [
The other corer sample was used for the analysis of Metals, Particle Size, Organic Matter and Chlorophyll-a. Sediment particle size and Organic Matter analysis were done following the procedure set by [
A PRIMER 6.0 which is a multivariate statistical package developed by Plymouth Marine Laboratory [
MI = ∑ i = 1 n v ( i ) ⋅ f (i)
was used to calculate the weighted average of the individual colonizer-persisters (c-p) values. The following symbols in the formular: v(i) represented the c-p value of the taxon, then i and f(i) was the frequency of that taxon.
A variation of sediment particle sizes was found in the four sites sampled in the Incomati River Estuary (
Site E3 and E4 were mostly characterised by coarse and very coarse particle sizes which were attributed to tidal action that washes the sand from small particles. Sediment grain sizes are important environmental factor especially that help in the structuring of meiofauna.
The highest percentage of Organic Matter was found at site E2 with a mean value of 2% (
The lowest percentage of Organic Matters was found a site E1with a mean value of 1.2%. At both sites E3 and E4, the mean percentage of Organic Matters
was 1.5%. A two-way ANOVA indicated that there was no significant different (p > 0.05) of Organic Matter concentration between the sites sampled.
The highest concentration of Chlorophyll-a was found at site E3 with a mean concentration value of 3.2 mg/m3 (
The second highest concentration of Chlorophyll-a was found at site E4 with a mean concentration value of 1.24 mg/m3. The lowest concentration of Chlorophyll-a was found at site E2 and E1 with a mean concentration of 0.87 mg/m3 and 0.95 mg/m3 respectively.
Ten metal concentrations (Cadmium, Colbat, Chromium, Copper, Iron, Manganese, Nickel, Vadium, Zinc, and Aluminium) were found (
PERMANOVA analysis indicated that there was a significant different (p < 0.05)
Metals (ppm) | E1 | E2 | E3 | E4 |
---|---|---|---|---|
Cd | 0.13 | 0.17 | 0.11 | 0.09 |
Co | 3.27 | 3.89 | 1.61 | 0.49 |
Cr | 10.28 | 14.92 | 20.05 | 7.87 |
Cu | 5.25 | 7.85 | 4.37 | 4.10 |
Fe | 4354.83 | 9125.12 | 2777.83 | 1537 |
Mn | 123.67 | 194 | 54.83 | 59.67 |
Ni | 8.38 | 11.97 | 3.45 | 3.57 |
V | 6.87 | 12.30 | 4.28 | 1.43 |
Zn | 13.68 | 12.6 | 6.75 | 8.88 |
Al | 4802 | 7935.33 | 2264.67 | 904.17 |
between sites sampled, but not between months. These results indicated that the concentration of metals changes spatial, but not temporal. The higher concentration of heavy metal in the study area especially at sites E1 and E2 was attributed to different anthropogenic activities from the upper catchments, and local informal settlements.
A total of 5989 nematodes individuals/10 cm2 were sampled in the Incomati River estuary. The highest nematode density of 2605 individuals/10 cm2 was found at site E4 which is situated in the Polyhaline Zone of the estuary, while a lowest density of 721 individual/10 cm2 was found at site E1 situated in the Oligohaline Zone (
Similarly, in a study conducted in the Swartkops River System, South Africa [
A total of 35 nematode genera were found in the Incomati River Estuary (Appendix A:
The Maturity Index (MI) which is a potential indicator of nematode assemblage under stress and the Shannon-Diversity Index of the four sites sampled were calculated (
At sites E2 and E1 the Maturity Index were found to be lower with Maturity
values of 2.38 and 2.44. The lower Maturity Index indicated that these sites were under stress, especially at site E2 which had higher concentration of heavy metals and total phosphate throughout the sampling period. Similarly, the Shannon-Diversity Index indicated the same finding as the Maturity Index.
A Bray-Curtis Cluster Analysis and NMDS ordinations (
Group 3 was formed by sites E3 and E4 at similarity 65%. The similarity at 65% indicated that the was no much change of meiofauna diversity and density at these sites, while the dissimilarities of sites E1 and E2 was attributed to the factors that these sites received different environmental factors, and meiofauna diversity changed at different period of sampling.
The K-dominance curve (
At both sites E3 and E4, the cumulative dominance was below 20% indicating that these sites were more diverse than sites E1 and E2. The K-dominance curve showed that the higher the salinity the lower the dominance of individual genera, and the higher the diversity of individual genera.
An RDA triplot indicated that the lower diversity and density of nematodes at site E2 was attributed to high concentration of metals such as Cadmium, Colbat, Chromium, Copper, Iron, Manganese, Nickel, Vadium, Aluminium and Organic Matters with had strong correlation with nematode feeding type 1B (
The higher diversity and density of nematodes at sites E3 and E4 were attributed to sediment particle size such as Coarse Sand, Very Coarse Sand and Chlorophyll-a because they had a strong correlation with nematode feeding types 2A and 2B.
Another strong correlation was observed between very fine sand, fine sand and Zinc with nematodes feeding types 1A.
The BIOENV analysis indicated that although other environmental factors correlated with nematodes diversity, Nitrates (NO3), Very Coarse sand, Coarse Sand, and Fine Sand were the most significant (Rho = 0.693; p < 0.05) environmental variables that structure nematodes community in the estuary especially when all environmental variables were combined (
According to [
Environmental Variables | Correlation or Rho | |
---|---|---|
Combined | Nitrate (NO3), Very Coarse Sand, Coarse Sand and Fine Sand | 0.693 |
Nematode diversity and density decrease with a decrease in salinity gradients in the study. Sites E2 and E1 were found to be the polluted sites with higher concetration of metals and organic matters. Nematodes genera such as Terschellingia, Theristus and Halalaimus were also found to be dominant at these sites E2 and E1. The positive correlation between nematodes genera such as Terschellingia, Theristus and Halalaimus with metals such as Cadmium, Colbat, Chromium, Copper, Iron, Manganese, Nickel, Vadium, Zinc, and Aluminium indicated that these nematode genera can be pollution indicators in the estuarine environments. A combination of Maturity Index, Shannon-Diversity Index and c-p values was good tool in identifying polluted sites in the study. It is recommended that further studies are done along the Mozambican Coast to identify nematodes that can be used as pollution indicators.
I would like to send my gratitude to the Inkomati-Usuthu Catchment Management Agency which is the first CMA to be established in South Africa for their funding for this study. I would also wish to thank my supervisor Dr. T Gyedu-Ababio for his advice and assistance in identification of meiofauna and nematodes during the study.
The authors declare no conflicts of interest regarding the publication of this paper.
Soko, M.I. and Gyedu-Ababio, T.K. (2019) Free-Living Nematodes as Pollution Indicator in Incomati River Estuary, Mozambique. Open Journal of Ecology, 9, 117-133. https://doi.org/10.4236/oje.2019.95010
NEMATODE GENUS | c-p values | Feeding types | E1 | E2 | E3 | E4 | ||||||||||||||||||||
---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
Salinity range amongst the sites | ||||||||||||||||||||||||||
0 - 3 NST | 3 - 5 NST | 5 - 18 NST | 18 - 26 NST | |||||||||||||||||||||||
Jun-17 | Aug-17 | Oct-17 | Dec-17 | Feb-18 | Apr-18 | Jun-17 | Aug-17 | Oct-17 | Dec-17 | Feb-18 | Apr-18 | Jun-17 | Aug-17 | Oct-17 | Dec-17 | Feb-18 | Apr-18 | Jun-17 | Aug-17 | Oct-17 | Dec-17 | Feb-18 | Apr-18 | |||
Adoncholaimus | 3 | 2B | 13 | 12 | 15 | 3 | 0 | 0 | 0 | 0 | 1 | 0 | 0 | 0 | 0 | 1 | 2 | 10 | 11 | 0 | 0 | 6 | 0 | 1 | 2 | 0 |
Aegialoalaimus | 4 | 1A | 3 | 0 | 0 | 4 | 2 | 0 | 0 | 0 | 2 | 0 | 0 | 0 | 0 | 0 | 3 | 0 | 10 | 0 | 0 | 11 | 12 | 6 | 0 | 8 |
Anoplostoma | 2 | 1B | 10 | 15 | 0 | 9 | 13 | 11 | 0 | 0 | 2 | 0 | 0 | 0 | 2 | 0 | 0 | 6 | 0 | 0 | 0 | 9 | 3 | 6 | 4 | 3 |
Axonolaimus | 2 | 1B | 3 | 15 | 16 | 12 | 3 | 26 | 0 | 10 | 9 | 10 | 10 | 20 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 11 | 0 | 10 | 4 | 4 |
Batylaiumus | 2 | 1B | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 10 | 0 | 0 | 11 | 0 | 50 | 0 | 0 | 0 | 0 | 0 | 4 |
Camacolaimus | 3 | 2A | 0 | 0 | 0 | 0 | 0 | 8 | 3 | 2 | 0 | 1 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 2 | 0 | 0 | 0 | 0 | 0 | 0 |
Cephalainticoma | 2 | 2A | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 2 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 2 | 0 | 0 |
Daptonema | 3 | 1B | 0 | 3 | 1 | 2 | 0 | 0 | 1 | 1 | 1 | 10 | 3 | 0 | 10 | 0 | 0 | 9 | 5 | 5 | 10 | 0 | 0 | 6 | 12 | 2 |
Dichromadora | 2 | 2A | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 3 | 0 | 0 | 0 | 20 | 0 | 12 | 2 | 0 | 3 | 10 | 8 |
Dolicholaimus | 2 | 2B | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 4 | 0 | 1 | 0 | 0 | 0 | 0 | 0 | 0 | 2 | 10 | 0 |
Enoplus | 5 | 2B | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 2 | 0 | 0 | 6 | 0 | 0 | 0 | 0 | 0 | 0 | 3 | 0 | 0 | 0 | 0 |
Filoncholaimus | 4 | 2B | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 4 | 0 | 0 | 6 | 20 | 5 | 0 | 9 | 0 | 2 | 0 | 0 | 0 | 0 | 0 |
Halalaimus | 4 | 1A | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 5 | 0 | 0 | 2 | 3 | 0 | 0 | 3 | 0 | 0 | 2 | 0 |
Haliplectus | 2 | 1A | 23 | 29 | 35 | 34 | 54 | 55 | 0 | 3 | 0 | 5 | 0 | 0 | 0 | 0 | 0 | 1 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 |
Leptolaimus | 2 | 1A | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 3 | 0 | 1 | 3 | 0 | 0 | 1 | 5 | 3 | 3 | 0 | 0 |
Metachromadora | 3 | 2A | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 8 | 0 | 0 | 0 | 5 | 5 | 7 | 10 | 4 | 8 | 0 |
Metacyatholaimus | 3 | 2A | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 2 | 1 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 |
Microlaimus | 2 | 2A | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 2 | 0 | 0 | 0 | 3 | 2 | 1 | 1 | 3 | 0 | 1 | 6 | 5 | 7 | 2 | 0 |
Monhystera | 2 | 1B | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 6 | 0 | 0 | 0 | 0 | 2 | 2 | 0 | 0 | 0 | 5 | 2 | 0 | 7 | 3 | 0 |
Neochomadora | 3 | 2A | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 3 | 7 | 6 | 9 | 4 | 0 | 0 | 0 | 13 | 0 | 0 |
Oncholaimellus | 3 | 2B | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 1 | 2 | 1 | 0 | 0 | 0 | 2 | 0 | 0 | 0 | 0 |
Oxystomina | 4 | 1A | 0 | 0 | 6 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 20 | 10 | 9 | 0 | 8 | 3 | 0 | 0 | 0 | 0 | 0 |
Paracyatholaimus | 2 | 2A | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 2 | 0 | 4 | 10 | 0 | 0 | 13 | 0 |
Paramonohystera | 4 | 1B | 0 | 4 | 3 | 4 | 13 | 0 | 14 | 4 | 9 | 6 | 8 | 0 | 1 | 19 | 12 | 5 | 2 | 3 | 2 | 1 | 0 | 3 | 4 | 1 |
Pomponema | 3 | 2B | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 3 | 2 | 5 | 0 | 6 | 0 | 0 | 2 | 4 | 32 |
Pseudochromadora | 3 | 2A | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 1 | 0 | 0 | 4 | 0 | 10 | 7 | 5 | 2 | 2 | 1 | 12 | 0 | 0 | 0 |
Rhabditis | 1 | 1A | 1 | 3 | 4 | 8 | 3 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 3 | 0 | 5 | 6 | 0 | 2 | 0 | 0 | 4 |
Sabatiera | 2 | 1B | 0 | 0 | 0 | 4 | 1 | 0 | 8 | 3 | 0 | 0 | 0 | 0 | 5 | 12 | 14 | 20 | 0 | 0 | 10 | 0 | 5 | 3 | 0 | 19 |
Scaptrella | 2 | 2B | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 3 | 4 | 6 | 5 | 0 | 0 |
Spirinia | 3 | 2A | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 3 | 1 | 0 | 2 | 3 | 5 |
Synonchium | 3 | 2B | 0 | 8 | 12 | 2 | 4 | 0 | 6 | 6 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 |
---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
Terschellingia | 3 | 1B | 2 | 5 | 2 | 8 | 4 | 0 | 56 | 56 | 50 | 30 | 52 | 41 | 0 | 4 | 9 | 0 | 0 | 0 | 10 | 6 | 10 | 10 | 8 | 0 |
Theristus | 2 | 1B | 6 | 3 | 3 | 4 | 0 | 0 | 12 | 10 | 13 | 31 | 25 | 34 | 36 | 3 | 5 | 4 | 0 | 1 | 0 | 5 | 10 | 0 | 0 | 1 |
Viscocia | 3 | 2B | 1 | 3 | 3 | 6 | 5 | 0 | 0 | 5 | 3 | 0 | 2 | 5 | 0 | 5 | 12 | 0 | 16 | 15 | 16 | 3 | 12 | 6 | 11 | 9 |
Xyala | 3 | 1B | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 1 | 0 | 0 | 0 | 0 | 2 | 10 | 1 | 0 | 0 |