Coastal pollution assessment is a pressing matter as the anthropogenic pressure continues to increase worldwide. A leading approach to assess coastal pollution is using bioindicators. However, identifying species is time-consuming and demands profound morphological knowledge. Our goal was to find the meiobenthic composition in each pollution level. By utilizing the meiobenthic assemblage’s ratios, we will be able to indicate the pollution level. We examined the meiobenthos distribution at three sites exposed to a pollution gradient. We quantified the changes in the fauna assemblage in the community phylum level, focusing on nematodes and foraminifera (90% of the total population). Over 400 samples were examined, covering an annual seasonal cycle. Nematodes population dominated in the polluted coast. Nematodes density increased with the pollution level, up to seemingly harmful levels of pollution. In contradiction, the foraminifera flourished in the control site and exhibited an inverse relationship to the nematodes. We witnessed drastic changes in the entire meiobenthic population in the winter, which we speculate that originated from winter turbulences. We suggest that nematodes-foraminifers’ population ratios may be utilized as bioindicators for assessing coast intertidal zone pollution levels.
The shores of the Mediterranean contain a variety of environments populated by different species that have adapted themselves to the different niches [
Furthermore, eastern Mediterranean biodiversity is under severe pressure caused by Lessepsian migration and global warming. The opening of the Suez Canal opened a doorway between the Red Sea and the Mediterranean that resulted in the migration of hundreds of tropical species towards the Mediterranean Sea. These species inhibit the Mediterranean and push aside the local fauna. This situation is amplified by the constant increase in seawater temperature. The increase assists the adaptation of migrating subtropical species and contributes to the “tropicalization” of the basin [
The coastal area is generally considered the most prosperous area in the basin, which brought human population to set up their homes in close proximity to the coastline. Today, more than 40% of the world’s population lives within a range of 100 km from the coastline. By 2025, the population near the coastline is predicted to exceed 50% of the total global population [
In the coastal ecosystem, the marine soil is an important key factor that regulates the entire ecosystem. It functions as a food and mineral source, breeding ground, protective layer, camouflage, and buffer zone [
The research was conducted in the Levantine Sea, in the southeastern basin of the Mediterranean Sea, along the coastline of Israel. Three rocky coasts re-pre- senting a pollution gradient along a 28 km strip, were selected according to Herut et al. (2014), Herut et al. (2015), Hoffman et al. (2011) and personal communication1 [
Meiobenthic core samples were collected from sandy areas parallel to the coastline at a 0.5 m depth and with 0.5 m intervals between samples. The core samples were taken by inserting 150 ml plastic cups (n = 5 - 14, 5.5 cm diameter, 6.8 cm in length) into the soil. The cores were then capped and maintained in a dark cooler with water and ice until they were transported to the lab. We chose to identify the organisms to the phylum level. The average size of meiobenthos in close proximity to the coast didn’t exceed 1 mm. Thus, recognition of species according to the morphology was a time consuming task. Thus, choosing to focus on the phylum level allowed us to analyze more samples in shorter time.
The abiotic parameters of the water, including temperature (t), pH, salinity (S), conductivity, oxygen concentration, oxygen saturation, oxidation reduction potential, specific resistance, partial pressure, and total dissolved solids, were monitored at each coast using a WTW Multi 3430 Multiparameter Meter equipped with SenTix 940, TetraCon 925, and FDO 925 sensors (WTW GmbH, Weilheim, Germany).
From January to September 2014, an amount of 5 cm3 soil from each sample was placed in a 15 ml conical tube and stained with 5 ml of Rose Bengal solution (g・l−1). The samples were stored for at least 10 days before counting and classifying the different phyla under a stereo microscope. Foraminiferal samples of dominant species were examined and identified to the genus or species level, when possible.
A volume of 30 cm3 soil from each sample was inserted into a 50 ml centrifuge tube and mixed with formaldehyde solution (4% formaldehyde, 96% artificial seawater) using a vortex; the rest of the sample was taken for organic-matter (OM) analysis. After 48 h, the solution was poured out and replaced with ethanol solution (70% ethanol, 30% artificial seawater) for preservation and storage. Extraction was initiated by pouring the sample into a 63 µm sieve and gently rinsing it with tap water. A volume of 30 cm3 of soil was taken from the sample and placed into a 50 ml conical tube. The sample was processed and its meiobenthos were extracted according to Burgess (2001) [
All organisms were identified to the phylum level according to Atkins (2002), Murray (2006), Guilini (2017), and Ridel (2010) [
Each of the samples was processed according to Eleftheriou & McIntyre (2005) and Avnimelech et al. (2001) [
The present study is among the few focusing on the effects of pollution on meiobenthic populations in the intertidal area of the southeastern basin of the Mediterranean. The study also examined the seasonal changes on the meiobenthic populations. The samples indicated a high presence (over 90% of the organisms in each sample) of nematode, foraminiferal, and annelid populations. The rest of the phyla were present in negligible numbers and, therefore, were not included in this study. Furthermore, a high variability in the number of organisms among samples, which caused a significant standard deviation, was observed in each coast. In our attempt to overcome this problem, we raised the number of samples at each site to up to 14. This attempt was not successful, as no significant reduction in standard deviation was observed. This led us to realize the mosaic-like nature of the complex, observed ecosystems, which are characterized by patchy population distribution. Future work would require a reduction of the number of samples and a concomitant increase in the size of each sample to at least 10 cm diameter [
When we evaluated the variety of organisms at the three coasts, a few trends became obvious. There was an opposite relationship between the nematode and foraminiferal assemblages (t test (p < 0.05), −0.556, Spearman rho (p < 0.05)): a growth in the number of nematodes was accompanied by a decline in the number of foraminifera, and vice versa. This situation can imply a prey-predator relationship, competition over resources, antibiosis, or a combination of these. This assumption is strengthened by previous studies. Evidence for a prey-predator relationship was found in a number of works on both nematodes and foraminifera. Furthermore, both taxa were described as “opportunists” that could change their nutritional habits or feed on a number of food sources [
We could also see that the foraminiferal population fluctuated with the seasons (
However, when we focused on each individual coast, new trends became evident. At the Na coast (
peak in the winter (as was the case with the nematodes) and a subsequent reduction in the population’s size compared to the previous year.
At the Mi coast, the trend was reversed (
its original size of the previous year. We assume the cause for this is a pollutant or other significant disturbances in the summer of 2013.
The Za coast meiobenthic distribution resembled that of the Mi coast (
Utilization of population ratios is a known approach for biomonitoring of the environment. Nematode-copepod ratios have been used in the past to assess different pollutants. However, nematode-foraminifera ratios have been mostly
overlooked [
We evaluated the diversity of the population at each coast (
Month Coast | January | March | May | August | September |
---|---|---|---|---|---|
Nahsholim | 0.53025 | 0.699969 | 0.779154 | 0.881065 | 0.948944 |
Mikhmoret | 0.722352 | 0.899955 | 0.500216 | 0.688553 | 0.594867 |
Zarqa | 0.916413 | 0.664822 | 0.590617 | 0.476568 | 0.538559 |
When we looked at the OM at each coast (Figures 1-4), we saw that there was a similar seasonal cycle of the OM in Mi and Za coasts but a different OM cycle in Na coast. Both polluted coasts (Mi and Za) exhibited an increase in OM in January and August while, at the clean coast (Na), we observed an increase only in January (that increase was maintained and even grew until the summer). Surprisingly, the OM amounts were higher at the clean coast compared to the polluted ones, opposite to the nematode assemblages. These observations led us to the conclusion that the nematodes that thrive in the polluted coasts feed on the OM and act as biofilters; therefore, this population grows as the OM declines.
If we compare the porosity in the different populations (
The meiobenthic population showed a dramatic change in numbers and in growth cycles, as the pollution levels rose. The winter climate assisted in diluting the pollution, which, in turn, shifted the coastal community and reinstated the natural community state. The winter acted as a buffer which offered the community time to revert to the natural state. At the same time, hindered pollution resilient meiobenthic species completely overtake this habitat. The foraminifera showed significant sensitivity to pollution while the nematodes were more resilient (as were the annelids) and thus became dominate. We suggest that pollutants harm the foraminifera while changing the natural food sources available. This provides the nematodes, which can thrive on diverse food sources, a competitive advantage. Therefore, we propose that the nematodes and foraminifera can be reliable bioindicators of polluted coasts. Furthermore, the nematode-fo- raminifers’ ratio can be utilized for a costal cleanliness evaluation.
Future research should study the changes that occur at the species or genus level while monitoring pollutants on a monthly basis. When we will be able to better quantify the level of pollution and how it affects the nematode-foramini- fers’ ratio we will be able to associate and evaluate the conditions of the different
coasts. We suggest that a metagenomic approach be used. The knowledge required and the time-consuming methods of extraction and identification by morphology are likely to cause errors throughout the study.
The use of data sets from the labs of Prof. Barak Herut and Dr. Gil Rilov, from Israel Oceanographic and Limnological Research Institution, is gratefully acknowledged. We also want to acknowledge the financial aid from Israel Ministry of Agriculture & Rural Development. We would like to thank Dr. Ahuva Almogi for assisting with the classification of the foraminifera and Dr. Yuri Kamenir with the statistics analysis. Lastly, we want to thank Sharon Victor and Roni Hendler for editing the manuscript.
Morad, T.Y., Dubinsky, Z. and Iluz, D. (2017) Meiobenthos Assemblages as Bioindicators for Coastal Po- llution Assessment. Open Journal of Marine Science, 7, 409-423. https://doi.org/10.4236/ojms.2017.73028