Use of the nematode-copepod ratio as an index of organic pollution

Marine Pollution Bulletin National Institute of Oceanography (NIO) (1976, 1977, 1978). Indian National Reports on Marine Pollution (Petroleum) Monitoring Pilot Project under the framework of Integrated Global Ocean Station System(IGOSS),NIO-CSIRTech. Repts. Goa, India. Oostdam, B. L. (1982). Distribution and dynamics of tar strandings on the beaches of Tobago, West Indies 1980/81. Internal Report, Institute of Marine Affairs, Trinidad. Oostdam, B. L. & Anderlini, V. (1978). Oil Spills and Tar Pollution

along the Coast of Kuwait. MPP Report, Kuwait Institute of Science Research, Kuwait. Piyukarnchana, T. (1978). A survey of tar balls along the beaches in Thailand in 1967-1977. IOC-WMO/MAPMOPP-II/6. Addl. UNESCO-IOC, World MeteorologicalOrganization. Straughan, D. (1979). Distribution of tar and relationship to changes in intertidal organisms on sandy beaches in Southern California. Proc. 1979OilSpillConference. AmericanPetroleumInstitute, Washington, D.C. Publ. No. 4308, pp. 591-602.

Marine Pollution Bulletin, Vo|. 14, No. 5, pp. 178-181, 1983 printed in Great Britain

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Use of the Nematode-Copepod Ratio as an Index of Organic Pollution S H A H I D A M J A D and J O H N S. GRAY Institutt f o r Marinbiologi Universitetet i Oslo, P.B. 1064, Blindern, Oslo 3, Norway

Controversy exists on the utility of the nematode.-copepod ratio as a method for assessing the effects of pollution on benthic communities. In a test of this ratio along a known gradient of organic enrichment in Oslofjord, the index showed the same trends as a previously undertaken macrofaunal survey. Copepod numbers decreased and nematode numbers increased along the gradient of increasing organic enrichment giving rise to changes in the ratio. Groin-size parameters showed no correlation with the ratio. Copepod numbers, however, showed a significant negative correlation with oxygen concentration 1 m above the sediment. The nematode-copepod ratio is suggested as being an acceptable addition to a suite of techniques for the assessment of organic enrichment effects on benthic communities, but does require special expertise. A decrease in the numbers of meiofaunal taxa along the organic enrichment gradent was found and is similar to the gradient in the nematodecopepod ratio. The fact that all indices show responses in Oslofjord may merely reflect the strong organic enrichment gradient that exists; it should not necessarily be coustrued that such results will be found everywhere. Recently Rafaelli & Mason (1981) have proposed that the ratio of the abundance of nematodes to copepods in marine sediments is a sensitive index of marine organic pollution. They based this conclusion on studies of a number of beaches affected by sewage pollution around the British Isles. However, the copepod specialists Coull et al. (1981) strongly criticized the ratio on the grounds that techniques for enumerating meiofaunal abundance were complex and, therefore, inexperienced persons might be misled in the interpretation of the ratio due to this lack of expertise. Warwick (1981), however, felt that the index was useful, especially if modified to take into account metabolic relationships of the two taxonomic groups studied. The real test of the index is whether or not it gives results comparable to those obtained by application of more traditional techniques. The Oslofjord is organically enriched, receiving sewage from the city of Oslo. As the fjord has a very limited water exchange (occurring only in mid-winter), gradients of organic enrichment are strong from the city towards the sill 178

at Dr0bak some 25 km distant. Studies of the macrofaunal communities have revealed strong gradients associated with the organic enrichment gradient. A study of the nematodecopepod ratio along this same gradient was initiated. It was anticipated that the data from Oslofjord would provide a reasonably objective comparative test of the effectiveness of the ratio against more traditional methods. For a general description of the fjord and its hydrography see Mirza & Gray (1981).

d

8• ~/

1.0 11

I

?

-I

'

9

I -/(

~0"

Fig. 1 Sampling stations in Oslofjord, Norway, for meiofaunal abundance estimates.

Volume 14/Number 5/May 1983

Methods

Results

Of the 76 stations sampled in Mirza & Gray's macrofaunal study, five were selected at random from within each of the four major pollution zones determined by Mirza & Gray. Figure 1 shows the sampling stations. Eleven (Nos. 1, 3, 5, 7, 10, 12, 13, 14, 16, 18, 19) were sampled on 20 October 1979 and the remaining stations on 8 October 1981. Replicate samples were taken at each station with a Reineck box corer (sampling 17 x 17 x 9 cm depth). Only box cores full with sediment were used. Sub-samples were taken with a plastic corer of ~ 6 cm. Two sub-samples were taken within each box for faunal analyses and two sub-samples taken with the corer for sediment analysis. The cores were carefully extracted by inserting a plunger from below and the sample separated into 0-5 and 5-10 cm depth. The sediment samples were taken to the laboratory and frozen. Grain size analysis was conducted on 25 g samples following methods recommended by Folk (1968). As descriptors of the sediment the graphic mean, inclusive graphic standard deviation, inclusive graphic skewness and graphic kurtosis were calculated following Folk (op. cit.). Salinity, temperature and oxygen 1 m above the bottom were recorded and the oxygen data obtained using Winkler's method (Andersen & FOyn, 1969). The meiofauna were extracted from the predominantly muddy sediments by washing and decanting. An upper screen limit of 1 mm diameter pores was used and a lower limit of 0.064 mm. This lower size is somewhat coarse for the nematodes but was nevertheless found to give high numbers from the Oslofjord sediments. Rose Bengal (1 g in 11.5070 neutral formalin) was added to the samples. With the exception of Foraminifera and ciliates, all organisms were counted and identified to the level of major taxa. Foraminifera are especially abundant in Oslofjord sediments. Checks revealed that sampling and counting efficiencywas between 90 and 95 070.

From the Oslofjord sediments the numbers of meiofauna ranged from 198 to 1250 individuals 10 cm -2, down to a depth of 10 cm. Of this fauna, 89.6o70 occurred in the upper 5 cm with nematodes dominating (77-98% of abundances) followed by copepods (0.5-9.9407o), kinorhynchs (0.15.5070), polychaetes (0.1-3.69070), ostracods (0.1-2.207o) bivalves (0.1-2.2O7o), nemerteans (<0.74%) and turbellarians (<0.5%), with gastrotrichs, halacarids, isopods, amphipods and tanaids making up the rest of the fauna. No clear correlation occurred between nematode numbers and any grain size factors or with oxygen concentration. The percentage dominance of nematodes did, however, increase on moving towards Oslo, i.e. with increasing organic enrichment. Copepod numbers, however, showed loose correlations with depth, a strong correlation with mean grain size (r = 0.87) and a negative correlation with oxygen concentration (r = - 0.64). Table 1 shows data on the depth, nematode numbers and nematode-copepod ratios. The nematode-copepod ratio shows a clear trend, with values of over 100 in the innermost zone grading to around 20 in the unpolluted zone. The ratio showed no correlation with any of the measured grain size parameters. Within zone 4, the unpolluted zone, there was a significant correlation using a logarithmic model between the nematode-copepod ratio and depth (r= 0.67), but overall there was not a signitic.ant correlation. The ratio showed a good correlation with oxygen concentration (Fig. 2). The general trend is that nematode numbers increase with increased organic enrichment whereas copepod numbers decrease.

Discussion The use of ratios to observe trends in marine data sets has been suggested by Margalef (1975). Margalef put forward a

TABLE 1 Station

1 2 3 4 5 6 7

Zone (Mirza & Gray, 1981)

Depth (m)

Nematode (No. 10cm-2)

Nematode-copepod ratio (S.D.)

2

33 18 76 37 23 60 11

258 1202 193 308 110 733 630

infin. 63 193 infin. 170 104 97 Mean 125.4 (54.1) 73 81 55 78 67 70 Mean 70.7 (9.22) 46 33 14 11 8 10 15 Mean 19.6 (14.3)

(polluted)

8 9 10 11 12 13

3 (slight pollution)

44 55 33 98 75 95

997 491 1172 626 203 494

14 15 16 17 18 19 20

4 (unpolluted)

127 106 72 34 26 50 60

280 202 329 274 531 295 213

179

Marine PollutionBulletin vaxiation might occur with season by studying trends along a gradient of samples taken at one time, the problem of seasonal variations, mentioned as a weak point with the ratio by Coun etal., should not be a major problem. Similar 100 .,O criticisms have been raised for a number of methods which seek to analyse trends in effects of pollution. 80 "O The main question raised, however, is does the nemaO tode-copepod ratio offer advantages over other more ,, 6 0 8 traditional methods of analysing pollution trends? The • 40 Oslofjord has a strong gradient of organic enrichment o which has persisted from the turn of the century. The nematode-copepod ratio shows the same trends as ~ 2o Z •e •e macrofaunal data, with the outer areas (zone 4) being I I I 1 I characterized as unpolluted. Yet the data are time1 2 3 4 5 consuming to obtain and quite considerable skills are Oxygen concentrotion, mt 1-~ required in order to obtain reliable data. Analysis of macroFig. 2 Correlation between the nematode:copepodratio and oxygen faunal data is also laborious but taxonomical problems are concentrationmeasured 1 m over the sea bed (Y= 192.15-37.58 much less with macrofaunal analyses. Whilst Warwick's x. r= -0.67). (1981) suggestion of a modification of the nematodecopepod ratio is interesting, the greatly increased requirement for expertise in nematode taxonomy probably series of ratios which increase when a planktonic ecosystem renders this approach less likely to be of universal applicais left alone but which decrease under disturbance (stress, tion. Our conclusion is that the nematode-copepod ratio upwelling and pollution). Amongst the ratios were the does illustrate trends where there are clear organic numbers of dinoflagellates to diatoms, zooplankton enrichment gradients and it may well be useful as an biomass to phytoplankton biomass and carnivore biomass additional tool to those already available, such as diversity to herbivore biomass. Clearly the nematode-copepod ratio indices and methods based on the distribution of individuals proposed by Rafaelli & Mason (1981) is in the same context. among species (see Gray & Pearson (1982) for review). We The nematode-copepod ratio is based on the well-known do not see the ratio for use in isolation but combined with a observation that nematode numbers tend to increase in fine suite of techniques and we are therefore, not so pessimistic sediments whereas copepod numbers show the reverse as Coull et al. trend (see Coull et ai., 1981, for a list of key works). Coull et Another alternative method using meiofauna is that using al. attack the suggestion of using such a ratio on the grounds taxon diversity proposed by Van Damme & Heip (1977). that it does not universally hold and that inexperienced They found a decrease in the number of taxa along an workers might wrongly interpret the data obtained. Yet the estuarine gradient and higher taxon diversity in sand than ratio, as we understand it, is not proposed as a universal mud. Using the taxa mentioned in the Methods section, a 'rule' but as a possible extra tool in helping our under- mean of 6.57 taxa occurred in zone 2, 8.5 taxa in zone 3 and standing of effects of pollution on marine benthic com- 9.6 taxa in zone 4. Taking account of the number of indimunities. The Oslofjord data support the original suggestion viduals by substituting taxa for species in the Shannonthat the ratio does reflect known pollution gradients found Wiener information statistic gave the same trend, but with in the macrofaunal communities (Mirza & Gray, 1981). In tittle gain in precision. The correlation between number of Oslofjord, as with Rafaelli & Mason's data from highly taxa per station and oxygen concentration was high organically enriched sediments, the ratio is over 100. This (r= 0.78). Here is a simple 'index' of pollution using meiovalue should not, however, be construed as a fixed index; the fauna which has about the same precision as the nematodedata rather show a gradient of responses but the upper figure copepod ratio for the Oslofjord data. However, it may just is probably maximal. Unlike Rafaelli & Mason's data, there be that Oslofj ord shows such strong gradients that whatever was no correlation between the ratio and any sediment method is used the trends are apparent. Clearly more work parameter. This is more in accordance with the finding of needs to be done on a comparative basis to evaluate the Coull etal. (1981). Yet the copepods did show a good corre- nematode-copepod ratio. lation with grain size, albeit over the limited range of sizes encountered. This correlation implies that the sediment becomes finer with increasing organic enrichment and the number of copepods is reduced correspondingly. However, Andersen, A. T. & F~yn, L. (1969). Common Methods for Chemical the majority of sediments within Oslofjord are medium to Oceanography. An Introduction (R. Langeed.), part II, pp. 111-149. Universiteteforlaget,Oslo. coarse silt and within this size range there is a large range of Coull, B. C., Hicks, G. R. F. & Wells, J. B. J. (1981). Nematode/ copepod abundances (1-26 individuals per 10 cm2). From copepod ratios for monitoring pollution: a rebuttal. Mar. Pollut. Bull., 12, 378-381. Table 1 it is clear that the pollution gradient in Oslofjord can be expressed simply as a trend in increased numbers of Folk, R. L. 0968). Petrology of Sedimentary Rock. Austin, Hemphills. Gray, J. S. & Pearson, T. H. (1982). Objective selection of sensitive nematodes or conversely in decreased number of copepods. species indicative of pollution-inducedchange in benthic communiThe nematode-copepod ratio merely amplifies these two ties. 1. Comparative methodology. Mar. Ecol. Progr. Ser., 9, 111-119. trends. Margalef, R. (1975). Assessment of the effectson plankton. In Marine We have no data on seasonal variation in the ratio, as our Pollution and Waste Disposal (E. A. Pearson & E. de. Frangipane, samples were taken at the same time of year. Although eds.), pp. 301-306. PergamonPress, Oxford. 193

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170

Volume 14/Number5/May 1983 Mirza, F. B. & Gray, J. S. (1981). The fauna of benthic sediments from the organically enriched Oslofjord, Norway. J. exp. Mar. Biol. Ecol. 54, 181-207. Rafaelli, D. G. & Mason, C. F. (1981). Pollution monitoring with meiofauna, using the ratio of nematodes to copepods. Mar. Pollut. Bull., 12, 158-163.

Marine Pollution Bulletin, VoL 14, No. 5, pp. 181-187, 1983 Printed in Great Britain

Van Damme, D. & Heip, C. (1977). Het meiobenthosin de Zuidelijke Noordzee. Final Report Project Sea. Ministryof Scientific Policy Brussels,Belgium. Warwick, R. B. (1981). The nematode/copepodratio and its use in pollutionecology.Mar. Pollut. Bull., 12, 329-333.

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Application of the Mussel Watch Concept in Studies of the Distribution of Hydrocarbons in the Coastal Zone of the Ebro Delta ROBERT W. RISEBROUGH,* BROCK W. DE LAPPE,* WAYMAN WALKER II,* BERND R. T. SIMONEIT, t JOAN GRIMALT, * JOAN ALBAIGES,* JOSE ANTONIO GARCIA REGUEIRO,§ ANTONI BALLESTER I NOLLA§ and MANUEL MARI~IO FERNANDEZ" •Bodega Marine Laboratory, University o f California, Bodega Bay, CA 94923, USA ,School o f Oceanography, Oregon State University, Corvallis, OR 97331, USA , Institut de Quimica Bio-Org~nica, C.S.L C., Jordi Girona Saigado, Barcelona 34, Spain §Institut d'Investigacions Pesqueres, Passeig Nacional, s/n Barcelona 3, Spain IIMinisterio de Sanidad y Seguridad Social Subdireccion General De Sanidad A mbiental, Paseo delPrado, 18, Madrid 14 Spain The Mussel Watch concept was applied in a study of maninduced chemical changes in the Ebro Delta on the Catalonian coast to obtain a preliminary assessment of the distribution of synthetic organic compounds, petroleum and biogenic hydrocarbons in the local coastal zone. Mussels, oysters and clams were selected as the indicator organisms. Levels of petroleum accumulated by mussels were generally high, in the order of 100-800 ~g-t dry weight, equivalent to those in mussels in the most polluted harbours and bays of California. The relative distributions of the steranes and pentacyclic triterpanes in the mussels were significantly different from those found in petroleum from a local field, indicating that local petroleum was not contributing to the present contamination. The composition of biogenic compounds was variable, probably reflecting differences in the composition of local plankton communities, PCB levels were high in relation to current levels in mussels from US sites, reflecting continuing PCB use in Spain. The Delta appears to be a point source of a number of organochlorine compounds, including HCB, the DDT compounds, endrin and ),-chlordane. Levels of the DDT compound o,p'-DDD, a pharmacologically active substance, were unexpectedly high; identification was confirmed by GS/MS. Many unidentified peaks were present on EC chromatograms, indicating a more complex pattern of contamination than might be suggested by printed summaries of data.

The Ebro River is one of the larger river systems of the Mediterranean Basin, draining approximately one-sixth of the Iberian Peninsula. The annual mean flow, currently in the order of 1.6 x 101° m 3, has decreased by approximately 14% since the early years of this century, a result of the

construction of dams for irrigation projects (Maldonado, 1975). The deforestation of northern Spain in historic times, and the consequent silting of the Ebro, greatly increased the area of the Ebro Delta; currently it is the fourth largest in the Mediterranean, covering 350 km 2 (Maldonado, 1977). A reduction in the silt input to the Delta has recently resulted in a reduction of its area and further changes in the physical environment are anticipated throughout the remaining years of the century. The Delta is devoted to intensive agriculture, principally dee culture. The adjacent Mediterranean supports both an extensive fishery and an expanding mariculture industry; both are dependent upon the input of nutrients into the coastal zone from the River and Delta. Just as the physical environment of the Delta has been profoundly altered by man, the chemical environment is also undergoing significant change. Biocidal chemicals are intensively used in the agricultural areas, and some have become persistent pollutants. The coastal waters receive wastes from local municipalities and industries. Offshore, submarine deposits of petroleum are being exploited, and a nuclear power plant is in operation immediately to the north of the Delta. The kind, the magnitude, and potential effects of chemical changes in the Ebro Delta are the subject of a three-year cooperative Spanish-US investigation of the water quality of the Ebro Delta and the adjacent Mediterranean. The present paper reports on some of the initial results. The Mussel Watch concept was used to obtain a preliminary assessment of the levels of hydrocarbons, including several synthetic organochlorine compounds, as well as both petroleum and biogenic compounds, in the local coastalecosystem(Goldbergetal., 1978; NationaiAcademy 181