Oil Pollution Effects to Marine Benthos in a Greek Bay

Transcription

1 Geodoumal by Kluwer Academic Publishers 305 Oil Pollution Effects to Marine Benthos in a Greek Bay Diapoulis, Aristidis, Dr.; Koussouris, Theodore, Dr., National Centre for Marine Research, Hellinikon, Athens, Greece Introduction So far, very little is known about and no systematic research has been done upon the marine flora of the Navarin bay. The bay of Navarin is a small area of about 16 km2, depths do not exceed 60 m and it communicates with the Ionion Sea by two channels, the S one is 1270 m wide and about 70 m deep, the N one is very shallow, about 1 m, and its width does not exceed 110 m. In February 1980, a Tanker ("Ireres Serenade") loaded with tons of crude oil got wrecked in the bay, and there was an oil spill. In June and December 1983 samples of marine flora and macrozoobenthos were taken inside (stations P and S) and outside the bay (Fig 1). The stations outside were, M southwards and R northwards. The purpose of this study is to assess the benthic communities' state three and a half years after the event, and compare it with that described by Haritonidis and Tsekos (1976). Methods Phytobenthos samples were taken from an area of 400 cm 2 (20 cm cm) at each station at depths ranging from. 1 to 3 m. The following indexes for data analysis were used: Ri is the covering of an area by one species. DRi is the quantitative predominance which is the covering of one algal group divided by the total covering (Rt) expressed as percentage (DRi=~; Rix 100/Rt), Q is the qualitative predominance, DQ is the number of species in one group divided by the total species found in a station expressed in percentage and finally the Soerensen (1948) similarity coefficient. Zoobenthic organisms were sampled by a Van Veen 0.1 m sampler and were sieved through a 1 mm metal sieve (Diapoulis and Bogdanos 1986). Results and Discussion Phytobenthos According to Haritonidis and Tsekos (1976) the station P was found to be the richest in terms of number of species: 89 species of which 14 Chlorophyceae, 20 Phaeophyceae and 55 Rhodophyceae. Total coverage was 60%. The total species number determined inside the Gulf after the oil pollution from the wrecked tanker and at two stations (P1 and S in June 1983 and P2 in December 1986), were 108 and distributed as: 18 to Chlorophyceae, (Tab 1). In terms of geographical distribution 7 floristic elements were identified in the bay of Navarin. The boreal (4 representatives), the atlantic tropical (11 representatives), the pantropical (10 representatives), the mediterranean (22 representatives) the atlantic boreal (8 representatives), the cosmopolitan (12 representatives) and the atlantic subtropical with 24 repesentatives. 17 species were not classified due to the lack of pertinent literature and, hence, these species were classified as other. The atlantic subtropical element predominates and it makes up together with the atlantic tropical element 38.5% of the total number of species identified as opposed to the atlantic temperate and temperate chloridic element which make up 13.1% of the number of species. In June 1983 the stations in the bay (Fig 1) were richest i.e. 76 species at station P, 71 at station S, as compared with 47 and 39 species at stations M and R respectiv-

2 306 GeoJournal 18.3/1989 Tab 1 The distribution of the marine algae in the Navarin bay

3 GeoJournal 18.3/ Tab 1 The distribution of the marine algae in the Navarin bay

4 308 Geodournal 18.3/1989 Tab 2 Qualitative and quantitative distribution of phytobenthos in the sampling stations Fig 1 Map of Navarin bay with the sampling stations ":" ;"':':":"t'"'"''':":"; )" i'l naut. m;le o6 ~ ~ ~ ~'..." e9 ol 0,12,73 o15,~;" ". ely. The same holds for total species covering, high values at the stations inside the bay, low values at the stations outside the bay. The values of covering as well as the number of species are listed in Tab 2, from which it is evident that, marine flora in Navarin bay is significantly richer than the flora outside the bay. Samples at station P during winter showed a physiological seasonal increase of Rhodophyceae covering and decrease of Phaeophyceae covering. Along the E coast of the bay, where the substrate is sandy, extensive meadows with marine Sperrnatophyta i.e. Posidonia oceanica and Cymodocea nodosa, which are sensitive to pollution generally (Peres and Picard 1975). Finally using the Soerensen similarity coefficient between the four studied stations we found that stations S and P inside the bay presented a high degree of similarity i.e. S=0.86, on the other hand the others reaching low degrees (i.e. from 0.43 to 0.56) practically considered unsimilar (Tab 3). The Soerensen similarity coefficient was used in order to identify any differences in the phytobenthos of the bay of Navarin in the years before (Haritonidis and Tsekos 1976) and after the wreck (present study). The coefficient attained a value of 0.33 which is indicative of the changes. e19 o20. ~.:. )',.-",.,%-, Zoobenthos Analysing qualitatively the duplicate samples of the two samplings (total area almost 6 m2), 249 species were identified in twenty stations (Fig 1). The relative proportions of the main groups were as follows: 124 species of 49.8% of the total belong to Polychaeta, 45 species or 18% to Mollusca (Bivalvia, Gastropoda, Scaphopoda, Aplacophora), 49 species of 20% to Crustacea (Curnacea, Mysidacea, Tanaidacea, Isopoda, Arnphipoda, Deca-

5 GeoJournal 18.3/ poda), 8 species of 3% to Echinodermata and the rest 23 species or 9.2% to miscellaneous minor groups (Porifera, Anthozoa, Sipunculida, Bryozoa, Phoronidea, Pantopoda, Ascidia) (Diapoulis and Bogdanos 1986). R R P1 S M Comparing the above data with the mean percentages of the groups from other bays in Greek waters, grown on similar soft substrates which is: Polychaeta 51%, Mollusca 15%, Crustacea 20%, Echinodermata 6,5% and Miscellaneous 7.5% (Zarcanellas and Bogdanos 1979, 1980; Bodganos and Satsmatzis 1983; Diapoulis and Bogdanos 1983), Polychaeta were found to be in the same percentages, Mollusca slightly increased, Crustacea almost the same, Echinodermata slightly decreased and Miscellaneous almost the same. The total point in our study lies on the fact that the percentage of Crustacea is almost the same with that of other similar unpolluted areas. According to other pertinent to the impact of oil pollution on marine biota, it has been defined that, Crustacea and especially Amphipoda, are very sensitive in oil pollution and can be used as negative oil pollution indicators (Sanders et al. 1980). In our study the contribution of Amphipoda to the total Crustacea found in Navarin bay was very high i.e. 47% or 23 species out of 49. Samples from station 7, the nearest to the wrecked ship, predominates normal value of parameters i.e. diversity index H'=3.42, organic carbon content 1.06% and dissolved oxygen by the bottom 6.13 ml/1, which also supports strongly the aspect that the once damaged communities have already recovered. Taking into account all above data we may point out that: P1 M Tab Trellis diagramm of Soerensen's affinity index a) During both sampling seasons the marine flora in the gulf was found to be rich enough from the viewpoint of species number and covering, b) Two samplings in neighborhood areas southwards and northwards outside the bay, showed after comparisons, that, the marine flora in the bay was richer in terms of species number and covering than outside the gulf (Tab 2). References Bogdanos, C.: Macrozoobenthic study of Pagasitikos Gulf. Biologia Gallohellenica 8, (1979) Bogdanos, C.: A preliminary benthic survey of an area in Oreos Channel (Greece). Rapp. Comm. inter. Expl. Sci. Mer Medit. 27, (1980) Bogdanos, C.; Satsmatzis, J.: The macrozoobenthos of an Aegean embayment. Thalasographica 6, (1983) Diapoulis, A.; Bogdanos, C.: Preliminary study of soft substrate macrozoobenthos and marine flora in the bay of Gera, Greece. Thalasographica 6, (1983) Diapoulis, A. ; Bogdanos, C.: Assessment of benthos after an oil spill in a Greek Embayment. Rapp. Comm. int. Mer Medit. 30, 139 (1986) Haritonidis, S.; Tsekos, I.: Marine aigae of the Greek West coasts. Botanica marina 19, (1976) Peres, J.; Picard, J.: Causes de la rarefaction et de la disparition des herbiers de Posidonia oceanica sur les cotes francaises de la Mediterranee. Aquatic Botany 1, (1975) Sanders, H. L.; Grassle, J. F.; Hampson, G. R.; Morse, S. L.; Garner-Price, S.; Jones, C. C.: Anatomy of an oil spill: Long term effects from the grounding of the barge Florida off west Falmouth Massachusetts. Jour. of Mar. Research 38, (1980) Soerensen, T.: A method of establishing groups of equal amplitude in plant sociology based on similarity of species content. Biol. Skr. 5, 4, 1-34 (1948) Zarkanellas, A.; Bogdanos, C.: Benthic studies of a polluted area in the upper Saronikos Gulf (Greece). Thalasographica!, 2, (1977)