Contaminants in Coastal Benthic Organisms

The distribution of benthic organisms on Antarctic shelves is largely affected by glacier transport of coarse materials into the sea, ploughing by floating icebergs, plucking by anchor ice and abrasion of shorelines by fast-, pack- and brash ice or by floes driven ashore and piled up by storms (push ice). In spite of these disturbances, most benthic assemblages of sessile and vagile organisms in Antarctic coastal ecosystems are characterised by high diversity and structural complexity, with most species having long life spans, low growth rates and lacking pelagic larvae (e.g. Dayton 1990; Gambi et al. 1994; Knox 1994). Although Antarctic seaweed does not have the trophic significance of phytoplankton, it contributes to primary productivity in coastal ecosystems and provides suitable habitats for a variety of animals. Some of the dominant species in Antarctica are Iridaea cordata in the infralittoral zone, Leptosomia simplex in the lower intertidal zone, Phyllophora antarctica at intermediate depths, and the largest Antarctic brown alga Himantothallus grandifolius down to depths of 25-30 m. The cell wall of algae consists of a variety of polysaccharides and proteins, some of them containing anionic carboxyl, sulphate or phosphate groups which are binding sites for metals. Owing to its abundance, limited mobility, and its ability to uptake metals and organic lipophilic compounds, seaweed has often been used to biomonitor persistent pollutants in the Arctic (e.g. Asmund et al. 1991; Johansen et al. 1991; Riget et al. 1997).

Very few data exist on trace metals and POP concentrations in Antarctic macroalgae. Average Cd, Cu, Fe, Hg, Pb and Zn concentrations in I. cordata samples from coastal sites in Terra Nova Bay were 2.8, 3.5,47, 0.12, 0.05 and 42 |g g-1 dry wt. respectively (Bargagli 2001). When compared with values measured by Riget et al. (1997) in samples of Fucus vesicolosus from relatively unpolluted coastal areas of West Greenland,the main difference was the much lower Pb content in Antarctic seaweed. Algae of the genus Desmarestia are abundant in the intertidal zone of the Antarctic Peninsula and South Shetlands. Montone et al. (2001b) determined concentrations of PCB congeners in Desmarestia sp. samples collected from various locations at Admiralty Bay (King George Island). Total PCB concentrations ranged from 0.46 to 3.86 ng g-1 dry wt., and the predominance of low-molecular weight congeners indicated that there were no significant local sources of PCBs at Admiralty Bay.

Sponges are one of the most striking epibenthic sessile organisms of Antarctica. Besides their significance in terms of benthic biomass, they are important substrates for epizoic animals and are the main source of densely populated biogenic sediments. Capon et al. (1993) found that aqueous ethanol extracts from Tedania carcoti specimens collected in Prydz Bay contained some mg g-1 dry wt. of Cd and Zn. The potent antibacterial properties of the extract were ascribed to the two metals, and it was speculated that their accumulation by sponges serves as a natural antibiotic or an agent against predation and fouling. However, sponges from Terra Nova Bay (Bargagli et al. 1996b) had lower Cd concentrations (mean 26±15 |g g-1 dry wt.), and their Zn content was similar to or lower than that in other benthic invertebrates from the same marine environment (Table 17). Although the average Cd content in surface sediments from Terra Nova Bay was very low (0.22±0.12 |g g-1) and roughly corresponded to that in Tyrrhenian Sea sediments of comparable grain size, Cd concentrations in benthic organisms from the Ross Sea were one order of magnitude higher than in related species from the Tyrrhenian Sea (Bargagli 1993). The enhanced bioavailability of Cd in Antarctic coastal marine environments is probably due to the rapid regeneration of the metal in the water column and/or to rapid mineralisation in surface sediments during early diagenesis. During the austral summer the upwelling of waters favours the ad/absorption of Cd on phytoplankton cells, and primary consumers uptake metal directly from water and food. Diatoms and benthic macroalgae at Terra Nova Bay have mean Cd concentrations of about 2.5 |g g-1 dry wt. Sponges draw in diatoms through their inhalant water system and exopinacocytes (which take in diatoms settling on the sponge surface and store them in the mesohyl matrix to strengthen the sponge cortex and as food reserve; Gaino et al. 1994). During the austral summer the amphipod Paramoera walkeri is a very important component of the fast-ice community and of the littoral benthos. Like sponges, it feeds mainly on diatoms (Gruzov 1977) and its Cd content is twice than of copepods (Bargagli et al. 1996b). Cad-

Table 17. Average concentrations (|ig g-1 dry wt.; mean±SD) of trace metals in coastal benthic organisms from Terra Nova Bay (Ross Sea; Bargagli 2001)

Invertebrate

Organ or tissue

Cd

Cu

Fe

Hg

Pb

Zn

Rhodophita (Iridaea cor data)

Whole

2.8±0.3

2.5±0.6

62±14

0.09±0.04

0.08±0.03

41±14

Ascidians (pooled across species)

Whole

26±15

11+3

307±97

0.08±0.05

0.46±0.23

48±13

Holothurians (pooled across species)

Whole

7.7±3.8

5.6±1.8

79±34

0.23±0.09

0.55±0.22

139±42

Polychaeta (Marmothoe spinosa)

Whole

6.8±2.8

7.5±3.1

318±49

0.07±0.02

0.11±0.07

76±24

Ophiuroids (pooled across species)

Arm

0.5±0.1

2.1±0.6

41±16

0.08±0.03

0.41±0.16

86±17

Central disk

14±5

15±6

324±143

0.14±0.07

0.69±0.24

306±94

Asteroidea (Odonaster validus)

Arm

14±2

15±5

63±20

0.11±0.06

0.51±0.22

47±7

Soft tissue

13±5

18±7

347±88

0.17±0.10

0.15±0.11

282±92

Echinoids (Sterechinus neumayeri)

Gonad

6.8±2.8

3.5±1.8

70±30

0.13±0.07

0.16±0.09

90±31

Soft tissue

13±5

6.7±3.1

418±129

0.09±0.05

0.49±0.15

129±36

Bivalves (Adamussium colbecki)

Muscle

1.2 ±0.6

3.2±1.6

50±21

0.20±0.10

0.11±0.03

58±13

Digestive gland

55±27

27±10

360±122

0.35±0.08

0.15±0.09

99±26

Prosobranches (Neobuccinum eatoni)

Muscle

6.1±3.5

8.5±3.3

105±24

0.28±0.15

0.08±0.02

71±22

Digestive gland

227±65

10±4

278±39

0.24±0.10

0.37±0.11

251±112

Amphipoda (Paramoera walkeri)

Whole

4.8±0.6

14±4

66±13

0.07±0.03

0.08±0.03

78±19

mium concentrations in other herbivorous organisms such as the sea urchin Sterechinus neumayeri are three times higher than the total body content in Arctic sea urchins (Fallis 1982). A toxicity test was developed to evaluate the effects of Cd, Cu, Pb and Zn on S. neumayeri larvae and embryos (King and Riddle 2001). Results showed that the long-term test with two-arm pluteus-stage embryos was more sensitive (especially to Cu) than the short-term test on hatched blastulae. The embryonic development of S. neumayeri was relatively insensitive to Pb.

Asteroidea is one of the most important benthic groups in the Ross and Weddell seas (e.g. Jarre-Teichmann et al. 1997). These organisms are opportunistic feeders, and some species feed on sponges. Data in Table 17 show that Antarctic starfish may accumulate high Cd concentrations. However, it is difficult to estimate the flow of metals and POPs through the dominant groups of benthic organisms because the ecophysiology of many Antarctic species is practically unknown. Starfish are probably major predators of sponges, whereas sea cucumbers, brittle stars and sea urchins feed on detritus, poly-chaetes and other invertebrates. Sponges and echinoderms are mostly inedible or of little value as food; moreover, several species of Antarctic sponges, tunicates, nemerteans, coelenterates and echinoderms produce toxic compounds against predation (McClintock 1989). Vagile polychaetes and other "worms" are probably major prey of fish, gastropods, isopods and echino-derms, and are the main path for the transfer of persistent contaminants to higher levels of the benthic food web.

In general, Hg concentrations in benthic invertebrates from Terra Nova Bay are low and accumulation patterns differ from those of Cd (Table 17). Although values are highly variable, probably as a consequence of marked differences in the life span, habitat and feeding habit of animals, the total body burden of Hg increases from primary consumers such as sponges and P.walk-eri to more omnivorous, opportunistic feeders and especially to scavengers and predators such as starfish. Data in Table 17 show that molluscs, particularly their digestive glands, accumulate the highest levels of Cd, Hg and other metals. The section below deals with the accumulation and detoxification of persistent contaminants in circumpolar species of Antarctic molluscs.

Was this article helpful?

0 0

Post a comment