Very little is known about the response of marine organisms to DGS. There have been numerous observations of GBT in marine fish and invertebrates; however, there is little quantitative data which can serve as a basis for numerical water quality guidelines. The data which do exist are summarized in the following sections.

7.1 Fish

Cornacchia and Colt (1984) reported that 10- to 31-day old striped bass larvae (Morone saxatilis) developed over-inflated swim bladders and bubbles in the intestinal lumen at TGP% levels of 102.9% and 105.6%. At a TGP% of 105.6% there was a 33% mortality in a 78-hour period. In other experiments, these authors found that 19-day old fish succumbed to a TGP% of 106.3% with a 35% mortality in a 72-hour period. However, in 29-day old fish TGP% levels of 106.3% did not produce any mortalities over a 72-hour period.

Gray et al. (1985) examined the tolerance of sea bass (Dicentrarchus labrax) and striped mullet (Mugil cephalus) to the effects of DGS at temperatures of 20 °C and 26 °C. They reported that at 20 °C post larval sea bass (30 mm in length) survived 96-hour exposures to a delta P of 152 mm Hg, but experienced 50% mortalities after 96 hours (LC₅₀) at a delta P of 207 mm Hg. At 26 °C, the 96-hour LC₅₀ was a delta P of 166 mm Hg. Fingerling sea bass (100 mm in length) survived a 96-hour exposure at a temperature of 20 °C and a delta P of 114 mm Hg, but suffered a 50% loss after 96 hours at a delta P of 122 mm Hg. Based on these observations, they concluded that the upper delta P limit for 100% survival at 20 °C is 152 mm Hg for post larval sea bass and 114 mm Hg for fingerling sea bass. They also reported that the fish were over-buoyant due to a large bubble inside the body cavity.

Interestingly, Johnson and Katavic (1984) reported a similar condition described as Swim Bladder Stress Syndrome (SBSS) involving over-inflated swim bladders in sea bass (Dicentrarchus labrax). Bagarinao and Kungvankij (1986) reported the same condition in hatchery-reared sea bass (Lates calcarifer). Although Johnson and Katavic (1984) cautioned that the condition was not related to GBT, they failed to report on dissolved gas levels in their experiments. Similarly, Bagarinao and Kungvankij (1986) described the conditions of SBSS but failed to report on dissolved gas levels.

In experiments with striped mullet (Mugil cephalus), Gray et al. (1985) found that at 20 °C, post larval fish (31 mm in length) survived 96-hour exposures at a delta P of 144.5 mm Hg, but experienced a 50% mortality after 96 hours at a delta P of 223 mm Hg. Fingerling striped mullet (130 mm in length) survived 96-hour exposures at a delta P of 114 mm Hg, but suffered a 50% mortality after 96 hours at a delta P of 188.5 mm Hg. Based on these observations, they concluded that the upper delta P limit for 100% survival is 144.5 mm Hg for post larval mullet and 114 mm Hg for fingerling mullet. It should be noted that for fingerling sea bass the upper delta P limit for 100% survival is the same as for the striped mullet. For post larval stages of these species, the upper delta P limit for 100% survival of the sea bass is slightly higher than that for the striped mullet. The data described above have been entered into Table D3 of Appendix D.

7.2 Invertebrates

The literature on DGS and GBT in marine invertebrates is also limited. Most studies have involved anecdotal observations with little in the way of mortality information related to levels of DGS. For example, Hughes (1968) reported GBT in lobster which had been exposed to DGS in a hatchery water supply. No information on dissolved gas levels was provided. The occurrence of GBT in three species of bi-valve molluscs (Crassostrea virginica, C. gigas, and Mercenaria mercenaria) was reported by Malouf et al. (1972). Massive blisters were found on the valves of oysters and bubbles were observed in gill filaments. DGS was produced by heating water in a closed container; however, dissolved gas levels were not reported. Lightner et al. (1974) reported on GBT in the juvenile brown shrimp (Penaeus aztecus). Stage II protozoeal, larval shrimp developed GBT after being exposed to DGS. Most animals had bubbles under the carapace and in the gut and there was 100% mortality. No actual dissolved gas levels were reported; however, the water was held at a delta P of 2585 mm Hg with subsequent decompression. Supplee and Lightner (1976) reported on the effects of GBT on California brown shrimp (Penaeus californiensis) as a result of exposure to oxygen supersaturation. Oxygen levels up to 309% were reported; however, total gas pressures were not given. Brock (1988) described GBT in the prawn (Macrobrachium rosenbergii). No dissolved gas levels were reported, but mortalities were high and many bubbles were present under the dorsal membrane. Johnson (1976) reported on GBT in the blue crab (Callinectes sapidus) in a laboratory environment. Air leaks in a water supply line was the cause of DGS. Again dissolved gas levels were not reported, but there were significant mortalities and evidence of gas emboli in gills and in the antennal gland. Elston (1983) described the occurrence of GBT in the red abalone (Haliotis rufescens Swainson) as a result of exposure to oxygen supersaturation (150 to 200%). Bubbles (presumed to be oxygen) were observed throughout muscle tissue and various other locations. Total dissolved gas levels were not reported. In another incidence involving a faulty water supply line, Brisson (1985) described GBT in two species of pink shrimp (Penaeus brasiliensis and Penaeus paulensis). Again, signs were described, but without information on dissolved gas levels.

The only work found in the literature which provided detailed information on mortalities in marine invertebrates and related dissolved gas levels was that by Bisker and Castagna (1985) for three species of clams (Mercenaria mercenaria Linne, Mulinia lateralis Say, and Mya arenaria Linne). Table 7 presents the results of their studies in terms of the mean days of survival (50% mortality) and water TGP levels. The authors report that for TGP% levels above 108%, M. lateralis floated to the surface and gas bubbles were visible in tissues. M. arenaria showed similar, though less severe, behaviour. Gas bubbles developed in body tissues and caused flotation; however, the percent of clams which floated for a given TGP level were less than for M. lateralis. M. mercenaria did not appear to be adversely affected by the levels of TGP which were imposed. Some mortalities were observed at a TGP of 120%, but these were not significantly different from those of controls. The data of Table 7 suggest that the upper limit of delta P for 100% survival of M. lateralis is somewhere between 109 and 114 mm Hg. Unfortunately, data on water depth was not reported by Bisker and Castagna (1985) for any of the experiments. The data of Table 7 have also been entered into Table D3 of Appendix D.

7.3 Plants and Algae

As with fresh water plants and algae, there is no information in the literature which described the effects of DGS on marine plankton, algae, or vascular plants. However, the discussion of Section 6.5, which provided some predictions of the effects which might be expected, would apply to marine plants and algae as well.

Table 7: Survival of Three Species of Clams for Various Levels of DGS

(Bisker and Castagna 1985)