Aspects of the ecology of the gutless protobranch bivalve, Soleymya reidi
Date
1986
Authors
Shepard, Penelope Anne Gee
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Abstract
The distribution and density of the gutless protobranch bivalve, Solemya reidi were examined in Alberni Inlet, British Columbia and related to environmental variables. Alberni Inlet houses both a pulp mill and extensive log booms. Density of S. reidi did not correlate with site depth, sediment particle size or temperature, or dissolved oxygen or salinity of bottom water. The density of S. reidi was highly positively correlated with thickness of the sediment surface woodfibre layer. Observations revealed that thickness of the woodfibre layer was not indicative of organic enrichment of the sediments. Sites with no woodfibre layer received deposition of particulate woodfibre from the pulp mill effluent stream, resulting in sediments which appeared to be more intensely reducing than those under thick fibre beds.
The sediment chemistry of two Alberni Inlet sites was compared in detail. Site 27, near the log booms, had a large, resident population of S. reidi and a thick woodfibre layer while this bivalve was rarely found at Site 5, which had no woodfibre layer present but received deposition from the pulp mill effluent. Both sites had reducing sediments ( <O mV Eh) , al though those at Site 5 were more so. This trend was also exhibited by the higher hydrogen sulfide, ammonia and phosphate concentrations and the lower sulfate levels found at Site 5. Both sites had high concentrations of amino acids present in the interstitial water (up to 156.93 uM). Comparison of the data for percent organics, percent woodfibre, cellulose and percent total organic carbon revealed that the carbon source at Site 5 was rapidly broken down by microbial degradation while the carbon source at Site 27 (twigs, large pieces of bark and fibre) was relatively refractory. The difference in microbial activity between the two sites was reflected in the completely anoxic bottom water at Site 5 and the presence of 1. 82 mgo 2/li t re at Site 27. It is suggested that this is the most pronounced difference between the two sites.
The Site 27 environment was discussed in relation to the modes of nutrition of S. reidi, uptake of dissolved organic material (DOM) and sulfide-oxidizing symbiosis. It is suggested that in environments with high concentrations of DOM (such as Site 27) uptake of DOM may contribute more to the animal's nutrition than had previously been determined experimentally. S. reidi's requirement for sulfide and oxygen for both the symbiosis, and oxygen for respiration, are unusual since these two elements are mutually exclusive in the marine environment. The bivalve's ability to regulate oxygen and sulfide in its immediate environment, as well as detoxification systems for sulfide, are discussed in terms of the habitat at Site 27. It is suggested that the high abundance of S. reidi at this site is due to the availability of both sulfide and oxygen. The deposition of wood materials from the log booms provides a source of organic enrichment, resulting in the formation and accumulation of sulfides. Because of the relatively refractory nature of the wood materials, however, reducing conditions do not develop to the point of anoxic sediment surface water, as was observed at Site 5.