Axinopsida serricata (Bivalvia) is abundant in coastal waters of British Columbia subjected to natural and anthropogenic disturbance. To investigate the monitoring potential of histological lesions, field populations were sampled in Holberg Inlet and Quatsino Sound, British Columbia, from benthic habitats affected by the submarine discharge of copper-mine tailings, and from a reference site in Mill Bay, Saanich Inlet. Based on a quantitative analysis of the digestive gland, ctenidia, kidney, gonad and stomach, the relationship between histological variation and site, size, season, sex and parasitism was explored. The relationship between occurrence of histological lesions in this species and further ecological consequences of mine-tailings discharge was also explored by comparing population characteristics of clams living in deposited tailings with clams from the reference site.
Between-sample differences were observed in the structure of digestive tubule digestive cells, digestive ducts, ctenidial frontal cells, laterofrontal cells, and abfrontal mucocytes, kidney concretions, and stomach epithelial cells. The pattern of differences in tissue structure between samples reflected proximity of the collection site to the mine-tailings discharge and seasonally-dependent reproductive activity. Simultaneous examination of six of the tissue variables (using a principal components analysis) showed that clams collected from three stations in Lower Holberg Inlet which were in closer proximity to the tailings discharge pipe were distinguishable from clams collected from the reference site, upper Holberg Inlet, and Quatsino Sound. Tissue structural variability in A. serricata was not influenced by sex, or ectoparasitism by a flagellate. Tissue variables were not causally related to clam size (and thus of age and duration of exposure). In spite of the notorious natural plasticity of molluscan tissues, the variability can be partitioned to provide a very effective interpretation of exposure to stressors.
Based on an increased abundance in degraded habitats, A. serricata, and the superfamily Lucinacea in general, have been described as r-selected or opportunistic species. An investigation of life-history traits showed that A. serricata has a maximum longevity of five years or longer, exhibits sporadic growth primarily in the summer months, and is an iteroparous, gonochoristic broadcast spawner with gamete release occurring primarily in November. The observed life span of the clam and presence of ova which are very large (maximum diameter is approximately 100 μm) and yolk-rich for a broadcast spawner are somewhat at odds with the contention that A. serricata is an r-selected species.
Tissue variations which occurred in the digestive tubules and ctenidia with increased incidence and severity closer to the tailings discharge pipe are similar to histopathological effects in molluscs as described by others. However, there is no evidence that tissue lesions in A. serricata negatively affect fecundity, growth, or abundance. The sub-population sampled closest to the discharge pipe is in a state of decline, but this is due to the absence of recruitment since 1986, rather than increased mortality in the established population.
The apparent decoupling of tissue-level and population-level effects may be due to a time lag in manifestation of decreased fitness at the population level, selection of stress-tolerant individuals in response to the stressor, a strategy of neglect of somatic maintenance and repair, or some other mechanism. It is possible that A. serricata and other small Thyasirids have an evolutionary history which provides pre-adaptation to environmental stressors. / Graduate
| Identifer | oai:union.ndltd.org:uvic.ca/oai:dspace.library.uvic.ca:1828/9507 |
| Date | 22 June 2018 |
| Creators | Bright, Doug Arthur |
| Contributors | Ellis, D.V. |
| Source Sets | University of Victoria |
| Language | English, English |
| Detected Language | English |
| Type | Thesis |
| Format | application/pdf |
| Rights | Available to the World Wide Web |
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