Environmental hypoxia but not minor shell damage affects scope for growth and body condition in the blue mussel Mytilus edulis (L.)

The effects of short-term (7 d) exposure to environmental hypoxia (2.11 mg O-2 L-1; control: 6.96 mg O-2 L-1) and varying degrees of shell damage (1 or 2, 1 mm diameter holes; control: no holes) on respiration rate, clearance rate, ammonia excretion rate, scope for growth (SFG) and body condition index were investigated in adult blue mussels (Mytilus edulis). There was a significant hypoxia-related reduction in SFG (>6.70 to 0.92J g(-1) h(-1)) primarily due to a reduction in energy acquisition as a result of reduced clearance rates during hypoxia. Shell damage had no significant affect on any of the physiological processes measured or the SFG calculated. Body condition was unaffected by hypoxia or shell damage. In conclusion, minor physical damage to mussels had no effect on physiological energetics but environmental hypoxia compromised growth, respiration and energy acquisition presumably by reducing feeding rates.

Family-level AMBI is valid for use in the north-eastern Atlantic but not for assessing the health of microtidal Australian estuaries

Analysis of benthic macroinvertebrate samples at a higher taxonomic level than species, e.g. family, potentially provides a more cost-effective protocol for environmental impact assessments and monitoring as it requires less time, funds and taxonomic expertise. Using the AMBI database, species ecological group scores are shown to be coherent within families. Faunal data from a wide range of environmental impact scenarios in the north-eastern Atlantic demonstrate that AMBI, calculated from mean values for families, exhibits a strong linear relationship with species-level AMBI, the correlation improving by using square-root transformed rather than untransformed abundances. In many regions of the world, however, the sensitivity of benthic macroinvertebrates to environmental perturbations is unknown, precluding the use of AMBI for environmental assessments. Yet the families are essentially the same as in the AMBI database. The utility of family-level AMBI is tested using data for four south-western Australian estuaries previously subjected to environmental quality assessments, but where only 17 species of the 144 taxa are included in the AMBI database. Although family-level AMBI scores reflect differences in environmental quality spatially and temporally within an estuary, they do not follow variations in environmental quality among estuaries. Indeed, south-western Australia estuaries are numerically dominated by families with high AMBI scores, probably due to the detrimental effects of natural accumulations of organic material in estuaries with long residence times. As taxonomic distinctness follows trends in environmental quality among estuaries, as well as temporally and spatially within a system, it provides an appropriate substitute for assessing the 'heath' of microtidal estuaries.