Assessing the relationship between community dispersion and disturbance in a soft‐sediment ecosystem

Abstract

Disturbed ecosystems often exhibit increased community heterogeneity when compared to nondisturbed systems. One way to measure community heterogeneity is statistical dispersion, a measure of how variable individual samples are from the multivariate average of the community condition (species presence/absence and density). In more specific manner, dispersion measures the distance between an individual data point and the centroid, the multivariate average of all data points. Statistical dispersion may be an important parameter to include in environmental assessments, or in studies that attempt to understand the role of disturbances in structuring biological systems. However, disturbances have been observed to increase, decrease, or not impact community dispersion (or community heterogeneity). Therefore, the usefulness of dispersion in studying or identifying disturbances is unclear. We tested if a mechanical disturbance increased community dispersion using the infaunal community of the intertidal mudflats along the north coast of British Columbia, Canada. We observed no statistically significant increase in community dispersion with varying frequency and intensity of a mechanical disturbance. This is likely a result of disturbed and nondisturbed treatments being dominated by the same six taxa, thus minimizing dispersion. Therefore, in ecosystems where differences in community successional stages are subtle (a result of changes in relative abundance rather than species replacement), community dispersion may not be an informative parameter when investigating disturbance. Despite this, we suggest that dispersion can be a useful variable to include in studies attempting to understand or identify disturbances; however, dispersion should only be one parameter amongst many used to understand or identify disturbances.

Survey of intertidal ecosystem reveals a legacy of potentially toxic elements from industrial activity in the Skeena Estuary, British Columbia, Canada

“…Benthic invertebrates are often used as indicators of environmental pollution since they live in sediments and are prey for many commercially important fish species [12–14]. Benthic invertebrates inhabiting estuaries are inherently resistant to physical and chemical change as they have adapted to living in a dynamic environment with wide spatial and temporal ranges of chemical and physical properties, such as pH, redox potential, salinity, and particle size [15–17]. Because the chemical and physical properties of estuarine sediment are temporally and spatially dynamic, it is difficult to predict the impact of industrial development on the fate and impact of PTEs [18].…”

“…Findings of previous surveys of the benthic invertebrates inhabiting the intertidal sediment in the Skeena estuary reveal an infaunal community that is relatively undisturbed at the estuary scale, but which still shows the scars of historic disturbance at finer-grained scales [10, 15, 21, 22]. Amphipods are powerful indicator species [23–27] whose high densities throughout the Skeena estuary [10, 15] suggests that current disturbances to intertidal areas are relatively limited. Similarly, we observe 40 intertidal species in this area, including multiple species at all trophic levels within the foodweb [10, 15], and such a complex community is often associated with non-disturbed habitats [4, 28–30].…”

“…Amphipods are powerful indicator species [23–27] whose high densities throughout the Skeena estuary [10, 15] suggests that current disturbances to intertidal areas are relatively limited. Similarly, we observe 40 intertidal species in this area, including multiple species at all trophic levels within the foodweb [10, 15], and such a complex community is often associated with non-disturbed habitats [4, 28–30]. Conversely, disturbed sites are often more easily invaded by invasive species [31, 32], and Capitellidae (Capitella capitate species complex) polychaetas are often observed in disturbed habitats, particularly areas that have been organically enriched [4, 27, 28, 33].…”

“…Conversely, disturbed sites are often more easily invaded by invasive species [31, 32], and Capitellidae (Capitella capitate species complex) polychaetas are often observed in disturbed habitats, particularly areas that have been organically enriched [4, 27, 28, 33]. Capitellidae polychaetas have a clumped distribution within the Skeena estuary and can be locally abundant at the scale of a 1m 2 plot [10, 15]. Similarly, abundant but localized populations of the invasive Cumacea Nippoleucon hinumensis , have been observed in the Skeena estuary [10, 15], and on other historically impacted mudflats along BC’s north coast [27].…”

“…Capitellidae polychaetas have a clumped distribution within the Skeena estuary and can be locally abundant at the scale of a 1m 2 plot [10, 15]. Similarly, abundant but localized populations of the invasive Cumacea Nippoleucon hinumensis , have been observed in the Skeena estuary [10, 15], and on other historically impacted mudflats along BC’s north coast [27]. While the universal presence and high abundances of amphipods, coupled with the complexity of the intertidal community at the estuary scale strongly suggest that these intertidal communities are relatively undisturbed, the locally abundant populations of invasive species and Capitellidae polychaetas offer contradictory evidence.…”