The influence of geology and season on macroinvertebrates in Belizean streams: implications for tropical bioassessment

Abstract

Considerable attention has been paid to the potentially confounding effects of geological and seasonal variation on outputs from bioassessments in temperate streams, but our understanding about these influences is limited for many tropical systems. We explored variation in macroinvertebrate assemblage composition and the environmental characteristics of 3 rd -to 5 th -order streams in a geologically heterogeneous tropical landscape in the wet and dry seasons. Study streams drained catchments with land cover ranging from predominantly forested to agricultural land, but data indicated that distinct water-chemistry and substratum conditions associated with predominantly calcareous and silicate geologies were key determinants of macroinvertebrate assemblage composition. Most notably, calcareous streams were characterized by a relatively abundant noninsect fauna, particularly a pachychilid gastropod snail. The association between geological variation and assemblage composition was apparent during both seasons, but significant temporal variation in compositional characteristics was detected only in calcareous streams, possibly because of limited statistical power to detect change at silicate sites, or the limited extent of our temporal data. We discuss the implications of our findings for tropical bioassessment programs. Our key findings suggest that geology can be an important determinant of macroinvertebrate assemblages in tropical streams and that geological heterogeneity may influence the scale of temporal response in characteristic macroinvertebrate assemblages.

Challenges using extrapolated family-level macroinvertebrate metrics in moderately disturbed tropical streams: a case-study from Belize

“…Consistent with previous conclusions (Carrie et al, 2015), compositional data indicated environmental variation associated with geology exerted stronger influence than that associated with human activities (Fig. 2).…”

“…Observations were weighted according to proximity to the stream channel, and summed to produce a site score describing the different categories of human activity following Kaufmann et al (1999) (AQEM Consortium, 2002). Sampling was limited to one season to control for the potentially confounding effects of seasonality on macroinvertebrate assemblages observed in the study streams previously (Carrie et al, 2015), and that others have linked to temporal variation in metric scores in other lowland neotropical streams (Helson and Williams, 2013). Sampling was timed to occur during low or base-flow conditions because human impacts are likely to be more pronounced and because streams are more accessible.…”

“…We hypothesized that family metrics would vary in relation to decreasing forested condition along a gradient from subsistence/non mechanized farming to residential 4 activities to commercial agriculture. Our study catchments were environmentally heterogeneous (Carrie et al, 2015) and since environmental and subsequent biological change can be associated with natural as well as anthropogenic gradients (Neff & Jackson, 2011), we expected to observe a response to both gradients. Ability to detect anthropogenic environmental change can be confounded by natural variation, particularly where disturbance effects are subtle and natural variability large (Hawkins et al, 2000, Metzeling et al, 2006, so we controlled for season, stream order and altitude and located our treatment categories separately within streams of different geological types (i.e., treatment group was nested within categories reflecting upstream geological influence).…”

Distribution and structure of lotic macroinvertebrate communities and the influence of environmental factors in a tropical cloud forest, Cusuco National Park, Honduras

“…This would be especially important in the case of Group 1 sites where lower macroinvertebrate abundance and taxon richness were recorded even though these are in areas with minimal anthropogenic disturbance. Furthermore, more groups may emerge, if more sites were sampled across a greater geographic area, for example the results indicated that substrate is likely to be influential and at least 1 other study in the region (Belize) has highlighted the importance of geology (Carrie et al, 2015). Therefore, further sampling, taking in a greater geographic area as well as more environmental variables, than could be covered in the present study, would be necessary to produce a comprehensive stream typology for the area.…”

“…While several studies of this nature have been undertaken in recent years in neotropical freshwater streams, for example Bücker et al (2010), Moya et al (2011) and Carrie et al (2015) descriptive studies of this nature are still relatively few in the region and much work remains to be done. Furthermore this has been identified as a research priority for freshwater ecosystems in Honduras by Lopez and Mora (2014) who go on to describe the availability of information on freshwater communities and their habitats in Honduras as practically nil and to emphasise the particular importance of research on the subject in protected areas.…”