Effects of macroconsumers on benthic communities: Rapid increases in dry-season accrual of calcium in a tropical karst stream

Abstract

Species loss from upper trophic levels can result in some major changes in community structure and ecosystem functions. Here, we experimentally excluded macroconsumers (e.g., fish and shrimp) in a Brazilian karst tropical stream during the dry season to investigate if their loss affected the accrual of calcium, dry mass (DM) and ash-free dry mass (AFDM) of sediment, benthic invertebrates, and chlorophyll-a. We found that the exclusion of macroconsumers decreased accrual of calcium. The absence of fish and shrimp may have promoted increased grazing by mayflies and snails in the electrified treatment as expressed by the depressed calcium accrual and shift in periphyton community composition. However, the exclusion of macroconsumers had no effect on DM and AFDM, chlorophyll-a, or total abundance of invertebrates. Our findings shed new light on the impact of macroconsumer loss and consequences for calcium accrual in karstic streams.

Do crayfish affect stream ecosystem response to riparian vegetation removal?

“…This and other studies on consumer response to riparian management (e.g. Corréa et al., 2019; Kaylor & Warren, 2017) demonstrate the potential for consumers to respond differently depending on the type and intensity of the riparian management action (e.g. subcanopy shrub removal, timber harvests, buffer zone widths) in the short‐term versus long‐term.…”

“…Pringle & Blake, 1994), we did not observe a reduction in either benthic sediment or fine benthic organic matter due to bioturbation by crayfish. Not all macroconsumers influence sediment and FBOM accumulation on benthic substrates (Ho & Dudgeon, 2016; Corréa et al, 2019), and bioturbation effects probably vary among contexts (Ho & Dudgeon, 2016) and may be overridden by effects of flow (Rice et al., 2016).…”

“…How streams respond to riparian management may depend on the type of management action, the nature of in‐stream species and their relative dominance (e.g. contribution to stream food web linkages and energy flow, Hall et al., 2000; species that structure benthic habitats, Taylor et al., 2006), and how the specific management action affects trophic interactions by stream consumers (Corréa et al., 2019).…”

“…Stream macroconsumers that are large‐bodied (proportionate to their habitat size) and relatively long‐lived often play dominant roles in stream benthic ecosystem processes through consumption of benthic food resources, physical disturbance of the substrate, and nutrient recycling (Corréa et al., 2019; Ho & Dudgeon, 2016; Schofield et al., 2001). Macroconsumers can decrease rates of algal growth and increase leaf litter breakdown through direct consumption (Schofield et al., 2001, 2008; Yang et al., 2020) or indirectly via trophic cascades (Bush et al., 2017; Marshall et al., 2012).…”

“…The dominant role of macroconsumers in stream ecosystems means that even small changes in macroconsumer populations (i.e. density or composition) following riparian management can have disproportionately large effects on stream ecosystem processes (Corréa et al., 2019; Schofield et al., 2001). Thus, the total loss of a macroconsumer can substantially alter stream ecosystems (Dangles and Guerold, 2001; Marshall et al., 2012).…”