Resilience of aquatic net‐spinning caddisfly silk structures to common global stressors

Abstract

Summary Two of the most common consequences resulting from land use and climate change are increased fine sediment loads and shifts in hydrological regimes in freshwater ecosystems. Although a growing number of studies indicate that these stressors are likely to directly affect community composition and organism physiology, little is known about how biological structures produced by aquatic organisms might respond. For example, hydropsychid caddisflies (Trichoptera) are a group of globally distributed aquatic insects that spin silk mesh nets that they use to filter feed. These silk mesh nets are important ecosystem engineering structures in flowing waters that can regulate sediment erosion, food particle delivery by altering near‐bed current velocities, and enhance habitat availability for other macroinvertebrates. We conducted two experiments in laboratory mesocosms to assess the effects of increased fine sediment and drought on hydropsychid caddisfly silk. We compared silk thread diameter, thread count, mesh pore area, and thread tensile strength across treatments in which the silk nets were exposed to high levels of total suspended solids or to stream drying over 2 weeks. We found that caddisfly silk was resilient to both forms of stress and maintained its overall structure and tensile strength. Our findings indicate that biological silk structures may be viable ecosystem engineering tools following short‐lived disturbances associated with increased sediment loads and drying events. Caddisfly silk may be resilient to various forms of environmental change, with important consequences for recovery of aquatic communities.

Occupied and abandoned structures from ecosystem engineering differentially facilitate stream community colonization

“…Second, this timescale is particularly relevant to the duration over which caddisfly silk material is known to last without the engineer itself present (Appendix S1: Fig. S1; Albertson and Daniels 2016). The East Branch of WCC is classified as a third-order piedmont stream with land use predominated by forest and agriculture (Newbold et al 1997).…”

“…, but see Hemphill and Cooper ). The nets also have the potential to show legacy effects following emergence, death, or downstream drift of the caddisfly itself (Albertson and Daniels ). For example, abandoned retreats have been shown to persist for timescales relevant to aquatic insect colonization (i.e., weeks) and withstand extended periods of drought and sediment pollution (Albertson and Daniels ).…”

“…The nets also have the potential to show legacy effects following emergence, death, or downstream drift of the caddisfly itself (Albertson and Daniels ). For example, abandoned retreats have been shown to persist for timescales relevant to aquatic insect colonization (i.e., weeks) and withstand extended periods of drought and sediment pollution (Albertson and Daniels ). Concurrently, caddisflies have been shown to be highly territorial and antagonistic toward animals surrounding their retreats (Hemphill and Cooper , Hemphill ).…”

“…These treatments, respectively, represent (1) the presence of caddisflies prior to colonization of other invertebrates, including conspecifics, because they are early colonists (Cardinale et al. ), (2) caddisfly structures alone persisting through a disturbance event (Albertson and Daniels ), (3) and a post‐disturbance scenario without early caddisfly colonization or legacy of the silk. We predicted that (1) the initial presence of caddisflies with silk and silk alone would increase invertebrate colonization rate and overall benthic density and biomass compared to controls, (2) the initial presence of caddisfly silk alone would increase invertebrate colonization rate, and overall benthic density and biomass, compared to a treatment with caddisflies initially present due to the potential negative effects (e.g., territorial interactions) of the caddisflies offsetting the positive effects of silk structures, and (3) the importance of initial silk or caddisfly presence would vary throughout the temporal duration of the experiment, if treatments converged over time when Hydropsychidae naturally colonized all treatments.…”

“…Furthermore, caddisfly engineering is highly relevant to colonization dynamics following disturbance events because net-spinners are early colonizers (Hemphill 1988, Cardinale et al 2004, but see Hemphill and Cooper 1983. The nets also have the potential to show legacy effects following emergence, death, or downstream drift of the caddisfly itself (Albertson and Daniels 2016). For example, abandoned retreats have been shown to persist for timescales relevant to aquatic insect colonization (i.e., weeks) and withstand extended periods of drought and sediment pollution (Albertson and Daniels 2016).…”