Nutrient recycling by caddisflies alleviates phosphorus limitation in case periphyton

Abstract

Selective feeding and differential nutrient excretion by aquatic invertebrates plays a substantial role in nutrient recycling. Grazing larvae of the caddisfly Glossosoma intermedium construct a portable case for protection that also serves as a good substrate for periphyton colonization because it is constantly fertilized by larval excreta. We tested whether case periphyton was nutrient enriched compared to streambed periphyton and whether selective feeding by caddisfly larvae on case periphyton facilitates P remineralization. We measured total N, total P, and N ∶ P in stream water and streambed cobble periphyton in 3 western Wisconsin streams. We collected larvae and measured N and P content and N ∶ P of case periphyton, G. intermedium body, and G. intermedium excretion products. Cobble periphyton N ∶ P at 2 streams suggested P limitation (368 ± 109 and 50 ± 10), but case periphyton N ∶ P at those streams did not (11 ± 3 and 11 ± 0.8, respectively). Neither cobble nor case periphyton N ∶ Ps suggested P limitation at the 3 rd stream. Measured excretion N ∶ P was more similar to the excretion N ∶ P predicted for caddisfly grazing on case periphyton than for caddisfly grazing on cobble periphyton. Our results suggest that larval excretion alleviated P limitation of case periphyton and that case periphyton may serve as an important dietary resource for the grazing caddisfly larvae. Feeding on this P-rich case periphyton promotes P remineralization in P-limited, lotic ecosystems.

High interspecific variation in nutrient excretion within a guild of closely related caddisfly species

“…While uptake by case‐associated microbes is certainly a plausible nutrient flux and has been demonstrated in other systems (e.g., Kahlert and Baunsgaard , Mooney et al. ), it appears to have negligible influence on the mass‐specific excretion rates presented here.…”

Geographically widespread 13C‐depletion of grazing caddis larvae: A third way of fuelling stream food webs?

“…There is some support for selective feeding within the genus Glossosoma: McNeely et al (2006) attributed the low glossosomatid δ 13 C values in small F I G U R E 5 Stream ambient methane concentration ± 1 SE (logarithmic scale) and caddis larval δ 13 C ± 1 SE, suggesting no overall difference in methane concentration among sandstone, limestone and chalk, but greater overall depletion of caddis on chalk than the others (see text for details) unproductive streams in northern California to selective uptake of algae, although the influence of methane was not assessed in their study. Similarly, Glossosoma intermedium caddis larvae are thought to employ nutrient-specific foraging, grazing on phosphorus-rich periphyton on conspecific cases instead of phosphorus-limited periphyton on stream bed cobbles (Mooney, Strauss, & Haro, 2014;Mooney, Strauss, & Haro, 2016). Overall, therefore, the uptake of methane-derived carbon in our study could be by direct ingestion of methanotrophs, which we think the most likely.…”

“…() attributed the low glossosomatid δ 13 C values in small unproductive streams in northern California to selective uptake of algae, although the influence of methane was not assessed in their study. Similarly, Glossosoma intermedium caddis larvae are thought to employ nutrient‐specific foraging, grazing on phosphorus‐rich periphyton on conspecific cases instead of phosphorus‐limited periphyton on stream bed cobbles (Mooney, Strauss, & Haro, ; Mooney, Strauss, & Haro, ). Overall, therefore, the uptake of methane‐derived carbon in our study could be by direct ingestion of methanotrophs, which we think the most likely.…”

“…Methane-oxidising bacteria could thus constitute a kind of ship's biscuit for these grazers-basic rations when higher quality food is unavailable. Glossosomatid larvae characteristically form very high-density aggregations and have been shown to graze on the surfaces of neighbouring conspecifics' cases (Cavanaugh, Haro, & Jones, 2004;Cox & Wagner, 1989;Mooney et al, 2014Mooney et al, , 2016. Note also that biofilms on caddis cases were shown to oxidise methane (Trimmer et al, 2009) and thus must contain MOB.…”

Substratum‐Associated Microbiota

“…Periphyton that colonized the case Glossosoma intermedium, experienced relief from P limitation from caddisfly excreta in contrast with the cobbles at two streams (Mooney et al, 2014). Nutrient ratios indicated that larva fed on case rather than cobble algal assemblages.…”