High-quality algae attached to leaf litter boost invertebrate shredder growth

Abstract

Algae are higher-quality food resources than allochthonous plant litter for stream invertebrates, in part, because of their higher content of polyunsaturated fatty acids (PUFAs). We tested the hypothesis that algal biofilms on the surfaces of leaf litter improve the nutritional quality of terrestrial inputs for invertebrate shredders. We used a laboratory feeding experiment with 2 light levels (open and shaded) and 2 nutrient regimes (ambient and enriched) to manipulate the algal biofilms that form on leaf surfaces (Lophostemon confertus). We assessed how these treatments affected the fatty acid (FA) composition of these biofilms and the somatic growth of a stream invertebrate shredder (Anisocentropus bicoloratus, Trichoptera) that feeds on the conditioned leaf litter. Shredders reached a significantly larger size when nutrients were added, and leaf mass loss was significantly greater in these treatments than in treatments without nutrients. Shredder growth was affected significantly by leaf PUFA content, and variations in shredder PUFA content were consistent with those in leaf PUFAs. Our results suggest that high-quality algae attached to leaf litter regulated the PUFA composition and improved the somatic growth of these shredders. Our data provide evidence that the availability of high-quality algae enhances dietary use of low-quality riparian leaf litter in stream food webs.

Feeding strategies for the acquisition of high‐quality food sources in stream macroinvertebrates: Collecting, integrating, and mixed feeding

“…Differences in the FA composition among aquatic macroinvertebrates, periphyton, and terrestrial leaves suggest that periphyton is the main LC‐PUFA (in particular EPA) source for macroinvertebrates. Although submerged leaves were not available in our study streams in summer and FA of biofilms attached to submerged leaves were not analyzed, previous studies report that submerged leaves as a whole contained no or very little EPA, < 1% (Brett et al ; Torres‐Ruiz and Wehr ; Guo et al c ), which is also confirmed by our leaf FA (Table ). Moreover, seasonal change is unlikely to affect the low‐EPA content of submerged leaves (Torres‐Ruiz and Wehr ).…”

“…Interestingly, although periphyton FA showed a limited effect on shredder FA, shredder EPA was still 6.9 times higher than in periphyton, suggesting shredders assimilate EPA very efficiently. It is well studied that shredders prefer feeding on conditioned rather than fresh leaves (Nolen and Pearson ; Pearson and Connolly ; Allan and Castillo ), and biofilms attached to leaf surfaces are a potential source of EPA (Torres‐Ruiz and Wehr ; Guo et al c ). However, in summer, conditioned leaves were not available in our streams, and it has been frequently reported in previous studies that shredders may face seasonal shortages of conditioned leaves during the late spring and summer period (Dobson and Hildrew ; Wallace et al ).…”

“…From each invertebrate sample 5–7 mg of dry mass, 10 mg dry mass from each periphyton sample, and 50 mg dry mass from each leaf sample were used for lipid extraction, respectively. Lipids were extracted and methylated according to the methods reported in Guo et al ( c ). Fatty acid methyl esters (FAME) were analyzed using a gas chromatograph (THERMO Trace; FID 260°C, carrier gas: He: 1 mL/min, detector gases: H 2 : 40 mL/min, N 2 : 45 mL/min, air: 450 mL/min, temperature ramp: 140°C (5 min)–4°C/min–240°C (20 min) = 50 min) equipped with a temperature‐programmable injector and an autosampler.…”

“…Macroinvertebrates are selective feeders and may preferentially feed on high‐quality food for LC‐PUFA (Bunn et al ; Guo et al c ; Brett et al ). Periphyton and terrestrial organic matter are two primary basal food sources in stream ecosystems.…”

Relationships of shredders, leaf processing and organic matter along a canopy cover gradient in tropical streams

“…These observations match with the prediction that even highly covered tropical streams have enough light incidence to sustain a reasonable level of primary produc- (Bunn et al, 1999a(Bunn et al, , 1999bLau et al, 2009). In this manner, we speculate that shredders may be consuming some autochthonous carbon along with their predominant diet of leaves and that they might benefit from algae attached to leaves (Guo et al, 2016).…”