DOI: 10.5061/dryad.4b2t6
title: Data from: Detrital subsidy from subtidal kelp beds is altered by the invasive green alga Codium fragile ssp. fragile

description: Invasive species have the potential to alter the dynamics of detrital
 subsidy from high to low productivity areas through changes in quantity
 and nutritional quality of detrital material. We examined the effect of
 the invasive alga Codium fragile ssp. fragile on the nature of detrital
 export from subtidal algal beds off Nova Scotia, Canada, by comparing
 changes in mass, nutritional quality (%C, %N, C/N ratio), concentration of
 dimethylsulfoniopropionate (DMSP, a secondary metabolite that deters
 grazers), and isotopic composition (δ13C and δ15N) between C. fragile and
 the native kelp Saccharina latissima at 4 wk intervals over 16 wk of
 degradation in cages on a sand bottom at 19 m depth. C. fragile degraded
 more slowly, and had a consistently lower C/N and higher DMSP
 concentration, than S. latissima. Isotope signatures did not differ
 between algal species: δ15N became slightly enriched (~1‰) after 16 wk of
 degradation, with no change in δ13C. We also compared macrofaunal
 communities associated with degrading thalli of each algal species and
 found significantly higher abundances of invertebrates (mainly capitellid
 polychaetes) on S. latissima after 8 wk of degradation, resulting in lower
 evenness (J’) and diversity (H’) on S. latissima compared to C. fragile.
 Macrofaunal community composition became similar between algal species at
 12 and 16 wk in concordance with decreases in C/N ratio in S. latissima
 and DMSP concentration in C. fragile. Our results indicate that
 differences in biochemical composition and the rate of degradation between
 C. fragile and native kelps result in community-level effects in areas
 linked to shallow algal beds via the transfer of detritus.
description: Degradation Experiment
 Algae Nutrition and Weight. A Canadian Healthy Oceans Network Ecosystem
 Function Project, EF-11This experiment
 monitored the nutritional characteristics of two algal species, one
 invasive (Codium fragile) and one native (Saccharina latissima) during
 degradation on sediments offshore of a shallow kelp bed. Twenty four mesh
 bags, each containing ~500g of either C. fragile or S. latissima were
 contained in cages and placed on sediments at 19 m water depth (2 species
 x 12 replicates = 24 total bags). Three bags of each species were
 collected at roughly monthly intervals. Change in mass from time 0 was
 then measured and used to calculate degradation rate. Stable isotope
 ratios of d13C and d15N, %C, %N, C/N and concentration of
 Dimethylsulfoniopropionate were measured on each sample. At each sampling
 time (T0, T1, T2, T3 = 0, 28, 56, 85, and 112 days) the same measures were
 taken on three control samples of C. fragile and S. latissima collected
 from the shallow algal bed (~5 m depth) inshore of the experiment
 location. Sample ID is a unique sample number, Treatment ID is the
 treatment number, Group indicates weather the sample was from the
 degradation or control group, and initial weight and final weight indicate
 the weight of the sample at T0 and at the time it was collected. Measures
 of changes in mass were not applicable in the control treatments, as these
 represent live algae in the shallowsDegradation Exp Algae Nutrition
 and Weight.xlsxDegradation Experiment
 Animal Abundances. A Canadian Healthy Oceans Network Ecosystem Function
 Project, EF-11At each sampling
 interval, the communities of organisms (body size &gt; 1 mm) found on each
 degrading algal sample were collected, identified and enumerated. This
 data sheet shows the abundances of each species identified on each
 sample.Degradation Exp
 Animals.xlsx