Detrital subsidy from subtidal kelp beds is altered by the invasive green alga Codium fragile ssp. fragile

Abstract

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 (δ C. 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.

Can ecosystem functioning be maintained despite climate‐driven shifts in species composition? Insights from novel marine forests

“…The stocks and fluxes of organic matter are central to the biological, geochemical, and physical processes that occur within kelp forest ecosystems, as well as in spatially disconnected habitats subsidized by kelp‐derived organic matter (Krumhansl & Scheibling, 2012a). To investigate how future kelp forests dominated by the warm‐temperate kelp L .…”

Detrital kelp subsidy supports high reproductive condition of deep-living sea urchins in a sedimentary basin

“…The slower response to the 60 m line (59 d had elapsed before the first urchins were observed there) suggests that sea urchins are unable to detect or respond to detritus 10s to 100s of meters distant, and may only encounter it through random movement. Once deposited, kelp detritus degrades slowly at depth and persists as a food source for macrofaunal communities for up to 4 mo in the absence of sea urchins (Krumhansl & Scheibling 2012b). We also observed minimal loss of transplanted kelp at the 60 m experimental line over nearly 2 mo before sea urchins located it.…”

“…The supply of detrital macroalgae, mainly kelp, likely explains the relatively high GI in deep urchins. Not only is kelp a high quality and preferred food of S. droebachiensis (Scheibling & Hatcher 2013), but the nutritional quality of kelp detritus is also enriched by microbial degradation (Duggins & Eckman 1997, Norderhaug et al 2003, Krumhansl & Scheibling 2012b. S. droebachiensis generally does not form dense populations below 30 m depth as it does in the shallow barrens along the coast of Nova Scotia , Brady & Scheibling 2005).…”

“…Since gonadal production in sea urchins is tightly linked to food availability (Keats et al 1987, Meidel & Scheibling 1999, Wahle & Peckham 1999, detrital subsidy is expected to enhance the reproductive capacity of deep-living sea urchins, and hence their contribution to the supply of larvae to shallow populations. Patterns of detrital kelp production (Krumhansl & Scheibling 2011, Filbee-Dexter & Scheibling 2012 and degradation (Krumhansl & Scheibling 2012b) have been measured in Nova Scotia, however the seasonal variation and extent of detrital deposition to deep subtidal habitats have not been quantified. Kelly et al (2012) found that sea urchins in habitats beyond the kelp bed edge (25 to 30 m depth and 240 m offshore) with access to kelp detritus had higher gonad indices than those living in barrens, but sea urchins at greater depths have not been studied.…”

Projected 21st‐century distribution of canopy‐forming seaweeds in the Northwest Atlantic with climate change

“…Under a business‐as‐usual RCP8.5 scenario, major changes in seaweed composition are expected from Long Island Sound into the Gulf of Maine, and potentially along the Scotian Shelf and southern Gulf of St. Lawrence, with hot spots for species loss. The loss of canopy‐forming species can have cascading effects on coastal ecosystems leading to changes in carbon storage (Schmidt et al, ), decreases in secondary production (Krumhansl & Scheibling, ), alterations in associated species composition and diversity (Dijkstra et al, ; Schmidt & Scheibling, ), and potential regime shifts (Wernberg et al, ).…”