Detrital production in Nova Scotian kelp beds: patterns and processes

Abstract

Connectivity via the transport of detrital material from areas of high to low productivity may be an important determinant of secondary productivity and biodiversity in receiving communities. On the Atlantic coast of Nova Scotia, detritus exported from subtidal kelp beds contributes to food webs in communities inhabiting deeper waters offshore. To estimate the amount of energy available via this pathway, we measured rates of detrital production via erosion of kelp blades in kelp beds at 5 sites varying in wave exposure. Specifically, we measured productivity and erosion of the 2 dominant species of kelp, Laminaria digitata and Saccharina longicruris, over 16 mo. We also examined the effect of environmental and biological factors on erosion rates, including temperature, wave exposure, grazing by snails and cover by the invasive bryozoan Membranipora membranacea. We observed clear seasonal and spatial patterns in productivity, with the highest production in spring. Erosion rate was highly variable across sites and seasons, and was strongly related to the cover of M. membranacea and the intensity of snail grazing at the distal end of kelp blades. Both factors cause tissue degradation, abrasions and perforations that weaken blades. Erosion rate was also positively related to water temperature and site exposure. Annual detrital production from the erosion of kelp blades increased linearly with kelp bed biomass, and ranged from 0.5 to 1.71 kg dry weight m -2 (150-513 g C m -2 ) across sites. These rates equal or exceed annual phytoplankton production off the Atlantic coast of Nova Scotia and estimates of detrital production in seagrass beds in North America.KEY WORDS: Detritus · Grazing · Invasive species · Kelp bed · Laminaria digitata · Membranipora membranacea · Productivity · Saccharina longicruris Resale or republication not permitted without written consent of the publisherMar Ecol Prog Ser 421: [67][68][69][70][71][72][73][74][75][76][77][78][79][80][81][82] 2011 The interaction between native and introduced species is another area of expanding interest and concern among marine ecologists and resource managers, as evidence of the negative impacts of biological invasions accumulates (Thomsen et al. 2009, Sorte et al. 2010. This research has primarily addressed the direct effects of introductions on native populations and the resulting changes in biodiversity and ecosystem function (Eastwood et al. 2007, Galil 2007, Schaffelke & Hewitt 2007. Indirect effects on the dynamics of material and energy exchange between invaded and adjacent native communities are largely unknown.Kelp ecosystems are amongst the most productive in the world (Mann 1972a, Smith 1988. In Nova Scotia, Canada, kelp beds often are located next to sea urchin barrens, characterized by low productivity and coralline-algal-dominated assemblages (Chapman 1981, Mann 1982, Scheibling et al. 1999. The faunal assemblages that inhabit these barrens (Balch & Scheibling 2000, Knip & Scheibling 2007 and adjacent sedimentary habitats in deeper ...

Production and fate of kelp detritus

“…The opposite was observed for populations of Laminaria pallida and Ecklonia maxima in South Africa, where dislodgement accounted for a small portion of biomass produced annually (6%) compared to erosion (70%) (Newell et al 1982). Erosion rate also exceeded dislodgement rate in populations of Laminaria digitata and Saccharina latissima measured in 2 separate studies in Nova Scotia (Chapman 1984, Krumhansl & Scheibling 2011a, and Ecklonia radiata in northern New Zealand and Western Australia (Novaczek 1984, Hatcher et al 1987. The relative importance of erosion and dislodgement to detrital production may be related to kelp morphology, with larger canopyforming kelps producing more detritus through dislodgement than smaller canopy-forming and prostrate kelps.…”

“…Never-284 Table 1. Estimated rates of productivity, blade erosion, dislodgement of whole fronds and thalli (g dry mass m Hayashida (1977) theless, dis lodgement and erosion are typically greater at sites with high wave exposure than at more protected sites (Duggins et al 2003, Krumhansl & Scheibling 2011a). The measured force to break kelp stipes and blades often exceeds the predicted hydrodynamic force acting on kelps (Utter & Denny 1996, Denny et al 1997, Mach et al 2007), suggesting that breakage and dislodgement are uncommon.…”

“…Poorly attached kelps, and those that have settled on small cobbles and biogenic structures such as mussels, are more likely to be come dislodged from the substratum at higher flow rates (Gunnill 1985, Witman 1987, Scheibling & Gagnon 2009). Erosion occurs continuously, even during relatively calm conditions (Reed et al 2008, Krumhansl & Scheibling 2011a). Loss of fronds and blade area may actually increase the survivorship of kelps in strong flow by reducing drag on thalli (Gunnill 1985.…”

Global patterns of kelp forest change over the past half-century

“…This result is strikingly different from that reported for many other marine and terrestrial systems that are experiencing consistent declines in species abundance across the globe (1-3, 6) and, in many ways, highlights the atypical resilience of kelps. However, where kelp resilience is eroding and leading to declines in abundance (7,18,54,64,66,67), impacts to ecosystem health and services can be far-reaching (19,25,26,68,69). Maintaining the resilience of kelp forest ecosystems into the future will rely on the continued monitoring of kelps and management of stressors on local and regional scales.…”

Regrowth and biofouling in two species of cultivated kelp in the Shetland Islands, UK

“…Parke 1948;Kain 1979;Bartsch et al 2008;Saunders and Metaxas 2008;Andersen et al 2011;Krumhansl and Scheibling 2011;Nielsen et al 2014). New tissue is formed in the meristem located at the base of the blade.…”