Organic enrichment by macrophyte detritus, and abundance patterns of megafaunal populations in submarine canyons

Abstract

Submanne canyons can provide large quantities of food in aggregated form on the deepsea floor by acting as conduits for manne macrophyte production produced in the intertidal and shallow subtidal zone. Longshore transport dehvers substantial quantities of macrophyte detntus fronl surfgrass Phyllospadix lorreyi, kelps Macrocystis pyrifera and Egregia menziesii, and other macroalgae to the heads of Scripps and La Jolla Submarine Canyons. Strong tidal and gravity currents distribute this material throughout much of the canyon System, where it is utilized as food and habitat by benthic fauna. Video data taken from remotely operated vehicles and submarines were used to evaluate differences in detrital Cover and megafaunal abundance In the canyons, and at nearby reference Stations.Within the canyons dense mats of detntus were common down to 550 m, and M. pyrifera holdfasts were observed at 700 and 900 m. Virtually no dnft material was observed out of the canyons. Comparisons of megafaunal invertebrates in and out of the canyons revealed generally higher densities at noncanyon sites due to large numbers of urchins. Species richness of all megafauna and abundance of nonurchin megafauna were greater in the canyons than out. It is likely that urchin abundance in canyons is reduced through disturbance by currents and detrital flows in the canyons. Species nchness and abundance of fishes were greater in the canyons at all depths for which comparative data were available (100 to 500 m). From 150 to 200 m in Scripps Canyon, juvenile Pacific hake Merlucciusproductus were so abundant at tirnes that their bodies obscured visibility. Turbot Pleuronichfhys sp. and zoarcids Lycodes pacifica were also abundant in Scripps Canyon from 100 to 300 m. Data from this study support the hypotheses that macrophyte detntus Covers large areas of the La JoLla and Scripps Canyon axis, and that megafaunal abundance 1s associated with detritus at both large and small spatial scales

Partitioning of primary production among giant kelp (Macrocystis pyrifera), understory macroalgae, and phytoplankton on a temperate reef

“…As a foundation species, Macrocystis provides structural habitat to a diverse community of organisms, most of which do not, at least directly, depend on giant kelp for food (Foster and Schiel 1985;Graham 2004). Much Macrocystis biomass is transported to beaches (Dugan et al 2003) or bathyal environments (Harrold et al 1998;Vetter and Dayton 1999), where it provides an important source of allochthonous production to these ecosystems. Understory algae provide reef fishes with foraging habitat and refuge from predators (Laur and Ebeling 1983;Ebeling and Laur 1985;Holbrook and Schmitt 1992), and phytoplankton is an important food source for a diverse array of benthic suspension feeders (Gili and Coma 1998;Page et al 2008), a trophically dominant group on many coastal reefs (Newell et al 1982).…”

“…The biomass of Macrocystis can be limited by wave disturbance (Graham et al 2007;) and nutrients (Jackson 1977;Gerard 1982), particularly during El Niñ o events when resulting thermal stratification can suppress Macrocystis canopies for multiple years (Zimmerman and Kremer 1986;Dayton et al 1999). At least some understory algal species appear to be less susceptible to nutrient limitation during El Niñ o events, possibly due to lower nutrient requirements or resistance to low-nutrient conditions, combined with lower temperatures and higher nutrient concentrations near the bottom (Dayton et al 1999). Moreover, the low profile of most understory algae offers less drag to hydrodynamic forces compared with Macrocystis.…”

Assessment of goods and services, vulnerability, and conservation status of European seabed biotopes: a stepping stone towards ecosystem-based marine spatial management

“…Fish abundance is enhanced in canyons (Stefanescu et al, 1994;Vetter & Dayton, 1999;Brodeur, 2001;Vetter et al, 2010), which are therefore regularly targeted by commercial and recreational fishermen exploiting bottom fish and invertebrates (Vetter et al, 2010). Some of the deep-water shrimp fishing grounds are located on the margin of submarine canyons (Sardá et al, 2004).…”

“…Canyons may serve as important nursery grounds for some fish and invertebrate species possibly due to increased structural diversity compared to adjacent slope areas (e.g. rock walls, boulders, and detritus patches) and increased availability of benthic or planktonic prey (Vetter & Dayton, 1999;Vetter et al, 2010). Enhanced availability of food in canyons may be especially important for allowing demersal fish and benthic invertebrates to reproduce in otherwise oligotrophic regions (Vetter et al, 2010).…”

Seasonal variability of meiofauna, especially harpacticoid copepods, in Posidonia oceanica macrophytodetritus accumulations

“…Such exported leaf litter mixes with drift epilithic macroalgae, uprooted living seagrass shoots with rhizomes, other seagrass litter, seeds, dead macrofauna and fine sediment to form detritus. The exported detritus form dense accumulations, especially on adjacent unvegetated sand patches, in relation to local hydrodynamics and sand patch morphology (Vetter and Dayton, 1999). The macrophytodetritus host many organisms which can participate in the degradation of this organic material, such as bacteria, fungi, diatom microalgae and invertebrates (Danovaro, 1996;Danovaro et al, 2002;Gallmetzer et al, 2005;Graca, 2001;Mancinelli and Rossi, 2002).…”