Response of the benthic foraminiferal community to a simulated short-term phytodetritus pulse in the abyssal North Pacific

Abstract

Foraminifera are an important faunal element of the abyssal ecosystem and largely depend on deposited particulate organic matter from the photic zone to sustain their metabolism for growth and reproduction. However, their role in the carbon cycle in deep-sea sediments is insufficiently studied. We investigated benthic foraminifera at Station M (4000 m depth) in the Northeast Pacific and assessed the response of individual species to a simulated phytodetritus pulse during an in situ feeding experiment. Sediments were incubated for 4 d with 13 C-labeled diatoms (Thalassiosira weissflogii) applied to the sediment surface. The living foraminiferal community (> 0.063 mm) of the upper 3 cm contained >100 species and was strongly dominated by a few taxa of soft-walled saccamminids. Population density of the entire living foraminiferal community was highest at the sediment surface (mean ± SD = 279 ± 72 ind. 10 cm −3 in background and 13 C-incubated cores) and decreased gradually with depth. Large differences were observed in the uptake of the algal material among species and between depth levels. During the experiment, 0.82 mg C m −2 were ingested, mainly by calcareous (~60%) and agglutinated (~40%) foraminifera. Uptake was highest at the sediment surface and 3 to 5 times less in deeper sediment horizons. Despite clear signs of vitality and a strong representation in the foraminiferal community, none of the soft-walled species showed a noticeable response to the offered algal material. We conclude that soft-walled foraminifera may not be important to the short-term phytodetrital matter cycling at the abyssal sea floor.

“Live” (stained) benthic foraminiferal living depths, stable isotopes, and taxonomy offshore South Georgia, Southern Ocean: implications for calcification depths

“…In a simulated phytodetritus event Sweetman et al (2009) found that the uptake of added carbon, labelled with 13 C, was confined to surface-living specimens of the deep-infaunal Globobulimina turgida. However, we note that Enge et al (2011) did not record a significant response by deeper infaunal taxa to a simulated phytodetritus pulse, although this may be due to the short duration (4 days) of their experiment. It is also important to note that it has been hypothesized that deep-infaunal taxa may have a preference for degraded organic matter (Caralp, 1989;Fontanier et al, 2003), which if correct may further delay their response to influxes of labile organic matter from phytodetrital pulses.…”

Algal pigments in Southern Ocean abyssal foraminiferans indicate pelagobenthic coupling

“…Indeed, subsamples taken within a single sediment core can greatly differ in terms of taxonomic composition, as shown using environmental DNA sequencing (Lejzerowicz et al, 2014). From our four species, only a relative of Bathysiphon could be sequenced while numerous species washed through the Agassiz trawl mesh such as those belonging to the small genus Epistominella may also contribute to the phytodetritus uptake (Enge et al, 2011;Gooday, 1988).…”

“…But it has also been shown that many deep-sea foraminiferans are associated with phytodetrital aggregates (Cornelius and Gooday, 2004) and can give a fast response to pulses of phytodetritus (Gooday, 1988(Gooday, , 2002. The response of foraminiferans to phytodetritus exposure has been extensively documented both in situ and experimentally (Enge et al, 2011;Heinz et al, 2001;Nomaki et al, 2005Nomaki et al, , 2009Witte et al, 2003). Indirectly, the distribution of benthic foraminiferal faunas, e.g., dominated by Epistominella exigua (Brady, 1884) in various Southern Ocean environments are a reflection of the importance of phytodetritus pulses (Mackensen et al, 1993(Mackensen et al, , 1995.…”

Uptake of phytodetritus by benthic foraminifera under oxygen depletion at the Indian margin (Arabian Sea)

“…In the laboratory, the 0-1 cm sediment sample was thawed and washed over a mesh (125 µm) with artificial seawater (composition see Enge et al, 2011). After sieving, the residue was frozen at −25 • C until further processing.…”

“…In situ feeding experiments using 13 C-labeled food have been shown to be an effective approach to study the metabolic response of foraminifera to phytodetritus deposition under natural conditions (e.g., Witte et al, 2003;Nomaki et al, 2005;Enge et al, 2011). In OMZ sediments on the Pakistan margin, Woulds et al (2007) and Andersson et al (2008) performed a series of labeling experiments along a depth transect (140-1850 m) focusing on the role of the benthic fauna in sedimentary processes.…”