Abstract
We used hyperspectral imaging to study short-term effects of bioturbation by lugworms (Arenicola marina) on the surficial biomass of microphytobenthos (MPB) in permeable marine sediments. Within days to weeks after the addition of a lugworm to a homogenized and recomposed sediment, the average surficial MPB biomass and its spatial heterogeneity were, respectively, 150-250% and 280% higher than in sediments without lugworms. The surficial sediment area impacted by a single medium-sized lugworm (~4 g wet weight) over this time-scale was at least 340 cm2. While sediment reworking was the primary cause of the increased spatial heterogeneity, experiments with lugworm-mimics together with modeling showed that bioadvective porewater transport from depth to the sediment surface, as induced by the lugworm ventilating its burrow, was the main cause of the increased surficial MPB biomass. Although direct measurements of nutrient fluxes are lacking, our present data show that enhanced advective supply of nutrients from deeper sediment layers induced by faunal ventilation is an important mechanism that fuels high primary productivity at the surface of permeable sediments even though these systems are generally characterized by low standing stocks of nutrients and organic material.
Highlights
Benthic phototrophs such as diatoms, cyanobacteria, chlorophytes and dinoflagellates, which are commonly referred to as microphytobenthos (MPB), are a major contributor to the primary productivity [1, 2], food web [3] and sediment stability [4] in coastal ecosystems
Chlorophyll a maps obtained in the laboratory containers showed that the surficial MPB biomass overall increased during the course of incubation but the variation generally entailed both a decrease and an increase (Fig 1)
By analyzing the chl a concentrations averaged over the entire sediment surface, we found that the surficial MPB biomass in containers with and without lugworms increased during the first 4 days, but the increase was significantly greater in the lugworm containers after 11 days of incubation (S1 Table)
Summary
Benthic phototrophs such as diatoms, cyanobacteria, chlorophytes and dinoflagellates, which are commonly referred to as microphytobenthos (MPB), are a major contributor to the primary productivity [1, 2], food web [3] and sediment stability [4] in coastal ecosystems. Their activity and distribution are mainly determined by light climate, nutrient levels and grazing pressure, and exhibit great spatio-temporal variability from mesoscopic to regional [5, 6] and PLOS ONE | DOI:10.1371/journal.pone.0134236. Their activity and distribution are mainly determined by light climate, nutrient levels and grazing pressure, and exhibit great spatio-temporal variability from mesoscopic to regional [5, 6] and PLOS ONE | DOI:10.1371/journal.pone.0134236 July 31, 2015
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