Importance Of Microphytobenthos Research Articles

Spatial variability in macrofaunal diet composition and grazing pressure on microphytobenthos in intertidal areas

AbstractMicrophytobenthos forms an important part of the diet of macrofauna (macrozoobenthos) in many intertidal ecosystems. It is unclear, however, whether the dependence of macrofauna on microphytobenthos varies spatially within and among tidal systems. We aim (1) to assess the spatial variability in the importance of microphytobenthos in the diet of macrofauna (i.e., between and within two tidal basins and as function of elevation), (2) to quantify grazing pressure of the macrofaunal community on different potential food sources (microphytobenthos, phytoplankton and terrestrial organic material) for several sites in two tidal basins and (3) to compare microphytobenthic production and summer/autumn grazing of the total macrofaunal community and grazing pressure per feeding type, with potential microphytobenthic production estimated from rates in early spring, when grazing was low. Using a natural stable isotope approach, we identified microphytobenthos as a more important food source for macrofauna than phytoplankton and terrestrial organic material. Microphytobenthos dependency differed between tidal basins for the genera Bathyporeia (sand digger shrimp), Macoma (Baltic tellin), and Peringia (mudsnail) and for sampled individuals of all genera combined, and did not vary as function of elevation. We showed that macrofaunal grazing on microphytobenthos is quantitatively important and, in some cases, approached microphytobenthic production rates in early spring. No positive relation between microphytobenthic production in early spring and macrofaunal grazing in summer/autumn was observed. This suggests that the studied consumer‐resource interactions are coupled on a larger spatial scale (i.e., mesoscale, ≈10 to 100 km), rather than the fine (mm to m) scale.

Impacts of a bivalve mass mortality event on an estuarine food web and bivalve grazing pressure

ABSTRACTDeclines in bivalve populations have been quite common worldwide, often associated with coastal development, pollution and climate change. In addition to the impacts of these chronic stressors, occasional mass mortality events may have severe consequences on ecosystem services and biodiversity. In this study, we examined the impact of a mass mortality event of the clam (Austrovenus stutchburyi) on an estuarine food web and the grazing pressure exerted by the bivalve population. In February 2009, c. 60% of the clam population died in Whangateau Harbour, New Zealand. Population clearance rate calculations suggest that the clam population do not exert significant top-down control on phytoplankton biomass in the estuary, and thus the impact of the mortality event on bivalve grazing pressure was less severe than the reduction in abundance would suggest. A trophic model shows that phytoplankton play a limited role in the estuary food web, which is instead dominated by microphytobenthos and clams. This study highlights the importance of microphytobenthos in shallow estuaries, and the application of the trophic model is a useful tool that can identify key components of the ecosystem and could help inform monitoring programmes.

The contribution of microphytobenthos to total productivity in upper Narragansett Bay, Rhode Island

In many coastal marine ecosystems, microphytobenthos (MPB) can contribute a significant fraction of total system primary production, particularly in shallow lagoons or systems with broad photic shoals. While the role of MPB has been quantified in several shallow systems around the world, their contribution to primary production on the extensive shoals that line a number of deeper estuaries has often been overlooked. We assessed the contribution of MPB to total primary production within four regions of upper Narragansett Bay, RI, USA to quantify the significance of benthic production on the extensive shallow shoals that line this relatively deep estuarine system. Our results indicate that surface sediment chlorophyll-a concentrations and daily benthic gross primary production rates in shallow portions of upper Narragansett Bay are within the range of previous studies conducted along the northeastern U.S. coast. Despite these high rates, our results when scaled to the system level emphasize the importance of phytoplankton production in most of the upper bay under current conditions, although MPB were found to contribute a significant fraction (up to one third) of total primary production in certain regions at certain times. Despite the high rates of benthic gross primary production in some portions of the upper bay, the benthos remained net heterotrophic throughout the spring, summer, and fall at most sites, although production within the Greenwich Bay sub-estuary was enough to drive the benthos slightly net autotrophic for short periods in the fall. While the current role of MPB appears to be limited in terms of its overall contribution to total gross primary production, the importance of MPB in the future may increase due to changing climate and reductions in anthropogenic nutrient loading.

Drivers of colonization and succession in polar benthic macro- and microalgal communities

Abstract Information on succession in marine benthic primary producers in polar regions is very scarce, particularly with regard to effects of abiotic and biotic drivers of community structure. Primary succession begins with rapid colonizers, such as diatoms and ephemeral macroalgae, whereas slow, highly seasonal recruitment and growth are characteristic of annual or perennial seaweed species. Colonization of intertidal and subtidal assemblages on polar rocky shores is severely affected by physical disturbance and by seasonal changes in abiotic conditions. Biotic factors, such as grazing, can strongly affect colonization patterns and also alter competitive interactions among benthic algae. Ambient UV radiation affects the diversity of macroalgal communities during early and later stages of succession. In contrast, microalgal assemblages have high tolerance to UV stress. Climate warming could alter algal latitudinal distribution and favor invasion of polar regions by cold-temperate species. Reduced sea ice cover and retreating glaciers could expand colonization areas but alter light, salinity, sedimentation and disturbance processes. Although the key role of macroalgae in coastal systems and, to a much reduced extent, the importance of microphytobenthos have been documented for polar regions, information on the successional process is incomplete and will benefit from further ecological studies.

Dynamics of microphytobenthic biomass in a coastal area of western Seto Inland Sea, Japan

This study focused on the causes of the variation in microphytobenthic biomass and the effects of this variation on macrobenthic animals in the western Seto Inland Sea, Japan, where the importance of microphytobenthos as the primary food source for benthic animals has been recently reported. We investigated the microphytobenthic biomass together with light attenuation of seawater, phytoplanktonic biomass, macrobenthic density and biomass at eight stations (water depth = 5–15 m) during four cruises in 1999–2000. The increased light attenuation coefficient of the water column associated with increased concentration of the phytoplanktonic Chl- a caused a decrease in light flux that reached the seafloor. The biomass of the microphytobenthos within the upper 1 cm of the sediment, 1.9–46.5 mg Chl- a m −2, was inversely correlated with the phytoplanktonic biomass in the overlying water column, 10.9–65.0 mg Chl- a m −2. Thus, interception of light by phytoplankton is considered to be a main cause of the variation in the microphytobenthic biomass. The microphytobenthos biomass showed a significant positive correlation with the macrobenthic density (78–9369 ind. m −2) and biomass (0.4–78.8 gWW m −2). It appears that the increase in oxygen production by the microphytobenthos allowed macrobenthic animals to become more abundant, as a consequence of oxygenation of the organically enriched muddy sediments (14.5 ± 2.69 mg TOC g −1). This study suggests that the variation in the microphytobenthic biomass is influenced by the phytoplanktonic biomass due to shading effect, and the balance between these two functional groups might affect the variability in the macrobenthic density and biomass.

Measuring carbon isotope ratios of microphytobenthos using compound‐specific stable isotope analysis of phytol

Carbon stable isotope analysis is one of the most common methods for validating theories about the role microphytobenthos (MPB) plays in estuarine food webs. However, difficulties extracting MPB from sediments to determine a pure isotope signature have hampered such studies. We have developed compound‐specific isotope analysis (CSIA) of phytol δ13C (δ13Cphytol) as an accurate proxy for δ13C of bulk MPB (δ13Cbulk). In most circumstances MPB is the dominant source of phytol in estuarine sediments, particularly in shallow water environments, so our method circumvents the need to extract MPB. We have demonstrated in the laboratory the relationship between δ13Cphytol and δ13Cbulk, and could predict δ13Cbulk within 1.8‰ (95% CI) of observed values at moderate replication (n = 5). If water temperature is included, δ13Cphytol predicts δ13Cbulk within 1.3‰. With greater replication (n = 10), predictions are extremely good (within 1.0‰). A two‐source mixing model assessed the usefulness of each method for estimating MPB contribution to consumer nutrition. At moderate replication (n = 5), for a gap between MPB and another producer of 6.0‰, estimates were more precise (i.e., 95% CIs were smaller) when both δ13Cphytol and temperature were used (95% CI 0.40) rather than only δ13Cphytol (0.46). The greatest difference in precision was for a gap of 6.0‰, close to the average gap in the literature (5.5‰). Given the difficulty of extracting MPB from sediment, carbon isotope studies of food webs could benefit by using CSIA of phytol, especially in conjunction with simple measurements of water temperature. The advance in methodology will allow a reevaluation of the trophic importance of MPB.

Influence of microphytobenthos on the nutrient flux between sediment and water- a laboratory study

The importance of microphytobenthos as a regulator of the flux of inorganic phosphorus and nitrogen between sediment and water was investigated in a laboratory study. Sediment from the SE Kattegat was incubated in nutrient-enriched seawater during exposure to varying light quantities (0, 5, 10, and 30 pE m-' S' ) . Microphytobenthos growth was limited by both inorganic nutrients and light quantity. When exposed to no-light conditions, chlorophyll a content of the sediment decreased only slightly and remained at an almost constant level (50 to 55 mg m-2) for several weeks, and increased rapidly when exposed to light. A relationship was observed between light quantity and the rate and direction of the flux of NH: and PO:-, but not NO;, between the sediment and overlying water The indirect influence of the microphytobenthos on the nutrient flux, i.e. by changes in the oxygen concentration, seemed more important than the direct effect by uptake by the algae. The rate of release of phosphate from the sediment exposed to darkness was up to 0.2 mm01 PO4 m-2 d-l The maximum mean rate of ammonia release was 1.6 mm01 m-' d-' in the dark and ca 0.1 mm01 m-2 d-' at 5 yE S-'. When the amount of light was 3 10 pE m-' S-', the microbenthic activity (oxygen production and increased nutrient requirements) prevented the release of PO4 and NH4 from the sediment.