An in situ instrument for planar O2 optode measurements at benthic interfaces

A new in situ instrument for two‐dimensional mapping of oxygen in coastal sediments is presented. The measuring principle is described, and potential mechanical disturbances, solute and particle smearing associated with the measurements, and calibration routines are evaluated. The first in situ measurements obtained in two different benthic communities are presented. In a shallow photosynthetic sediment (1 m of water depth), an extensive horizontal and temporal variation in the O2 distribution caused by benthic photosynthesis and irrigating fauna was resolved. Repetitive planar optode measurements performed along a transect in central Øresund, Denmark (17 m of water depth) revealed a positive correlation between the apparent O2 penetration depths (OP) measured with a lateral distance <5.0 mm, whereas OP measured with a larger horizontal distance (up to 50 m) were not correlated. Consequently, the OP varied in patches with a characteristic size of 5.0 mm. The instrument described is a powerful new tool for in situ characterization of spatiotemporal variations in O2 distributions within benthic communities. The instrument can be adapted for use at full ocean depths, e.g., on deep‐sea landers or remote operating vehicles

Late Miocene to early Pliocene biofacies of Wanganui and Taranaki Basins, New Zealand: Applications to paleoenvironmental and sequence stratigraphic analysis

The Matemateaonga Formation is late Miocene to early Pliocene (upper Tongaporutuan to lower Opoitian New Zealand Stages) in age. The formation comprises chiefly shellbeds, siliciclastic sandstone, and siltstone units and to a lesser extent non-marine and shallow marine conglomerate and rare paralic facies. The Matemateaonga Formation accumulated chiefly in shelf paleoenvironments during basement onlap and progradation of a late Miocene to early Pliocene continental margin wedge in the Wanganui and Taranaki Basins. The formation is strongly cyclothemic, being characterised by recurrent vertically stacked facies successions, bounded by sequence boundaries. These facies accumulated in a range of shoreface to mid-outer shelf paleoenvironments during conditions of successively oscillating sea level. This sequential repetition of facies and the biofacies they enclose are the result of sixth-order glacio-eustatic cyclicity. Macrofaunal associations have been identified from statistical analysis of macrofossil occurrences collected from multiple sequences. Each association is restricted to particular lithofacies and stratal positions and shows a consistent order and/or position within the sequences. This pattern of temporal paleoecologic change appears to be the result of lateral, facies-related shifting of broad biofacies belts, or habitat-tracking, in response to fluctuations of relative sea level, sediment flux, and other associated paleoenvironmental variables. The associations also show strong similarity in terms of their generic composition to biofacies identified in younger sedimentary strata and the modern marine benthic environment in New Zealand

Effects of a Large Fishing Closure on Benthic Communitites in the Western Gulf of Maine: Recovery from the Effects of Gillnets and Otter Trawls

The recovery of benthic communities inside the western Gulf of Maine fishing closure area was evaluated by comparing invertebrate assemblages at sites inside and outside of the closure four to six years after the closure was established. The major restriction imposed by the closure was a year-round prohibition of bottom gillnets and otter trawls. A total of 163 seafloor sites (~half inside and half outside the closure) within a 515-km2 study area were sampled with some combination of Shipek grab, Wildco box corer, or underwater video. Bottom types ranged from mud (silt and clay) to boulders, and the effects of the closure on univariate measures (total density, biomass, taxonomic richness) of benthos varied widely among sediment types. For sites with predominantly mud sediments, there were mixed effects on inside and outside infauna and no effect on epifauna. For sites with mainly sand sediments, there were higher density, biomass, and taxonomic richness for infauna inside the closure, but no significant effects on epifauna. For sites dominated by gravel (which included boulders in some areas), there were no effects on infauna but strong effects on epifaunal density and taxonomic richness. For fishing gear, the data indicated that infauna recovered in sand from the impacts of otter trawls operated inside the closure but that they did not recover in mud, and that epifauna recovered on gravel bottoms from the impact of gillnets used inside the closure. The magnitudes of impact and recovery, however, cannot be inferred directly from our data because of a confounding factor of different fishing intensities outside the closure for a direct comparison of preclosure and postclosure data. The overall negative impact of trawls is likely underestimated by our data, whereas the negative impact of gillnets is likely overestimated

Benthic communities in Spartina alterniflora and Phragmites australis dominated salt marshes

The benthic communities were investigated in Phragmites australis and Spartina altemiflora salt marshes, conducted in natural and mitigated salt marshes located in a highly urbanized area, the Hackensack Meadowlands, New Jersey. Benthic samples were taken with a 5-centimeter core at two habitats, the creek bank and the edge of the vegetation in the low marsh zone. Salinity levels and textural and structural sediment characteristics were also collected at each site. A recolonization experiment that utilized sediment from an undisturbed and uncontaminated salt marsh was conducted to determine if substrate is important in benthic colonization. The results suggest that there were differences in abundance, taxa richness, diversity, and composition in the benthic communities found among the different types of grasses as well as the mitigated and natural marshes. The Phragmites australis marsh had a more diverse benthic community than the natural and mitigated Spartina alterniflora marshes. The mitigated marshes had a greater abundance and lower diversity than the natural marshes. However, there were differences in salinity levels (oligohaline to polyhaline) between the mitigated and natural marshes that could result in different types of benthic communities. Substrate and contamination did not seem to be a factor in the recolonization of benthic communities. The principles of opportunism were responsible for shaping the benthic communities in the recolonization experiment. This study shows that Phragmites australis supports a healthy benthic community. The benthic community of the mitigated marsh did not resemble the natural marshes after 12-years of establishment

Climate Change and invasibility of the Antarctic benthos

Benthic communities living in shallow-shelf habitats in Antarctica (&lt;100-m depth) are archaic in their structure and function. Modern predators, including fast-moving, durophagous (skeleton-crushing) bony fish, sharks, and crabs, are rare or absent; slow-moving invertebrates are the top predators; and epifaunal suspension feeders dominate many soft substratum communities. Cooling temperatures beginning in the late Eocene excluded durophagous predators, ultimately resulting in the endemic living fauna and its unique food-web structure. Although the Southern Ocean is oceanographically isolated, the barriers to biological invasion are primarily physiological rather than geographic. Cold temperatures impose limits to performance that exclude modern predators. Global warming is now removing those physiological barriers, and crabs are reinvading Antarctica. As sea temperatures continue to rise, the invasion of durophagous predators will modernize the shelf benthos and erode the indigenous character of marine life in Antarctica

Declines in Puget Sound sediment-dwelling communities and a new focus on climate, nutrient, and other ecosystem stressors

The Washington State Department of Ecology has been collecting data on Puget Sound sediment-dwelling (benthic) invertebrates since 1989, as part of the Marine Sediment Monitoring Program. Benthic organisms serve key functions, including processing and storage of organic material and cycling of nutrients needed by other components of the ecosystem. Benthic invertebrates are an integral part of the marine food web and biogeochemical processes that support salmon, orcas, and humans and are a key component of the Puget Sound ecosystem. We are finding significant declines in the overall condition of benthic communities, with 44% of the study area adversely affected. Many of the adversely affected benthic communities were found in terminal inlets and bays. Throughout Puget Sound, an increase of pollution/hypoxia-tolerant species and a decrease in sensitive species has occurred over time. Deterioration of benthic communities does not correspond well with changes in individual chemical contaminants measured or laboratory tests of sediment toxicity. The spatial distribution of benthic communities is in part defined by the changing physical and oceanographic habitat. Changes in the abundance and composition of the benthic invertebrate community over time may indicate responses of the ecosystem to climatic stressors and large-scale ecological shifts such as changing hydrological, nutrient, oxygen, or acidic conditions

Use of axial tomography to follow temporal changes of benthic communities in an unstable sedimentary environment (Baie des Ha! Ha!, Saguenay Fjord)

In the upper layer of the sediment column, organic matter recycling is greatly influenced by bioturbation. However, there are many physical changes in the nature of the sediment that may disturb benthic communities and create a biogeochemical imbalance. Following a very heavy rainfall between 26 and 29 July 1996, an intense flash flood in the Saguenay Fjord caused discharges of 6 million cubic metres of sediments into Baie des Ha! Ha!. Unstable sediment deposits located at the top of the delta of the Rivie`re des Ha! Ha! were sporadically exported to the deep basin. After this physical disturbance, meiobenthic and macrobenthic organisms progressively re-colonised the sediment column. To determine the impacts of such sedimentary depositions on benthic fauna, two stations, one at the head and one at the mouth of the Baie des Ha! Ha!, have been monitored since 1996. During this survey, we developed a new method for the quantification of biogenic structures using computer axial tomography (CAT-Scan). Benthic fauna analysis showed that the two stations were characterised by different temporal changes in the benthic dynamics according to their geographic location. Using CAT-Scan analysis of sediment cores, we were able to characterise the stability of the sediment column for the two stations in 1999 and 2000. Scan results suggest that colonisation processes were closely linked with the stability of the sediment column. Erosion and redeposition of surficial sediments caused a succession in the formation of biogenic structures. These variations were characterised for the first time using CAT-Scan, which is a nondestructive, rapid, and precise method. Tomographic analysis showed the importance of the production and destruction rates of biogenic structures and the sedimentation rate for the preservation of burrows and potentially reactive components. This study finally demonstrated that each erosional event could be followed by a rapid formation of biogenic structures, allowing the re-oxidation of old deposits

Let's Get to the Bottom of the Arctic!

In this lesson students investigate benthic communities in the deep Arctic Ocean to determine the factors that influence their compositions. As a result of this activity, students will be able to identify the three realms of the Arctic Ocean and describe the relationships between these realms. They will also be able to describe different species associations in a benthic community, infer probable feeding strategies used by benthic organisms, and relate these strategies to sediment characteristics. Students will also review the relationship between variety, relative abundance, and diversity of organisms. Educational levels: High school