The depth of the apparent RPD in the sediment column is an important time-integrator 

 of dissolved oxygen conditions within sediment pore waters. In the absence of bioturbating 

 organisms, this high reflectance layer (in muds) will typically be 1- to 3-mm thick (Rhoads, 

 1974). This depth is related to the rate of supply of molecular oxygen (by Fickian diffusion) 

 into the bottom, and the consumption of that oxygen by the sediment and associated 

 microflora. In sediments which have very high sediment-oxygen demand (SOD), the 

 sediment may lack a high reflectance layer even when the overlying water column is 

 aerobic. In the presence of bioturbating macrofauna, the high reflectance layer may be 

 several centimeters thick. 



Infaunal successional stage. The mapping of successional stages was based on the theory 

 that organism-sediment interactions follow a predictable sequence after a major seafloor 

 perturbation (Rhoads and Germano, 1982; Rhoads and Boyer, 1982; Maurer et al., 1985; 

 Pearson and Rosenberg, 1978). This theory states that primary succession results in "the 

 predictable appearance of macrobenthic invertebrates belonging to specific functional types 

 following a benthic disturbance." The term "disturbance" includes natural processes, such as 

 seafloor erosion, changes in seafloor chemistry, foraging disturbances which cause major 

 reorganization of the resident benthos, or anthropogenic impacts, such as dredged material 

 or sewage sludge dumping, thermal effluents from power plants, pollution impacts from 

 industrial discharge, etc. 



The designation of successional status in REMOTS™ images was based on the 

 recognition of two end-member assemblages. Disturbed benthic environments are commonly 

 associated with dense tube aggregations at or near the sediment surface. These appear as 

 small hair-like tube projections at the sediment surface. They are usually spaced 10 or more 

 per linear cm along the imaged sediment surface. These "enrichment" assemblages typically 

 consist of spionid or capitellid polychaete populations and were mapped as Stage I seres. In 

 the absence of further disturbance, these early successional assemblages are eventually 

 replaced by infaunal deposit feeders; the start of this "infaunalization" process was 

 designated arbitrarily as a Stage II sere. These seres were identified as shallow-dwelling 

 bivalves or tubicolous amphipods, such as those belonging to the genus Ampelisca. These 

 amphipods were also occasionally densely aggregated at the sediment surface. The other 

 end-member infaunal assemblage (Stage III) was dominated by polychaetes which have 

 larger body sizes, are less abundant, and feed head down several centimeters below the 

 surface (conveyor-belt species). These species were usually not imaged per se, but rather the 

 feeding pockets or voids that develop around their head ends could be seen in profile 

 images. Active voids were lenticular in shape and the bottoms of these were typically 

 filled with coarse particles. Inactive voids appeared as "collapsed" or relic structures 

 which were recognizable only by their lenticular shape and coarser grain size. These 

 infaunal stages were typically represented by maldanid or orbiniid polychaetes and mapped 

 as Stage III seres. They were typically present on those parts of the seafloor which did not 

 experience severe, frequent (i.e., several times a year) physical disturbance or organic 

 enrichment. This trophic type is apparently adapted to sediments which are relatively 

 "oligotrophic" (Rice and Rhoads, in press). 



The pattern described above for primary succession, or the pattern of changes in benthic 

 community functional types after a radical disturbance or the opening of a new patch in the 

 physical environment for colonization, has been repeatedly documented in REMOTS™ 

 monitoring of severely disturbed areas such as dredged material disposal sites. However, it 

 is also quite common when monitoring "ambient" seafloor areas to detect a combination of 

 successional seres in the same image (e.g., a Stage I on Stage III, or Stage II on Stage III). 

 This designation documents the process of secondary succession, which is usually the result of 

 mild physical disturbances or biological interactions such as competition and predation. 

 Secondary succession is the process of re-establishment of conditions similar to the original 

 community after a temporary disturbance. 



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