Showing papers by "Peter A. Jumars published in 1984"

Fluid and Sediment Dynamic Effects on Marine Benthic Community Structure

Abstract: Fluid and sediment dynamics affect benthic community dynamics and structure in manifold ways. We single out three community-structuring processes that are both strongly affected and amenable to controlled manipulation: microbial population growth, faunal recruitment, and particle feeding. Attachment and colony growth rates of microbes depend on the details of near-bed fluid exchange. Their emigration and colony growth rates are affected by erosion of microbial filmsand by abrasion during sediment transport. Recruitment and successional patterns of metazoans, especially those resulting from the settlement of weakly swimming, small larvae and juveniles, also are very sensitive to local variations in boundary layer flow pattern and strength. While the importance of particle fluxes to suspension feeders has long been apparent, the foraging patterns of a growing number of surface deposit feeders are being found to reflect a dependence upon sediment transport. Although these three processes have spatial and temporal scales amenable to both laboratory and field experimentation, proper dynamic scaling of laboratory model flows may not always be easy. Even the simplest two-phase (particles plus liquids, where particles can be bacteria, floes, larvae, or sediments) flows must match appropriate laboratory and field Reynolds number, Froude number, particle-fluid density (weight per unit volume) ratio, and the ratio of boundary layer thickness to particle size, if the laboratory flow model is to provide accurate results.

Effects of benthos on sediment transport: difficulties with functional grouping

Abstract: No consistent functional grouping of organisms as stabilizers vs destabilizers, respectively decreasing or enhancing erodibility, is possible. Benthic organisms can affect erodibility in particular—and sediment transport in general—via alternation (1) of fluid momentum impinging on the bed, (2) of particle exposure to the flow, (3) of adhesion between particles, and (4) of particle momentum. The net effects of a species or individual on erosion and deposition thresholds or on transport rates are not in general predictable from extant data. Furthermore, they depend upon the context of flow conditions, bed configuration, and community composition into which the organism is set. Separation of organism effects into these four categories does, however, allow their explicit incorporation into DuBoys-type and stochastic sediment dynamic models already in use and thus permits the specification of parameters whose measurement will enhance predictability of sediment transport modes and rates in natural, organism-influenced, marine settings. If the variable of prime concern is the total amount of sediment transported, rather than the frequency of transport events or the spatial pattern of erosion and eposition, and if most transport occurs in rare but intense bouts (e.g., winter storms on boreal continental shelves), then it may be possible to ignore organism effects without major sacrifices in accuracy or precision. Under high transport rates, suspended load effects override organism-produced bottom roughness, abrasion removes adhesives from transporting grains, and transport rates (normalized per unit width of the channel or bed) exceed feeding and pelletization rates. Moreover, at high rates most material transports as suspended load, effectively out of reach of the benthos. The transport rates at which organism effects are overridden, however, remain to be determined. For lower transport rates, foraging theory promises to provide insights into organism effects.

Variable ingestion rate and its role in optimal foraging behavior of marine deposit feeders

Abstract: Tests of optimal foraging theory have focused generally on food item selection by mobile, high-trophic-level predators. Deposit-feeding invertebrates are aquatic organisms with limited mobility and hence limited ability to forage actively for food-rich patches. In addition, there is little evidence for a major role of behaviorally mediated food item choice in these animals, and growing evidence of mechanical limitations in food particle choice. Given such limited food-selection ability, varying ingestion rate in response to changes in food value is likely to be an important animal response affecting feeding energetics. A previously developed optimal foraging model predicted that ingestion rate and food value should covary positively in order to maximize net time rate of energy gain. To test this general prediction, we fed three species of deposit-feeding polychaetes artificial sediments which varied only in protein content (food value); other physical and chemical properties which might affect ingestion rate were kept constant. In support of the model, ingestion rates increased as protein levels increased.

Transport and breakdown of fecal pellets: Biological and sedimentological consequences1

Abstract: Fecal pellets of benthic animals are important in sediment transport processes, yet few quantitative data are available on their salient physical characteristics. We measured, directly and independently, the densities (specific gravities), sizes, and settling velocities of pellets produced by Amphicteis scuphobrunchiata, a deposit-feeding polychaete worm. Pellet density was measured by an isosmotic density gradient technique. Densities ranged from 1.086 to 1.282 gacm-3 and settling velocities from 3.03 to 5.94 cmes-I. Pellets transported as bedload for variable distances; the oldest pellets tested (6 h after production) traveled a median distance of 3.1 m, while freshly egested pellets traveled 9.5 m before disintegrating. Worms would reingest disaggregated pellets, but feeding rates correlated positively with pellet age, consistent with previous findings that this species feeds at a faster rate on energetically more profitable sediment. These results suggest substantial interactions among benthic animals, fecal pellets, and sediment transport processes. Fecal pellets produced by aquatic organisms affect sedimentary processes in two ways. Because fecal pellets are aggregates of particles, pellet sinking rates can be much greater than the rates of their smaller constituents (Haven and Morales-Alamo 1968; McCall 1979). Thus, pellets enhance material fluxes through the water column by increasing sedimentation rates; this can also lead to deposition of particles that, because of hydrodynamic or chemical characteristics, otherwise might not be deposited in a given environment (Haven and MoralesAlamo 1968; Smayda 1969; Small et al. 1979; Robison and Bailey 198 1; Silver and Bruland 198 1). Most interest in such vertical sedimentation processes has focused on pellets of planktonic origin. Fecal pellets also play a role in sediment transport processes operating within the benthic boundary layer. Deposit feeders comprise the dominant trophic group in softbottom environments and ingest and package ambient sediment particles during their feeding activities. Although it has been recognized for some time that pellets can affect sediment transport via both bedload and suspended load transport modes (Rhoads

Effects of sediment transport on deposit feeding: Scaling arguments1

Abstract: At least five dimensionless variables are needed for dimensional analysis of an individual surfacedeposit feeder using particles containing microbial food both locally produced (by in situ growth) and advected (via sediment transport). From scaling arguments which provide the relationships among these variables, it is apparent that food availability is determined primarily by the ratios of geophysical sediment transport rate into the particle pool from which the animal feeds to its ingestion rate, and of particle residence time in the feeding pool to the microbial doubling time, Increasing sediment transport can either increase or decrease local food availability. Transport patterns beneath waves have dramatic effects: wave mixing makes available to the animal particles which otherwise would be literally out of reach. Specialization on advected particles and reliance on microbial gardening are favored under different environmental conditions, specified in terms of dimensionless ratios. The scaling model also places previous models of deposit feeding in an environmental context. It contrasts with an alternative, nutrient spiraling approach in having a basis in natural selection for its optimization arguments.

The foraging strategy of a subtidal and deep-sea deposit feeder1

Abstract: Tht ampharetid polychaete Amphicteis scaphobranchiata is a marine, surfacedeposit feeder inhabiting cohesive sediments from continental shelf depths off British Columbia to abyssal habitats off southern California. It uses a previously undescribed method of removing fecal pellets from its feeding area via an elastic (Young's modulus = 7 MNm\"-), mucous sling fashioned about the modified anterior median branchiae for which the species was named. This sling imparts a force of 4 x 10~' Pa, sufficient to ' Supported by contract NOOO14-80-C-0252 with the Office of Naval Research. Contribution 1339 from the School of Oceanography, University of Washington. yield a maximal pellet velocity of 27 cm • s ' and thereby to remove the pellet from the normal radius swept out by the animal's feeding tentacles. These observations indicate that this sedentary animal's food supply depends predominantly on the rate of sedimentation into the pit that is produced via its feeding and defecating activities, rather than on the rate of microbial regeneration or production that goes on within