BENTHOS

•Substrate determines distribution:

Macro - > or equal to 0.5 mm

Meio - < 0.5 mm (selected for uniform body shape)

Micro - < 0.1 mm

• Soft-Sed. Parameters-

• grain size analysis:

<62 mm (silt-clay fraction); % clay <4 mm

Biogenic Sorting:

• organisms ingesting sediment prefer to consume small particles - transfer to surface

• maldanid polychaete - Clymenella torquata ingests <1 mm (conveyor-belt feeders)

• bioturbation can affect depth of redox potential discontinuity (RPD)

Biotic Effects on Chemical Properties:

• Rhoads, 1974

1) rate of exchange of dissolved or adsorbed ions, compounds, and gases across sed/water interface

2) vertical gradients - pH, Eh, pO2, depth RPD

3) cycles of C, N, P, S -Fe

4) transfer of reduced compounds from below the RPD to surface-oxygenated sediments

Aller &Yingst, 1975 - burrow walls had brown-orange oxygenated halo a few mm surrounded by black (Fe-sulfides) sediment

Zobell, 1938 - pellets enriched in microbiota

Hylleberg, 1975 - irrigation stimulates growth of microorganisms

Biological Influences on Mass Properties of Sediments:

• pseudofeces

• feces both produced in upper 2-5cm

Sediment Water and Oxygen Content:

• flocculent zone (Sanders, 1960)

• pelletized layers

• Increase of water content alters mass properties of the sediment and greatly reduces the effort needed for burrowing to penetrate the substratum

• High water content – thixotropic - speed of burrowing

Properties of the Sed-Water Interface and Turbidity of Overlying Water:

• Effects of burrowers on laminar flow or turbulent flow - and sediment resuspension

• Topography – Callianassa spp.– burrowing shrimp, can go down to 2-3 m.

• Molpadia oolitica - holothurian - permits colonization by several spp. of suspension-feeding, tube-dwelling polychaetes (Rhoads & Young, 1971; Rhoads, 1974)

• Ingestion rates of individual deposit-feeders - pop. effects - reworking of sediments

• Deposit-feeding bivalve Nucula annulata:

• rework the annually deposited sediment 1- 5 times/d-1 - thus, sediments are often pelletized

• Suspension-feeders - enrich sediments with fecal pellets – populations of Cardium

edule biodeposits 100,000 metric tons of suspended matter/yr -1 in Dutch Wadden Sea

• Particulate Organic Matter (POM) in sediments

• Detritus - inputs

• In pelagic realm 60-90% of the 1° production is consumed by herbivores

* the remaining goes into sediments

• Much of the 1° production of benthic seaweeds, kelp forests, sea grasses, mangroves, and marsh grasses - is thought to not be consumed – recent work challenges this theory

• The larger majority of benthic primary production (5000-1000 gC m-2yr -1) enters the food chain as detritus

• N. Atlantic kelp - Laminaria longicruris

• Mann, 1972 - dominant inputs to benthos, much of it is consumed

• In contrast Zostera marina decays more slowly - not so important as a benthic food source

• St. Margarets Bay, Nova Scotia - 15% of the seaweed production reaches the sediment as deposited organic detritus

• Georgia - 90% of detritus in estuarine creeks is of Spartina spp. origin

Adaptation of Benthic Organisms:

Epibenthos - barnacles, seaweeds, oysters, serpulid polychaetes

1) Adoption of short squat profile to minimize exposure to shear stress (i.e., anemones)

2) Hiding in holes (cryptic)

3) Stout rigid support structures (thick byssal threads) (i.e., Mytilus californianus)

4) extensibility

• Metridium senile - tall

• Anthopleura xanthogrammica - short

•Acropora palamata - strong

• Montastrea annularis - weak and massive

• Sea Fans - Gorgonia - prefered orientation to the current

Swimmers:

• Octopus - compressible mantle cavity

• Pecten

• Polychaetes - sinusoidal waves

Infauna:

• In order to penetrate soft sediments, infauna must exert a forward thrust within the sediment while maintaining points against which force can be exerted

• soft-bodied - form a penetration anchor, then a terminal anchor

• lugworm - Arenicola - proboscis exerted

Abarenicola

• streamlined bivalves in sand – razor clam

• Ensis directus - rapid borrower

• broad-shaped bivalves

• Mya arenaria

• Many bivalves squirt water with siphons to facilitate burrowing

• Many infaunal animals make permanent burrows

• Maldanid - ice-cream cone worm, Pectinaria - even-sized sand grains

• Many find sediment-dwelling infauna do not maintain vertical burrows and burrow laterally

• Yoldia limatula & Nucula - protobranch bivalves

• Nephthys incisa - polychaetes - responsible for fluidized nature of sediments