Marine Zoology & Ecosystem: Soft Sediments

Why is soft sediment crucial

-nutrient recycling

-carbon storage

-habitat provision for benthic organisms

-biogeochemical cycling

-bioturbation & sediment stabilisation by fauna

What is a benthic organism

live on/in bottom sediments of aquatic environments

What is biogeochemical cycling

movement/transformation of chemical elements between living organisms, atmosphere & crust

(re)cycling of essential nutrients

What is bioturbation & sediment stabilisation

-physical movement of soil by fauna or plant roots

-rework of soils & sediments by animals/plants

Global distribution of Marine Sediments:

-70% earth covered in soft sediment

-soft sediment habitat=ecological zones(distinct region characterised by unique features)

-Estuaries, lagoons, fjords, intertidal zones, continental shelf

What is oxic sediment

oxygenated, nearest water column to surface

What is anoxic sediment

oxygen penetration decreases, further into ground

What is redox potential discontinuity

where organic matter can/cannot be oxidised

found between oxic & anoxic sediment

Forbes Azoic hypothesis

-marine life decreased with depth

-nothing in soft sediment- no ss habitats

-later proven wrong

9 environmental drivers

Sediment grain size

wave energy

turbidity

oxygen

nutrient

temp

salinity

organic matter

depth

Sediment grain size

key driver to what community lives there.

water retention- important because of interstitial spaces

smaller interstitial space= less poor water & less O2 penetration= higher organic material

More biological O2 demand

What is interstitial spaces (grain size)

space between grain sizes

grain size difference= difference in interstitial space

Wave Energy

fine sediment implies low energy environment

energy of waves sorts out particles

Wave energy- estuary

low habitat & fine particles build over time

Wave energy- fast flowing rivers

course sediment, fine particles move away & accumulate indifferent region

Low current

infaunal

mobile

deposit feeding

Soft substrate

infaunal

mobile

deposit feeding

infaunal organisms

live within sediment of ocean floor

Epifaunal organisms

live on the sea floor

High current

epifaunal

sessile

filter feeding

Hard substrate

epifaunal

sessile

filter feeding

Benthic community food web

Primary production

Detrital matter

Secondary production

Main predators

Bacterial loop

Primary production

happens through seaweed/algae/diatoms

produce organic matter & mucus

eat messily & ends on sea floor

Detrital matter

imported from other system (river/marine source)

organic matter decomposed into small particles

broken down by soft sediment animals

Secondary production

mainly deposit feeders- some suspension/filter

limited filter due to turbid waters (full of sediment)

can get clogged

Main predators

seabirds, fish, crabs

Bacterial loop

all stages of food web produce mucus/ organic matter

bacteria work on matter & hungry for O2

cause high biological O2 demand= stressful environment

Meiofauna size

between 32μm-1mm

Meiofauna Habitat

infaunal

Meiofauna Feeding

bacteria, microalgae, detritus, other meiofauna

Macrofauna Size

>1mm

Macrofauna Habitat

Infauna or epifauna

Macrofauna Feeding

deposit, suspension, grazers, predators

Macrofauna Mobility

mobile, burrow, crawl, short distance swimming

Ecological importance: Nutrient cycling

infauna break down organic matter & recycling nutrients

Ecological importance: Food web

food source for larger invertebrates & fish

Ecological Importance: Bioindicators

sensitive to environmental changes, making them useful for monitoring ecosystem health

Ecological Importance: Bioturbation

macrofauna rework sediments, enhance o2 penetration & nutrient cycling

Ecological Importance: Habitat engineering

species modify physical structure of sediments, influencing habitat availability for other organisms

Ecosystem engineers: Arenicola marina

dense population= high bioturbation

species dominance

Ecosystem engineers: artificial tube worm experiment

higher sediment stability

stimulated development of diatom biofilm & mucilage

more abundant meio & macrofauna communities

Ecosystem engineers: blue mussel

provide 3D benthic tertiary habitat

root stabilisation

immigration of new benthic species

increase biodiversity

Benthos meaning

community of organisms that live on/in/near the bottom of water (benthic zone)

Microfauna meaning

animals <0.1mm in size

protozoa/bacteria

Meiofauna meaning

animal <0.5mm in size

interstitial

nematodes, small amphipods

Macrofauna meaning

animals >0.5mm in size

crabs, shrimp, starfish, molluscs

Feeding modes: Deposit

feed on organic matter that settle on sediment

Deposit: What do they eat

organic detritus, bacteria, microalgae, mucus

Deposit: How do obtain food

ingest sediment

use palps/tentacles to collect particles

Deposit: Where do they feed

subsurface feeders: within sediment column, head down

surface feeder: on/just below sediment- water interface

Deposit: Ecological matter

bioturbated sediment

regulate communities

sediment stability

organic matter breakdown

Feeding mode: Suspension

filter particulate organic matter directly from water column

Suspension: What do they eat

suspended organic particles, detritus, phytoplankton, micro-zooplankton

Suspension: How do obtain food

siphons, tentacles, cilia, mucus nets

siphons- water & food particles filter through siphon, filtered water with particles removed is expelled

Suspension: Where do they feed

above sediment/surface

many live buried but feeding appendage into water column

Suspension: Ecological matter

benthic-pelagic coupling- as they filter they recycle nutrients, use suspending material

transfer co2 down

influence particle resuspension, turbidity, sediment stability

Feeding modes: Carnivores/Scavengers

actively hunt prey/consume dead organic material

Scavenger: What do they eat

other infaunal animals

Scavenger: How do obtain food

active hunting using jaws

scavenging on organic debris

Scavenger: Where do they feed

in/across upper sediment layers

mobile

Scavenger: Ecological matter

prevent dominance by few opportunists

maintain biodiversity

promote sediment mixing

Feeding modes: Chemosymbiotic

harbour bacterial symbionts that oxidise reduced compounds

Chemo: What do they eat

they don't

rely on symbiotic bacteria in tissue

Chemo: How do obtain food

absorbing products of chemical chemoautotrophy

Chemo: Where do they feed

Anoxic/micro-oxic sediment zones

where hydrogen sulphide is abundant o2 is low

Chemo: Ecological matter

link oxic & inoxic layers

detoxify sediments by consuming sulphide

sustain life where no photosynthesis

Spatial feeding patterns

vertical resource partitioning

different feeding guilds occupy different vertical niches in sediment

Temporal feeding patters

tidal partitioning

high tide= suspension feeders dominate

mudflats- nocturnal

Feeding windows

if all feed at same time: survival trade-offs & energy access

if they overlap too much: lose functional complementarity, homogenised bioturbation, comp exclusion

3 types of diversity

taxonomic

functional

phylogenetic

Taxonomic: Focus

species identity & counts

'who's there'

Taxonomic: Measures

species richness/ evenness

Taxonomic: Examples

no. of polychaete, bivalve & amphipod species

Taxonomic: Why it matters

indicates basic biodiversity level

Functional: Focus

ecological roles & traits

'what do they do'

Functional: Measures

feeding mode, mobility, burrowing type

Functional: Examples

mix of deposit, suspension & predatory feeders

Functional: Why it matters

links biodiversity to ecosystem function

Phylogenetic: Focus

evolutionary history 'how are they related'

Phylogenetic: Measures

branch lengths on phylogenetic tree

Phylogenetic: Examples

representation of multiple phyla

Phylogenetic: Why it matters

reflects evolutionary potential & resilience

Species richness

amount of different species in an ecosystem

how balanced a community is

What equation is used for biodiversity

Shannon-Weiner Index- combine richness & evenness

Functional Richness : Metric

FRic

Functional Richness: what it measures

range of functional traits present in community

Functional Richness: Ecological interpretation

mudflat with feeding types= high FRic

1 feeding type= low FRic

Functional Evenness: Metric

FEve

Functional Evenness: what it measures

How evenly species & abundance are distributed across trait space

Functional Evenness: Ecological interpretation

high FEve= surface & deep-burrowing deposit feeders equally abundant

low FEve= 1 more dominant type

Functionally redundant

species that serve same functional role in functional group

ecosystems with greater functional diversity= more resilient than lower functional diversity ones

if 1 species in group affected by disturbances, another species will carry out role

Biodiversity-Ecosystem Function (BEF)

theory that levels of ecosystem functions and stability of functions depend on levels of biodiversity

denitrification= process of turning nitrate into nitrogen gas through anaerobic microbial action

BEF threats

Bottom trawling- disturbs sediment layers, remove key species, reduces habitat complexity

Pollution- microplastics alter community structure & function

Climate change- temp change, hypoxia & acidification affect species tolerance & interactions

Coastal development- habitat loss & fragmentation reduce richness & connectivity

Why is redundancy important in ecosystems under stress?

multiple species perform similar roles

under stress if 1 species declines, other can maintain function

making ecosystems more resilient, less likely to collapse