Food Chains

Name the full name of these acronyms:

DOM

DIN

POM

HNAN

PNAN

PP

DOM=Dissolved Organic Matter

DIN=Dissolved Inorganic Nitrogen

POM=Particulate Organic Matter

HNAN=Heterotrophic Nanoflagellates

PNAN=Photosynthetic Nanoflagellates

PP=Primary Production

Plankton size classification

-Femtoplankton (<0.2 um)

-Picoplankton (0.2-2 um)

-Nanoplankton (2-20 um)

-Microplankton (2-200 um)

Mesoplankton (0.2-20 mm)

Macroplankton (2-20 cm)

Megaplankton (>20 cm)

What organism is almost every organosm in the sea depend on?

Phytoplankton

Bottom-up control

Abundance at a particular trophic level is controlled by resources availability at the next lower level

Top-down control

Abundance at a particular trophic level is controlled by predation from the next higher level

Trophic cascade

Top down control of community structure by predators; conspicuous indirect effects two or more links distant from the primary one

Example of top down control?

Otters, kelp forest food web

What does the paper “Multi-level trophic cascades in a heavily exploited open marine ecosystem” show?

This study examines multi-level trophic cascades in the Baltic Sea, demonstrating how overfishing and climate change impact marine food webs. Using 33 years of field data, the researchers identified a four-level trophic cascade, showing how changes at the top of the food chain ripple through the ecosystem.

Key points in “Multi-level trophic cascades in a heavily exploited open marine ecosystem“

Overfishing-Induced Trophic Cascade

-Decline in Atlantic cod (tope predator) due to overfishing led to an increase in sprat, a zooplankton fish

-The rise in sprat reduced zooplankton biomass, which altered phytoplankton abundance

Four-Level Trophic Cascade Identified

-Top down control demonstrated across 4 trophic levels:Cod→Sprat→Zooplankton→Phytoplankton

-Reduction in cod caused higher sprat predation on zooplankton, leading fewer grazers for phytoplankton

Climate and Ecosystem Effects

-Ocean warming amplified sprat population growth, reinforcing the trophic cascade

-Phytoplankton shifts influenced marine primary production and carbon cycling

Implications for Ecosystem Management

-Preserving higher trophic levels could help regulate harmful algal blooms

Citate “Multi-level trophic cascades in a heavily exploited open marine ecosystem”

Casini et al., 2008

What does the paper ”Human–environment interaction in the Baltic Sea” show?

This study explores the complex interactions between human activities and the Baltic Sea ecosystem, focusing on environmental management and sustainability.

Key points in “Human–environment interaction in the Baltic Sea“

Human Impacts on the Baltic Sea Ecosystem

-Industrial activity, agriculture, and urbanisation have altered nutrient cycles, leading to eutrophication and harmful algla blooms

-Overfishing has disrupted trophic structures, particularly affecting cod populations and cascading through marine food webs

Climate Change Effects

-Rising temperatures have accelerated biological and chemical processes, modifying species distribution and ecosystem stability

-Changing salinity levels due to altered freshwater inflow impact plankton communities and fisheries

Governance and Sustainability Challenges

-Multinational cooperation is required to address pollution and overexploitation, given the Baltic Seas shared jurisdiction

-Marine spatial planning and ecosystem based management are key strategies to improve sustainability

Policy and Conservation Efforts

-Efforts to reduce nutrient inputs (such as limiting fertiliser runoff) have slowed eutrophication, but long-term effects remain uncertain

-Ongoing discussions on balancing economic development with ecosystem preservation highlight governance complexities

Citate “Human–environment interaction in the Baltic Sea“

Lowe et al., 2013

What was the problem of the 1980s food chain?

Quantification of microbial abundance, biomass and production were very poor

-At best estimated 10% of actual bacterial numbers

What caused the 1980 food chain view to be altered drastically?

Microbial loop

What was found out about phytoplankton due to the microbial loop?

DOM: phytoplankton exude up to 60% of PP as DOM

Are bacteria good scavengers of DOM at low concentrations?

Yes

What did the paper “Estuarine and oceanic microflagellate predation of actively growing bacteria: estimation by frequency of dividing-divided bacteria“ show?

This study examines microflagellate predation on actively growing bacteria in estuarine and oceanic environments, using the frequency of dividing-divided bacteria (FDDC) as an estimation method

Key points “Estuarine and oceanic microflagellate predation of actively growing bacteria: estimation by frequency of dividing-divided bacteria“

Microflagellate Predation on Bacteria

-Heterotrophic microflagellates play a crucial role in bacterial populations control

-Predation rates were estimated using the FDDC method, which tracks bacterial division frequency

Experimental Approach

-Researchers isolated flagellate species from Narragansett Bay and the Sargasso Sea

-Bacterial growth was monitored in filtered seawater enriched with nutrients

Finding on Bacterial growth & Predation

-Actively growing bacteria were more susceptible to flagellate predation

-Predation rates varied by flagellate species and environmental conditions

Implications for Marine Microbial Ecology

-Highlights the importance of microflagellates in regulating bacterial populations.

-Suggests that bacterial division rates can serve as an indicator of predation pressure.

What is the percentage of dinoflagellates are heterotrophic?

>50 %

Do heterotrophic dinoflagellates employ a large variety of feeding strategies?

Yes

What are the three mechanisms of feeding of heterotrophic dinoflagellates?

-Ingestion of whole cells

-Use of a feeding tube (peduncle)

-Use of a cytoplasmic veil (pallium)

Who to heterotrophic dinoflagellates compete with?

Copepods

Who has a better growth rate dinoflagellates or metazoans?

Dinoflagellates

What does the paper “Growth and decline of a diatom spring bloom phytoplankton species composition, formation of marine snow and the role of heterotrophic dinoflagellates” show?

This study examines the growth and decline of a diatom spring bloom, focusing on phytoplankton species composition, the formation of marine snow, and the role of heterotrophic dinoflagellates in controlling bloom dynamics.

Key points “Growth and decline of a diatom spring bloom phytoplankton species composition, formation of marine snow and the role of heterotrophic dinoflagellates”

Phytoplankton Species Composition

-The bloom was dominated by Detonula confervacea, Chaetoceros diadema, Skeletonema costatum and Thalassiosira nordenskioeldii

“Growth and decline of a diatom spring bloom phytoplankton species composition, formation of marine snow and the role of heterotrophic dinoflagellates

Bloom Growth and Disruption

-Diatoms initially showed exponential growth (0.112 day-1) until a storm disrupted the system

-Winds exceeding 15m/s triggered massive phytoplankton aggregation

Marine Snow Formation & Sinking

-Aggregated diatom cells formed marine snow, which rapidly sank out of the water column

-This process removed significant biomass, hastening the bloom decline

Role of Heterotrophic Dinoflagellates

-After the bloom peaked, Gyrodinium cf. spirale (a heterotrophic dinoflagellate) began proliferating

-Intense grazing pressure prevented further diatom resurgence

Nutrient Availability & Bloom Termination

-Nitrate and silicate remained sufficient, but phosphate limitation may have contributed to the decline.

-Bloom dynamics were shaped by physical disturbances and grazing pressure.

Citate “Growth and decline of a diatom spring bloom phytoplankton species composition, formation of marine snow and the role of heterotrophic dinoflagellates”

Tiselius & Kuylenstierna, 1996

Features of mixotrophic ciliates

-Both photosynthesise & feed

-Nutrient cycling (Regenerate nutrients/Require DIN)

Features of mixotrophic flagellates

-Photosynthetic flagellates, feed on bacteria

-Significant grazing impact

What are aggregates responsible for?

Most of the particulate flux in the oceans

Does marine snow enhance microbial activity?

Yes

What types of species does marine snow have?

Planktonic & Benthic species

Why is aggregates important?

-Supply DIN & DOM to pelagic microbes

-Support species of bacterivorous protozoa that are unable to survive in water column

-Provide food source to larger zooplanktons

What is the ultimate DOM production?

Phytoplankton

Ways to produce DOM and the amount they produce?

Directly

-Lysis, leaking (25%)

Protozoa

-Egest phyto dissolved products (53%)

Mesozooplankton

-Sloppy feeding (12%)

Viral infection (10%)

DOM composition

Carbohydrates

-Mono/Oligo & polysaccharides

Nitrogenous compounds

-aa/peptides/proteins

Organic acids

-Glycollate

Lipids

What is the percentage of DOM released?

>90%

-Consumed & respired on a time scale of days or less