Synthesis on colonization experiments associated with chemosynthetic
environments
Types of experiments close to or in chemosynthetic ecosystems
1. Large organic food fall is deposited on natural substrates (incl. sediments, …) mimicking
natural food fall conditions
(eg MPI exps, Carcace whale fall (or mammal))
2. Experimental units left on the seafloor with different substrates (organic and inorganic)
in small but standardized amounts (controls are not always included in the experimental
design – should be mentioned if controls are present not)
 Chemecoli: standardized comparison of 3 substrates (Wood, Alfalfa, Carbonate) in
basket on seafloor
 Experimental substrates in boxes not in direct contact with the seafloor (Azores)
 Implantation of permeable cores with defaunated sediments enriched with
photosynthetic-derived food in sulphidic sediments of a cold seep (UGent)
Main observations + recommendations & questions:
Observation 1:
 No or little colonization in less than 1 month for macro/mega-fauna
o unsure for the microbiota?
o biofilm first?
o sometimes bacteria present very quickly?
o Shrimps attracted but not really colonizers, true opportunists? Shrimps may
stay for a short time but their presence may not be random
o Are scavengers colonizers? YES
o Does mobility define a colonizers or grazer… Dependence on the substrate
(shelter, fixation, food) defines a colonizer
o Temporary but not random may be included
 Major colonization during first year for microbiota and macrofauna
o Temporal variability? (starting time of submergence as well as time-window
of submergence)
 Insufficient data on year 2 to make conclusions (Relatively little change during second
year for large food falls, or occasional collapse for small food falls (e.g. alfalfa
chemecoli))
R: Increase frequency of sampling during first and consecutive years to understand initial
successional stages (and degradation of the OM)
Questions/unknowns: Which are the pioneering species? How important are they for establishment
of other species? Which are the persisters? What are the climax communities? Is there a climax
community (succession including degradation-bioerosion processes)? Is there temporal variability for
the pioneering species (starting time of submergence as well as time-window of submergence)?
Different exps – different conditions
Observation 2a: Direct contact of food falls with the natural seafloor (type of seafloor: sediment, hard
substrates, etc.) creates different sulphidic conditions compared to when there is no contact (i.e. PVC
plate or other separate substrate and seafloor)
Observation 2b: The size and quality of the food fall drives the extent of the sulphidic conditions and
other biogeochemical conditions in the immediate environment. Large food falls – high amount of
OM – high respiration – O2 quickly runs out.
Observation 2c: The distance of the exp from naturally occurring reducing env influences the
immediate biogeochemical conditions.
Observation 2d: Duration/persistence of sulphidic conditions is dependent on the size of organic fall
R1: The effect of the variables mentioned above should be investigated with appropriate
experiments to determine the importance of natural food falls for the distribution and evolution of
chemosynthetic species
Questions


Are food falls stepping stones for distribution and/or evolution for chemosynthetic species?
(What are the differences between contact and non-contact exps, small vs big, short vs long,
regarding sulphide concentrations and other biogeochemical conditions in the immediate
environment? Sediment vs non-sediment exps? Sediment matters, even the type of
sediment matters – coarse vs fine grain?) contained in observations above.
Observation 3b: The degree of colonization by chemosynthetic species is variable Reproductive
stages/ontogeny of specimens recovered from exps are often unknown
R(b). Information is needed on specialized species and we need to identify developmental stages of
fauna
Q: Are the populations of arrivals chemosynthetic species on falls always able to (1) sustain growth,
(2) reproduce?
What influences and drives the variability observed (cf. 3b)?
Does time of deployment and duration of submergence matter?
Observation 4: The structure and composition of the colonizing communities and the process of
colonization can vary with
 Nature of substrate
 Water depth (shallower sites have higher diversity but lower contribution of
chemosynthetic species)
 Geography (large scale)
R: Future research should include characterization of and/or data on (1) biogeochemical conditions
(incl. temp., …), (2) trophic conditions, (3) biogeography (regional species pool), (5) oceanographic
conditions (fronts, currents, etc.), in order to infer the drivers of structure and function of colonizing
fauna. Cf. General recommendations for precondition measurements.
Q: How do species pools interact with the environment?
Observation 5: Experimental food falls are colonized both by (non-chemosynthetic) background
communities and by specialized (woodborer and/or chemosynthetic) taxa. They are characterized by
the presence of endemic, specialized taxa on top of the presence of background taxa.
R. Always combine characterization of the food-fall biota with the background biota (both chemo and
non-chemo).
R. Need for taxonomic and functional investigations (and molecular characterization)
Q. What is degree of endemism?
How many species are specialists?
What is the degree of cryptic speciation?
Are food falls biodiversity hotspots?
What are the functional capacities of the biota and which biota (this incl. fungi and microbiota) are
important?
Are the food falls changing the function of the present communities?
What is the contribution of food falls to regional biodiversity?
Observation 6: The food falls cause a community to settle which is different from the background
community, which suggest the presence of cues.
R. Manipulative (in-situ/ex-situ) experiments are needed to identify cues for settlement and
development (larval development, chemical release, biofilm, conspecifics, biogeochemical
conditions)
Q. What are the cues that attract biota and promotes settlement, colonization, succession patterns
(across size classes and functional groups)?
The GREAT unknowns (this should be put in a box) – Needs to be completed
1) We don’t know where the propagules (this needs to be defined, dispersive stages,
individuals, STUFF) come from?
R. Population genetics, and other methods need to be explored to answer the “where”
questions
Q. Self-recruitment or continuous recruitment from more distant places? The first settlers
are important here… depending on them
Origin of the recruiters, whatever life-stage they are?
GENERAL RECOMMMENDATIONS.
Preconditions need to be measured (biogeochemically), all faunal groups should be covered
(subsampling schemes and fixation should be standardized and catered for the different faunal
groups). In many exps (e.g. CHEMECOLIs) all the material is collected, but some material awaits
processing and analysis. CHEMECOLIs can be used to cover all size-classes, and should perhaps be put
forward as a good standardized method to investigate bottom/food-fall colonization (small falls).
Make use of observatories
Follow-up needed, the community needs to reassemble at next occasions
Summary review for publication (letter, recommendations)
New workshop ?
Circulate report for adoption
Meet again at the HERMIONE Meeting in September
International collaboration needs to be stimulated