13 Benthic Life Habits. Notes for Marine Biology: Function, Biodiversity, Ecology By Jeffrey S. Levinton

Transcription

1 13 Benthic Life Habits Notes for Marine Biology: Function, Biodiversity, Ecology By Jeffrey S. Levinton

2 Benthos Size Classification Size Class Size Examples Macrobenthos > 0.5 mm clams, polychaete worms, sea cucumbers Meiobenthos 0.5 mm> meiobenthos>0.1 mm nematodes, gastrotrichs, Microbenthos <0.1 mm protozoa, diatoms

3 Life in Mud and Sand Sediments: Particle size 3 measures 1. Grain diameter: indicates current strength -Median grain diameter - measured usually by sieving and weighing size fractions 2. Silt-clay fraction - % of weight of sediment < 62µm 3. Sorting: spread of particle sizes, well-sorted vs. poorly sorted; estimate of variation of current strength

4 Sedimentary Structures Can result from physical processes: Ripple marks on an intertidal sand flat

5 Sedimentary structures Burrow hole X-section Fecal mound Can result from biogenic processes Polychaete Arenicola marina

6 Burrowing in sediment Burrowers use (1) hydromechanical and (2)mechanical digging mechanisms Watery sediments with high silt clay content have thixotropy - but burrowing also propagates cracks in muddy sediments with lower water content - particles coated with organic polymers stick together Dorgan et al Nature 433:475

7 Burrowing in sediment Hydromechanical burrowing - combines muscle contraction working against rigid, fluid filled chamber (skeleton) Form penetration anchor first to allow further extension of body into sediment Form terminal anchor to allow pulling of rest of body into the sediment

8 Burrowing in sediment -bivalve foot Muscle contraction PA Longitudinal muscles Circular muscles TA PA = penetration anchor TA = terminal anchor Hydromechanical burrowing

9 Lugworm, Arenicola marina Longitudinal muscle contracting Circular muscle contracting Terminal anchor Eversion of pharynx Penetration ancthor

10 =rta6c2qskuo

11 Burrowing-mechanical digging Inarticulate brachiopod Burrowing crab

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13 Burrowing in sediment Biogenic structures - burrowing and processing of sediment affects sedimentary structure and sedimentary processes mechanical and chemical 1. Burrowing in mud increases water content of sediment 2. Increases grain size (fecal pellets) 3. Alters vertical and 3-D mechanical, grain size chemical structure

14 Burrowing in sediment Biogenic graded bedding bamboo worm Clymenella torquata Annelid ingests small particles at depth and deposits them on surface

15 Burrowed, pelletized layer, with small bivalves (<5 mm long) Depth cm Water content Soft-sediment microzone

16 Interstitial animals many groups evolved wormlike form, reduced structures Harpacticoid Hydroid copepod Polychaete Gastrotrich Opisthobranch gastropod

17 Soft-Sediment Microzone Organic matter enters system usually as particulate organic matter Strong vertical chemical gradients Gradients affect microbial community that decomposes organic matter Chemical gradients strongly affected by biological activity such as burrowing, construction of tubes

18 Particulate Organic Matter Detritus Deposition Pathways Phytoplankton seagrasses phytodetritus Benthic seaweeds microalgae Microbial activity decomposition, aided by burrowing, ingestion

19 ciliate bacteria diatom

20 Soft-Sediment Microzone Oxic Redox Potential Discontinuity Anoxic

21 Soft-Sediment Microzone Aerobic bacteria (use oxygen to break down organic substrates) RPD H 2 S oxidizing bacteria RPD Fermenting bacteria (break down organic cpds. --> alcohols, fatty acids) Sulfate-reducing bacteria (reduce SO 4 to H 2 S) Methanogenic bacteria (break down organic cpds. --> methane) Grey = no oxygen in pore waters ALSO: Denitrification below RPD

22 Deposit feeders Egestion Transport to surface of deep sediment Microbial consumption POM deposition Free-burrowing bivalve Sediment stirring RPD Stimulation of microbial growth Tube POM, (mechanically, Chemically, Transformed) Metal, sulfur, dissolved organic carbon exchange Metal, sulfur, dissolved organic carbon exchange Dissolved oxygen Ingestion of sediment

23 Burrowing brings dissolved oxygen into sediment Volkenborn et al 2010 Limnology and Oceanography Pressure measured with pressure sensors Oxygen Arenicola marina burrow

24 Sediment Recap Sediment affected by physical processes: currentsàgrain size, physical structures Sediment affected by burrowing: grain size, water content, internal sediment structure Strong vertical chemical gradient: oxidized near surface to lack of oxygen at depth (boundary is RPD; complex microbiology based upon use of different substances and oxidative-reductive processes Without burrowing, oxygen enters sediment from above diffusion, turbulence near

25 Benthic Feeding Types Deposit feeders Suspension feeders Herbivores (macroalgae or microalgae) Carnivores Scavengers

26 Deposit Feeders Feed upon sediment, within the sediment or at sediment surface, digest and assimilate organic matter (what is that?) Head-down deposit feeders feed within the sediment at depth, usually on fine particles, defecate at surface Surface browsers often feed on surface microorganisms such as diatoms

27 Hobsonia Deposit Feeders Yoldia Macoma Surface tentacle feeding polychaete Pectinaria Tentacle feeding bivalve Corophium Deep feeding polychaete Surface feeding amphipod Surface siphonate feeding bivalve Arenicola Deep feeding polychaete

28 25 mm Lagis koreni Southern North Sea, Belgium Hans Hillewaert

29 Parastichopus californicus

30 Particulate Organic Matter Detritus Deposition Pathways Phytoplankton seagrasses phytodetritus Benthic microalgae seaweeds Microbial activity decomposition, aided by burrowing, ingestion older organic matter

31 Deposit feeders Microbial stripping hypothesis: deposit feeders are most efficient at digesting and assimilating sediment microbial organisms (diatoms, bacteria), POM is not very digestible BUT, In some sediments non-living organic matter is abundant, so even a low assimilation efficiency returns some nutrition for deposit feeders; microbes much less abundant

32 Deposit feeders At some times of years, fresh phytoplankton sinks and is added to the bottom: another source of non-living food for deposit feeders Detritus from seaweeds is probably more digestible than detritus from seagrasses and marsh grasses, which have much relatively indigestible cellulose

33 Deposit feeders Deposit feeders feed on sedimentary grains, strip off microbial organisms living on particulate organic particles Feeding activity accelerates microbial attack on detritus - grazing stimulates microbial metabolism, results in tearing apart of organic particles Some deposit feeder guts - surfactant activity - emulsify particles solubilizes fatty acids from particles

34 Deposit Feeders - Main Points Ingest sediment including nonliving particulate organic matter (POM) and microbes Microbes digested more efficiently than POM, but bacteria not abundant enough to support most macrobenthic deposit feeders Some deposit feeders have surfactant digestive activity - loosen POM from sediment particles POM often dominates total organic matter, so poor digestion can still bring a reward Surface-feeders (better food) vs. deep head-down feeders (more refactory food) Spring deposition of POM from water column can bring a nutritious source of food in a pulse Some environments (mangroves) have a continuous and nutritious source of organic matter.

35 Suspension Feeders Passive versus active suspension feeders: Passive = whole animal has structure that is in current and particles impact the structure Active = current produced by animal is used to direct particles, suck them in

36 Sea fan, passive Bivalve siphon, active

37 Suspension Feeders Bivalve, x-section Polychaete Serpula Barnacle Balanus Active suspension feeders

38 Active suspension feeders - issues Concentration of particles - saturation and even clogging Selection for high-quality particles many poor particles in water, e.g., clay Hard to feed at high water velocity

39 Acorn barnacle cirri- active suspension feeding

40 Bivalve Feeding - compartments Gill Palp rejected Gut Food Siphon Pseudofeces Feces

41 Fiber-optic light source Endoscope Video connecto Oyster

42 Mussel Mytilus edulis

43 Oyster gill lamella

44 Oyster, Crassostrea virginica

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47 Ward et al. 1997, Nature 390: Ventral tract Basal tract Bivalves are particle selective (on gills in case of oyster Crassostrea gigas)

48 Suspension Feeders Sea squirt Styela montereyensis Passive suspension feeding mechanism, combined with active ciliary pump

49 Cetorhinus maximus 6-8 m long (12 m) Suspension feeding of a basking shark

50 Passive suspension feeders - issues Orientation in current Current velocity - pressure drag Particle concentration - saturation of feeding structure (e.g., polyp processing)

51 Recap - Deposit Feeders and Suspension Feeders Deposit Feeders - process particles on bottom Particles range from inorganic (e.g., sand grains) to organic Organic range from indigestible (cellulose) to very digestible (living digestible bacteria, microalgae; settling phytodetritus); all sources may matter in combination Quantity important (e.g., bacteria not sufficient as food for most larger deposit feeders)

52 Recap continued Suspension feeders - gather particles either passively (protrude structure into current) or actively(suck water into siphon) Suspension feeders have access different particle qualities - clay, non-living organic matter, microalgae of varying quality (some poisonous some indigestible) Gathering of particles important, but selectivity also important Digestive strategies and throughput also important issues Flow very important - causes change in animal form

53 Feeding Classification Deposit feeders Suspension feeders Carnivores Herbivores (macroalgae or microalgae) Scavengers

54 Carnivores Bivalve Cuspidaria oystercatcher Gastropod Nucella Polychaete Glycera Crab Callinectes sapidus

55 Carnivore issues Low population size, mobility, movement to patches of prey Detection and capture of prey Physiological limitations (depth of swimming, sensory biology, intertidal zone)

56 Poison: cysteine-rich peptides - attack ion channels, acetylcholine receptors (nerve and neuromuscular junctions) READ HOT TOPICS 13.1 P. 302 Conus, over 500 spp. Mainly in coral reefs

57 C. geographus C. striatus

58 C. striatus C. geographus

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60 Herbivores Polychaete Nereis vexillosa Parrot fish radula Chiton Urchins

61 Herbivore issues Ability to mechanically attack plants, seaweeds Chemical defense of plants, seaweeds Feeding, while avoiding predation by other species

62 Aristotle s Lantern Sea urchin

63 Parrotfish, family Scaridae

64 Cellulose feeder Bivalve Teredo foot Greatly elongated mantle Obtains nitrogen with symbiotic nitrogen fixing bacteria

65 The End