Life in the Mud.! Benthic productivity versus pelagic productivity

Transcription

1 Life in the Mud! Benthic productivity versus pelagic productivity

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3 The Benthos! By definition: organisms (animals and plants) that live on, in or attached to the sea floor! Includes 98% of all marine species! Coral Reefs alone contain 25% of all marine species!! Community composition determined by benthic composition! (Parts of Chapters 7, 8, 10)

4 Most phyla are found in marine sediments--and life may have originated at a vent seep! Dunn et al., Nature 452:

5 Benthic vs. Pelagic! Benthic organisms are not adapted to wide ranges in pressure! There are very few transparent organisms! Generally stay to a smaller spatial area (they don t move around as much)! We classify them in relation to the type of shoreline or bottom structure

6 Benthic Substrates! Rocky, sandy, or muddy intertidal! Muddy deposits or hydrothermal deposits in the deep sea! Biomass is closely related to surfacewater primary production

7 Benthic Diversity, Biomass! Benthic diversity is largely controlled by! Temperature (more in warmer waters)! Currents (this affects the benthic structure)! Wave Energy (infauna vs. epifauna)! Benthic Biomass is largely controlled by! Water column primary productivity! High Biomass often equals Low Diversity

8 Primary Production Benthic Biomass

9 The Shallow Benthos Similar to the pelagic environment, much of the benthos is dominated by detritus (the microbial web)

10 The Shallow Benthos Continental shelves also dominated by the microbial web

11 The Shallow Benthos Continental shelves also demonstrate complex food webs, with many interchangeable organisms

12 Deep Benthic monotony. The deep benthos is generally static dark, cold, weak currents. However, the seasonal deposition of organic matter (food) is highly regulated by overlying surface production

13 Species diversity generally peaks at ~2000 m, and decreases with increasing depth HOWEVER, when normalized to the number of individuals encountered, diversity stays constant with depth It is (currently) unclear whether the deep benthos is more or less diverse than other biomes

14 The abundance of organisms generally decreases with depth (as does the TOTAL biomass), but the size of individuals generally increases.

15 Deep-Sea Gigantism Meter-long isopod (pillbug-like organism) Why? Several theories. 1)! Slower metabolism 2)! Delayed onset of sexual maturity 3)! Evolutionary trend for food-capture 4)! Low mutation rate

16 Whale Falls Deep-Sea Oases of Productivity

17 At any given time, a large food source (such as a whale fall) increases biomass of organisms (feeding on the carcass) but decreases species diversity (because of specialization). However, the whale can be thought of as a successional community

18 Differences between land and ocean:! Ocean currents move ocean animals around!! Small animals in the ocean can be pushed around by currents, and may not be able to choose where they go.! Adult fish and mammals can swim strongly, and adult invertebrates cling to the bottom, but babies are at the mercy of the currents

19 Standard ecological theory (land): Animals are found in comfortable environments Marine ecological theory: Animals may be found where the currents put them. Depends on animal s lifestyle. Whether they survive or not is largely dependent on the availability of food or suitable habitat (subtrate) in that environment.

20 Distance from Santa Cruz: San Francisco: ~100km Los Angeles: ~ 500 km Salt Lake City: ~1000 km

21 Many marine species have bipartite life histories 1.! Planktonic dispersive early stage 2. benthic or site attached adult stage PLANKTONIC LARVAE SETTLEMENT *Larva: an independent, often free-living, developmental stage that undergoes changes in form and size to mature into the adult; especially common in insects and aquatic organisms. (From a Latin word meaning "ghost" or "mask.") REPRODUCTION BENTHIC ADULTS

22 More facts of nature: you don t see the bipartite lifestyle often on land

23 Marine organisms: complex life cycles

24 Example of life cycle for species with larvae

25 Most larvae bear little resemblance to adults Sea star Phoronid worm Octopus Snail

26 Giant kelp have spores that disperse

27 Most seafood species have larvae Mussel Crab Lobster Tuna Dinner Adults Larvae

28 Most fouling organisms have larvae Barnacle life cycle Feeding Non-feeding (Oceanographers are always looking for better ways to keep barnacle larvae from settling on their boats and instruments!)

29 Sea urchin Starfish Sea cucumber Bryozoa Phoronid Polychaete Gastropod crabs barnacle nemertean

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32 Bipartite Lifestyles! A major component of benthic ecology deals with recruitment! The larvae are often very different from the adult life stage! While planktonic, many larvae do not consume food (they rely on internal reserves)! Some larvae utilize the DOM, acting as (essentially) very large bacteria

33 What makes larval transport so important?! Population dynamics!ecologically important!edible species (valuable +$)!Fouling organisms and invasive species (costly -$)! Biogeography --!geographic distributions!range expansions! Conservation --!design of marine reserves

34 ! Larval Transport: Horizontal movement of larvae from one point to another! Larval Dispersal: Spread of larvae from spawning sites to wherever they die or settle! Population Connectivity: The exchange of individuals among distinct populations! Settlement: When a larva metamorphoses and adopts a benthic lifestyle! Recruitment: Defined by when we first observe the new recruit in the population

35 Figure 1. Relationship between the spatial and temporal components of larval transport, larval dispersal, and reproductive population connectivity for a sessile species. Note that the sum of larval transport distances can be larger than the dispersal distance. White circles are locations in space with coordinates x-y at times t. All locations are pelagic except x0, y0, and x4, y4, which are benthic. Distance could also be represented in two dimensions (e.g., x,y as cross- and alongshore axes.) From Pineda et al. 2007

36 Demographically closed! Retention Pelagic fisheries perspective! Hjort (1914)! Stock-recruitment! relationships!

37 Demographically closed! Retention Benthic ecology perspective! Thorson (1950)! For organisms with multi-phase life histories, understanding the biotic and physical mechanisms that regulate abundance/distribution of adults requires integrating the dynamics and distributions of several aspects of the life cycle.! Dispersal Larval pool Demographically open!

38 Demographically closed Retention Tagging Studies Swearer et al. 1999! Jones et al (Nature)! Genetic pop. structure:! Barber et al (Nature)! Larval pool Larval pool Mixture of larval inputs Dispersal Demographically open

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42 Reserves and Species Persistence From Botsford, Hastings, and Gaines Ecology Letters!! Reserves can meet conservation goals in two ways:!large Individual Size! > mean dispersal distance! 2-3x mean dispersal distance with advection!large Total Network Area

43 Larvae are unobservable in transit, so larval transport and dispersal are difficult to study.! Where/when are larvae most concentrated?! Sampling larvae at sea! Where are recruits found?! Put out settlement plates to collect recruits! Where did recruits come from?! Population Genetics! Trace Element Tags! Where do larvae go and why?! Mathematical Models! Drifters, smart drifters

44 Model Domain Pacific Ocean Los Angeles Dong & McWilliams CSR (2007)

45 Example 30 Day Trajectories Red dots: locations after 30 days Surface following

46 Dispersal from San Nicolas -2 [ km ] millions of water parcel releases

47 Dispersal from Other Sites -2 [ km ] Advection time = 30 days

48 Seasonal Variability Advection time = 30 days

49 Interannual Variability Advection time = 30 days

50 Deep-Sea Communities issue_pdfs/20_1/20.1_ramirez_et_al.pdf

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52 Abundance and diversity!! The vent fauna comprises a list of mainly new and undescribed species!! 1991: 223 of the 236 species listed were new to science!! 1998: 443 species were listed!! Preponderence of three phyla: molluscs, arthropods and annelids!! The list of species is still growing!! deep sea: 85 spp. on 61 manganese nodules at 2 sites!! vents: 236 spp. from ~30 dives!! intertidal boulder field: 214 invertebrate spp. in m 2 samples!! temperate corals: 309 spp. on 8 coral heads "! most species are endemic to vents "! some deep-sea taxa are absent from vents "! most species are sessile with a few highly mobile ones "! ~75% of species only occur at one site

53 Abundance and diversity The main determinant of spatial and temporal patterns "! variation in vent flow Results in variations in: Temperature Chemical composition of the fluid Bacterial production

54 Spatial patterns Within vent fields Diffuse flows: density and composition decrease concentrically e.g. EPR (e.g. 9 ºN)!! Tubeworms!! at vent openings: the obturaculum has to be exposed to absorb H 2 S and O 2!! in big clusters or small tufts!! Mussels!! grow everywhere!! form patches or beds (100s-1000s of individuals)!! Clams!! in cracks (for ideal positioning of foot and siphon) between lava pillows or on sheets!! away from high temperatures!! in areas of low fluid flux;!! Crabs and fish!! very motile!! within or near animal clumps to distances of up to 500 m

55 East Pacific Rise 9 ºN Tubeworm zone Bivalve zone Serpulid zone Periphery

56 Shank et al. (1998) Microbial material 11 months: Tevnia 32 months: Riftia overtaking Tevnia 42 months 55 months

57 Everything is everywhere, but the environment selects

58 Larval dispersal and supply!! Stepping stone model "! A population divided into discrete subpopulations "! Dispersal occurs primarily between neighboring subpopulations "! Gene flow decreases as the number of steps between subpopulations increases!! Island model "! All subpopulations are equally accessible to dispersing larvae "! Long-range dispersal among subpopulations predominates "! No relationship between genetic divergence and geographic distance Examples!! SS: tubeworms and shrimp at Galapagos and EPR (Riftia pachyptila, Tevnia jerichonana, Oasisia alvinae, Ventiella sulfuris)!! IM: tubeworms at JdFR (Ridgeia piscesae) mussels, clams and limpets at EPR (Bathymodiolus thermophilus, Calyptogena magnifica, Eulepetopsis vitrea, Lepetodrilus pustulosus)

59 Mesoscale hydrodynamic processes (km s 100s km s)!! Larvae near the bottom can travel between vents (100s m s) within a 6-h tidal excursion!! Larval entrainment in the hydrothermal plume "! diluted 10 4 x by volume "! vertical velocities = 10 cm s -1 "! vertical volume fluxes = 500 m 3 s -1!! When plumes become neutrally buoyant "! they spread laterally "! they form vortex pairs "! retention of larvae within the plume "! vortex shedding "! delivery of a concentrated patch of larvae

60 Coral Reefs Similar to hydrothermal vents, they are NOT distributed in relation to pelagic productivity (i.e. we don t find coral reefs in high productivity waters)

61 Coral Reef Food Webs

62 Coral Reefs are Highly Regenerating Food goes in, but does not get out--the coral reefs can survive in oceanic (low biology) regions by being highly efficient at recycling organic material

63 What is the future of coral reefs? Many corals see large fluctuations in ph related to PDO and other oscillations, and may be somewhat resilient to changes in ph (to a point). Pelejaro et al., 2005 Science 309:

64 What is the future of coral reefs? De ath et al., Science 2009, 323:

65 Summary Benthic ecology is largely controlled by: - Substrate Type - Depth - Food Availability The benthos generally closely tracks surface productivity, except at vents and coral reefs A fundamental difference between land and ocean is that most organisms take advantage of the movement of water Why study the benthos? - probably the origins of life on this planet - most of the marine genera are found in the benthos - ultimate sink for biogeochemistry