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Spring 2017 Biophysical Interactions: from Barnacles to Jellyfish 11:628:410, 3 credits Prerequisites: this class and Calculus II Low Reynolds numbers Drag and shape Swimming and Propulsion Turbulence and encounters Schooling and Swarming Biogenic mixing Flux and diffusion Boundary Layer Flows Larval Settlement Benthic Filter Feeding
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Estuarine Larval Transport
Estuarine biological/physical environment Selective Tidal Stream Transport Endogenous rhythms vs. exogenous cues Scalar vs. vector cues A few examples of crab larval behavior
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River Shallower Warmer Fresher Ocean Deeper Colder Saltier
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Water level goes up and down
with tidal cycle. Range can be a few meters. Diurnal tide: ~24 hour cycle Semidiurnal tide: ~12 hour cycle
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Low tide High tide
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Estuarine ecosystem includes intertidal zones
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Estuaries have terrestrial and aquatic predators
Sea birds Raccoons Sea turtles Sharks & rays Many fish Jellyfish Ctenophores Juvenile fish
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Estuaries are regions of environmental extremes
Depending on balance of tidal forcing and river input: Temperature Shallow water warms up faster than deep water Temperatures up to >30 oC, like bath water Can vary by many degrees in a single tidal cycle Salinity From 0 ppt (fresh) to 32 ppt or more (marine) Can vary by many ppt in a single tidal cycle
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Low salinity can be a major stressor for marine and estuarine animals
Human blood has a salinity of about 9, maximum of about 15 Osmoregulation: Active regulation of the salt content in bodily fluids
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Adult animals can bury themselves in the mud where salinity and temperature are relatively constant.
Larvae are in the water column and have no protection against heat and low salinity.
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Currents can be used by larvae to get into or out of estuary
Salt-wedge Partially Mixed Well-Mixed
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Flux of larvae (horizontal motion) depends on velocity and concentration
Flux = velocity x concentration [#/m2/s] [m/s] x [#/m3] Queiroga & Blanton 2005
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Vertical migration patterns lead to Selective Tidal Stream Transport (STST)
Flood-tide Transport Move into estuary Ebb-tide transport Move out of estuary Nocturnal flood-tide transport Move into estuary at night Forward & Tankersley 2001
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Two crabs from San Diego Bay: different STST strategies
Lined shore crab Pebble crab DiBacco et al. 2001
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Shore crab Pebble crab Surface Surface Mid-depth Mid-depth Bottom
(Ebb-tide transport) (NO migration) Surface Surface Mid-depth Mid-depth Bottom Bottom Ebb tide Ebb tide DiBacco et al. 2001
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Virtual larvae with and without vertical migration have different export rates
Ebb tide transport No vertical migration Flood: sink to bottom Ebb: swim to surface Shore crab Pebble crab DiBacco et al. 2001
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Behavior can have internal or external cues
Endogenous rhythms Synchronized with day/night or tidal cycle Responses to Exogenous cues Physical cues: temperature, salinity, light, pressure, currents, turbulence Chemical cues: from food, predators, others of same species
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Tides affect environmental conditions (exogenous cues)
Flood tide (water comes in from sea) Temperature drops Salinity increases Depth/pressure increase Ebb tide (water goes out to sea) Temperature increases Salinity drops Depth/pressure drop
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Exogenous cues - two types of behaviors
-kinesis Non-directional movement in response to a stimulus Temperature Thermokinesis Pressure Barokinesis Salinity Halokinesis -taxis Directional movement in response to a stimulus Light Phototaxis Gravity Geotaxis Current Rheotaxis
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Two types of cues Scalar Cue has only magnitude, no direction
Includes most water column properties: temperature, salinity, density, concentration of chemicals Vector Cue has both magnitude and direction Velocity is a vector (by definition) Gravity, light, pressure (pseudo-vector)
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Vector cues increase/decrease vertically
+ - Light Pressure Gravity Taxis is positive or negative depending on direction of movement
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Blue crab life cycle Adult Zoea (7 stages): 1 to 1.5 months
Megalopa stage: up to 2 months Juvenile crab (20 molts) Blue crabs live 1-3 years, respond quickly to changes in environment, fishing etc. Salinity tolerance Larvae: >20 ppt Adults: 3 to 15 ppt
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Blue crab fishery Tastiest crab species in US?
Chesapeake Bay fishery worth: $200 million in 1994 $55 million in 2000 Fishery affected by: Habitat loss Pollution prey shortage: oysters, clams excess predators: birds, fish low recruitment since 1998
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Chesapeake Bay is a major blue crab habitat
Adults tolerate this salinity range Larvae tolerate this salinity range
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Blue crab life cycle with migration
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-Females do the work of getting larvae out to sea -Larvae use nocturnal ebb migration to escape
HWS = High Water Slack LWS = Low Water Slack Queiroga & Blanton 2005
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Megalopae return by nocturnal flood tide transport
HWS = High Water Slack LWS = Low Water Slack Queiroga & Blanton 2005
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Megalopae swim up in response to increasing pressure, salinity (flood tide indicators)
Percent of larvae in top of chamber Tankersley et al. 1995
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Even more megalopae swim when both turbulence and salinity increase (flood tide indicator) [but not when salinity decreases (ebb tide indicator)] Welch and Forward 2001
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Blue crab megalopae have complex behaviors
Exogenous cues for swimming up on nocturnal flood tide Increase in pressure (pseudo-vector) Increase in salinity (scalar) Increase in turbulence (scalar) Dark But…. Increase in turbulence + decrease in salinity Daytime + estuarine water No reaction
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Harris mud crab Native to East coast of North America
-Has invaded inland lakes, Panama Canal -Alters food webs -Fouls water intake pipes -Virus carrier, infects shrimp and blue crabs Larvae: Tolerate wide range of salinities >2.5 ppt Have long spines to deter predators Better equipped to stay in an estuary
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Mud crab map
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Early stages stay at mid-depth
Late stages sink HWS = High Water Slack LWS = Low Water Slack Queiroga & Blanton 2005
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Mean depth of early-stage mud crab larvae
Salinity Current velocity Mean depth of early-stage mud crab larvae Cronin 1982
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Mud crab larvae have complex behaviors
Swim up in response to: Increase in salinity (scalar) Decrease in temperature (scalar) Increase in pressure (pseudo-vector) Sink in response to: Decrease in salinity (scalar) Increase in temperature (scalar) Decrease in pressure (pseudo-vector)
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Crab larvae have many different behavioral strategies for migration in/out of estuaries
Pebble crabs Larvae do not vertically migrate High dispersal within estuary, little export Blue crabs Early-stage larvae exported to shelf Late-stage larvae have complex behaviors for getting back into the estuary Mud crabs Early-stage larvae have complex behaviors for staying in the estuary Estuarine throughout life cycle
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