Post on 16-Dec-2015
Spring 2015 course: 11:628:410, 3 credits Biophysical Interactions: from Barnacles to Jellyfish
Tues-Thurs 2:15-3:35
•Life at low Reynolds numbers•Drag and Lift•Feeding and Escape•Swimming and Propulsion•Larval Dispersal•Schooling and Swarming•Vertical Migration•Biomixing•Flux and diffusion•Boundary Layer Flows•Benthic Filter Feeding•Fronts and Waves
Prerequisite: Dynamics (this class) and 2 semesters of calculus
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
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
Sea birds Raccoons Sea turtles
Sharks & rays Many fish
Jellyfish Ctenophores Juvenile fish
Estuaries have terrestrial and aquatic predators
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
Low salinity can be a major stressor for marine and estuarine animals
Osmoregulation: Active regulation of the salt content in bodily fluids
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.
Flux of larvae (horizontal motion) depends on velocity and concentration
Flux = velocity x concentration
[#/m2/s] [m/s] x [#/m3]Queiroga & Blanton 2005
Vertical migration patterns lead to Selective Tidal Stream Transport (STST)
Forward & Tankersley 2001
Flood-tide TransportMove into estuary
Ebb-tide transportMove out of estuary
Nocturnal flood-tide transportMove into estuary at night
Two crabs from San Diego Bay: different STST strategies
Lined shore crab
Pebble crab
DiBacco et al. 2001
Shore crab Pebble crab
Surface
Mid-depth
Bottom Bottom
Mid-depth
Surface
Ebb tideEbb tide
DiBacco et al. 2001
DiBacco et al. 2001
Ebb tide transport No vertical migrationFlood: sink to bottomEbb: swim to surface
Virtual larvae with and without vertical migration have different export rates
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
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
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
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
Vector cues increase/decrease vertically
+
-
-
+
-
+
Light Pressure Gravity
Taxis is positive or negative depending on direction of movement
Salinity toleranceLarvae: >20 pptAdults: 3 to 15 ppt
Zoea (7 stages):
1 to 1.5 months
Megalopa stage:
up to 2 months
Juvenile crab
(20 molts)
Adult
Blue crab life cycle
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
Blue crab abundance vs. management target2008 - Fishery declared a federal disaster - New rules on harvest of females 2010 - Recovery to above target
Chesapeake Bay is a major blue crab habitat
Adults tolerate this salinity range
Larvae tolerate this salinity range
Queiroga & Blanton 2005
HWS = High Water SlackLWS = Low Water Slack
-Females do the work of getting larvae out to sea-Larvae use nocturnal ebb migration to escape
Megalopae return by nocturnal flood tide transport
Queiroga & Blanton 2005
HWS = High Water SlackLWS = Low Water Slack
Megalopae swim up in response to increasing pressure, salinity (flood tide indicators)
Tankersley et al. 1995
Per
cent
of
larv
ae in
top
of
cham
ber
Welch and Forward 2001
Even more megalopae swim when both turbulence and salinity increase (flood tide indicator)[but not when salinity decreases (ebb tide indicator)]
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
Blue crab megalopae have complex behaviors
No reaction
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 pptHave long spines to deter predatorsBetter equipped to stay in an estuary
Queiroga & Blanton 2005
HWS = High Water SlackLWS = Low Water Slack
Early stages stay at mid-depth
Late stages sink
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)
Plus a negative feedback model: in dark, negative geotaxis (vector; swim up)in light, negative phototaxis (vector; sink)
Mud crab larvae have complex behaviors
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