1. 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

2. 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

3. River
Shallower
Warmer
Fresher
Ocean
Deeper
Colder
Saltier

4. 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

5. Low tide
High tide

6. Estuarine ecosystem includes intertidal zones

7. Estuaries have terrestrial and aquatic predators
Sea birds Raccoons Sea turtles
Sharks & rays Many fish
Jellyfish Ctenophores Juvenile fish

8. 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

9. 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

10. 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.

11. Currents can be used by larvae to get into or out of estuary
Salt-wedge
Partially
Mixed
Well-Mixed

12. Flux of larvae (horizontal motion) depends on velocity and concentration
Flux = velocity x concentration
[#/m2/s] [m/s] x [#/m3]
Queiroga & Blanton 2005

13. 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

14. Two crabs from San Diego Bay: different STST strategies
Lined shore crab
Pebble crab
DiBacco et al. 2001

15. 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

16. 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

17. 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

18. 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 

19. 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

20. 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)

21. Vector cues increase/decrease vertically+ -
Light Pressure Gravity
Taxis is positive or negative depending on direction of movement

22. 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

23. 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

24. Chesapeake Bay is a major blue crab habitat
Adults tolerate this salinity range
Larvae tolerate this salinity range

25. Blue crab life cycle with migration

26. -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

27. Megalopae return by nocturnal flood tide transport
HWS = High Water Slack
LWS = Low Water Slack
Queiroga & Blanton 2005

28. Megalopae swim up in response to increasing pressure, salinity (flood tide indicators)
Percent of larvae in top of chamber
Tankersley et al. 1995

29. 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

30. 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

31. 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

32. Mud crab map

33. Early stages stay at mid-depth
Late stages sink
HWS = High Water Slack
LWS = Low Water Slack
Queiroga & Blanton 2005

34. Mean depth of early-stage mud crab larvae
Salinity
Current velocity
Mean depth of early-stage mud crab larvae
Cronin 1982

35. 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)

36. 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