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

A couple of words about the exam….

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

River Shallower Warmer Fresher Ocean Deeper Colder Saltier

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

Low tide High tide

Estuarine ecosystem includes intertidal zones

Sea birds Raccoons Sea turtles Sharks & raysMany fish JellyfishCtenophoresJuvenile 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 o C, 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.

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

Flux of larvae (horizontal motion) depends on velocity and concentration Flux = velocity x concentration [#/m 2 /s] [m/s] x [#/m 3 ] Queiroga & Blanton 2005

Vertical migration patterns lead to Selective Tidal Stream Transport (STST) Forward & Tankersley 2001 Flood-tide Transport Move into estuary Ebb-tide transport Move out of estuary Nocturnal flood-tide transport Move 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 Mid-depth Surface Ebb tide DiBacco et al. 2001

Ebb tide transport No vertical migration Flood: sink to bottom Ebb: 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 tolerance Larvae: >20 ppt Adults: 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 target Fishery declared a federal disaster - New rules on harvest of females Recovery to above target

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

Blue crab life cycle with migration

Queiroga & Blanton 2005 HWS = High Water Slack LWS = 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 Slack LWS = Low Water Slack

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

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 ppt Have long spines to deter predators Better equipped to stay in an estuary

Mud crab map

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

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

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