Physical and chemical factors affecting the upstream migration of amphidromous shrimp in the Luquillo Experimental Forest D.A. Kikkert, T.A. Crowl, and A.P Covich

Persistent, undistracted movement from one habitat to another at specific life stages (sensu Dingle 1996). Among aquatic biota the best studied migrations are those of diadromous fishes such as salmonids and eels. MIGRATION

DIADROMY MIGRATIONS BETWEEN MARINE AND FRESHWATER ENVIRONEMNTS AT PARTICULAR LIFE STAGES (MYERS 1949) AMPHIDROMY ANADROMY SPEND MAJORITY OF LIVES IN THE SEA, MIGRATE INTO FRESHWATER TO BREED CATADROMY SPEND LIVES IN FRESHWATER, MIGRATE TO THE SEA TO BREED

AMPHIDROMY Migration between fresh water and sea for purpose other than breeding Migration usually occurs during the larval life stage Most common on tropical oceanic islands where it may be necessary for dispersal.

Freshwater Ocean Adults Larvae Post Larvae Adults

Luquillo Experimental Forest (LEF) Humid, subtropical climate Annual rainfall ranges from 1000 to 6000mm Slightly seasonal with a dry season from February-April Nine streams originate within the LEF

Luquillo Experimental Forest STREAMS

Headwater streams characterized by steep gradient (10-20%) Primarily boulder and cobble lined with bedrock glides and waterfalls common Discharge is highly variable with flows increasing rapidly during rainfall Luquillo Experimental Forest STREAMS

SHRIMP Headwater streams dominated by 2 species of atyid shrimp (Xiphocaris elongata and Atya spp.) and the freshwater prawn Machrobrachium spp. Adult populations in headwater streams are well studies as part of an NSF long term monitoring program Little is known about the upstream migration of post-larvae

UPSTREAM MIGRATION Nocturnal migration Hypothesized increase in migration during times of low predation risk Critical for recruitment into adult populations Increasing human development in the coastal plain Road / stream intersections could act as barriers (Biocomplexity project)

UPSTREAM MIGRATION

OBJECTIVES Quantify upstream migration of Xiphocaris elongata, Atya spp., and Macrobrachium spp. Identify regular patterns in shrimp migration rates Identify environmental factors that may affect upstream migration

METHODS FIELD STUDY ARTIFICIAL STREAMS

FIELD STUDY Sampled shrimp migration over 5 months (N=46 nights) Used multiple regression to determine if environmental variables explain variation in shrimp migration rate and timing

RESULTS

Atya spp. F=3.18 p=0.07 Xiphocaris elongata F=12.77 p= Macrobrachium spp. F=24.86 p= DRY SEASON SAMPLING (N=12) WET SEASON SAMPLING (N=34)

RESULTS REGRESSION ENVIRONMENTAL VARIABLES CLOUD COVER (0-1) PERCENT MOON ILLUMINATED MOON PRESENCE/ABSENCE OBSERVED MOONLIGHT MOON POWER (% ILL.*P/A*CLOUD COVER*TIME SINCE MOONRISE) PRECIP (IN) PREVIOUS DAYS DISCHARGE INSTANTANEOUS DISCHARGE MEAN DISCHARGE (PREVIOUS 24 HOURS) CV DISCHARGE (PREVIOUS 24) NUMBER OF FLASHFLOODS / WEEK TIME SINCE LAST FLASHFLOOD TIME SINCE 1% EXCEEDANCE FLOOD (Q323) TIME SINCE 25% EXCEEDANCE FLOOD (Q23)

RESULTS REGRESSION Atya Spp. MODEL PARAMETER ESTIMATESAIC (∆ i )r2r2 Adj r 2 N CLOUD COVER MOON POWER PRECIP CV (Q) FF / WEEK TIME SINCE FF TIME SINCE 1% EXCEEDANCE FLOOD

RESULTS REGRESSION Xiphocaris elongata MODEL PARAMETER ESTIMATESAIC (∆ i )r2r2 Adj r 2 N ORDINAL DAY CLOUD COVER PRECIP TIME SINCE Q TIME SINCE Q

RESULTS REGRESSION Xiphocaris elongata - WET SEASON ONLY MODEL PARAMETER ESTIMATESAIC (∆ i )r2r2 Adj r 2 N Q INSTANTANEOUS MEAN DISCHARGE NUMBER OF FF / WK

RESULTS REGRESSION Macrobrachium spp. MODEL PARAMETER ESTIMATESAIC (∆ i )r2r2 Adj r 2 N ORDINAL DAY CLOUD COVER PRECIP PREVIOUS DAYS Q TIME SINCE Q

RESULTS REGRESSION Macrobrachium spp. - WET SEASON ONLY MODEL PARAMETER ESTIMATESAIC (∆ i )r2r2 Adj r 2 N ORDINAL DAY OBSERVED MOONLIGHT PRECIP Q INSTANTANEOUS

ARTIFICIAL STREAMS

TREATMENT METHOD ( APPLIED TO ONE SIDE OF EACH STREAM ) PREDATOR PRESENCE/ABSENCE FISH (MOUNTAIN MULLET) INCREASED FLOWINCREASE INSTANTANEOUS Q TURBIDTYSEDIMENT ADDED LEAF LITTERCONDITIONED LEAF PACKS

RESULTS ARTIFICIAL STREAMS Atya spp. ** * * * DENOTES SIGNIFICANCE AT P=0.05

RESULTS ARTIFICIAL STREAMS Xiphocaris elongata ** * * DENOTES SIGNIFICANCE AT P=0.05

CONCLUSIONS Atya spp. make up majority of shrimp migration Xiphocaris elongata and Macrobrachium spp migrations seasonal Macrobrachium make up a large component of the shrimp migration in August Ayta spp effected by light levels and flow regime with increased migration following spates Xiphocaris and Macrobrachium spp. migrate during periods of low Migration rates of all species decrease during extended periods of low flow

CONCLUSIONS Atya and Xiphocaris avoid channels with possible low water quality (turbidity and leaf litter) Spates may increase water quality and shrimp migration Chemical cues from fish predators may play a role in shrimp migration Atya appear to be positively rheotactic, following the highest flow

Acknowledgments Todd Crowl Katie Hein Alan Covich Wyatt Cross Ecology Center (Utah State University) Ruth Kikkert (All the fieldwork)