Drifters Follow surface currents to show speed, direction, and dispersion

Biophysical influence on coral abundance and diversity in Hurricane Hole, St. John, United States Virgin IslandsSophia McKenzie, Nasseer Idrisi, Caroline Rogers, Vanessa Wright, and Laurent Cherubin

University of the Virgin Islands

Purpose: To study the current patterns in Hurricane Hole and their possible affect on the variation in distribution and abundance of corals growing on the roots of mangrove trees in the four inner bays.

Hydrolab Measures temperature: can be

used to determine flow

Current MeterMeasures speed and direction of bottom currents

Four observations per day during current meter deployment (12/2/2010 – 1/31/2011)

Drifter Trajectories in Hurricane Hole

West Mid East Inner Bays Mouth

Wind Speed (m/s) and DirectionDuring Drifter Trials

Methods

Equipment

Acknowledgements Thanks to Jon Moore, Shaun Kadison, Shawn, Kevin Brown, Joanna Gyory, James Herlan, USGS, and EPSCoR for your support. References C.S. Rogers, USGS, personal observation, 2005.

Conclusions• Wind driven current• Onshore surface flow and offshore bottom flow indicative of downwelling• Inner bays protected from wind• Current does not explain high coral abundance in east bays• Other factors at work determining coral abundance• Temperature and water chemistry likely to affect coral abundanceThrough continued study of Hurricane Hole, we hope to better understand the mechanisms by which corals are thriving in an environment typically not suitable for their survival.

Borck

Princess

Otter

Water

1

1

1

2

2

2

3

3

3

4

4

4

Borck Princess Otter Water27.627.727.827.9

2828.128.228.328.428.528.6

InnerMidOuter

Tem

pera

ture

(°C)

1 2 3 426.5

27

27.5

28

28.5

29

29.5

30

HH MouthCoral Bay Inner MouthCoral Bay Outer Mouth

Location

Tem

pera

ture

(°C)

Inner Bay Temperatures

Note: Inner locations are closest to shore

Mouth Temperatures

Hurricane Hole Mouth

Coral Bay Outer Mouth

Coral Bay Inner Mouth

Clusters• Northwest movement• Angles of tracks correspond with variation in wind speed • Wind showed small south component during trials

Transects• Borck ,Water, and most Princess drifters moved southwest• Southeast direction for inner Princess•Mouth and Otter moved directly east

Current Meter

Average CurrentSpeed: 0.0424 m/s

Variance: 0.0260 m/sDirection: 159.21°

(southeast)

Results Results

Hydrolab

0.0079 m/s

0.0739 m/s

0.0979 m/s

West Cluster Mid Cluster East Cluster Inner Bay Transects Mouth Transect

Drifter Cluster Release Current Meter Hydrolab Cast