0

0.005

0.01

0.015

0.02

0.025

0.03

0.035

0.04

0.045

Bare (0 -1) Sparse (2-3) Dense (4-5)

Mea

n U

rch

in D

en

sit

y (

ind

/m2)

Thalassia testudinum Density (BB)

ANOVA

p<0.0001

A

AB

B b.

0

0.005

0.01

0.015

0.02

0.025

0.03

0.035

0.04

Absent (0 - 1) Present

Mea

n U

rch

in D

en

sit

y (

ind

/m2)

Thalassia testudinum Density (BB)

a.

*

Investigation of herbivorous sea urchins in Thalassia testudinum beds in the Florida Keys

National Marine Sanctuary using data from a long-term seagrass monitoring program

Mia Lamirand, University of Hawai′i at HiloResearch Mentors: Riki Bonnema, Sara Wilson and Dr. James Fourqurean, Biology

Discussion and Future Studies

lamirand@hawaii.edu

This material is based upon work supported by the National Science Foundation under Grant No. HRD-1547798.. This NSF Grant was awarded to Florida International University as part of the Centers of Research Excellence in Science and Technology (CREST) Program. Any opinions, findings, and conclusions or recommendations expressed in this material are those of the author(s) and do not necessarily reflect the views of the National Science Foundation.

Acknowledgements: Thank you to Chris Lopes, Kaya Carrion, Bryce Van Dam, Guanglong Qiu, David Barahona and Kai Lopez, along with Brad Schonhoff, Rita Teutonico, Todd Crowl and my CREST REU cohort for making this internship a memorable experience.

Invertebrate Composition

• At each site (n=40), divers survey

a 1m x 50m transect to quantify

invertebrates within the area

MethodsIntroduction Results continued

Goals and Hypotheses

Score Cover

0 Taxa absent from quadrat

0.1 Taxa represented by a solitary shoot, <5% cover

0.5 Taxa represented by a few (<5) shoots, >5% cover

1 Taxa represented by many (>5) shoots, <5% cover

2 Taxa represented by many (>5) shoots, 5 - 25% cover

3 Taxa represented by many (>5) shoots, 25 - 50% cover

4 Taxa represented by many (>5) shoots, 50 - 75% cover

5 Taxa represented by many (>5) shoots, 75 - 100% cover

p < 0.01y = -0.0007x + 0.0607

R² = 0.012

0

0.2

0.4

0.6

0.8

1

1.2

1.4

10 30 50 70 90 110

Mea

n U

rch

in D

en

sit

y (

ind

/m2)

Thalassia testudinum N:P content

d.

N:P = 30:1

(Optimal for

T. testudinum)

Increasing

Decreasing

Decreasing

0

0.2

0.4

0.6

0.8

1

1.2

1.4

1.6

0 1 2 3 4 5

Mea

n U

rch

in D

en

sit

y (

ind

/m2)

Thalassia testudinum Density (BB)

c.

Goals

•Investigate the spatial and temporal trends of

Thalassia testudinum and sea urchin densities in the

FKNMS.

•Evaluate optimal T. testudinum densities for sea

urchin populations.

•Determine if there is a correlation between urchin

density and T. testudinum tissue nutrients.

Hypotheses

• There is a positive correlation between T. testudinum

density and sea urchin density. We expect that both

may be declining.

• There is no correlation between T. testudinum tissue

nutrients and sea urchin density.

Seagrass Importance

• Carbon storage

• Support biodiversity and fisheries

• Nursery habitat and feeding grounds

Monitoring Program and Water Quality

• FKNMS contains one of largest

documented seagrass beds

• Seagrasses are indicators of local

nutrient regimes

Other Factors Affecting Seagrass Beds

• Herbivorous animals, over-grazing

Urchins

Echinoderms

Gastropods

Bivalves

Crustaceans

Other Benthic Fauna

Thalassia testudinum

Syringodium filiforme

Halodule wrightii

Halophila decipiens

Halophila engelmannii

Ruppia maritima

• First analysis of SERL benthic invertebrate survey data

• Researchers can leverage long-term habitat monitoring programs to

investigate other ecological questions (e.g. invertebrates, decomp.)

• Since T. testudinum tissue nutrients exert control over sea urchin

densities, this could suggest a bottom-up system

Future Studies

• Compare Dry Tortugas National Park to current study

• More inclusive herbivore surveys to better understand all

interactions in this complex system

Nutrient Analysis/ Lab Work

• Homogenize dried samples

• Measure N content with elemental analyzer

• Analyze P content spectrophotometrically

Increasing

Seagrass Density

• Braun-Blanquet survey along transect

• 10 quadrats (0.5m x 0.5m)

• Score assigned based on cover

Results

T-Test

p < 0.0001

p < 0.001

y = 0.008x + 0.02

R² = 0.01

e. f.

(a) Higher sea urchin densities in areas with seagrass present. (b) Highest sea urchin

densities in locations with 5-50% seagrass coverage. (c) There is a positive correlation

between T. testudinum density and sea urchin density. (d) There are larger concentrations

of sea urchins where T. testudinum N:P ratios approach 30:1 (higher tissue P).

Rate of change in T. testudinum (e) and sea urchin (f) density from 1996 to 2018.