Increased Algal coverage as a Result of Decreased Urchins Herbivory

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Increased Algal coverage as a Result of Decreased
Urchins Herbivory

• Today I will
• -Discuss Herbivory levels of Urchins after the
  urchin Die-Out of 1983.
• -Provide reasoning why lower urchin populations
  correlate to higher algae levels.
• -Show some introductory data.
• -Introduce some goals for the my thesis and the
  project in general.
• Project Site Middle Caye, Glovers Reef Atoll.
  Belize, Central America
• Mentor Dr. Tim McClanahan, Wildlife Conservation
  Society.

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Why Study Urchins?

• -Because Algae is taking over the reef!
• -Algae-Coral Coverage Ratios have changed from
• From 80 Coral- 20 Algae
• To 25 Coral- 75 Algae
• Curiously, algal populations started increasing
  when the Diadema Urchin died out in 1983.
• Goal I would like to prove that the correlation
  between these two (algaeDiadema) is not mere
  chance.

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The solution.
Hungry Urchins
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Urchins eat Algae. Diadema
Echinometra
Feeding Location On top of reef (they group
together to make a conglomerate of spines for
safety)
Feeding Location Under coral substrate, between
cracks. (They also forage at night, when fish are
asleep)
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Urchins

• Echinometra. Avg. wt 28g
• -Diadema. Avg. wt 96g
• Why I need know Weights
• -Tracking Urchin weights throughout the
  experiment allows me to see which species are (or
  are not) growing.
• -I also hope to correlate their growth with algal
  coverage levels in order to indicate herbivory
  levels.
• My Findings
• Thus far, due to inadequate data collection
  techniques, the urchin growth data may be too
  flawed to allow me to draw any conclusions.

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Data Collection Techniques Procedures
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Daily Duties -Urchin Counts, Fish Counts, Cage
cleaning. Weekly Duties -Nighttime urchin
feeding locations, algae height/biomass
measurements, algal species cover, fish
counts/herbivory assessment. Every Other
Week Wet, Dry decalcified algal weight
measurements. -3 minute fish counts
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Site Stats -Patch Reef edge (5-8feet
deep) -16-cages Materials-PVC Mesh.
60x60x20cm 200grams of Urchin in each
cage -Urchins weighed with triple-beam
balance -Algal biomass measured in Lab
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Some extraneous data may prove to be beneficial
for future experiments.
For example -Fish herbivory levels plotted
against species specific algal coverage levels
will indicate how much noise fish herbivory
creates. -Primary growth algae rates may be
indicative of which urchins prefer which
algae. -Nighttime feeding Location charts
indicate preferred (predator-free) feeding
locations of the Diadema and Echinometra
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ImperfectionsYes even paradise isnt perfect
This was the projects first year. Therefore,
many of our field techniques and equipment need
improvement. -Cages need to be more secure
(urchins are escape artists) -Algal mass
measurements need to be more accurate -We need to
observe more nighttime feeding locations.
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Recap
In my presentation I discussed -Change in Algal
Coverage levels. -Change in Algal Mass vs.
Time -Urchins may solve the Algae problem -Urchin
Stats. -Data Collection Site stats -Expected
relevance of peripheral Data -Imperfections
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• Thesis goals
• -Process remaining data with mentor.
• -Find correlations between Urchin feeding habits
  and relative Algal biomass levels.

Project Goals -Provide a framework for future
projects. -If Diadema prove to be the main
consumer of Algae we may push for a
reintroduction effort or Diadema farms.
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• Thanks to
• -Tim McClanahan (mentor)
• -Brie Cokos (graduate field assistant)
• -Emily Seidman (co-worker)
• -Don Melnick (Enviro.Bio. Department Director)
• -My Mom and Dad