Elkhorn forests, viral and encrusting fire corals, oh my!!

The date is July 13, 2013.  It's becoming increasingly difficult to recap everything I've been doing here at CCMI.  Yesterday was probably the most fun-filled/stressful day since I've been here.  I'll save the fun stuff for later, but we had our ID test last night... 135 questions.  Corals, fish, macroalgae, and invertebrates- common and latin names.  I don't mean to boast, but I got a 132.5 out of 125.  I never though in a million years I would be able to retain so much information in just 2 short weeks.  I came to the Caribbean not knowing much about coral identification.  I knew "brain coral"- that was about it.  But now I'm able to identify, by genus and species, almost a dozen species of brain corals.  Don't even get me started about the other Scleractinians (stony corals)... Porites, Montastrea, Acropora, Meandrina, Diploria, Colpophyllia, the list goes on.

All the researchers at CCMI have really opened my eyes into how much work there is to be done in the field of marine science.  I have so many questions that seem so easy to answer, yet are so complex that nobody can give me a definitive answer.  As a little bit of background information, we are required to design an independent study, collect data, and present and discuss our findings with a panel of Ph.D scientists from around the island.  For our study, my group and I chose to conduct an observational survey of stony coral species that had colonized dead Acropora palmata (elkhorn coral) skeletons on the reef crest of Grape Tree Bay, Little Cayman.  A. palmata, one of only two Acropora species in the Caribbean (the other being A. cervicornis, the staghorn coral) is assessed as Critically Endangered under IUCN redlist categorization.  

A massive colony of A. palmata- one of the fastest growing coral species in the Caribbean

The two Acropora species are proposed as the fastest growing corals in the Caribbean- up to 10 cm per year compared to the average 0.5-2 cm per year of other corals.  However, the Acropora are less hardy than most species, and die even if you look at them the wrong way.  From thermal anomalies to high wave action, every conceivable stressor kills these corals.  While we were out snorkeling and diving surveying coral diversity around the island, we literally saw fields of dead elkhorn coral.  I stand at 6 feet, 1 inch, and some of these colonies were wider in diameter than I am tall.  Simply amazing

Anyway... we noticed that there were almost no stony corals re-colonizing these skeletons.  Quite perplexing considering everything else under the sea was not having any trouble doing so- fire corals (hydroids), gorgonians (soft corals, i.e. sea fans, sea plumes, etc), and various species of algae.  Is there some factor that makes these skeletons less suitable for stony coral recruitment?  (Recruitment essentially refers to how coral larvae disperse and settle for form new colonies)

We logged almost 150 GPS points of dead A. palmata skeletons in just 2 days, and observed that most of the stony coral growth was from Porites asteroides (mustard hill coral).  This is very interesting to me, because P. asteroides is one of the few brooding coral species.  About 75% of corals reproduce via massive, synchronized spawning events where gametes are released and externally fertilized, then carried long distances before settling.  Brooding coral species, however, fertilize their eggs internally, releasing planulae (planktonic, or free-floating, larvae) that are larger and better developed than those fertilized externally through spawning.  These planulae are heavier, and thus settle closer to the parent colony.  

Perhaps there is a spatial connection between P. asteroides colonization on dead A. palmata skeletons- i.e. there could be parent colonies scattered around the skeletons that are responsible for the P. asteroides colonization observed.  The pilot study that we are conducting fortunately raises more questions than answers- our hope is that other researchers will use this information to better understand various aspects of coral reef ecosystem connectivity such as-

• settlement preference of stony corals-- do stony coral planulae settle by chance (random), or do the parent colonies somehow synchronize planulae or gamete release (in spawning) with temporal variables such as changes in current velocity/direction, lunar phases, diurnal cycles, seawater chemistry, nutrient availability, etc.
• competition between corals-- take for example fire "corals"..these colonial organisms technically aren't corals because they are actually Hydrozoans and more closely related to jellyfish and anemones.  For anybody that doesn't know, they are called fire coral because like jellies and anemones, they are armed with thousands of nematocysts (stinging cells)-- upon close examination, they actually appear fuzzy to the naked eye (you probably wouldn't want to get that close though- take it from personal experience, heed my warning!)  These organisms are almost like weeds in that you will see them ABSOLUTELY EVERYWHERE!  Most field guides give a general description of their shapes, but they can actually "take over" existing coral species and take on their shape

Fire coral beginning to encrust a sea plume (Pseudoteroptgorgia; above)
Over time, the fire coral can overtake the entire organism, almost like a
virus, like the picture on the right (displays a fire coral encrusting
a sea fan, genus Gorgonia)

- Stan