Histological analysis of Caribbean acroporid corals collected in September 2014 before and after exposure to thermal stress in St. Thomas, U.S. Virgin Islands.

Website: https://www.bco-dmo.org/dataset/752550
Data Type: experimental
Version: 1
Version Date: 2019-01-08

» Collaborative research: Is hybridization among threatened Caribbean coral species the key to their survival or the harbinger of their extinction? (Coral Hybridization)
Fogarty, NicoleNova Southeastern UniversityPrincipal Investigator
Biddle, MathewWoods Hole Oceanographic Institution (WHOI BCO-DMO)BCO-DMO Data Manager

Histological analysis of Caribbean acroporid corals collected in September 2014 before and after exposure to thermal stress in St. Thomas, U.S. Virgin Islands.


Spatial Extent: Lat:18.31701 Lon:-64.98923
Temporal Extent: 2014-09-20 - 2014-09-22

Dataset Description

A pilot project was conducted in the St. Thomas, U.S. Virgin Islands to examine the effects of thermal stress on the three acroporid taxon. 

Acquisition Description

Two 10 cm fragments (1 for control tank and 1 for treatment tank) from five colonies of each acroporid taxon were collected from Flat Cay the day prior to the experiment and left under ambient temperature conditions overnight. Tissue samples (2cm) were collected immediately prior to and immediately after the experiment and preserved in a Z-Fix Concentrate: seawater (1:4) solution. One fragment (putative genotype) from each taxon was placed in a control tank (n=5) and one was placed in a treatment tanks (n=5).  Powerheads that were slightly tilted out of the water to provide aeration and water movement were placed in all tanks. The ambient tanks were placed in a large tank with constant flowing seawater that served as a water bath. The five treatment tanks, each with an individual heater, were place in a neighboring large tank with no running seawater. All tanks were under a covered porch, but exposed to ambient light conditions. 

A Hobo temperature logger was placed in each tank and a water temperature measurement was collected every 30 seconds. The control tanks ranged from 27.5 to 29.4C with an average of 28.2C and the heated tanks ranged from 29.1 to 32.7C with an average of 31.3C over the 48 hour experimental period. 

Processing Description

The semi-quantitative rubric was designed by Dr. Esther Peters for the histological analysis.  

Data legend:
ND = No Data
NS = not enough tissue to determine, not seen

Lesion Description: 
H = healthy
WBD = white band disease
RTL = rapid tissue loss
BL = bleaching

0 = none
1 = paling
2 = bleaching

Bleaching Distribution:
1 = focal
2 = multifocal distinct
3 = multifocal indistinct
4 = diffuse

Condition Scores: 
0 = excellent
1 = very good
2 = good
3 = fair
4 = poor
5 = very poor

Intensity/Severity Scores:
0 = no change
1 = minimal
2 = mild
3 = moderate
4 = marked
5 = severe

P = present
A = absent
SI = staining issue
NS = not seen
N/A = not available
N = no

Epidermal mucocytes:
0 = not larger than ciliated columnar cells, uniform distribution
1 = slightly hypertrophied, numerous
2 =  many hypertophied, abundant mucus release
3 =  uneven, hypertrophied vs reduced 
4 =  atrophy, necrosis, and epidermal foci lacking mucocytes
5 =  atrophy and most mucocytes lacking

Mesenterial Filament (CGB Epithelium) Mucocytes:
0 = none to few
1 = less than 1/2 area, not hypertrophied
2 = about 1/2 area, some hypertrophied
3 = about 1/2 area, all hypertrophied 
4 = about 3/4/ area, some vacuolated
5 = much of area vacuolated, necrotic, loss of mucocytes

Calicodermis Condition:
0 = cells squamous but "thick," cover mesoglea
1 = cells slightly atrophied in some foci
2 = 1/2 of cells atrophied
3 = Most cells atrophied, beginning separation from mesoglea
4 = Cells atrophied and loss or sloughing present

Costal Tissue Loss:
0 = none, tissue over costae intact
1 = a few gaps noted
2 = 1/4 of costae exposed
3 = 1/2 of costae exposed
4 = 3/4 of costae exposed
5 = Most costae exposed, tissues attenuated, retracted?

0 - none present
1 - single cells in mesoglea
2 - early oocytes
3 - mid-development
4 - mature
5 - spawned

0 - none present
1 - clusters of single cells in mesoglea
2 - few, early spermaries
3 - numerous spermaries, spermatocytes
4 - mature, spermatozoa
5 - spawne

BCO-DMO Processing Notes:

  • added conventional header with dataset name, PI name, version date
  • modified parameter names to conform with BCO-DMO naming conventions
  • added lat, lon columns

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LabAcademic affiliation unitless
Histo_NumberSample number unitless
StudyStudy title unitless
CollectorPI on project unitless
SpeciesA.cerv = Acropora cervicornis; A.pal = Acropora palmata; A. pro = Acropora prolifera unitless
Sample_LocationCollection location (18.31701 -64.98923) unitless
Field_or_Lab_Numberassigned coral identifier unitless
Date_Collectedcoral collection date in MM/DD/YY format unitless
Sample_Typelocation within coral colony unitless
Lesion_DescriptionHealthy (apparently) (H); White band disease (WBD); Rapid tissue loss (RTL); Bleaching (BL) unitless
Bleaching0 = No; 1 = Paling; 2 = Bleaching unitless
Colony_Bleaching_Distribution1 = Focal; 2 = Multifocal Distinct; 3 = Multifocal Indistinct; 4 = Diffuse unitless
Tissue_LossIs the skeleton void of tissue? (Y or N) unitless
In_situ_PhotoWas a photograph taken during the experiment? (Y or N) unitless
Gross_Photo_Fixed_SampleWas a photograph taken after the sample was preserved? (Y or N) unitless
Collection_Notesanything notable about photographs unitless
Sample_NumberThe assigned unique identifier unitless
Piece_NumberPre= collected before experiment; Post= collected after experiment unitless
Number_of_Blocks_MadeThe number of samples embedded in paraffin to be sectioned and mounted on slides unitless
Fixationpreservative used (Zfix:seawater in 1:4) unitless
EnrobingWas the sample enrobbed in agarose gel to preserve the oritentation of cells and tissues while processing and embedding the sample? (Typically required if there is tissue sloughing on the sample) unitless
DecalThe solution used to decalcifiy the coral skeleton unitless
EmbedMedium used to embed tissue sample unitless
Number_of_Slides_MadeNumber of slides made from each block count
Number_Stained_with_H_ENumber of slides stained with hematoxylin and eosin (H&E) stain count
Other_StainsAdditional stains used on samples (Yes = Stain specified or N = No) unitless
General_Condition_10xObserved tissue condition at 10x maginfication. Combines all parameters into a general score- 0=Excellent; 1= very good; 2= good; 3 =fair; 4 = poor; 5= very poor unitless
Zooxanthellae_10xObserved symbiont (zooxanthellae) condition at 10x magnification. 0=Excellent; 1= very good; 2= good; 3 =fair; 4 = poor; 5= very poor. Scores related to the number of zooxanthellae present and their overall apperance (atrophy or hypertrophy). unitless
Epidermal_Mucocytes_ConditionObserved condition of the unicellular secretory gland cells that secrete mucus through an apical pore to aid in protection; sediment removal; and feeding. Epidermal mucocytes are those found in the epidermis; the outermost tissue layer in corals. Condition of mucocytes; 0 - not larger than ciliated columnar cells; uniform distribution; 1 - slightly hypertrophied; numerous; 2 - many hypertophied; abundant mucus release; 3 - uneven; hypertrophied and/or reduced in number; 4 - atrophy; necrosis; and epidermal foci lacking mucocytes; 5 - atrophy and most mucocytes lacking unitless
Mesenterial_Filament_MucocytesObserved mucocyte condition in the cnidoglandular band area of mesenterial filaments. These are the internal longtiduinal partitions of tissue that provide structual support and increase surface area within the gastrovacular cavity. These regions aid in digestive processes and gonad development. 0=Excellent; 1= very good; 2= good; 3 =fair; 4 = poor; 5= very poor unitless
Degeneration_Cnidoglandular_BandsObserved condition of the free edge or middle ridge of the mesentary in the gastrovascular cavity. Scores related to reduction in cell height or number of cells; and atrophy of the epithelium in the cnidoglandular band. 0=Excellent; 1= very good; 2= good; 3 =fair; 4 = poor; 5= very poor unitless
Dissociation_of_Mesenterial_FilamentsObserved condition of cells in the mesenterial filaments. Scores related to loss of cells and atrophy of cells. 0 - none to few; 1 - less than 1/2 area; not hypertrophied; 2 - about 1/2 area; some hypertrophied; 3 - about 1/2 area; all hypertrophied; 4 - about 3/4/ area; some vacuolated; 5 - much of area vacuolated; necrotic; loss of mucocytes unitless
Calicodermis_ConditionObserved condition of the basal surface lining epithelium which contains calicoblasts- cells responsible for secreting a matrix to promote crystallization of calcium carbonate; thus assiting in the formation of coral skeleton. 0 = cells squamous but "thick;" cover mesoglea; 1 = cells slightly atrophied in some foci; 2 = 1/2 of cells atrophied; 3 = Most cells atrophied; beginning separation from mesoglea; 4 = Cells atrophied and loss or sloughing present; 5 = Multifocal necrosis or sloughing of atrophied cells or absent on mesoglea unitless
Calicodermis_RepairIs there evidence of repair of the calicodermis? Are there columnar calicoblasts with extensions of plasmallema present? (Present = 1; Not Present = 0) unitless
Costal_Tissue_LossObserved condition of tissue over the costal ridges (extensions of the septa of the corallite); 0 = none; tissue over costae intact; 1 = a few gaps noted; 2 = 1/4 of costae exposed; 3 = 1/2 of costae exposed; 4 = 3/4 of costae exposed; 5 = Most costae exposed; tissues attenuated; retracted unitless
Necrotic_Cell_SpherulesAre there signs of necrotic (dying) cell or group of cells present? (Present = 1; Not Present = 0) unitless
WBD_Bacterial_AggregatesNumber of bacterial aggregates associated with white band disease observed. count
Epidermal_RLOsNumber of Rickettsia-like organisms observed in the epidermal tissue layers. count
Filament_RLOsNumber of Rickettsia-like organisms observed within the mesentary filaments. count
Gastrodermal_RLOsNumber of Rickettsia-like organisms observed within the gastrodermis. count
Surface_BacteriaNumber of bacteria present on the outer epidermal layer. count
CoccidiaNumber of single-celled intracellular parasites belonging to apicomplexans observed. count
Zooxanthellate_CiliatesAre single-celled protozoans with hair-like organelles called cilia observed with zooxanthellae? (Present = 1; Not Present = 0) unitless
Non_zooxanthellate_CiliatesAre single-celled protozoans with hair-like organelles called cilia present in other locations of sample? (Present = 1; Not Present = 0) unitless
Oocytes_Stage_in_DevelopmentEgg cells found in the mesentaries: 0 - none present; 1 - single cells in mesoglea; 2 - early oocytes; 3 - mid-development; 4 - mature; 5 - spawned unitless
Spermaries_Stage_in_DevelopmentLocation of developing spermatozoa in the mesentaries. 0 - none present; 1 - clusters of single cells in mesoglea; 2 - few; early spermaries; 3 - numerous spermaries; spermatocytes; 4 - mature; spermatozoa; 5 - spawned unitless
latlatitude coordinates with North positive decimal degrees
lonlongitude coordinates with East positive decimal degrees

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Dataset-specific Instrument Name
Hobo Pro v2 data logger
Generic Instrument Name
Temperature Logger
Dataset-specific Description
A Hobo temperature logger was placed in each tank and a water temperature measurement was collected every 30 seconds.
Generic Instrument Description
Records temperature data over a period of time.

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Project Information

Collaborative research: Is hybridization among threatened Caribbean coral species the key to their survival or the harbinger of their extinction? (Coral Hybridization)

Coverage: Caribbean and North-West Atlantic

NSF Award Abstract:
Reef-building acroporid corals form the foundation of shallow tropical coral communities throughout the Caribbean. Yet, the once dominant staghorn coral (Acropora cervicornis) and the elkhorn coral (A. palmata) have decreased by more than 90% since the 1980s, primarily from disease. Their continuing decline jeopardizes the ability of coral reefs to provide numerous societal and ecological benefits, including economic revenue from seafood harvesting and tourism and shoreline protection from extreme wave events caused by storms and hurricanes. Despite their protection under the U.S. Endangered Species Act since 2006, threats to the survival of reef-building acroporid corals remain pervasive and include disease and warming ocean temperatures that may lead to further large-scale mortality. However, hybridization among these closely related species is increasing and may provide an avenue for adaptation to a changing environment. While hybrids were rare in the past, they are now thriving in shallow habitats with extreme temperatures and irradiance and are expanding into the parental species habitats. Additional evidence suggests that the hybrid is more disease resistant than at least one of the parental species. Hybridization may therefore have the potential to rescue the threatened parental species from extinction through the transfer of adapted genes via hybrids mating with both parental species, but extensive gene flow may alter the evolutionary trajectory of the parental species and drive one or both to extinction. This collaborative project is to collect genetic and ecological data in order to understand the mechanisms underlying increasing hybrid abundance. The knowledge gained from this research will help facilitate more strategic management of coral populations under current and emerging threats to their survival. This project includes integrated research and educational opportunities for high school, undergraduate and graduate students, and a postdoctoral researcher. Students in the United States Virgin Islands will take part in coral spawning research and resource managers will receive training on acroporid reproduction to apply to coral restoration techniques.

Current models predict the demise of reefs in the next 200 years due to increasing sea surface temperatures and ocean acidification. It is thus essential to identify habitats, taxa and evolutionary mechanisms that will allow some coral species to maintain their role as foundation fauna. Hybridization can provide an avenue for adaptation to changing conditions. Corals hybridize with some frequency and results may range from the introduction of a few alleles into existing parent species via introgression, to the birth of a new, perhaps better adapted genetic lineage. The only widely accepted coral hybrid system consists of the once dominant but now threatened Caribbean species, Acropora cervicornis and A. palmata. In the past, hybrid colonies originating from natural crosses between elkhorn and staghorn corals were rare, and evidence of hybrid reproduction was limited to infrequent matings with the staghorn coral. Recent field observations suggest that the hybrid is increasing and its ecological role is changing throughout the Caribbean. These hybrids appear to be less affected by the disease that led to the mass mortality of their parental species in recent decades. Hybrids are also found thriving in shallow habitats with high temperatures and irradiance suggesting they may be less susceptible to future warming scenarios. At the same time, they are expanding into the deeper parental species habitats. Preliminary genetic data indicate that hybrids are now mating with each other, demonstrating the potential for the formation of a new species. Further, hybrids appear to be capable of mating with both staghorn and elkhorn coral, perhaps leading to gene flow between the parent species via the hybrid. Research is proposed to address how the increase in hybridization and perhaps subsequent introgression will affect the current ecological role and the future evolutionary trajectory of Caribbean acroporids. Specifically, this collaborative project aims to answer the following questions: 1) What is the historic rate, direction, and degree of introgression across species ranges and genomes? Linkage block analysis based on genome-wide SNP genotyping across three replicate hybrid zones will answer this question. 2) What is the current extent and future potential of later generation hybrid formation? Morphometric and genetic analyses combined with in vitro fertilization assays will be used. 3) What mechanisms allow hybrids to thrive in hot, shallow waters? A series of manipulative in situ and ex situ experiments will determine whether biotic or abiotic factors favor hybrid survival in shallow waters. 4) Are hybrids more disease resistant than the parentals species? Disease transmission assays in reciprocal transplant experiments and histological analysis to determine the extent of disease will be conducted. A multidisciplinary approach will be taken that combines traditional and cutting edge technology to provide a detailed analysis of the evolutionary ecology of Caribbean corals.

Note: PI Nicole Fogarty's original award OCE-1538469 was issued while at Nova Southeastern University. This was replaced by OCE-1929979 upon moving to the University of North Carolina Wilmington.

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Funding SourceAward
NSF Division of Ocean Sciences (NSF OCE)

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