MEANDRINA MEANDRITES AUTUMNAL BLEACHING CYCLE on the GULF STREAM REEF SYSTEM, BOYNTON BEACH, FLORIDA

Transcription

1 MEANDRINA MEANDRITES AUTUMNAL BLEACHING CYCLE on the GULF STREAM REEF SYSTEM, BOYNTON BEACH, FLORIDA Prepared April 2004 By: Ed Tichenor P.O. Box 207 Boynton Beach, Florida (561)

2 CONTENTS Section 1.0 INTRODUCTION 1.1 Background 2.0 INVESTIGATION 2.1 Methodology 3.0 OBSERVATIONS 3.1 Bleaching Characteristics 3.2 Bleaching Cycle 4.0 DATA DEFICIENCIES 5.0 CONCLUSIONS LIST OF APPENDICES Appendix Description A Report of Coral Bleaching to NOAA, October 2000 Report of Coral Bleaching to NOAA, November 2001 Appendix B Description Photograph #1 Bleached Meandrina meandrites Photograph #2 Bleached Meandrina meandrites Photograph #3 Recovered Meandrina meandrites Photograph #4 Recovered Meandrina meandrites Photograph #5 Dark Pigmentation Meandrina meandrites Photograph #6 Dark Pigmentation Meandrina meandrites Photograph #7 Partially Bleached Meandrina meandrites Photograph #8 Partially Bleached Meandrina meandrites Photograph #9 Close-up Bleached Meandrina meandrites Photograph #10 Close-up Pigmented Meandrina meandrites (i)

3 Table Description LIST OF TABLES I II 2000 to 2003 Meandrina meandrites Bleaching Data 2003 Meandrina meandrites Bleaching Data LIST OF FIGURES Figure Description #1 Gulf Stream Reef, Location Map #2 Autumnal Bleaching Cycle 2000 to 2003 #3 Ocean Water Temperature 2000 to 2003 # Autumnal Bleaching Episode #5 Hours of Daylight, 25 o N (ii)

4 1.0 INTRODUCTION Meandrina meandrites (Maze Coral) colonies located on Gulf Stream Reef ( N, W), Boynton Beach, Florida have been observed to bleach and recover on a predictable annual cycle. A four year investigation ( ) was performed to document this annual occurrence. 1.1 Background On October 7, 2000 bleaching Meandrina meandrites colonies were observed on Gulf Stream Reef (GSR). Post-dive interviews were conducted with the dive boat personnel of Splashdown Dive Charters, Boynton Beach, Florida. The boat captain, Lynn Simmons, a marine biologist with over 20 years local diving experience stated the Maze Coral bleaches every autumn and recovers a short time thereafter. An additional six dives were conducted in the area (Figure 1), approximately one week apart, until December 2000, at which time the coral colonies had recovered. For the next three years ( ) bleaching and recovery of M. meandrites on GSR was observed to occur within the same approximate timeframe. Notification of the bleaching events was transmitted to NOAA in 2000 and 2001 (Appendix A). 2.0 INVESTIGATION During the months of September though December 2000 to 2003 dives were conducted in the study area; visual observations and water temperatures were recorded (Table I). These data were employed to generate graphs depicting the percentage of bleaching vs. time and ocean water temperature vs. time (Figures 2 and 3). Qualitative estimates of bleached colonies were obtained for the years 2000, 2001 and A quantitative protocol was employed for 2003 to provide a more accurate enumeration of the bleaching event (Table II, Figure 4). 2.1 Methodology For all years studied observations generally consisted of two dives per weekly trip (conditions permitting), performed at a depth of between ft. below surface in the area between N to N. Each dive covered approximately miles depending on current velocity. The search patterns were random along the top and inshore slope of the reef, observing all M. meandrites colonies encountered. For the years 2000, 2001 and 2002 a visual estimate of bleached colonies was recorded. During 2003 the same random search pattern was executed; however, a more accurate tabulation of coral colonies was employed. On each dive the total number of M.

5 meandrites colonies observed was recorded. In addition, colonies greater than 5% and less than 85% bleached were recorded as partially bleached (Photos # 7 and 8) and colonies greater than 85% bleached were recorded as completely bleached. These data were employed to calculate the percentage of completely bleached, partially bleached and total affected colonies (Table II). 3.0 OBSERVATIONS 3.1 Bleaching Characteristics The bleaching results in snow white colonies, completely devoid of pigmentation (Photos #1, 2 and 9), followed by complete re-pigmentation resulting in honey colored colonies (Photos #3, 4 and 10). However, on occasion it was noted that if light were physically blocked from a portion of a recovering colony, such as in the case of a sponge or other object falling on the M. meandrites, the area in the shadow would remain white, while the rest of the colony would develop pigment. It appears that there may be two distinct color variations in the M. meandrites colonies. Prior to bleaching the colonies exhibit a brown/green coloration (Photos #5 and 6), repigmented colonies are a lighter brown/honey color (Photos #3 and 4). This may be due to different zooxanthellae densities or variation in symbiont type. Throughout the calendar year dive trips are conducted at a frequency of roughly one per week on GSR. At no time has bleaching of other coral species (other than an occasional isolated colony) been detected, nor has there been bleaching of M. meandrites outside the September to December cycle. Further, no dead M. meandrites have ever been found, suggesting that all bleached colonies recovered. 3.2 Bleaching Cycle For all years studied (2000 through 2003) bleaching initiated within days following the Autumnal Equinox, September 22 (Figure5). The bleaching peak (the total number of colonies bleached at any one time) for the years 2000 and 2003 occurred about 35 days following that date. For 2000 and 2003 recovery/re-pigmentation followed the peak by about 35 days, making the complete bleaching and recovery cycle about 70 days from beginning to end. The peak bleaching date for 2002 is not known due to insufficient observations. For 2001 the recovery and possibly the peak shifted to a later date. No observations were made from October 20 until November 10, 2001 due to rough weather and the influence of hurricane Michelle which resulted in winds up to 40 kts. and increased turbidity in the study area. The later recovery date may have been an effect of these weather conditions and resulting lower light levels. It is possible the 2001 peak bleaching date may have occurred during the lapse in observations. If the 2001 data is extrapolated for the period of missing observations the date of peak bleaching is more consistent with the years 2000 and 2003.

6 4.0 DATA DEFICIENCIES 1) Meandrina meandrites colonies were never tagged; therefore specific observations could not be performed on individual colonies through the term of the bleaching cycle. 2) Pre and post bleaching zooxanthellae were not collected for identification. 3) The frequency of dives leaves gaps in the data. 4) Due to the methodology employed it could not be determined if only a portion of the population bleached each year or if all colonies were involved with never more than 20-30% being completely bleached at any one time. However, the protocol employed in 2003 showed 66% of the colonies were involved in the episode at a given point in time. 5.0 CONCLUSIONS There is sufficient data to suggest the M. meandrites bleaching and recovery is likely an annual occurrence, possibly triggered by photoperiodism and perhaps a deciduous adaptation of the species at the northern limit of it s range, or even a trait specific to the GSR M. meandrites population. The predictability of the GSR M. meandrites cycle provides a natural laboratory for the study of the coral bleaching phenomenon.

7 APPENDIX A Correspondence

8 COPY OF Report of Coral Bleaching October 2000 Subj: Re Report of Coral Bleaching, Boynton Beach FL Date: 10/25/00 4:28:19 AM Eastern Standard Time From: To: WHEN: While diving October 21, 2000, I observed bleaching of Maze Coral (Meandrina meandrites) from Gulfstream Reef, north to Lynn's Reef off Boynton Beach Fl. WHERE: this reef system is located south of the Lake Worth Pier (Latitude N Longitude W) and approximately one mile south of the Boynton Inlet. The reef lies in ft of water. WHAT: The bleaching has occurred within the last two weeks (as of 10/21/00). Approximately 10-20% of this species is now affected, with some colonies completely snow white. I generally dive this site every weekend. I will provide you with any additional relevant observations. If you have any questions, please do not hesitate to me. Ed Tichenor

9 COPY OF Report of Coral Bleaching November 2001 Subj: Reoccurrence of Maze Coral bleaching, Boynton Bch., FL Date:11/11/01 5:32:44 PM Central Standard Time From: To: CC: Approximately one year ago I reported to you an episode of coral bleaching of Maze Coral (Meandrina meandrites) in the Boynton Beach, FL reef system (a copy of my initial correspondence is presented below). By mid-december 2000 most of the bleached colonies had regained pigmentation. The purpose of this is to report a reoccurrence of the bleaching. While diving the reef system on October 6, 2001, I noticed a few bleached colonies of Maze Coral. On Oct. 21, 2000 approximately 20% were bleached and on Oct. 28, 2000 > 20% were affected (date) (temp.) (observation) (date) (temp.) (observation) F F F F bleaching first observed F bleaching first observed F F F approx. 20% bleached F approx. 20% bleached F >20% bleached F >20% bleached F unchanged F recovered A comparison of 2000 and 2001 data show a bleaching reoccurrence almost to the day. According to Captain Lynn Simmons ( a local dive boat operator with 20 years experience in Boynton," the Maze bleaching is an annual event". This bleaching may be in response to dropping water temperatures or photoperiodism? If it is indeed an annual cycle this may be useful in the study of bleaching and recovery. Please me if you have any questions. Ed Tichenor

10 APPENDIX B Photographs

11 Bleached Meandrina meandrites PHOTO # 1 Photograph by E. Tichenor PHOTO # 2 Photograph by E. Tichenor

12 Recovered Meandrina meandrites PHOTO # 3 Photograph by E. Tichenor PHOTO # 4 Photograph by E. Tichenor

13 Dark Pigmentation Meandrina meandrites PHOTO # 5 Photograph by E. Tichenor PHOTO # 6 (partially bleached) Photograph by E. Tichenor

14 Partially Bleached Meandrina meandrites PHOTO # 7 Photograph by E. Tichenor PHOTO # 8 Photograph by E. Tichenor

15 Close-up Bleached Meandrina meandrites PHOTO # 9 Photograph by E. Tichenor

16 Close-up Pigmented Meandrina meandrites PHOTO # 10 Photograph by E. Tichenor

17 TABLES & FIGURES

18 Table I 2000 to 2003 Meandrina meandrites Bleaching Data Gulf Stream Reef Boynton Beach, Florida (completely bleached colonies) date % temp F date % temp F date % temp F date % temp F 9/23 no bleaching 85F 9/22 no bleaching 84F 9/21 no bleaching 85F 9/20 no bleaching 82F * * 9/28 bleaching 84F * 10/07 bleaching 82F 10/06 bleaching 82F * 10/ % 81F 10/14 bleaching 80F 10/13 bleaching 81F * 10/ % 81F 10/21 ~ 20% 81F 10/20 ~ 20% 80F * 10/ % 79F 10/28 ~>20% 79F * * 10/ % 80F * * * 11/ % 78F * 11/10 ~>20% 78F * 11/ % 78F 11/18 ~<5% 78F * * 11/ % 79F * 11/25 ~<10% 77F * 11/ % 77F 12/02 0% 76F * 11/30 no bleaching 75F 11/ % 76F * 12/08 ~<5% 76F * 12/ % 75F * 12/15 0% 76F * 12/ % 74F (See Figures 2 and 3)

19 Table II 2003 Meandrina meandrites Bleaching Data Gulf Stream Reef Boynton Beach, Florida Date m/d/y Completely Bleached Colonies Partially Bleached Colonies Total Affected Colonies 09/20/ % 0.00% 0.00% 10/05/ % Not recorded Not calculated 10/11/ % 28.6% 42.9% 10/18/ % 41.5% 66.0% 10/29/ % 21.3% 47.6% 11/06/ % 13.3% 31.5% 11/08/ % 13.4% 27.8% 11/15/ % 11.3% 18.8% 11/22/ % 6.86% 10.78% 11/30/ % 2.30% 2.30% 12/06/ % 0.00% 0.00% (See Figure 4)

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21 Figure 2 Figure 3

22 Figure 4 Figure 5