NOVA SOUTHEASTERN UNIVERSITY OCEANOGRAPHIC CENTER
MACROBENTHIC SPATIAL PATTERNS AND COMMUNITY STRUCTURE ON THE BROWARD COUNTY, FLORIDA (USA) REEFS. By Ryan P. Moyer
SUBMITTED TO THE FACULTY OF NOVA SOUTHEASTERN UNIVERSITY OCEANOGRAPHIC CENTER IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF SCIENCE WITH SPECIALTY IN:
MARINE BIOLOGY
NOVA SOUTHEASTERN UNIVERSITY 9 APRIL 2003
MOYER, RYAN P. MarineBiology)
(M.S.,
MACROBENTHIC SPATIAL PATTERNS AND COMMUNITY STRUCTURE ON THE BROWARD COUNTY, FLORIDA (USA) REEFS (April 2003) Master’s Thesis at Nova Southeastern University, Oceanographic Center ABSTRACT: High latitude reef communities consisting of typical Caribbean fauna of variable composition and density exist on four parallel ridges at varying depths along the Broward County (FL, USA) coast. At least two of these ridges, at 7-13m and 15-30m depth, are drowned early Holocene coral reefs of 5 ky and 7 ky uncorrected radiocarbon age, respectively. Previous work has shown that the present reef communities growing on these ridges can be detected and mapped using acoustic remote sensing and has suggested that different benthic assemblages may exist between each of these reefs. In this study, in situ community data was taken in four corridors on each reef using fifty-meter line-intercept transects. Multidimensional scaling analyses of the in situ community data show distinct differences in benthic community structure across several spatial gradients within the county. This clustering agrees well with an acoustic data set, taken in the same four corridors along the Broward County coast. Analysis of diversity statistics revealed that whereas species diversity (H’) was consistent throughout the county, species richness (d) and eveness (J’) increased along a north-south gradient. Total scleractinian cover was generally low in all areas (<6% mean cover), and also increased along a north-south gradient in the reef communities closest to shore (ridge complex communities). Percent scleractinian coral cover on all other reef communities (inner, middle, and outer reefs) was consistent throughout the county with Montastrea cavernosa being dominant over the M. annularis complex, which is the more typically dominant reef builder in Caribbean systems. Notably absent from the scleractinian fauna of this area was the major Caribbean reef-builder Acropora palmata. A rich alcyonacean fauna (12 genera) was present on all reefs in the county, and typically was the faunal group with highest cover (~20% mean cover countywide) and most important in terms of determining community structure. Although 2-year average water temperature never fell below 21 degrees C, which is within generally accepted limits for reef building, scleractinia were small in size and though not directly investigated, no observable evidence for late Holocene reef building exists. Habitat maps produced from this study show evidence for the unevenly distributed existence of at least six different community types within Broward County: Type 1: shallow, sponge-dominated community; Type 2: shallow, stony- and soft coral-dominated community; Type 3: shallow, zoanthid and soft coral-dominated community; Type 4: soft coral-dominated community; Type 5: zoanthid and macroalgae-dominated community; Type 6: Macroalgae, massive sponge, and soft coral-dominated community.
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TABLE OF CONTENTS I: INTRODUCTION……..………………………………………………………………….......
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STRUCTURE OF THE BROWARD COUNTY REEF SYSTEM……….…………………………
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REMARKS ON THE USE OF THE TERM “REEF” IN THIS STUDY..……………...……………
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ACOUSTIC REMOTE SENSING…………………………………………………………….
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PURPOSE OF THE STUDY………………………………………………………………….
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II: METHODS……….……....……………………………………………………..…………...
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STUDY AREAS….………………………………………………………………………...
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Broward County Overview…………………………………………………….
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Corridor 1……………………………………………………………………...
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Corridor 2……………………………………………………………………...
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Corridor 3……………………………………………………………………...
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Corridor 4……………………………………………………………………...
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ACOUSTIC DATA COLLECTION.…………………………...……………………………..
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ECOLOGICAL DATA COLLECTION………..……………………………………………...
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STATISTICAL ANALYSIS………….…………………………………………..……….…
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Acoustic Data Analysis…………………………………………………….….
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Ecological Data Analysis……………………………………………………...
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APPLICATION, THEORY, AND INTERPRETATION OF STATISTICS AND STATISTICAL GRAPHICS……………………………………………………………………...
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III: RESULTS………………...………………………………………………….……………..
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CORRIDOR 1…………………………...…………………………………...……………
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Acoustic Data Analysis……………………………………………………….
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Ecological Data Analysis……………………………………………………..
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CORRIDOR 2………………………………………...…………………………...………
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Acoustic Data Analysis……………………………………………………….
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Ecological Data Analysis……………………………………………………..
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CORRIDOR 3……………………………………………………...…………………...…
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Acoustic Data Analysis……………………………………………………….
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Ecological Data Analysis……………………………………………………..
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CORRIDOR 4…………………………………………………………………...………..
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Acoustic Data Analysis……………………………………………………….
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Ecological Data Analysis……………………………………………………..
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COMPARISONS AMONG ALL CORRIDORS….……………………………………………
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REEF EDGE-REEF CREST ANALYSIS……………………………………………………
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IV: DISCUSSION…………….………………………………………………...……………..
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CORRIDOR 1……………………………………………………………………………
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CORRIDOR 2……………………………………………………………………………
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CORRIDOR 3…………………………………………………………………………....
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CORRIDOR 4……………………………………………………………………………
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AMONG ALL CORRIDORS………………………………………………………………
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REEF EDGE-REEF CREST ANALYSIS…………………………………………………...
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ECOLOGICAL SIGNIFICANCE OF OBSERVED SPATIAL PATTERNS………………………
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DEVELOPMENT OF SAMPLING TECHNIQUES AND METHODS…………………………..
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ESTIMATE OF SAMPLING EFFICIENCY NEEDED………………………………………..
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ESTIMATE OF EFFICIENCY OF ACOUSTIC REMOTE SENSING FOR REEF HABITAT MAPPING…………………………………………………………………….
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FIELD KEY FOR IDENTIFYING REEF HABITATS/ZONES……………………………...…
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V: CONCLUSIONS………………………………..…………………………..……………..
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VI: REFERENCES…………………………..……………..……………….………………..
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than the organisms growing on the reef in defining the returning acoustic echo shape that leads to the habitat classification. Therefore the QTC View Series V system can be used as a reliable tool to produce general habitat maps in coral reef environments. Further study needs to examine what seafloor features (i.e. fauna, substrate, or a combination of these) are most important in defining the returning echo shape and producing the acoustic data classes. Field Key for Identifying Reef Habitats/Zones
The following community types are suggested to be further investigated as possible “type communities” in Broward County: -
Type 1: Shallow, sponge-dominated reef community. Shallow ridge complexes, wide
distribution. -
Type 2: Shallow stony and soft coral dominated reef community. Shallow ridge
complexes, patchy and localized distribution. -
Type 3: Shallow zoanthid and soft coral reef community. In this more widely distributed
community, the stony corals are replaced by encrusting zoanthids. Shallow ridge complexes, wide distribution. -
Type 4: Soft coral (gorgonian) dominated reef community. Widely distributed on
medium deep reefs (inner reef), variable density of live cover. -
Type 5: Zoanthid and macroalgae dominated reef community. Widely distributed on
medium deep reefs (inner reef), variable density of live cover. -
Type 6: Macroalgae, massive sponge and soft coral dominated reef community. Widely
and uniformly distributed on deep reefs (middle and outer reefs). Can vary in dominance of macroalgae depending on the season.
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V: CONCLUSIONS •
Community structure on the reefs of Broward County is highly variable according to location and the associated physical factors (depth, distance from shore, underlying geology, etc.).
•
Evidence for a patchy distribution of at least six different community types within Broward County is shown in this study.
•
Generally, percent living cover on each reef increases with distance from shore and depth, the outer reef typically having the greatest values for percent live cover.
•
A clear difference between ridge complex communities in the north and south corridors within the county is evident, structural control (vertical relief) is believed to be the reason for this north-south gradient (lower in the north).
•
Ridge complex communities in the north (Corridors 1 and 2) have low live cover and are dominated mainly by sponges.
•
Ridge complex communities in the south (Corridors 3 and 4) have greater living percent cover than those in the north, and are dominated by soft corals, scleractinian corals, and encrusting zoanthids.
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The ridge complex community of Corridor 3 had unexpectedly high percent cover by scleractinian corals (13%), and this phenomenon was observed nowhere else within the other three corridors.
•
The inner reef communities throughout Broward County were dominated by “mixed” faunal assemblages typical of both neighboring shallow and deep reef communities.
•
On the deep reefs (middle and outer reefs), a possible seasonal algal dominance was shown, where deep sites sampled in the fall showed little abundance of macroalgae, while deep sites sampled in the spring showed high dominance by macroalgae. Massive sponges and soft corals were dominant on deep reefs when macroalgae was not dominant.
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The following community types are considered typical for specific environments within Broward County: Ridge Complexes and Nearshore Hardgrounds:
-
Ridge complexes and nearshore hardgrounds in the north: Shallow, sponge-dominated reef community
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Ridge complexes and nearshore hardgrounds in the south: Corridor 3: Shallow, stony and soft coral dominated reef community Corridor 4: Shallow, zoanthid and soft coral reef community. In this more widely distributed community, stony corals are replaced by encrusting zoanthids.
Inner Reef:
-
Inner reef overall: Corridor 2: Soft coral dominated reef community All other corridors: Zoanthid and macroalgae dominated reef community
Middle and Outer Reefs:
-
Deep reefs (middle and outer reefs): All corridors: Macroalgae-dominated reef community Corridor 4, outer reef: massive sponge and soft coral dominated reef community (this is probably the same community as in all other corridors. The lack of algae is possibly a seasonal effect).
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