Coastal
Planning & Engineering, Inc. (CPE) was selected by Collier
County to conduct its largest nearshore hardbottom characterization.
The comprehensive marine resources investigation was carried out along
the county’s nearshore
habitat between Florida Department of Environmental Protection (FDEP)
survey control monuments R-17 and R-89,
along approximately 13.5 miles of coastline. A side-scan sonar survey
of the nearshore region of the study area for Collier County in February
2003 documented the presence of coastal low relief ephemeral hardbottom
habitats that may be affected by beach nourishment activities. Approximately
500 acres of hardbottom formations were identified within 1,000 ft
of the shoreline along the 13.5 mile long study area.
The
focus of the investigation was assessment and characterization of
the nearshore hardbottom resources which may be within the zone
of influence of the beach nourishment project, cross-shore beach profile
adjustment, or long-shore fill diffusion. All work was conducted within
300 m of shore. A total of 68 hardbottom sites (60 transects and 8
points) directly offshore of Collier County were selected for exploratory
verification, assessment, and characterization in coordination with
the Florida Department of Environmental Protection (FDEP). These 68
sites were sorted into six study segments; Delnor-Wiggins State Park
(9 transects and 2 points), Vanderbilt Beach (10 transects and 3 points),
Pelican Bay (6 transects), Clam Pass Park (10 transects), Park Shore
(17 transects and 2 points), and Naples (8 transects and 1 point).
Benthic communities along transects were evaluated using both a modification
of the Atlantic and Gulf Rapid Reef Assessment (AGRRA) protocol (Ginsburg,
2000) and GPS-integrated video surveys. AGRRA methods were employed
at 638 quadrats covering a total of 319 m2. An extensive database of
assessments and identifications was created to include both biotic
factors (coral density, macroalgae cover, fish identifications) and
abiotic factors (sediment depth, substrate type, substrate relief),
supplemented with a photographic library comprised of over 1100 still
images and 64 videos.
The segment averages varied widely, with generally greater biotic
cover and relief towards the north, and greater sand cover towards
the south. The overall frequency of quadrats with 100% sand cover was
0.32. At least one-third of the study area was sand covered, and the
remaining two-thirds were partly or completely exposed hardbottom.
The data sorted segments into three relatively distinct groups. The
two northernmost segments had relief, sediment, and biotic cover close
to the overall averages. The two central segments had the greatest
relief, low sediment, and high biotic cover. The two southernmost segments
had the lowest relief, greatest sediment cover, and lowest biotic cover
of all segments. Generally, macroalgae percent cover was negatively
correlated with both sand cover and average sediment depth. The two
most dominant macroalgae genera were Gracilaria, and Hypnea. Both are
known to be consumed by juvenile green sea turtles. Caulerpa spp.,
Sargassum spp., Dasya spp., and Botryocladia occidentalis were occasional.
Gorgonacea were infrequent, with less than one colony encountered
per average transect. The transects found more Gorgonacea in the northernmost
(0.31 colonies m-2) and southernmost segments (0.23 colonies m-2).
Within these segments, distribution of Gorgonacea was patchy, and ranged
from zero to 1.09 colonies m-2. Gorgonacea were essentially absent
from the four interior segments, Vanderbilt Beach, Pelican Bay, Clam
Pass Park, and Park Shore. Those encountered loosely followed shore-parallel
distribution patterns, and were likely underreported by conducting
shore-perpendicular transects.
Scleractinia
density was surprisingly high for this turbid nearshore habitat.
The vast
majority
of coral
records were Siderastrea spp., and three other genera were occasional;
Oculina sp., Phyllangia sp.,
and Solenastrea sp. There were approximately twice as many Scleractinia
colonies m-2 in the northern three segments than in the southern three
segments. This survey found anomalously few <2 cm colonies relative
to 2-5 cm colonies. The size-frequency results suggest that the nearshore
habitat was chronically disturbed with respect to Scleractinia in the
last decade or so. There was a loose negative correlation between Scleractinia
density and both sediment depth and sand cover. Because mobile sediment
effectively prevents Scleractinia larvae recruitment, mobile sediment
may be greater today than decades ago.
During the fish surveys, twenty-one species were noted. The highest
number of species (14) was recorded in the Park Shore Segment, though
this high number is biased by the larger size of the Park Shore Segment.
The Pelican Bay Segment supported the second highest number of species
(10).
CPE has developed an inclusive database, and archived all field data
into an easily accessible GIS product with tables, representative imagery,
and video documentation that allows users to evaluate information themselves.
The Collier County database will continue to grow with future monitoring
and documentation, providing accurate temporal analysis of the nearshore
habitat.
CPE’s uniquely thorough exploratory hardbottom characterizations
have developed into a substantial database. We now know that the Collier
County nearshore hardbottom has greater biotic cover than hardbottom
analogues on Florida’s south and east coasts.
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(561)
391.8102 
(561)
391.9116
email@coastalplanning.net
