CPE - Town of Palm Beach

The Mid-Town Beach Renourishment and Expansion Project, conducted between January 19 and February 21, 2003, placed approximately 1.2 million cubic yards of beach quality sand from an offshore borrow area onto a 2.4 mile segment of shoreline in the Town of Palm Beach. The project was constructed between Florida Department of Environmental Protection (FDEP) monuments R-90.4 and R-101.4. This was the first renourishment of the original 1995-1996 Mid-Town project that included placement of 880,000 cubic yards of sand between R-95 and R-100 and included construction of 11 groins.

An environmental monitoring program was conducted to determine if the project affected biological communities associated with hardbottom formations immediately seaward of the equilibrium toe of fill, and to assess effects to green turtle foraging habitat. The project monitors five sites on natural hardbottom approximately 150-230 m from shore (named R-90, R-93, R-97, R-99, and R-101), and one site on an artificial reef. The northernmost site, 122 m north of construction, was designated the control site. Each site was permanently marked with stainless steel pins delineating a 50 m long shore-perpendicular transect with a 1.0 m2 station at the east and west ends. All sites were assessed 1-month pre- (between December 23, 2002 and January 10, 2003), mid- (February 17, 2003 to February 20, 2003), immediate post- (March 8, 2003 to March 10, 2003), 6-months post- (August 4, 2003 to August 6, 2003) and 12 months post-construction (March 8, 2004 to March 17, 2004). Benthic cover and coral density along each transect was assessed with 16 0.0625 m2 quadrats (1.0 m2 total), and video for Point Count analysis. Benthic cover and coral density was assessed in the two 1.0 m2 stations, and digital images were taken. Benthic cover was assessed using standard methods, i.e. FDEP modified AGRRA or BEAMR (Miller 2003; Baron and Lybolt 2004). Large-scale sediment movements were tracked using a line-intercept method. The 12-month post-construction dataset is available from the Town of Palm Beach.

Town of Palm Beach Fishes were censused using stationary counts and timed swims at the five natural hardbottom sites, and at the Breakers Rock Pile high-relief (BR-2) and low-relief (BR-1) stations. Stationary counts were made using a modified version of Bohnsack and Bannerot’s (1986) method. Timed swim counts were performed as a modification of Kimmel’s (1985) method.

Visual fish censuses conducted during this field survey yielded the fewest species and individuals yet recorded during the monitoring program. Early life stages were not numerically dominant during this survey as they were during previous surveys. Reasons for the general decline in numbers and kinds of fishes observed during this survey were not clear. Project-related habitat loss was only apparent at the inshore Breakers Rock Pile station. Rough sea conditions may temporarily displace shallow water inhabitants to deeper water, and before fishes were censused, local sea conditions were very rough. Turbidity, however, was very low during the field survey. Previous surveys of nearshore hardbottom in Palm Beach County indicated that recruitment and settlement of grunts, damselfishes, drums, and snappers were generally lowest during winter and highest during spring, summer, and early fall. It was also possible that the decrease in macroalgae cover has diminished the value of this habitat as a grazing food source.

In general, sand cover data gleaned from quadrat-transect assessments were either highly variable, or increased from pre- to post-construction. There were no transects with decreases from pre- to post-construction. Analyses for significant changes were inconclusive in all tests. None of the increases were significant (2-tail t-test p>0.05), but several were marginally significant (2-tail -test 0.05<p<0.10). Overall, the frequency of samples with 100% sand cover increased, despite a decrease from post- to 6-months post-construction. Frequency of samples with 100% sand cover at the control transect R-90, and at R-99 was the same pre- and 12-months post-construction. At the other three transects, the frequency of 100% sand covered quadrats was higher. Chance played a role in the frequency data for R-99. Had we conducted transect sampling several days earlier, R-99 would have had the first ever records of sand-covered quadrats.

Town of Palm Beach All methods detected considerable variability in biotic cover both between sites and between sampling intervals. Line intercept was a better measure of the large-scale sand masses and their locations, while Point Count analyses were very robust, relatively low-resolution assessments of a large area (20 m2 site-1). Point Count detected a significant decrease in macroalgae cover at all sites from 19% pre- to 7% 12-months post-construction (2-tailed paired t-test p-0.0183,a=0.05). This decline was ecologically relevant, since macroalgae comprise the majority of benthic biota on the nearshore hardbottom on Palm Beach. Total faunal cover was very low at all transects and all sampling intervals, and was much too low for a valid analysis.

Quadrat-transect analyses were very high-resolution assessments of a relatively small area (1 m2 site-1). Total biotic cover was highly variable and, on average, essentially unchanged from pre- to 12-months post-construction. Quadrat-transect analyses detected a significant decrease in macroalgae cover at all sites from 26% pre- to 15% 12-months post-construction (2-tailed paired t-test p-0.0435, a=0.05). There was an increase in the frequency of 100% sand-covered quadrats at all sites from 0.13 pre- to 0.36 12-months post-construction and this increase was not significant (2-tailed paired t-test p-0.1172, a=0.05). The increase in frequency of sand-covered quadrats did not correspond to a decrease in total biotic cover, and there were insufficient data to ascribe decreased macroalgae cover to increased sand cover. Because quadrat-transect analyses are much more sensitive than Point Count, there was considerably more variability in the dataset.

Unexpected rapid sediment movements were recorded at 4 of 5 sites during the 12-month post-construction sampling event. Sediment movements were measured over a 10 day period, twice before a high surf advisory, and once after. Prior to the surf advisory at site R-90, a 12 m sand bar disappeared in one day. Sand at site R-93 was exceptional in its stability. There was little motion in the two day period preceding the surf advisory, and a moderate 7.0 m extension of the sand bar seven days later. At site R-97 a prominent 2.0 m wide sand bar developed in one day. Seven days later this feature was still present, but had moved 2.0 m east and extended to 4.0 m. At site R-99, prior to the surf advisory, a 23.0 m wide sand bar moved 6.0 m west in two days (Photo 1) and had disappeared from the site seven days later (Photo 2). R-99 had been uniquely free of sand bars for seven prior observations over nine months. At site R-101 a discrete 21.0 m wide sand bar was reduced to 16.0 m in 2 days. Seven days later it had increased to 21.0 m wide.

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	Town of Palm Beach Mid-Town Beach Renourishment and Expansion Project
	Pictures
	The Mid-Town Beach Renourishment and Expansion Project, conducted between January 19 and February 21, 2003, placed approximately 1.2 million cubic yards of beach quality sand from an offshore borrow area onto a 2.4 mile segment of shoreline in the Town of Palm Beach. The project was constructed between Florida Department of Environmental Protection (FDEP) monuments R-90.4 and R-101.4. This was the first renourishment of the original 1995-1996 Mid-Town project that included placement of 880,000 cubic yards of sand between R-95 and R-100 and included construction of 11 groins. An environmental monitoring program was conducted to determine if the project affected biological communities associated with hardbottom formations immediately seaward of the equilibrium toe of fill, and to assess effects to green turtle foraging habitat. The project monitors five sites on natural hardbottom approximately 150-230 m from shore (named R-90, R-93, R-97, R-99, and R-101), and one site on an artificial reef. The northernmost site, 122 m north of construction, was designated the control site. Each site was permanently marked with stainless steel pins delineating a 50 m long shore-perpendicular transect with a 1.0 m2 station at the east and west ends. All sites were assessed 1-month pre- (between December 23, 2002 and January 10, 2003), mid- (February 17, 2003 to February 20, 2003), immediate post- (March 8, 2003 to March 10, 2003), 6-months post- (August 4, 2003 to August 6, 2003) and 12 months post-construction (March 8, 2004 to March 17, 2004). Benthic cover and coral density along each transect was assessed with 16 0.0625 m2 quadrats (1.0 m2 total), and video for Point Count analysis. Benthic cover and coral density was assessed in the two 1.0 m2 stations, and digital images were taken. Benthic cover was assessed using standard methods, i.e. FDEP modified AGRRA or BEAMR (Miller 2003; Baron and Lybolt 2004). Large-scale sediment movements were tracked using a line-intercept method. The 12-month post-construction dataset is available from the Town of Palm Beach. Fishes were censused using stationary counts and timed swims at the five natural hardbottom sites, and at the Breakers Rock Pile high-relief (BR-2) and low-relief (BR-1) stations. Stationary counts were made using a modified version of Bohnsack and Bannerot’s (1986) method. Timed swim counts were performed as a modification of Kimmel’s (1985) method. Visual fish censuses conducted during this field survey yielded the fewest species and individuals yet recorded during the monitoring program. Early life stages were not numerically dominant during this survey as they were during previous surveys. Reasons for the general decline in numbers and kinds of fishes observed during this survey were not clear. Project-related habitat loss was only apparent at the inshore Breakers Rock Pile station. Rough sea conditions may temporarily displace shallow water inhabitants to deeper water, and before fishes were censused, local sea conditions were very rough. Turbidity, however, was very low during the field survey. Previous surveys of nearshore hardbottom in Palm Beach County indicated that recruitment and settlement of grunts, damselfishes, drums, and snappers were generally lowest during winter and highest during spring, summer, and early fall. It was also possible that the decrease in macroalgae cover has diminished the value of this habitat as a grazing food source. In general, sand cover data gleaned from quadrat-transect assessments were either highly variable, or increased from pre- to post-construction. There were no transects with decreases from pre- to post-construction. Analyses for significant changes were inconclusive in all tests. None of the increases were significant (2-tail t-test p>0.05), but several were marginally significant (2-tail -test 0.05<p<0.10). Overall, the frequency of samples with 100% sand cover increased, despite a decrease from post- to 6-months post-construction. Frequency of samples with 100% sand cover at the control transect R-90, and at R-99 was the same pre- and 12-months post-construction. At the other three transects, the frequency of 100% sand covered quadrats was higher. Chance played a role in the frequency data for R-99. Had we conducted transect sampling several days earlier, R-99 would have had the first ever records of sand-covered quadrats. All methods detected considerable variability in biotic cover both between sites and between sampling intervals. Line intercept was a better measure of the large-scale sand masses and their locations, while Point Count analyses were very robust, relatively low-resolution assessments of a large area (20 m2 site-1). Point Count detected a significant decrease in macroalgae cover at all sites from 19% pre- to 7% 12-months post-construction (2-tailed paired t-test p-0.0183,a=0.05). This decline was ecologically relevant, since macroalgae comprise the majority of benthic biota on the nearshore hardbottom on Palm Beach. Total faunal cover was very low at all transects and all sampling intervals, and was much too low for a valid analysis. Quadrat-transect analyses were very high-resolution assessments of a relatively small area (1 m2 site-1). Total biotic cover was highly variable and, on average, essentially unchanged from pre- to 12-months post-construction. Quadrat-transect analyses detected a significant decrease in macroalgae cover at all sites from 26% pre- to 15% 12-months post-construction (2-tailed paired t-test p-0.0435, a=0.05). There was an increase in the frequency of 100% sand-covered quadrats at all sites from 0.13 pre- to 0.36 12-months post-construction and this increase was not significant (2-tailed paired t-test p-0.1172, a=0.05). The increase in frequency of sand-covered quadrats did not correspond to a decrease in total biotic cover, and there were insufficient data to ascribe decreased macroalgae cover to increased sand cover. Because quadrat-transect analyses are much more sensitive than Point Count, there was considerably more variability in the dataset. Unexpected rapid sediment movements were recorded at 4 of 5 sites during the 12-month post-construction sampling event. Sediment movements were measured over a 10 day period, twice before a high surf advisory, and once after. Prior to the surf advisory at site R-90, a 12 m sand bar disappeared in one day. Sand at site R-93 was exceptional in its stability. There was little motion in the two day period preceding the surf advisory, and a moderate 7.0 m extension of the sand bar seven days later. At site R-97 a prominent 2.0 m wide sand bar developed in one day. Seven days later this feature was still present, but had moved 2.0 m east and extended to 4.0 m. At site R-99, prior to the surf advisory, a 23.0 m wide sand bar moved 6.0 m west in two days (Photo 1) and had disappeared from the site seven days later (Photo 2). R-99 had been uniquely free of sand bars for seven prior observations over nine months. At site R-101 a discrete 21.0 m wide sand bar was reduced to 16.0 m in 2 days. Seven days later it had increased to 21.0 m wide. Top
	Pictures Rob Baron conducting a BEAMR assessment at site R-93 Fish communities were concentrated at the Breakers Rock Pile Matt Lybolt conducting a BEAMR assessment of the 1.0 square-meter station at the east end of site R-97 Transect R-97 was partly covered by sand on March 17, 2004 This colony of Solenastrea bournoni was covered by sand on March 10, 2004 and uncovered by March 17, 2004 Matt Lybolt conducting a BEAMR assessment at site R-99 Zoanthid cover was relatively high at the Breakers Rock Pile high-relief monitoring station, and over most of the Breakers Rock Pile Site R-99 was covered by sand on March 10, 2004 Site R-99 was entirely exposed hardbottom on March 17, 2004 This colony of Oculina diffusa was covered by sand on March 10, 2004 and uncovered by March 17, 2004 West monitoring station at site R-93 This colony of Solenastrea bournoni was covered by sand on March 10, 2004 and uncovered by March 17, 2004 Top