... primary production were estimated for an 800-slip marina previously planned for Davids Island, located in the extreme western portion of Long Island Sound, ...
Estuaries
Vol. 19, No. 2A, p. 257-271
June 1996
Habitat Disturbance and Marina Development: An Assessment of Ecological Effects. I. Changes in Primary Production Due to Dredging and Marina Construction. TIMOTHY J. IANNUZZI 1
ChemRisk~, a Division of McLaren/Hart, Inc. Stroudwater Crossing 1685 Congress Street Portland, Maine 04102 MICHAEL P. WEINSTEIN
TEVA Environmental Associates, Incorporated 854 Ridgewood Road Millburn, New Jersey 07041 KEVIN G. SELLNER
The Academy of Natural Sciences Benedict Estuarine Research Laboratory Benedict, Maryland 20612 JEW~:v C. BARRETT R2 Resources, Incorporated 15250 AtE 95th Street Redmond, Washington 98052 ABSTRACT: Potential impacts on primary production were estimated for an 800-slip marina previously planned for Davids Island, located in the extreme western portion of Long Island Sound, New York. Macroalgal and microalgal production in the area of the proposed marina was analyzed on the basis of six depth zones ranging from an existing seawall (at about +2.2 m MLW) seaward to a d e p t h of - 2 . 4 m MLW. Productivity measurements were based on in situ ~4C uptake studies, chlorophyll a determinations, and varying light exposures within the euphoric zone that were the result of turbidity and semidiurnal rides. The surface area of each depth zone was multipled by the corresponding estimate of daily production calculated for eight dominant macroalgae and microalgae, and summed to estimate existing production in the proposed marina. Similarly, post-construcrion production was estimated by applying the calculated daily production to the appropriate areas of hard substrate (breakwater, pilings, etc.) in the euphoric zone. Pre- and post-construction macroalgal production values were 50,608 and 42,152 g C d -l, respectively. This represents a 17% reduction in macroalgal production. It should be noted, however, that production on the seafloor of the marina was not accounted for. Consquently, reductions in macroalgal production that might occur are likely overestimated. Microalgal production constituted less than 3% of total primary production in the nearshore areas of Davids Island. The pre- and post-construction microalgal production values were 1,542 and 743 g C d -t, respectively. This represents a 48% reduction in microalgal production in unconsolidated sediment. However, micoalgal production would likely occur on hard substrates in the marina. Overall, pre- and post-construction estimates of primary production were remarkably similar, suggesting that production on hard substrates in the marina would compensate for lost production from deepening of the nearshore zone during construction.
Corresponding author; tele 207/7744)012; fax 202/774-8263. 9 1996 Estuarine Research Federation
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T.J. lannuzziet al. Introduction
Study A r e a a n d B a c k g r o u n d
Marinas are generally p r o t e c t e d environments where considerable shoreline alteration has taken place and where recreational vessels are isolated from potentially destructive wave action and strong currents. Construction of a marina along a segm e n t of the shore often requires dredging, shoreline stabilization, and, if the marina is sited on an o p e n coast, some form o f breakwater to ameliorate the effects o f strong wave action. These changes in physiographic features of the s h o r e f r o n t may have several effects on marine resources, the consequences o f which are often difficult to predict. T h e difficulty stems from the n e e d to quantify several interactive changes associated with habitat alteration, water quality, and hydrodynamics. For example, after the marina is dredged, not only will the water c o l u m n be d e e p e n e d , but light reaching the b o t t o m may also be attenuated by increased turbidity in the post-construction marina and from the shadows cast by m o o r e d vessels and docks in tile facility. MoreoveL any heterogeneity that might have b e e n originally present in substrate composition o f the seafloor (including the presence of sand, gravel, cobble, rock, etc.) will likely be gradually replaced by a uniform, increasingly m u d d y substrate on the new marina floor. T h e latter will be especially true in o p e n coastal environments where construction o f the marina will create a new q u i e s c e n t e n v i r o n m e n t favoring s e d i m e n t a t i o n . C o n s e q u e n t l y , h a b i t a t complexity, m i c r o h a b i t a t availability, a t t a c h m e n t surfaces, and o t h e r important features of the e n v i r o n m e n t may be r e d u c e d or otherwise altered. F r o m a "global" view, these potential impacts can be offset, perhaps in their entirety, by creation o f diverse habitats associated with marina pilings, bulkheads, s u b m e r g e d portions of floating docks, rip-rapped areas, and breakwaters (especially those o f rock-rubble design). Such structures provide well-lighted a t t a c h m e n t surfaces for plants, as well as create myriad microhabitats and refugia for animals. Additionally, in high-energy areas, such wave-swept beaches, the newly created quiescent habitat may be m o r e conducive to microalgal colonization. It is the purpose o f this p a p e r to estimate the potential impacts o n primary p r o d u c t i o n prior to construction of an 800-slip marina for Davids Island (40~ ", 73~ located in the e x t r e m e western portion of Long Island Sound. T h e assessment will be linfited to effects on attached macroalgae and benthic microalgae. A c o m p a n i o n p a p e r o n effects of the project on benthic fauna and secondary p r o d u c t i o n is in preparation.
Situated approximately 1.0 km off o f the mainland shoreline o f New Rochelle, Westchester County, New York (Fig. 1), Davids Island formerly was the site o f the United States Army base known as Fort Slocum. T h e p r o p o s e d marina was to be constructed o n the western and s o u t h e r n sides of the island. Several old piers and o t h e r in-water structures are located in the area o f the p r o p o s e d marina and the island is s u r r o u n d e d by a deteriorating seawall located at about m e a n high water (MHW). High tidal amplitude (approximately 2.2 m) c o m b i n e d with a relatively shallow beach slope expose the intertidal zone for lengthy periods. In these areas, the d o m i n a n t organisms are small green algae, especially Enteromorpha intestinalis, and barnacles (Balanus sp.), both occurring on rock surfaces (including seawall rubble). Where the intertidal zone narrows, rocks along the seawall are colonized by extensive patches of attached algae, including Fucus vesiculosus and E. intestinalis. Most o f the intertidal area in the vicinity of the old docks and piers consists o f coarse sand, e x t e n d i n g roughly 90 m to the n o r t h o f the pier complex and 50 m toward the south. Cobble, gravel, and rock rubble cover most of the remaining intertidal area o f tile p r o p o s e d marina. Macroalgae typically d o m i n a t e the intertidal and subtidal areas of the region. Rocky substrates in the lower intertidal zone o f Davids Island are abundantly colonized by barnacles, blue mussels (Mytilus edulus), and patches of macroalgae ( d o m i n a t e d by F. vesiculosus). Seasonal windrows of maroalgae, principally Ulva lactuca, are also present. Subtidal sediments are p r e d o m i n a n t l y m u d d y except in n e a r s h o r e areas (MLW to about the 2.4 in d e p t h c o n t o u r ) , where sands are abundant. Rocky substrate also occurs frequently in the shallow subtidal zone. T h e p r o p o s e d Davids Island d e v e l o p m e n t project called for an 800-slip marina on the southwestern side of the island enclosed by a 564 m rock-rubble breakwater with a 1.66-ha " f o o t p r i n t " on the b o t t o m o f Long Island S o u n d (Fig. 1). More than 9.7 ha of intertidal and unconsolidated b o t t o m habitat (interspersed with occasional rock outcrops and boulders) would be disrupted by dredging to a relatively u n i f o r m d e p t h of 2.4 m below m e a n low water (MI,W). M o n g with d e p t h alteration, there would be c o n c o m i t a n t changes in the quantity of incident light reaching the marina floor and in substrate composition as a conseq u e n c e of the gradual accumulation o f fine sediments in the marina. In addition, the breakwater would replace soft-bottom habitat with hard substrate, creating potentially significant changes in
EcologicalEffectsof MarinaDevelopment
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Northernand Southwestern 9 Boundariesof ProposedMarina MacroalgaeSamplingTransects
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MicroalgaeSampling Stations
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Fig. 1. Map of study site and map of approximate locations of macroalgae mapping and collection transects and microalgae sampling stations in the proposed Davids Island marina area and on Aunt Phebe Rock, New York.
the composition a n d structure o f the local benthic community. Studies c o n d u c t e d in the s u m m e r of 1990 were designed to address the changes in primary production and benthic c o m m u n i t y structure that m i g h t a c c o m p a n y construction o f the marina. Here we describe changes in p r i m a r y p r o d u c t i o n that would accrue from differences in the light regime when the marina is constructed. A "balance sheet" is p r e s e n t e d l hat quantitatively assesses these changes. Materials and Methods
IAGHT A'ITFNUATION IAght attenuation in the water c o l u m n was measured in ,July and August 1990 at seven randomly selected locations, three in the " s o u t h e r n m a r i n a " a n d four in the "western m a r i n a " (Fig. 1). At each location, irradiant energy (IzE m -2 s ") was recorded at l-m d e p t h intervals using a m o d e l 185A I,iCor p h o t o m e t e r until levels approximately 10% o f surface irradiance (Io) were obtained. In addi-
tion, secchi disk readings were taken at several locations a r o u n d Davids Island. An ANOVA for equality o f slopes a m o n g regressions of light attenuation data from the seven locations indicated that no significant differences occ u r r e d (F = 0.03; df = 6, 27; p > 0.99); consequently, a m e a n light extinction coefficent (k = 0.34) was calculated from thesc data. An indcpend e n t estimate of k was also c o m p u t e d from secchi disk readings taken at several locations a r o u n d Davids Island. This value, k = 0.33, c o m p a r e d favorably with the results o f the p h o t o m e t r i c survey, allowing us to use secchi disk readings to confirm that light attenuation r e m a i n e d relatively constant during each sampling event. MACROALGAI.DISTRIBUTIONS Distributions and densities o f d o m i n a n t macroalgae were d e t e r m i n e d in the p r o p o s e d Davids Island marina, as well as on A u n t P h e b e Rock, a small m a n - m a d e rock island in New Rochelle, New York, located approximately 250 m west o f Davids
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TABI,E 1. Description of d e p t h zones used to calculate macroalgal biomass a n d productivity for the n e a r s h o r e waters of Davids Island. All d e p t h s c o r r e s p o n d to m e a n low water (MLW). Depth Zone
Depth Range (m)
Upper intertidal Lower intertidal Nearshore subtidal Subtidal Subtidal
+2.2 to +1.1 + 1.1 to 0 0 to -0.6 - 1.2 to -1.8 -2.4 to -3.0
Island (Fig. 1), a n d on floating docks in the n e a r b y H u g e n o t Marina. Because the size a n d composition o f the rocks (and their slope, a p p r o x i m a t e l y 3:1) c o m p r i s i n g the island are similar to that of the p r o p o s e d breakwater, A u n t P h e b e Rock was used as a surrogate for predicting m a c r o a l g a e populations that may be e x p e c t e d to colonize the Davids Island breakwater (and associated wave screen). I,ikewise, tile floating docks in the H u g e n o t Marina were used as a surrogate for those in the prop o s e d Davids Island marina. To sample macroalgal distribution, f o u r transects, covering a r a n g e of b o t t o m habitats including mudflats, mussel beds, rock rubble a n d rock outcrops, were established p e r p e n d i c u l a r to the western a n d s o u t h e r n shorelines of Davids Island (Fig. 1). A fifth transect was r a n d o m l y located along the side slope of Aunt P h e b e Rock. Macroalgae were collected along each transect at five depth-intervals receiving 100%, 50%, 25%, 10% a n d 1% of incident surface irradiation (I,,), as det e r m i n e d by light transmittance data (Table 1). At each station, three replicate 0.17-m 2 quadrats were released at the surface a n d allowed to settle at the p r e s c r i b e d depths; divers then collected all m a c r o a l g a e within each quadrat. In e x p o s e d intertidal areas, algae were scraped f r o m duplicate rand o m l y selected locations within 0.0026 m e quadrats. Similar quadrats were used to collect macroalgae f r o m s u b m e r g e d portions of floating docks in the n e a r b y H u g e n o t Marina. Wet weights o f d o m i n a n t taxa in each q u a d r a t were d e t e r m i n e d (in the field) to the nearest 0.1 g. A p p r o x i m a t e l y 25% o f the samplcs were frozen over d r y ice a n d r e t u r n e d to the Benedict Estuarine Research I , a b o r a t o r y (BERL), Benedict, Maryland, for s u b s e q u e n t dry weight d e t e r m i n a t i o n . Dry weights were d e t e r m i n e d by oven-drying each sample to constant weight at 60~ for 2 A 48 h. Biomass estimates (g m - z ) in each d e p t h zone were calculated for all taxa as a function o f d e p t h a n d light intensity. Total macroalgal standing crops were calculated for each d e p t h zone as the p r o d u c t of m e a n macroalgal wet weight a n d estimates o f substrate acreage within that zone.
MICROALGAL PIGMENTS DISTRIBUTIONS C o n c e n t r a t i o n s of active chlorophyll a a n d p h a e o p i g m c n t s were d e t e r m i n e d in the u p p e r 1 cm o f s e d i m e n t at five stations in the p r o p o s e d m a r i n a (Fig. 1). T h e s e sites were c h o s e n to represent various spatial positions and substrate types. Stations MB-1 a n d MB-2 were located in the mid-intertidal zone, r e p r e s e n t i n g sand (coarseg r a i n e d ) a n d m u d (fine-grained) substrates, respectively. MB-2 was located in a mussel bed. Stations MB-3 t h r o u g h MB-5 were located in the subtidal z o n e ( - 0 . 6 m to - 1 . 8 m MLW) at d e p t h s w h e r e fine-grained sediments, similar to those exp e c t e d following m a r i n a c o n s t r u c t i o n , occur. At each station, divers collected surface s e d i m e n t samples by inserting 1.6 cm (inside d i a m e t e r ) glass coring tubes into the substrate. Triplicate samples were collected fl'om the two intertidal stations (MB-1 a n d MB-2) a n d d u p l i c a t e samples f r o m the t h r e e subtidal stations (MB-3 t h r o u g h MB-5). T h e u p p e r 1 cm o f s e d i m e n t f r o m e a c h core was r e m o v e d a n d t r a n s f e r r e d into c e n t r i f u g e tubes, c a p p e d , a n d frozen over d r y ice for shipm e n t to BERL. In the laboratory, samples were analyzed for active c h l o r o p h y l l a a n d p h a e o p i g m e n t c o n c e n t r a t i o n s a c c o r d i n g to the p r o c e d u r e s of Strickland a n d Parsons (1972). MACROALGAL PRODUCTMTY Macroalgal productivity was estimated for d o m inant taxa: the chlorophytes Ulva lactuca a n d Enteromorpha intestinali~ the r h o d o p h y t e s Chondrus cris-
pus, AgardhieUa tenera, Ca'inellia americana, Ceramium stricture; a n d the p h a e o p h y t e Fucus vesiculosus. T h e s e species c o m p r i s e d g r e a t e r than 90% of the m a c r o a l g a e in the n e a r s h o r e waters of Davids Island. At e a c h s a m p l i n g l o c a t i o n (Fig. 1), w h o l e intact m a c r o a l g a e w e r e c o l l e c t e d by divers, identified a n d i n s p e c t e d f o r physical c o n d i t i o n . Viable s p e c i m e n s o f e a c h t a x o n w e r e d i v i d e d i n t o triplicate samples and transferred into either 145-ml o r 1,000-ml glass jars, d e p e n d i n g o n t h e i r size. S a m p l e j a r s w e r e c o v e r e d with m e s h s c r e e n i n g to s i m u l a t e light i n t e n s i t i e s c o r r e s p o n d i n g to 100%, 50%, 25%, 10%, a n d 1% o f Io. S a m p l e s w e r e allowed to a c c l i m a t e to test c o n d i t i o n s f o r 30 m i n in a w a t e r - c o o l e d incub a t o r , i l l u m i n a t e d by c o o l - w h i t e f l u o r e s c e n t lighting. F o l l o w i n g a c c l i m a t i o n , a p p r o x i m a t e l y 5 - 2 0 tzCi NaH]4CO3 was a d d e d to e a c h o f the s a m p l e s w h i c h w e r e t h e n r e t u r n e d to the incub a t o r f o r 2 - 4 h. F o l l o w i n g i n c u b a t i o n , s a m p l e s w e r e twice r i n s e d with a m b i e n t seawater, b l o t t e d dry, w e i g h e d , a n d i m m e d i a t e l y f r o z e n o v e r d r y ice f o r r e t u r n to BERL.
Ecological Effects of Marina Development
In the laboratory, samples were dried at 60~ pelletized, and transferred to 20-ml scintillation vials. Pelletized samples were oxidized in a Packard Oxidizer (Model 306); released 14CO~ was captured in scintillation vials. Sample ~4C activity was c o u n t e d using liquid scintillation spectrometry according to m e t h o d s outlined in Strickland and Parsons (1972). All activities were c o r r e c t e d for surface adsorption of the label using time zero (to) activities. Conversion o f d p m g-~ o f tissue to hourly carbon fixation rates (~gC g 1 h-~) as per Arnold and Littner (1985), using carbonate alkalinity values estimated from Strickland and Parsons (1972). Carbon fixation rates for each species was comp u t e d as the geometric m e a n o f three replicate samples. Additionally, those for E vesiculosus were c o m p u t e d as the mean of rates measured on both the old and new growth of the plants. Depth-specific carbon fixation rates were comp u t e d for individual species and seven d e p t h zones, including the five d e p t h zones identified in Table 1, and two additional subtidal zones ( - 0 . 6 m to - 1 . 2 m MLW and - 1 . 8 m to - 2 . 4 m MI.W). These rates were calculated as the p r o d u c t of m e a n wet weights measured at each d e p t h zone (corresponding to 100%, 50%, 25%, 10%, and 1% Io) for the five transects and the c o r r e s p o n d i n g m e a n species-specific carbon fixation rates. For the latter two d e p t h zones (for which macroalgal biomass and productivity were not measured), p r o d u c t i o n was estimated as the m e a n o f rates calculated for the d e p t h zones immediately above and below these depths. Total carbon fixation t o t each d e p t h zone was c o m p u t e d as the sum o f carbon fixation for all individual species at each d e p t h zone. Hourly rates were then converted to daily p r o d u c t i o n rates (ixg C M -'~ d l) using concepts developed by Keefe et al. (1981), employing a multiplier o f 0.8 times the hours o f sunlight at each d e p t h zone. Because light penetration in the water c o l u m n is substantially red u c e d as the sun departs from the vertical, diurnal light periods of 14 h, 12 h, l0 h, 8 h, a n d 6 h were assigned to the five d e p t h intervals c o r r e s p o n d i n g to 100%, 50%, 25%, 10%, and 1% Io. This resulted in estimated sunlight exposures of 11.2 h, 9.6 h, 8.0 h, 6.4 h, and 4.8 h, respectively. T h e estimated sunlight exposures were then adjusted for effects of semidiurnal tides (i.e., exposure, submergence, and d e p t h fluctuations) as follows. For the high intertidal zone (+1.1 m to +2.2 m MLW), algae would be s u b m e r g e d for approximately 7.0 h, followed by 4.2 h of e m e r g e n c e d u r i n g low tide. Because macroalgae can c o n t i n u e to photosynthesize during air exposure as long as plants remain hydrated (Madsen and Maberly 1990), it was assumed that p r o d u c t i o n c o n t i n u e d for 50% of the expo-
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sure period or 2.1 h. Daily p r o d u c t i o n rates were then c o m p u t e d for each species as the p r o d u c t o f the hourly productivity rates at 100% Io and the c o r r e c t e d photosynthetic p e r i o d (9.1 h). For the low intertidal zone (0 m to +1.1 m MLW), subm e r g e d algae would receive 6 h o f light at 50% Io (during high tide) and 1.6 h at 100% I,, (during the ebbing tide). An additional 1.0 h o f p r o d u c t i o n would occur during e m e r g e n c e at 100% Io (i.e., one-half of the e m e r g e n c e time when algae are adequately hydrated to photosynthesize). Total diurnal light periods are then 8.6 h (6.0 h at 50% Io, and 2.6 h at 100% Io). Daily p r o d u c t i o n rates were then c o m p u t e d by summing the products o f the hourly productivity rates for each species at the prescribed d e p t h zones (incident light levels), the hours exposed to each light level, and the biomass of each species (wet weights) in the low intertidal zone. For the n e a r s h o r e subtidal zone (0 m to - 0 . 6 m MLW), algae would be exposed to 25% Io for approximately 4.5 h (during high tide), 50% Io for 2.5 h (during ebbing tide), and 100% I,, for 1.0 h (during low tide). For the - 1 . 2 m to - 1 . 8 m MLW d e p t h zone, p r o d u c t i o n was c o m p u t e d assuming 4.0 h, 1.4 h, and 1.0 h exposures, respectively, for 10%, 25% and 50% Io. For tile most light-restrictive depth zone ( - 2 . 4 m to - 3 . 0 m MLW), p r o d u c t i o n was c o m p u t e d assuming 1.0 h at 10% and 3.8 h at 1% of Io. For the remaining intermediate d e p t h zones ( - 0 . 6 m to - 1 . 2 m MLW and - 1 . 8 m to - 2 . 4 m MLW), p r o d u c t i o n was estimated as the m e a n o f rates calculated for the d e p t h intervals immediately above and below these depths. ESTIMATION OF IMPACT ON PRIMARY PRODUCTION
Estimates o f macroalgal biomass on hard and soft substrate following construction of the Davids Island Marina were calculated for six o f the seven d e p t h zones previously described using engineering projections of areas o f hard substrate. (i.e., rock rubble, concrete structures, seawall, breakwater, and wave screen) and soft substrate surface areas (Table 2). T h e six d e p t h zones ranged from the existing seawall (at about +2.2 m MLW) seaward to a d e p t h of - 2 . 4 m MI.W. T h e approximate surface area of each o f these zones was estimated by p l a n i m e t r y o n available e n g i n e e r i n g drawings from the site. T h e relevant surface areas o f the concrete peirs, breakwater, wave screen, and tloating docks were derived from data provided by Sasaki Associates, Inc., the marina designers (V. Hagopian, personal c o m m u n i c a t i o n ) . Mean macroalgal wet weights for each d e p t h zone measured in the fixed transects off Davids Island were multiplied by acreages at similar depth intervals for tuture projected surface areas of concrete pilings, the seawall, and soft substrates in the
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TABLE 2. Engineering projections of available substrates for algal colonization in the proposed Davids Island Marina. All depths correspond to mean low water (MLW). AttachmentSubstrates Existing Substrates
Future Concrete Pilings
Future Breakwater/ Wave Screen
Future Floating Docks
SurfaceArea(m-j) Pre-construction Post-consu-ucdon
Depth Zone(m) ttigh Intertidal (+2.2 to +1.1) Seawall/Rock Sandflat/Cobble I,ow Intertidal (+1.1 to 0) Subtidal 0 to -0.6 -0.6 to -1.2 -1.2 to -1.8 -1.8 to -2.4 High Intertidal (+2.2 to +1.1) Low Intertidal (+1.1 to 0) Subtidal 0 to -1.2 -0.6 to -1.2 -1.2 to -1.8 -1.8 to -2.4 High Intertidal (+2.2 to +1.1) Low Intertidal (+1.1 to 0) Subtidal 0 to -0.6 -0.6 to -1.2 -1.2 to -1.8 -1.8 to -2.4 Subtidal O to -0.6
Totals
(13,068) 7,945 5,123
(10,097) 7,945 2,152
13,068
7,488
12,942 15,014 18,369 14,213
a a a a 941 941 538 538 538 538
--
4,292 4,292 2,453 2,453 2,453 2,453
86,674
4,185 44,200
" For a conservative analysis, production on the seafloor of the marina was assumed to be zero. marina. Those for individual depths along the A u n t P h e b e R o c k t r a n s e c t w e r e m u l t i p l i e d by fut u r e a c r e a g e s o f t h e b r e a k w a t e r a n d wave s c r e e n . T h o s e f o r t h e H u g e n o t M a r i n a w e r e m u l t i p l i e d by the area of submerged portions of docks projected for t h e Davids I s l a n d M a r i n a . The following approach and generally conservative a s s u m p t i o n s w e r e e m p l o y e d in c a l c u l a t i n g t h e m a c r o a l g a e p r o d u c t i o n v a l u e s in t h e p r e - a n d p o s t - c o n s t r u c t i o n m a r i n a : (1) t h e i n t e r t i d a l z o n e was d i v i d e d i n t o low (0.0 m to +1.1 m M L W ) a n d h i g h ( t - l . 1 m to + 2 . 2 m MLW) i n t e r t i d a l z o n e ; (2) as p a r t o f t h e m a r i n a d e s i g n , a b o u t 4 2 % o f t h e h i g h i n t e r t i d a l z o n e w o u l d b e p r e s e r v e d as a n app r o x i m a t e l y 6.5 m w i d e b u f f e r strip; (3) p r o d u c t i o n in t h e h i g h i n t e r t i d a l z o n e was c a l c u l a t e d o n t h e basis o f p r o d u c t i v i t y o f a l g a e occupying available substrates; approximately 61% of production in t h e h i g h i n t e r t i d a l z o n e was a s s o c i a t e d with p r o ductivity o f a l g a e c o v e r i n g p o r t i o n s o f t h e e x i s t i n g seawall i n c l u d i n g d e t e r i o r a t e d p o r t i o n s ( m o s t l y
large rock and concrete rubble), while the remaini n g p r o d u c t i o n ( a b o u t 39% o f t h e total) was ass u m e d to b e a s s o c i a t e d with a t t a c h e d a l g a e in t h e s a n d a n d c o b b l e z o n e b e l o w t h e seawall; (4) p r o ductivity m e a s u r e d in situ in t h e a r e a o f t h e p r o p o s e d m a r i n a was u t i l i z e d to e s t i m a t e p r o d u c t i o n f o r a l g a e c o l o n i z i n g t h e seawall, p r o t e c t e d b u f f e r strip, a n d c o n c r e t e s t r u c t u r e s in t h e f u t u r e m a r i n a ; (5) p r o d u c t i v i t y m e a s u r e d in situ at A u n t P h e b e R o c k was u s e d to e s t i m a t e p r o d u c t i o n f o r a l g a e colo n i z i n g t h e p r o p o s e d b r e a k w a t e r a n d wave s c r e e n ; (6) p r o d u c t i v i t y m e a s u r e d in situ f o r a l g a e c o l o n i z i n g f l o a t i n g d o c k s in t h e H u g u e n o t M a r i n a was u s e d to e s t i m a t e p r o d u c t i o n f o r a l g a e e x p e c t e d to c o l o n i z e t h e d o c k system in t h e p r o p o s e d Davids I s l a n d M a r i n a ; (7) to p r o v i d e a n a c c e p t a b l e d e g r e e of resolution for the productivity estimates, the s u b t i d a l z o n e was d i v i d e d i n t o 0.6-m d e p t h i n t e r vals, o u t to a d e p t h o f - 2 . 4 m MLW; (8) in o r d e r to assess i n t e r s p e c i f i c a n d i n t r a s p e c i f i c c h a n g e s in algal p r o d u c t i v i t y with d e p t h , p r o d u c t i v i t y was m e a -
Ecological Effects of Marina Development
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TABLE 3. Distribution of macroalgae (g m ~) in the proposed marina location for Davids Island. Values represent geometric means (and standard errors, SE) for wet weights of each taxon. Ulva = Ulva lactuca, Ent = Enteromorpha intestinalis, Bryop = Bryopsis plunwsa, Fucus = Fucus vesiculosus, Gymno = Gymnogongrus griffithsiae, Porph = Porphyra umbilicalis, C h o n d = Chondrus crispus, Agard = Agardhiella tenera, Grin = Grinella americana, Ceram = C~eramium strictum. All depths correspond to the m e a n low water (MLW). Taxon
Depth Range (m) U p p e r Intertidal (+2.1 to +1.1) Lower Intertidal (+1.1 to 0) Subtidal (0 to - 0 . 6 ) Subtidal ( - 0 . 6 to - 1 . 2 ) Subtidal ( - 2 . 4 to - 3 . 0 )
Mean . SE Mean SE Mean SE Mean SE Mean SE
Ulva
Ent
Bryop
Fucus
0.0 0.0 2.2 1.4 22.6 2.6 28.9 3.8 3.3 1.6
348.1 137.8 1.9 1.0 0.0 0.0 0.0 0.0 0.0 0.0
0.0 0.0 0.0 0.0 0.3 0.3 0.0 0.0 0.0 0.0
29.1 4.6 8.9 4.0 1.7 0.8 1.6 1.6 0.0 0.0
sured at 100%, 50%, 25%, 10% a n d 1% of surface irradiance It; (9) productivity was c o m p u t e d for each d e p t h zone based o n varying light exposures a n d tidal influences as previously described; and, (I0) future macroalgal p r o d u c t i o n on the m a r i n a floor ( - 2 . 4 m to 3.0 m MLW) was assumed to be zero d u e to d e e p e n i n g o f the water c o l u m n a n d the shading effects f r o m various structures. Because it is likely that s o m e p r o d u c t i o n will occur, b o t h on the m a r i n a floor a n d the h a r d substrates created, this may be an overly conservative estimate.
Gymno 0.0 0.0 0.0 0.0 0.0 0.0 0.2 0.2 0.0 0.0
Porph
Chond
Agard
Grin
Ceram
"Ibtal
0.2 0.1 0.4 0.3 0.03 0.03 0.0 0.0 0.0 0.0
0.0 0.0 0.6 0.3 42.0 4.2 25.3 4.3 0.0 0.0
0.0 0.0 0.0 0.0 0.03 0.03 12.9 3.7 7.6 3.2
0.0 0.0 0.0 0.0 0.0 0.0 0.5 0.5 0.01 0.01
0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0
377.4 14.0 66.7 69.4 10.9
was captured. Sample 14C activity was c o u n t e d using liquid scintillation s p e c t r o m e t r y according to m e t h o d s previously described. T h e d p m g-1 o f tissue were n o r m a l i z e d to total s e d i m e n t weight o f the original 1-cm sample a n d expressed as hourly c a r b o n fixation rates (l~g C cm 2 h - l ) . Daily rates o f microalgal p r o d u c t i o n were c o m p u t e d for each d e p t h interval using the previously discussed ass u m p t i o n s r e g a r d i n g incident light exposures a n d tidal stage. Results
I,IGIIT-ATTENUATION BENTHIC MICROALGAL PRODUCTIVITY
Five s e d i m e n t cores collected for the microalgal p i g m e n t analyses were c o n c u r r e n t l y analyzed for microalgal productivity. Water i m m e d i a t e l y above the s e d i m e n t surface of the cores was s i p h o n e d o f f a n d r e p l a c e d with a m b i e n t water f r o m the study area which h a d b e e n filtered t h r o u g h W h a t m a n G F / F glass-fiber filters. A p p r o x i m a t e l y 5-20 txCi NaH14CO~ was a d d e d to each o f the samples; they were t h e n i n c u b a t e d for 1-2 h as follows. Samples collected f r o m stations MB-1 a n d MB-2 were incub a t e d at 100% a n d 25% I o, c o r r e s p o n d i n g to the r a n g e o f incident light e n c o u n t e r e d by surficial algae in tile intertidal zone d u r i n g a tidal cycle. Samples collected f r o m stations MB-3 t h r o u g h MB-5 were i n c u b a t e d at 10% a n d 1% Io, c o r r e s p o n d i n g to incident light levels f r o m the d e e p e r subtidal zone to the limits o f the e u p h o t i c zone. Following incubation, water over the s e d i m e n t in each sample was s i p h o n e d off, a n d the u p p e r 1 cm of sedi m e n t was t r a n s f e r r e d into a weighing p a n containing a d r o p o f c o n c e n t r a t e d H C I a n d frozen over d r y ice for s h i p m e n t to BERI,. In the laboratory, samples were dried at 60~ a n d subsamples were r e m o v e d , weighed, and transf e r r e d to 20-ml scintillation vials. Samples were oxidized in a Packard Oxidizer a n d released 14CO2
Vertical distributions of light n e a r Davids Island were similar in July a n d August; r e c o r d e d secchi d e p t h s r a n g e d f r o m 1.8 m to 2.0 m. T h e m e a n (+SE) light extinction coefficient (k) for July was 0.34 -+ 0.01 m -x a n d in August r a n g e d f r o m 0.26 m 1 to 0.28 m -1. Using the relationships, k = 1.7/ secchi d e p t h (Poole a n d Atkins 1929) a n d k = (2.3/Z) (log It - Iz) where z is the sampling d e p t h a n d It a n d Iz light readings at the surface a n d d e p t h z (Sverdrup et al. 1942), respectively, d e p t h s to which light p e n e t r a t e d to yield 100%, 50% 25%, 10% a n d 1% o f incident light (It) were estimated at m e a n high water to be 0.0 m, 1.0 m, 2.3 m, 3.0 m, a n d 5.9 m, respectively. T h e s e light levels corr e s p o n d e d to the region of the water c o l u m n where algae would receive sufficient light for photosynthesis (i.e., levels potentially s u p p o r t i n g algal growth). M,ACROALGAE DISTRIBUTIONS
Because their distributions are highly variable and patchy in the study area, all wet weights presented for m a c r o a l g a e (Table 3) are expressed as the g e o m e t r i c m e a n for individual taxa across all transects. Zonation was obvious, with distinct pat, terns in algal distributions evident across all d e p t h s in the intertidal a n d subtidal zones. T h e p h a e o -
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TABLE 4. Distribution of m a c r o a l g a e ( g m 2) on A u n t P h e b e Rock located a p p r o x i m a t e l y 50 m west of Davids Island. Values r e p r e s e n t g e o m e t r i c m e a n s (and s t a n d a r d errors, SE) for wet weights of each taxon. UIva = Ulva lactuca, Ent = Enteromorpha intestinalis, Bryop = Bryopsis plumosa, Fucus = Fucus vesiculosus, Gymno = Gymnogongrus griffithsiae, P o r p h = Porphyra umbilicalis, C h o n d = Chondrus crispus, Agard = AgardhMla tenera, Grin = Orinella americana, C e r a m = Ceramium strictum. All d e p t h s c o r r e s p o n d to m e a n low water (MLW). Taxon
Depth Range (m) U p p e r Intertid al (+2.1 to +1.1) Lower In tertid al (+1.1 to 0) Subtidal (0 to - 0 . 6 ) Subtidal ( - 0.6 to - 1.2) Subtidal ( - 2 . 4 to - 3 . 0 )
Mean SE Mean SE Mean SE Mean SE Mean SE
l.Jlva
Ent
Bryop
0.0 0.0 0.13 0.13 0.6 0.6 7.6 4.0 0.0 0.0
27.4 27.4 1.9 1.0 0.0 0.0 0.0 0.0 0.0 0.0
0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0
Fucus 84.4 3.7 62.6 8.1 11.9 5.1 0.0 0.0 0.2 0.0
phyte Fucus vesiculosus and the chlorophyte Enteromorpha intestinalis d o m i n a t e d macroalgal biomass in the intertidal zone with 29.1 + 4.69 g m - ' and 348.1 _+ 137.7 g m ,2, respectively. However, specitic location in the intertidal zone was also important; for example, E. intestinalis was heterogeneously distributed on seawall rocks in the u p p e r intertidal zone (+1.1 m to +2.2 m MI,W) where lowest biomass was r e c o r d e d at the high tide line and maxi m u m levels observed at the base of the seawall. F. vesiculosus, on the o t h e r hand, d o m i n a t e d in the lower intertidal zone (0.0 m to +1.1 m MLW) with 8.9 + 4.0 g m z. O t h e r macroalgae m a d e proportionately lower contributions here, including Ulva lactuca (2.2 g m-2), E. intestinalis (1.9 g m-~), Chondrus crispus (0.6 g m "), and Porphyra umbilicalis (0.4 g m z). Macroalgal biomass increased in the nearshore subtidal zone (0.0 m to - 0 . 6 m MI,W). Mean wet weight for the r h o d o p h y t e (2. crispus averaged 42.0 -+ 4.2 g m 2 in the study area while mean biomass for the attached green algae U. /actuca increased to 22.6 + 2.6 g m z. Mean biomass for the two d o m i n a n t intertidal taxa, E vesiculosus and E. intestinalis, declined dramatically in the subtidal to
