Potential Impacts Of Restored Oyster Reefs Environmental Sciences Essay

Seagrass is one of the most of import intertidal and/or subtidal Marine home grounds. It plays a cardinal function in coastal ecosystem by supplying home ground to some of the commercially of import animate beings like bluish crab and juvenile phases of some fish species. In add-on to supplying home grounds, they are besides known for stifling the moving ridge actions ; stabilising the deposits with their root systems, bettering H2O quality and cycling of foods. When used in concurrence with other home grounds like salt fens, they act as buffer zone for the coastal eroding and stabilise the deposit via their root systems. However, despite being commercially and ecologically of import, this home ground is shriveling throughout the universe in an unprecedented rate. Some of the grounds responsible for the shrinkage of seagrass hayfields are light fading due to eutrophication and suspended deposits, dislodgment due to moving ridges, and inordinate air plants growing.

Similarly, salt marsh vegetation is an emergent home ground which is utilized by different life phases of free swimming nektons. They use it as a safety and seek their nutrient. It is besides a home ground where organisms fell from their marauders and marauders come looking for their quarry. Coastal eroding is one of the premier grounds that shrink the of import salt marsh vegetation.

Breakwaters made of oyster shells can be deployed as a possible answer for alarmingly gnawing shorelines of the universe. Made up of solid stuffs and constructed perpendicular to the predominating air currents groins are an technology technique that attenuate and dissipate moving ridges generated offshore go forthing the slack, unagitated H2O on their leeward side. Therefore, they combat the shoreline eroding and protect the littoral zone and minimise the effects of long shore impetus. Breakwaters therefore protect the seagrass beds that prevarication instantly behind them, stabilise shorelines and assist fens from being eroded off. They besides provide home ground for commercially and ecologically of import species of fish. Small fish come to the reefs seeking to avoid their marauders while marauder species come to look for their quarry. In add-on to this, the reefs besides provide shelter for different species of fish during major storm events.

Deploying oyster reefs as the groins offshore in a coastal environment is comparatively newer thought than utilizing traditional bulkhead, inguens, revetment walls or breakwater which are associated with perpendicular eroding down the barrier, loss of critical intertidal home ground and net loss of piscary. Oyster reefs have advantages over other above mentioned traditional difficult nucleus preventative steps because of their associated biological advantages. Some advantages are: oyster reefs stabilize shorelines functioning as life groins, and unlike other techniques they provide home ground and nutrient for both finfish and shellfish hence augmenting commercial crop of fish. Some fish ( e.g. gudgeons, blennies, frying pan fish, and oyster toadfish ) deposit their eggs inside the oyster valves where they are less likely to be eaten by the marauders. Apart from finfish and shellfish they besides provide home ground for mussels, clay worms, sea pip-squeaks, sea windflower, cirripeds and pediculosis pubis. As filter feeders, oysters clear the H2O column by taking suspended solids, phytoplankton, organic and inorganic affair. Good H2O quality in bend promotes submerged aquatic flora ( SAV ) which is place for pediculosis pubis, fish and other beings. Bing filter feeders when phytoplankton and debris come to oysters, they consume them and re-mineralize as their imposter fecal matters let go ofing urea, N, ammonium hydroxide, P, and other foods which act as fertilisers for seagrass, and may besides originate some debris nutrient ironss.

Sing above points, oyster reefs were deployed to rarefy the moving ridge energy and to analyze their possible impacts on H2O quality, seagrass beds, marsh grass vegetation and piscary production and copiousness. For the appraisal of the effectivity of the oyster reefs as groins and their ecological function in a subtidal and intertidal system the structural and functional parametric quantities recognized by NOAA, National Oceanic and Atmospheric Administration were measured. In add-on, procedure of denitrification will besides be studied in this survey. It is expected that those parametric quantities will assist in better understanding the effectivity of oyster reefs as life groins.

Chapter I: My focal point in this chapter will be on analyzing the growth/enhancement of seagrass beds after the deployment of the reefs. It is hypothesized that the SAV will thrive behind the groins ( experimental sites ) than without the groins ( command sites ) due to the protective advantage provided by the oyster reefs. It is besides expected that the strength of light making the underside behind the experimental sites will be higher than the control 1s because of calmer H2O ensuing into less cloudy status and besides due to high biological filter feeding activities of oyster, which feed upon the suspended solids and particulate organic affairs, nevertheless to document this biological portion it might take certain old ages. Different variables that are indexs of prosperity of the seagrass will be compared sporadically among the seagrass spots of control versus the experimental secret plans and will be correlated with the sum of light making the underside. Two attacks have been incorporated for the seagrass survey. One is random trying attack and another is repeated measuring ( piece particular ) sampling. Random sampling is the technique in which we randomly took the samples of segrass with a PVC corer ( 7.62 centimeter ) from 5m radius of lasting markers ( situated at distance of 0m, 50m and 100m from the shoreline ) for both the experimental and control site, irrespective of presence or absence of seagrass. While for the perennial measuring we took samples from the same specific spots repeatedly to see how the seagrass in those spots respond throughout the clip after the deployment of reefs.

Following variables were measured for the random and spot specific attack.

Random trying Repeated spot sampling

Abundance of seagrass Yes No

( expressed as per centum )

Density of shoots Yes Yes

Number of foliages per shoot Yes Yes

Length and breadth of leaves No Yes

Aboveground ash free dry weight Yes Yes

Belowground ash free dry weight Yes Yes

CNP content of aboveground tissue No Yes

CNP content of belowground tissue No Yes

Chapter-II: In this chapter I will analyze how salt marsh vegetations Spartina alterniflora responds to the oyster reef groins. I will analyze if there is important difference in the ( 1 ) Aboveground biomass ( AFDW ) ( unrecorded and dead ) , ( 2 ) Belowground biomass ( AFDW ) ( 3 ) Food ( CNP ) content of the above land tissue ( unrecorded and dead ) ( 4 ) Food content ( CNP ) of the below land tissue ( roots and rootstock ) ( 5 ) pore H2O food of low and high fen ( 6 ) copiousness of infauna ( designation up to household degree ) residing in the low and high fen, which is matching to the tall and short signifier of S. alterniflora severally. It is expected that the both high and low fen will heighten at the experimental sites due to protection from the reefs, which in bend will hold a important positive impact on the above mentioned parametric quantities at the experimental sites than at the control 1s. The above and below land biomass of S. alterniflora is expected to be higher behind the experimental site ensuing in higher copiousness of infauna due to the complex root and rootstock system supplying home ground to them. However, it is expected to be merely change by reversal for the instance of porewater foods. Since the root and rhizome system of S. alterniflora is expected to be complex and robust behind the experimental sites, they will absorb more foods available to them in the signifier of dissolved signifier from the pore H2O so what shall be left in pore H2O will be the lone little concentration of fresh or extra foods.

Chapter-III: This chapter will chiefly cover with overall impact of groin in the intertidal and subtidal system. I will mensurate the physical parametric quantities peculiarly, ( 1 ) turbidness, ( 2 ) sum suspended solids, ( 3 ) particulate organic affair ( POM ) , ( 4 ) visible radiation handiness ( or fading ) at the underside ( 5 ) ball disintegration rate through the H2O column and ( 6 ) denitrification potencies and the overall impacts of ( 1 ) , ( 2 ) , ( 3 ) , and ( 4 ) on ( a ) benthic and ( B ) H2O column chlorophyll, which are placeholder of quantification of photosynthetic microorganisms. Those physical parametric quantities can be used as a placeholder for finding of moving ridge energy that is attenuated behind the groins. It is expected that turbidness will be lower at the experimental sites due to the calmer status provided by the reefs so as it will be the instance for TSS and POM. Light handiness will be higher behind the reefs ( experimental sites ) due to lowered turbidness, TSS and POM. Due to the calmer conditions behind the reefs, clod disintegration rate ( measured as alteration in mass of gypsum salt in one full tidal rhythm ) will be lesser than that at control sites. All these conditions lead to a comfortable benthal vegetations i.e. seagrass and benthal algae. Seagrass will be covered in item in Chapter-I so benthal and oceanic chlorophyll-a will merely be included in this chapter. I will besides compare possible denitrification rates in experimental and command sites. It is expected that the nitrification and denitrification potencies will be higher behind the experimental sites than the control 1s due to the increased microbic activities around the close locality of the oyster reefs.

A brief overview of the survey site:

The survey site is situated in Point-aux-Pins, an embayment in the Mississippi Sound of the northern Gulf of Mexico, Alabama where both seagrass and salt fens are prevailing ( Morgan et al 1996 ) ( Fig: 1 ) . It is a long fringing fen land which is located along the nor’-east shore of a peninsula located to the sou’-west of Bayou la Batre, about 20 kilometers from Mobile Bay. This is a pristine, intertidal site that receives fresh H2O input from the Mobile Bay estuary. The maximal air current velocity is merely diffident of 17 km/hour. This is a polyhaline estuarine environment with the salt changing between 20 and 27 parts per 1000 ( ppt ) ( Morgan et al 1996 ) , which may drop down by up to 10 ppt after a heavy rainfall ( personal observation ) . Bing a shallow embayment the summer temperature remains about around 300C ( Stutes 2000 ) . Point-aux-Pins is a low energy site with extended natural wetland and stable shoreline constellation ( Shafer et al 2003 ) with some occasional scarps, which is substantiated by the fact that the site is protected from the moving ridge exposure and the current velocity ranges from 1.3 to 4.3 cm/s. The tides are diurnal and occasional semidiurnal tides happening every 2 hebdomads during minimal tidal amplitude. The average tidal amplitude is about 43 centimeter ( Morgan et al 1996 ) .

Treatment ( three oyster reefs of dimensions 25mX5mX1m ) and controls ( no reefs ) are assigned in braces ( 4 braces ) of which the intervention and control have site similarities in footings of deepness, orientation, fetch, sediment type and shoreline flora. So this survey is a Before-After Control-Impact Approach. Pairing of control and intervention ( experimental ) sites helps us to compare between the two and at the same clip it will besides assist to minimise the random effects that might be due to the other factors apart from the oyster reefs. For each of the variables that we measure we will hold Block ( 1, 2, 3, 4 ) and intervention ( experimental or control ) as the factors. There are three transects perpendicular to the oyster reefs that run parallel to each other in each of the intervention and the control sites which are 25 thousand apart ( Fig: 3 ) .

The dominant seagrass nowadays in the survey site are shoal grass ( Halodule wrightii ) and widgeon grass ( Ruppia maritima ) ( Heck et al 2001 ) which are frequently found in spots. This site is marked by cloudy H2O most of the clip throughout different seasons so seagrasses are non able to set up themselves in H2O deeper than 1m ( personal observation ) . The irregular spots of the seagrass spread from 1m to 60m offshore and the country of the spots varies from merely a few square centimetres to the graduated table of square metres. During the spring, widgeon grass dominates the site while during the early autumn shoal grass dominates. The mean leaf length is 14cm in early autumn with leaf denseness of 5000 foliages per sq m ( Stutes 2000 ) . The major species of saltmarsh found are short and long signifiers of smooth cord grass ( Spartina alterniflora ) , saltmeadow cord grass ( Spartina patens ) , black needlerush ( Juncus roemerianus ) in order of their happening from seaward to landward way with occasional presence of oxeye daisy ( Leucanthemum vulgare ) . Scattered spots of eastern oyster Cassostrea virginica are found in shallow H2O.

Coastal Areas of Mississippi Sound ( Alabama )

The coastal countries of Mississippi sound, Alabama are bordered by salt fens chiefly smooth cord grass ( Spartina alterniflora ) and blackneedle haste ( Juncus roemerianus ) like most of the northern Gulf of Mexico part. Tall signifier Spartina alterniflora is found asea while short signifier Spartina alterniflora is found landward ( Writings and Bertness 2001 ) . There are intertidal and subtidal oyster shells along the shorelines excessively. Apart from the regular erosional jobs Mississippi Sound besides faces occasional job of hurricane which consequences in the desolation of the submerged aquatic flora and fringing salt fen vegetation ( Stockdon et al 2010 ) . At least five species of seagrass are known to be in the Alabama seashores of Mississippi sound ( Humm 1956 ) , nevertheless merely two species, H. wrightii and R. maritima exist in the survey site ( personal observation, Heck et al 2001 ) .

Fig 1: Study site, Point-aux-pins in Mississippi Sound in Alabama

Construction of oyster reef groin

Breakwaters made of oyster shells were deployed 110m offshore in September 2009. The reefs are of dimension 25 mX5 m X 1 m, each devouring about 75-120 three-dimensional metre of eastern oyster Crassostrea virginica. Three units of such groins were placed at a distance of 5m apart lying straight perpendicular to the dominant bing wind way of SE. Thus the three separate units would move as a functional unit of groin. The conventional diagram of a unit of groins is shown as below:


Fig 2: Conventional design of a functional unit of constructed groin in Point-aux-pins, AL





Fig 3: Survey site at the Point-aux-Pins, AL