Cathodically protected steel as an alternative to plastic for oyster restoration mats
Introduction
Over the past several years the health of the Indian River Lagoon (IRL), an estuary located along Florida's east coast, has undergone a serious decline. The system has seen an increase in the presence of total suspended solids, as well as high nutrient concentrations, which in turn have fueled large scale algal blooms, such as those observed in 2012 by the brown tide pelagophyte Aureoumbra lagunensis (Gobler et al., 2013). Both the rise in turbidity and algal cell density has had a negative impact on the IRL system, blocking sunlight from reaching the benthos and leading to a decline in seagrass beds and fauna mortality (Gobler et al., 2013; Morris and Virnstein, 2004).
Oyster populations throughout the IRL have also decreased as a result of overharvesting, habitat degradation, and low salinity (Wilson et al., 2005; Garvis et al., 2015). Oyster reefs are known for providing many benefits to coastal ecosystems, one of which is their ability to filter large volumes of water (Ehrich and Harris, 2015). This process removes suspended particulates from the water column, including harmful algal species, and improves water clarity. The lack of oysters in the IRL is also thought to contribute to the frequent and persistent algal blooms. Like many estuaries worldwide, there are ongoing efforts in the IRL to restore the oyster populations to their natural abundance or to a state where they can provide sufficient ecosystem services. Currently oyster restoration efforts in the IRL utilize aquaculture plastic mesh to construct oyster mats and bags (e.g. Garvis et al., 2015). However, plastics do not break down or mineralize in seawater, instead they break down into smaller and smaller pieces eventually becoming what is termed “microplastics” (Hidalgo-Ruz et al., 2012). These small plastics are commonly mistaken as a food item for marine organisms ranging in size from plankton to whales. Plastics can also leach out chemicals into the ocean, as well as, adsorb pollutants (Ashton et al., 2010). It is now believed that these plastic pollutants may get passed up the food chain (Mattsson et al., 2017).
As oyster restoration efforts continue to comprise a large portion of estuarine management plans, there is a need to find environmentally friendly alternatives. Thus, different materials have been or are currently under investigation such as crab traps coated with concrete (Hernández et al., 2018), oyster castles (Hernández et al., 2018), Biodegradable Elements for Starting Ecosystems (BESE) (Herbert et al., 2018), burlap ribbon (Soucy, 2020), basalt (Soucy, 2020), and coconut coir (Soucy, 2020). One such possibility may be the use of a mild steel as the base material for oyster mats. This concept is based on prior research that has used cathodically protected steel to develop mineral accretion and enhance calcareous marine growth to form reefs (Hilbertz, 1979). Electricity is supplied to steel to prevent corrosion and cause a rise in the local pH. This causes calcium and magnesium ions to combine with bicarbonate and hydroxide ions and precipitate as CaCO3 (aragonite) or Mg(OH)2 (brucite) on the steel surface (mineral accretion) (Borell et al., 2010). The resulting calcium carbonate which is formed through seawater electrolysis is similar to reef substratum or limestone, and is thus an environmentally friendly approach commonly used in coral reef rehabilitation (Borell et al., 2010, Goreau and Hilbertz, 2005, Romatzki, 2014). It allows for increased survival and growth through reinforced substrate stabilization (Hilbertz and Goreau, 1996). Research with coral transplants has found they are quickly cemented onto the steel, facilitating firm attachment to the substrate. Additionally, the coral has enhanced skeletal growth rates due to an increase in available electrons (Hilbertz and Goreau, 1996).
Similar benefits have been reported for oysters where placing the organisms in a cathodic field increased survival rate and growth (Berger et al., 2012; Shorr et al., 2012). The few published studies on mineral accretion for oyster restoration have utilized substrates such as: rebar (Piazza et al., 2009), a steel structure fixed to a dock piling (Latchere et al., 2016), and a steel helix-shaped structure (Shorr et al., 2012). While each of these field experiments have shown the potential for mineral accretion to enhance the biological performance of oysters, there still remain many uncertainities (Koster, 2017). Especially how would the mineral accretion process be translated to successfully assist in restoration processes that utilize structures other than rebar and wire, and how the electrical measurements driven via a solar panel should be implemented for successful oyster recruitment and growth in estuarine settings.
This study was designed to determine the efficacy of mineral accretion using oyster mat structures, which are commonly used along the east coast of Florida, with the process driven by the use of a solar panel instead of DC power sources reported in previous studies. Steel mesh oyster mats were attached to an impressed current cathodic protection system to develop mineral accretion. The objective was to determine if mineral accretion mats were as effective at promoting the growth of oysters as plastic oyster mats, as well as to record changes in mineral accretion at three different locations in the IRL. It is believed the creation of the mineral accretion structures will enhance oyster growth, which in turn provides increased filtration and improvement to local water quality. The structures will also create habitat for organisms associated with oyster reefs, such as juvenile fish, barnacles, crabs, shrimp, mussels, tunicates, snails, and algae (Barber et al., 2010; Weaver et al., 2018).
Section snippets
Field preparation and deployment
A flattened expanded steel mesh with 0.64 cm openings was selected for this study, as that it is often the mesh size used for the plastic oyster restoration mats (Garvis et al., 2015). The steel mesh was cut into 45.7 × 45.7 cm replicates, and affixed with 36 dead and dried oyster shells (Fig. 1) (Wall, 2004). Oyster shells were attached to steel mats using stainless steel screws, washers, and nuts. Undamaged oyster shells (ranging in length from 6.5 to 9.5 cm) were attached perpendicular to
Results
Each of the three test sites had slightly different water quality conditions. Over the period of immersion, Port Canaveral had an average salinity of 34.7 ± 1.7 ppt, with an average temperature of 28.7 ± 1.6 °C and pH 8.1 ± 0.06. The Grant site had an average salinity of 20.5 ± 8.6 ppt, with an average temperature of 31.8 ± 2.2 °C and pH 8.04 ± 0.1. The Melbourne Beach site had an average salinity of 23.5 ± 6.8 ppt, with an average temperature of 30.8 ± 2.2 °C and pH 8.2 ± 0.2. There were
Discussion
Over the course of the three-month immersion period, mineral accretion and oyster growth were observed at all of the test sites. The steel mats were effective at promoting the growth of oysters, but the overall recruitment was dependent on the test site and each varied based on environmental and ecological conditions. At the Melbourne Beach location, there was a significantly greater presence of oysters on the steel compared to the plastic. At Port Canaveral and Grant, oyster growth at times
Conclusions
In addition to this work being of great interest to scientists and engineers working in coastal ecosystems, there is a growing pressure from the public to use plastic alternatives, such as mineral accretion, for restoration work. It is believed this method may enable a permanent oyster reef structure to become established by the deposition and chalks, promoting the growth of calcareous marine organisms (e.g. oysters, barnacles, tubeworms, mussels) and providing a firm substrate for the growth
Declaration of Competing Interest
The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
Acknowledgements
This work was funded by a grant from the Space Coast Office of Tourism - 2018/19 Lagoon Grant, Brevard County, Florida, USA. The authors would like to acknowledge the support of the Environmentally Friendly Endangered Lands Program, especially Nichole Perna, and Chris Potzar from Rib City at Grant Station, for their support and providing dock space for deployments. Thank you to Dr. Travis Hunsucker for assistance performing analysis in MATLAB.
References (42)
- et al.
Association of metals with plastic production pellets in the marine environment
Mar. Pollut. Bull.
(2010) - et al.
A review of existing oyster filtration rates models
Ecol. Model.
(2015) - et al.
Expansion of harmful brown tides caused by the pelagophyte Aureoumbra lagunensis Deyoe et Stockwell to the US east coast
Harmful Algae
(2013) - et al.
Effect of electrolysis treatment on the biomineralization capactites of pearl oyster Pinctada margaritifera juveniles
Est. Coat. Shelf Sci.
(2016) - et al.
Oyster mortality in Delaware Bay: Impacts and recovery from Hurricane Irene and Tropical storm Lee
Estuar. Coast. Shelf Sci.
(2013) - et al.
Potential for restoring biodiversity of macroflora and macrofauna on oyster reefs in Mosquito Lagoon, Florida
Fla Sci
(2010) - et al.
- et al.
Differential physiological responses of two congeneric scleractinian corals to mineral accretion and an electric field
Coral Reefs
(2010) - et al.
The importance of habitat created by molluscan shellfish to managed species along the Atlantic Coast of the United States
Cathodic Protection Design Recommended Practice. DNVGL-RP-B401
(2017)
Quantifying the impacts of oyster reef restoration on oyster coverage, wave dissipation and seagrass recruitment in Mosquito Lagoon, Florida. Master’s Thesis
Formation, movement, and restoration of dead intertidal oyster reefs in Canaveral National Seashore and Mosquito Lagoon, Florida
J. Shellfish Res.
Marine electrolysis for building materials and environmental restoration
Marine ecosystem restoration: cost and benefits for coral reefs
World Resour. Rev.
Historical changes in intertidal oyster (Crassostera virginica) reefs in a Florida lagoon potentially related to boating activities
J. Shellfish Res.
A laboratory study of reef growth by electro-deposition
JCR.
Fish species in relation to restored oyster reefs, Piankatank River, Virginia
Bull. Mar. Sci.
Mitigating erosional effect induced by boatk wakes with living shorelines
Sustainability
Restoring the eastern oyster: how much progress has been made in 53 years?
Front. Ecol. Environ.
Microplastics in the marine environment: a review of the methods used for identification and quantification
Environ. Sci. Technol.
Electrodeposition of minerals in sea water: experiments and applications
IEEE J. Ocean Eng.
Cited by (5)
First quantitative biomonitoring study of two ports (marina, commerce) in French littoral area: Evaluation of metals released into the marine environment and resulting from galvanic anodes
2023, Science of the Total EnvironmentCitation Excerpt :This observation is in line with the conclusion of other scientists that the contribution of anodes to the inputs of trace metals seemed negligible compared to continental inputs on a regional scale (Caplat et al., 2010; Deborde et al., 2015; Mao et al., 2011; Gabelle et al., 2012). However, this environmental approach should not be put aside, and other studies have been carried out on the subject of cathodic protection, in particular on the development of oysters with the replacement of plastic by steel (Hunsucker et al., 2021), or for the protection of offshore wind turbines (Erdogan and Swain, 2021). Other studies, using an experimental approach, have been conducted on oysters or mussels for example (Mao et al., 2011; Mottin et al., 2012), but none on black scallops.
Modeling Benthic Community Settlement and Recruitment on Living Dock Restoration Mats
2023, Environments - MDPIThe Impact of Benthic Organisms to Improve Water Quality in the Indian River Lagoon, Florida
2023, Water, Air, and Soil PollutionAssessing the Biological Performance of Living Docks—A Citizen Science Initiative to Improve Coastal Water Quality through Benthic Recruitment within the Indian River Lagoon, Florida
2022, Journal of Marine Science and EngineeringContemporary Oyster Reef Restoration: Responding to a Changing World
2021, Frontiers in Ecology and Evolution