Aquaculture Gear Research Articles

The use of food grade oil in the prevention of vase tunicate fouling on mussel aquaculture gear

Current mitigation strategies against invasive tunicates on mussel aquaculture gear in Prince Edward Island concentrate on labour-intensive and costly fouling removal. Instead of removal, this study focused on preventing the settlement of the vase tunicate Ciona intestinalis and other fouling organisms by applying a layer of food grade oil to gear prior to recruitment. Laboratory tests established the adherence and persistence of shortening, a food grade oil with a melting point exceeding ambient water temperatures, to rope and mussels. In situ tests showed that shortening decreased C. intestinalis weight and abundance on buoys, spat collector ropes and collector plates but not on mussel socks. Fouling by algae and other tunicates was significantly reduced on most substrates. There were no detrimental effects of shortening treatment on mussel length and abundance on mussel socks, but total mussel weight was significantly lower on shortening-treated socks. Shortening treatment did notsignificantly affect mussel spat settlement on spat collector ropes, but further evaluation is required. Overall, shortening application has considerable potential for reducing tunicate and other fouling, particularly on buoys.

An initial assessment of native and invasive tunicates in shellfish aquaculture of the North American east coast

Summary The objective of the study was to assess the distribution of native and invasive tunicates in the fouling community of shellfish aquaculture gear along the U.S. east coast of the Atlantic. Since the 1980s, several species of invasive tunicates have spread throughout the coastal waters of the North American east coast and have become dominant fouling organisms on docks, boat hulls, mooring lines, and in shellfish aquaculture. Invasive and native tunicates negatively impact shellfish aquaculture through increased maintenance costs and reduced shellfish growth. While the presence of alien tunicates has been well documented at piers, harbors, and marinas, there are few published reports of invasive tunicate impacts to aquaculture. We surveyed shellfish aquaculture operations at Martha’s Vineyard, Massachusetts and shellfish aquaculturists in other areas along the North American east coast and report high levels of fouling caused by seven invasive, three native, and two cryptogenic species of tunicates. All study sites were fouled by one or more tunicate species. Biofouling control treatments varied among aquaculture sites and were effective in removing tunicates. Invasive and native tunicates should be considered when assessing the economic impacts of fouling organisms to the aquaculture industry.

Viability of golden star tunicate fragments after high-pressure water treatment

High-pressure water spray is one of the mitigation strategies used by mussel growers against invasive colonial tunicates fouling aquaculture gear. However, this treatment leads to fragmentation of tunicate colonies and can potentially lead to increased recolonization of adjacent suspended aquaculture gear. We demonstrate that colony fragments of the golden star tunicate ( Botryllus schlosseri) are viable for at least 18 days following high-pressure water treatment. Therefore, future studies need to investigate the fate of colonial tunicate fragments after high-pressure washing to determine fragment viability under field conditions. Potentially, mitigation strategies against colonial tunicates need to incorporate techniques ensuring fragment mortality.

A comparison of the habitat value of sub-tidal and floating oyster (Crassostrea virginica) aquaculture gear with a created reef in Delaware’s Inland Bays, USA

The culture of the Eastern oyster (Crassostrea virginica) in containment gear has become a viable component of restoration programs in many states on the East Coast of the United States, and it has been suggested that these operations may provide many of the same ecological services as natural or restored reefs. Our two-part study comparing the diversity and abundance in macro-epifaunal communities associated with a sub-tidal-created oyster reef and ‘modified rack and bag’ cage system (Part I) and floating oyster cages for restoration (Part II) occurred over the summer and fall of 2006 and 2007, respectively. In Part I, a greater total abundance and species richness (P 0.05) was found in species diversity according to Simpson’s index by habitat type, but it was significant (P 0.05). These results suggest that created reefs in conjunction with ‘rack and bag’ cage systems, as well as floating cage systems, support ecologically and economically important macro-epifauna, even at very small scales.

Effects of Oyster Depuration Gear on Eelgrass (Zostera marinaL.) in a Low Density Aquaculture Site in Long Island Sound

Oyster (Crassostrea virginica) aquaculture has a long history and tradition in Long Island Sound (Connecticut, USA). Although most of the producers practice traditional on-bottom aquaculture, there are a growing number of individuals utilizing bottom gear for cultivation and depuration. The use of this gear presents a potential conflict in eastern Long Island Sound where the last remaining populations of eelgrass (Zostera marina L.) exist. Shellfish aquaculture activity has been identified as a potential source for negative impacts to eelgrass populations. However, bivalve aquaculture has also been shown to provide an equivalent or greater degree of ecosystem services as submerged aquatic vegetation. The effects of short-term oyster depuration activity were gauged by comparing eelgrass reference sites and experimental plots (eelgrass areas containing oyster depuration cages with and without oysters) in triplicate. Changes in sheath length of the eelgrass 1 m from the cages were used as a proxy for growth rate. The aquaculture gear had no effect on this measure of growth rate of eelgrass in any of the deployments. Sediment characteristics (sediment chlorophyll, sediment % organics) in the cage footprint and 1m from the cages also failed to show an effect of the depuration cages on the local environment. Video monitoring of the footprints and local area indicated little physical damage to the eelgrass beds as a result of the short deployment of the aquaculture gear. The water column at all three sites was vertically well mixed and no effect of the cages on water column light and other characteristics was detectable. The results of this study indicated that at the current level of activity, short-term depuration of oysters has minimal effect on eelgrass growth, water quality and the sediment characteristics measured. However, if depuration activity expands in terms of the amount of gear and/or individual operations, it may result in measurable effects. Understanding the interactions between shellfish aquaculture activity and the marine environment is necessary for sustainable growth of the industry.

Market potential for Styela clava, a non-indigenous pest invading New England coastal waters

Styela clava is a solitary tunicate that has spread rapidly from its native waters in the Philippines and is now a dominant resident in marine habitats of much of the world. It was first reported on the east coast of the U.S. at Beverly, Massachusetts in 1970 and is now commonly found in marine environments throughout the state. The alien sea squirt is a pest to the shellfish aquaculture industry that causes nuisance fouling on aquaculture gear. In southern Korea, Styela clava is considered to be a seafood delicacy and has acquired a cultural distinction as an aphrodisiac. A consumer market already exists for the fouling tunicate in Korean markets in the U.S. that sell imported frozen Styela clava at a retail price of at least $8 per pound ($3.63/kg). It is suspected that local fresh tunicate product, if available, could sell for an even higher price. A market study to turn this alien pest into a profitable seafood product is proposed.

Limited value of the common periwinkle snail Littorina littorea as a biological control for the invasive tunicate Didemnum vexillum

Didemnum vexillum is an invasive tunicate that aggressively grows on and fouls all manner of substrates in coastal New England habitats. Most alarmingly, D. vexillum acts as a shellfish pest and is capable of completely encapsulating and smothering bivalves, causing them to have reduced growth or be killed. Fouling by D. vexillum on aquaculture gear and product requires remediation. While there are numerous manual eradication methods, they are labor intensive and expensive. We investigated whether the common periwinkle snail Littorina littorea can be utilized as a biological control for D. vexillum. The only known predator of senescing D. vexillum is the snail L. littorea and there are no known predators of healthy D. vexillum. Field observations indicated that L. littorea may be consuming, scouring, or otherwise removing stressed D. vexillum from rocks in intertidal pools at Sandwich, Massachusetts, during all seasons. We used two methods to investigate whether L. littorea could be used as a biological control by either consuming or scouring D. vexillum off shellfish. We examined L. littorea’s fecal pellets and conducted a laboratory experiment to determine if the snails would “clean” unhealthy D. vexillum from aquaculture product. Fecal pellets from L. littorea collected on unhealthy D. vexillum contained the characteristic spicules of this tunicate, thus confirming that L. littorea consumes D. vexillum under field conditions. The laboratory experiment indicated that L. littorea did not notably consume or scour D. vexillum from shellfish under the conditions we provided. At this time, we recommend that manual eradication methods be considered the primary defense for shellfish aquaculturists and others interested in controlling D. vexillum and that L. littorea should merely be considered as a supplement to these more reliable control methods.

Impact of the invasive colonial tunicate Didemnum vexillum on the recruitment of the bay scallop (Argopecten irradians irradians) and implications for recruitment of the sea scallop (Placopecten magellanicus) on Georges Bank

The invasive colonial tunicate Didemnum vexillum has become widespread in New England waters, colonizing large areas of shell-gravel bottom on Georges Bank including commercial sea scallop (Placopecten magellanicus) grounds. Didemnum vexillum colonies are also fouling coastal shellfish aquaculture gear which increases maintenance costs and may affect shellfish growth rates. We hypothesized that D. vexillum will continue to spread and may affect shellfish larval settlement and survival. We conducted a laboratory experiment to assess interactions between larval bay scallops (Argopectin irradians irradians) and D. vexillum. We found that larval bay scallops avoid settling on D. vexillum colonies, possibly deterred by the low pH of the tunicate’s surface tissue. The results of this study suggest that widespread colonization of substrata by D. vexillum could affect scallop recruitment by reducing the area of quality habitats available for settlement. We propose that the bay scallop can serve as a surrogate for the sea scallop in estimating the negative impact D. vexillum could have on the recruitment of sea scallops on Georges Bank.

A Comparison of the Macrofaunal Communities Inhabiting a Crassostrea virginica Oyster Reef and Oyster Aquaculture Gear in Indian River Bay, Delaware

The eastern oyster (Crassostrea virginica) is a vital species in the estuaries of the mid-Atlantic United States. Whereas their filtering activity and biodeposition play an important role in the ecology of these systems, the reefs they form are one of the few sources of hard bottom habitat for fouling organisms and are the foundation of a rich biological community. This species has experienced drastic declines throughout the mid-Atlantic region in the last two centuries due to overfishing, habitat loss, and disease. Much interest and effort is now focused on restoring this important commercial and ecological resource. Whereas oyster reef restoration is central to the recovery of this species and the habitat it creates, oyster aquaculture can provide many of these same services albeit on a smaller scale. This is a two-part study, assessing the macrofaunal communities associated with subtidal modified rack and bag aquaculture, conducted over the summer and fall of 2006. The first part of this study compares the macro-epifaunal communities associated with two oyster habitats: a created oyster reef and oyster aquaculture cages. Both habitats were sampled with lift nets and compared using two-way ANOVAs between habitat and time. Secondly, we compared the sediment composition and macro-infaunal communities below the oyster cages with a nearby reference area of open sand/mud bottom. A significantly greater (P < 0.05) total abundance and species richness was found in the oyster cages, but significantly greater (P < 0.05) species evenness was found on the reef with species diversity similar between habitats. The sediments below the oyster cages showed a slight but significant (P < 0.05) reduction in it's silt/clay fraction. The results of this study show that, this method of oyster aquaculture supports additional populations of ecologically and economically important macrofauna compared with a created oyster reef. Furthermore this study demonstrates that off-bottom oyster aquaculture operations in the mid-Atlantic United States are a beneficial addition to host estuaries and associated natural communities.

Detecting and Managing Coastal Fisheries and Aquaculture Gear Using Satellite Radar Imagery

Fishing and shellfish aquaculture are important sources of income for coastal communities in Thailand and other parts of tropical Asia, but environmental impacts associated with these small-scale activities can effect water quality, nearshore habitats, and fish populations. The management of coastal fisheries and aquaculture has, therefore, become a major concern for government fisheries officials who are searching for cost effective measures to improve the regulation of these sectors. Synthetic aperture radar (SAR) images from the RADARSAT-1 satellite were acquired to determine if stationary fishing and aquaculture gears within a coastal study site in the Upper Gulf of Thailand could be identified, and if automatic signature separation of gear types was possible. The use of SAR imagery for a coastal monitoring application was also evaluated and the potential of this technology to improve resource management outcomes considered.