An integrated assessment of the continued spread and potential impacts of the colonial ascidian, Didemnum sp. A, in U.S. waters

Didemnum sp. A is a colonial ascidian or “sea squirt” of unknown geographic origin. Colonies of Didemnum sp. A were first documented in U.S. waters in 1993 at Damariscotta River, Maine and San Francisco Bay, California. An alarming number of colonies have since been found at several locations in New England and along the West Coast of the contiguous continental United States. Originally believed to be restricted to artificial structures in nearshore habitats, such as ports and marinas, colonies of Didemnum sp. A have also been discovered on a gravel-pavement habitat on Georges Bank at depths of 40-65m. The wide distribution of Didemnum sp. A, the presence of colonies on an important offshore fishing ground, and the negative economic impacts that other species of noninidigenous ascidians have had on aquaculture operations have raised concerns about the potential impacts of Didemnum sp. A. We reviewed the available information on the biology and ecology of Didemnum sp. A and potentially closely related species to examine the environmental and socioeconomic factors that may have influenced the introduction, establishment and spread of Didemnum sp. A in U.S. waters, the potential impacts of this colonial ascidian on other organisms, aquaculture, and marine fisheries, and the possibility that it will spread to other U.S. waters. In addition, we present and discuss potential management objectives for minimizing the impacts and spread of Didemnum sp. A. Concern over the potential for Didemnum sp. A to become invasive stems from ecological traits that it shares with other invasive species, including the ability to overgrow benthic organisms, high reproductive and population growth rates, ability to spread by colony fragmentation, tolerance to a wide range of environmental conditions, apparent scarcity of predators, and the ability to survive in human dominated habitats. At relatively small spatial scales, species of Didemnum and other nonindigenous ascidians have been shown to alter the abundance and composition of benthic assemblages. In addition, the Canadian aquaculture industry has reported that heavy infestations of nonindigenous ascidians result in increased handling and processing costs. Offshore fisheries may also suffer where high densities of Didemnum sp. A may alter the access of commercially important fish species to critical spawning grounds, prey items, and refugia. Because colonial ascidian larvae remain viable for only 12–24hrs, the introduction and spread of Didemnum sp. A across large distances is thought to be predominantly human mediated; hull fouling, aquaculture, and ballast water. Recent studies suggest that colony growth rates decline when temperatures exceed 21 ºC for 7 consecutive days. Similarly, water temperatures above 8 to 10 ºC are necessary for colony growth; however, colonies can survive extended periods of time below this temperature threshold as an unidentified overwintering form. A qualitative analysis of monthly mean nearshore water temperatures suggest that new colonies of Didemnum will continue to be found in the Northeast U.S., California Current, and Gulf of Alaska LMEs. In contrast, water temperatures become less favorable for colony establishment in subarctic, subtropical, and tropical areas to the north and south of Didemnum’s current distribution in cool temperate habitats. We recommend that the Aquatic Nuisance Species Task Force serve as the central management authority to coordinate State and Federal management activities. Five objectives for a Didemnum sp. A management and control program focusing on preventing the spread of Didemnum sp. A to new areas and limiting the impacts of existing populations are discussed. Given the difficulty of eradicating large populations of Didemnum sp. A, developing strategies for limiting the access of Didemnum sp. A to transport vectors and locating newly established colonies are emphasized. (PDF contains 70 pages)

Applying Habermas's critical theory to public administration and policy: A case study of Florida Everglades restoration program

The foundation of Habermas's argument, a leading critical theorist, lies in the unequal distribution of wealth across society. He states that in an advanced capitalist society, the possibility of a crisis has shifted from the economic and political spheres to the legitimation system. Legitimation crises increase the more government intervenes into the economy (market) and the "simultaneous political enfranchisement of almost the entire adult population" (Holub, 1991, p. 88). The reason for this increase is because policymakers in advanced capitalist democracies are caught between conflicting imperatives: they are expected to serve the interests of their nation as a whole, but they must prop up an economic system that benefits the wealthy at the expense of most workers and the environment. Habermas argues that the driving force in history is an expectation, built into the nature of language, that norms, laws, and institutions will serve the interests of the entire population and not just those of a special group. In his view, policy makers in capitalist societies are having to fend off this expectation by simultaneously correcting some of the inequities of the market, denying that they have control over people's economic circumstances, and defending the market as an equitable allocator of income. (deHaven-Smith, 1988, p. 14). Critical theory suggests that this contradiction will be reflected in Everglades policy by communicative narratives that suppress and conceal tensions between environmental and economic priorities. Habermas’ Legitimation Crisis states that political actors use various symbols, ideologies, narratives, and language to engage the public and avoid a legitimation crisis. These influences not only manipulate the general population into desiring what has been manufactured for them, but also leave them feeling unfulfilled and alienated. Also known as false reconciliation, the public's view of society as rational, and "conductive to human freedom and happiness" is altered to become deeply irrational and an obstacle to the desired freedom and happiness (Finlayson, 2005, p. 5). These obstacles and irrationalities give rise to potential crises in the society. Government's increasing involvement in Everglades under advanced capitalism leads to Habermas's four crises: economic/environmental, rationality, legitimation, and motivation. These crises are occurring simultaneously, work in conjunction with each other, and arise when a principle of organization is challenged by increased production needs (deHaven-Smith, 1988). Habermas states that governments use narratives in an attempt to rationalize, legitimize, obscure, and conceal its actions under advanced capitalism. Although there have been many narratives told throughout the history of the Everglades (such as the Everglades was a wilderness that was valued as a wasteland in its natural state), the most recent narrative, “Everglades Restoration”, is the focus of this paper.(PDF contains 4 pages)

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.

Fishery development and administration in India

This paper deals with the importance of fisheries administration in effective planning and successful execution of fisheries development programmes. The great diversity in the organisation of fisheries departments in the states of India is described.