SUMMARYArctica islandica is the longest-lived non-colonial animal found so far, and reaches individual ages of 150years in the German Bight (GB) and more than 350years around Iceland (IC). Frequent burrowing and physiological adjustments to low tissue oxygenation in the burrowed state are proposed to lower mitochondrial reactive oxygen species (ROS) formation. We investigated burrowing patterns and shell water partial pressure of oxygen (P O2 ) in experiments with live A. islandica. Furthermore, succinate accumulation and antioxidant defences were recorded in tissues of bivalves in the normoxic or metabolically downregulated state, as well as ROS formation in isolated gills exposed to normoxia, hypoxia and hypoxia/reoxygenation. IC bivalves burrowed more frequently and deeper in winter than in summer under in situ conditions, and both IC and GB bivalves remained burrowed for between 1 and 6days in laboratory experiments. Shell water P O2 was <5kPa when bivalves were maintained in fully oxygenated seawater, and ventilation increased before animals entered the state of metabolic depression. Succinate did not accumulate upon spontaneous shell closure, although shell water P O2 was 0kPa for over 24h. A ROS burst was absent in isolated gills during hypoxia/reoxygenation, and antioxidant enzyme activities were not enhanced in metabolically depressed clams compared with normally respiring clams. Postponing the onset of anaerobiosis in the burrowed state and under hypoxic exposure presumably limits the need for elevated recovery respiration upon surfacing and oxidative stress during reoxygenation.

An ecosystem-based approach to bivalve aquaculture management is a strategy for the integration of aquaculture within the wider ecosystem, including human aspects, in such a way that it promotes sustainable development, equity, and resilience of ecosystems. Given the linkage between social and ecological systems, marine regulators require an ecosystem-based decision framework that structures and integrates the relationships between these systems and facilitates communication of aquaculture-environment interactions and policy-related developments and decisions. The Drivers-Pressures-State Change-Impact-Response (DPSIR) management framework incorporates the connectivity between human and ecological issues and would permit available performance indicators to be identified and organized in a manner that facilitates different regulatory needs. Suitable performance indicators and modeling approaches, which are used to assess DPSIR framework components, are reviewed with a focus on the key environmental issues associated with bivalve farming. Indicator selection criteria are provided to facilitate constraining the number of indicators within the management framework. It is recommended that an ecosystem-based approach for bivalve aquaculture be based on a tiered indicator monitoring system that is structured on the principle that increased environmental risk requires increased monitoring effort. More than 1 threshold for each indicator would permit implementation of predetermined impact prevention and mitigation measures prior to reaching an unacceptable ecological state. We provide an example of a tiered monitoring program that would communicate knowledge to decision-makers on ecosystem State Change and Impact components of the DPSIR framework.KEY WORDS: Bivalve aquaculture management · Ecosystem-based approach · DPSIR framework · Indicators · Thresholds · Benthic effects · Pelagic effects · Social-ecological systems Resale or republication not permitted without written consent of the publisher

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For centuries human populations have moved live shellfish around the world for consumption or aquaculture purposes; being relayed from their area of origin for growout or sale. This is in contrast to the inadvertent anthropogenic spreading of species via e.g. ballast waters. There are inherent risks associated with transfer of shellfish including introducing of alien species, diseases, pests, bacteria and viruses associated with the translocated species in addition to the potential impact on genetic integrity and biodiversity of local stocks. Many examples of severe ecological impacts have been documented worldwide owing to the intentional or unintentional translocation of animals. It is therefore important to develop risk reduction methods which have not yet been documented to be incorporated into current fish health or environmental legislation. This part of the study describes the impacts of transfer activities of cultured bivalve shellfish along the European Atlantic coast; identifies hitch hiker species, fouling organisms or infectious agents which can be translocated with a target species. Further, the study highlights the need for thorough, standard risk reduction measures designed to minimise the impact on ecosystems worldwide. In a companion paper details of actual transfer activities in Atlantic Europe are presented and all levels of legislation dealing with transfer activities on a global, regional and national scale are carefully reviewed. Highlights► We provide a full list of threats related to bivalve transfer activities. ► We draw the intention to the large spectrum of non-target species transferred with bivalves. ► We show the impact of transfers as potential vectors for the introduction of alien species. ► We provide detailed recommendations for a suitable risk assessment for impacts reduction.MS to be submitted Bivalve Aquaculture Transfers (Part B) 3

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