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Coastal embayments are at risk of impacts by climate change drivers such as ocean warming, sea level rise and alteration in precipitation regimes. The response of the ecosystem to these drivers is highly dependent on their magnitude of change, but also on physical characteristics such as bay morphology and river discharge, which play key roles in water residence time and hence estuarine functioning. These considerations are especially relevant for bivalve aquaculture sites, where the cultured biomass can alter ecosystem dynamics. The combination of climate change, physical and aquaculture drivers can result in synergistic/antagonistic and nonlinear processes. A spatially explicit model was constructed to explore effects of the physical environment (bay geomorphic type, freshwater inputs), climate change drivers (sea level, temperature, precipitation) and aquaculture (bivalve species, stock) on ecosystem functioning. A factorial design led to 336 scenarios (48 hydrodynamic × 7 management). Model outcomes suggest that the physical environment controls estuarine functioning given its influence on primary productivity (bottom-up control dominated by riverine nutrients) and horizontal advection with the open ocean (dominated by bay geomorphic type). The intensity of bivalve aquaculture ultimately determines the bivalve-phytoplankton trophic interaction, which can range from a bottom-up control triggered by ammonia excretion to a top-down control via feeding. Results also suggest that temperature is the strongest climate change driver due to its influence on the metabolism of poikilothermic organisms (e.g. zooplankton and bivalves), which ultimately causes a concomitant increase of top-down pressure on phytoplankton. Given the different thermal tolerance of cultured species, temperature is also critical to sort winners from losers, benefiting Crassostrea virginica over Mytilus edulis under the specific conditions tested in this numerical exercise. In general, it is predicted that bays with large rivers and high exchange with the open ocean will be more resilient under climate change when bivalve aquaculture is present.

The objective of this study was to determine whether osmotic pump delivery of 3,5,3′-triiodo-L-thyronine (T3), thyroid inhibitors (potassium iodide, methimazole, and thiourea), or gonadal hormones (estradiol-17β and testosterone) could modify the thyroidal status of wild Atlantic cod Gadus morhua. Osmotic pumps implanted intraperitoneally delivered on average 3% (SE = 0.5%) of their initial volume per day under the experimental conditions (depth, 25 m; temperature, 5.2–7.6°C). The administration of T3 significantly increased serum levels of both T3 and L-thyroxine (T4). Treatment with either methimazole or thiourea significantly depressed serum T3 levels to about 55% of control values, whereas treatment with testosterone significantly reduced T4 levels to about 35%. We conclude that the delivery of thyroid or antithyroid agents by osmotic pumps is an effective means for creating experimental hyper- or hypothyroidism in wild Atlantic cod.