Consumer stress models of ecological theory predict that predators are more susceptible to stress than their prey. Intertidal mussels, Mytilus californianus, span a vertical stress gradient from the low zone (lower stress) to the high zone (higher thermal and desiccation stress), while their sea star predators, Pisaster ochraceus, range from the low zone only into the lower edge of the mussel zone. In summer 2003, we tested the responses of sea stars and mussels to environmental stress in an experiment conducted on the Oregon coast. Mussels were transplanted from the middle of the mussel bed to cages in the low and high edges of the mussel bed. Sea star predators were added to half of the mussel cages. Mussels and sea stars were sampled between June and August for indicators of sublethal stress. Mussel growth was measured, and tissues were collected for heat shock protein (Hsp70) analyses and histological analyses of reproduction. Sea stars were weighed, and tissues were sampled for Hsp70 analyses. Mussels in high-edge cages had higher levels of total Hsp70 and exhibited spawning activity earlier in the summer than mussels in the low-edge cages. Sea stars suffered high mortality in the high edge, and low-edge sea stars lost weight but showed no differences in Hsp70 production. These results suggest that stress in the intertidal zone affected the mobile predator more than its sessile prey, which is consistent with predictions of consumer stress models.
Nile tilapia Oreochromis niloticus are routinely transported 1,200–1,400 km from Idaho to live markets in the greater Vancouver, British Columbia, area. Direct hauling mortality is typically very low, but significant economic losses occur during retail holding owing to a deterioration in physical appearance that results in fish that cannot be sold and their subsequent mortality. To address this problem, information was collected on hauling systems and protocols, holding systems and water management protocols, and water quality in the retail holding systems. During hauling, fish are exposed to high levels of dissolved oxygen, carbon dioxide, and bacteria. The transfer of fish from hauling systems to retail holding systems can subject them to rapid changes in temperature, dissolved oxygen, carbon dioxide, and pH. Problem areas in retail holding include low water temperatures, high un‐ionized ammonia concentrations, and elevated levels of gas supersaturation. Determination of the causes of high mortality in transportation and retail holding is difficult to clearly identify because of sampling difficulties and commercial restrictions; improvements in hauling protocols may depend on simulated hauling experiments followed by commercial verification.
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