Global warming is widely recognized as a key driver of current and future changes in marine ecosystems. Parasitic trematodes are highly sensitive to temperature changes, which can lead to drastic impacts on surrounding communities. Copiatestes spp. (Family Syncoelidae) are relatively little-known trematodes with atypical life cycles that have been associated with a mass mortality event of seabirds in the Chatham Islands. As they forage at sea, seabirds get their legs tangled with the sticky, free-living infective stages of Copiatestes, which impairs their ability to take off and land. We tested the impact of seasonally fluctuating sea temperature on the dynamics of Copiatestes thyrsitae at various life stages (infecting second-intermediate host, Nyctiphanes australis euphausiid, and the third free-living infective stage in the water column) by sampling plankton biweekly for 12 months in Otago Harbour, New Zealand. We reveal that higher temperatures are significantly correlated with increases in prevalence and abundance of Copiatestes infections in euphausiids, with a rapid response observed within days to weeks following temperature increases. No correlation was observed between temperature and abundance of free-living stages. Infected euphausiids were smaller in size compared to uninfected individuals. The higher infection levels in euphausiids following warmer temperatures suggest a heightened risk of entanglement for coastal seabirds at these times. Smaller-bodied, surface-feeding seabird species that consume euphausiids are particularly at risk of entanglement. Our findings suggest that even short-term heatwaves can lead to higher risk of seabirds being entangled with Copiatestes filaments, with potentially dire ecological consequences during mass parasite releases.

There are currently at least six commercial fisheries harvesting six different species of euphausiid, or krill: Antarctic krill (Euphausia superba), fished in the Antarctic; North Pacific krill (Euphausia pacifica), fished off Japan and off western Canada; Euphausia nana, fished off the coast of Japan; Thysanoessa inermis, fished off the coast of Japan and off eastern Canada; and Thysanoessa raschii and Meganyctiphanes norvegica which have been experimentally harvested off eastern Canada. The current world catch of all species of krill is over 150 000 tonnes per annum but few fisheries are being exploited to their maximum theoretical potential. The size of the world krill harvest is currently limited by lack of demand, although some fisheries are being deliberately managed at low levels because of ecological concerns. We have outlined the history of these krill fisheries to determine where there are common trends and issues which will affect their future development. Krill products are currently mostly used for the aquaculture and sport fishing market but considerable effort has also been put into developing products for human consumption, partiularly from Antarctic krill. The future development of krill fisheries is examined in the light of information on trends in krill products which include pharmaceutical and industrial uses in addition to nutritional products. Because of the central ecological role of krill in many marine ecosystems, the subject of krill harvesting is a sensitive issue and krill fisheries require careful management. This requirement has spawned an innovative international management regime in the Antarctic - the Convention for the Conservation of Antarctic Marine Living Resources (CCAMLR) - which has developed procedures for managing the harvest of Antarctic krill that may be applicable to other fisheries. The common problems of managing krill fisheries are outlined particularly those relating to the role of krill in many coastal ecosystems, and as prey for many other species which are commercially fished.