Search for: All records

Abstract. The nitrogen (N) isotope composition (δ15N) of cold-water corals is a promising proxy for reconstructing past ocean N cycling, as a strong correlation was found between the δ15N of the organic nitrogen preserved in coral skeletons and the δ15N of particulate organic matter exported from the surface ocean. However, a large offset of 8 ‰–9 ‰ between the δ15N recorded by the coral and that of exported particulate organic matter remains unexplained. The 8 ‰–9 ‰ offset may signal a higher trophic level of coral dietary sources, an unusually large trophic isotope effect or a biosynthetic δ15N offset between the coral's soft tissue and skeletal organic matter, or some combinations of these factors. To understand the origin of the offset and further validate the proxy, we investigated the trophic ecology of the asymbiotic scleractinian cold-water coral Balanophyllia elegans, both in a laboratory setting and in its natural habitat. A long-term incubation experiment of B. elegans fed on an isotopically controlled diet yielded a canonical trophic isotope effect of 3.0 ± 0.1 ‰ between coral soft tissue and the Artemia prey. The trophic isotope effect was not detectably influenced by sustained food limitation. A long N turnover of coral soft tissue, expressed as an e-folding time, of 291 ± 15 d in the well-fed incubations indicates that coral skeleton δ15N is not likely to track subannual (e.g., seasonal) variability in diet δ15N. Specimens of B. elegans from the subtidal zone near San Juan Channel (WA, USA) revealed a modest difference of 1.2 ± 0.6 ‰ between soft tissue and skeletal δ15N. The δ15N of the coral soft tissue was 12.0 ± 0.6 ‰, which was ∼6 ‰ higher than that of suspended organic material that was comprised dominantly of phytoplankton – suggesting that phytoplankton is not the primary component of B. elegans' diet. An analysis of size-fractionated net tow material suggests that B. elegans fed predominantly on a size class of zooplankton ≥500 µm, implicating a two-level trophic transfer between phytoplankton material and coral tissue. These results point to a feeding strategy that may result in an influence of the regional food web structure on the cold-water coral δ15N. This factor should be taken into consideration when applying the proxy to paleo-oceanographic studies of ocean N cycling. 

Abstract The Anthropocene has brought substantial change to ocean ecosystems, but whether this age will bring more or less marine disease is unknown. In recent years, the accelerating tempo of epizootic and zoonotic disease events has made it seem as if disease is on the rise. Is this apparent increase in disease due to increased observation and sampling effort, or to an actual rise in the abundance of parasites and pathogens? We examined the literature to track long‐term change in the abundance of two parasitic nematode genera with zoonotic potential:Anisakisspp. andPseudoterranovaspp. These anisakid nematodes cause the disease anisakidosis and are transmitted to humans in undercooked and raw marine seafood. A total of 123 papers published between 1967 and 2017 met our criteria for inclusion, from which we extracted 755 host–parasite–location–year combinations. Of these, 69.7% concernedAnisakisspp. and 30.3% focused onPseudoterranovaspp. Meta‐regression revealed an increase inAnisakisspp. abundance (average number of worms/fish) over a 53 year period from 1962 to 2015 and no significant change inPseudoterranovaspp. abundance over a 37 year period from 1978 to 2015. Standardizing changes to the period of 1978–2015, so that results are comparable between genera, we detected a significant 283‐fold increase inAnisakisspp. abundance and no change in the abundance ofPseudoterranovaspp. This increase inAnisakisspp. abundance may have implications for human health, marine mammal health, and fisheries profitability.