Kate J Willis

Diel vertical migration of Arctic zooplankton during the polar night

High-latitude environments show extreme seasonal variation in physical and biological variables. The classic paradigm of Arctic marine ecosystems holds that most biological processes slow down or cease during the polar night. One key process that is generally assumed to cease during winter is diel vertical migration (DVM) of zooplankton. DVM constitutes the largest synchronized movement of biomass on the planet, and is of paramount importance for marine ecosystem function and carbon cycling. Here we present acoustic data that demonstrate a synchronized DVM behaviour of zooplankton that continues throughout the Arctic winter, in both open and ice-covered waters. We argue that even during the polar night, DVM is regulated by diel variations in solar and lunar illumination, which are at intensities far below the threshold of human perception. We also demonstrate that winter DVM is stronger in open waters compared with ice-covered waters. This suggests that the biologically mediated vertical flux of carbon will increase if there is a continued retreat of the Arctic winter sea ice cover.

Mitochondrial DNA reveals multiple Northern Hemisphere introductions of Caprella mutica (Crustacea, Amphipoda)

Caprella mutica (Crustacea, Amphipoda) has been widely introduced to non‐native regions in the last 40 years. Its native habitat is sub‐boreal northeast Asia, but in the Northern Hemisphere, it is now found on both coasts of North America, and North Atlantic coastlines of Europe. Direct sequencing of mitochondrial DNA (cytochrome c oxidase subunit I gene) was used to compare genetic variation in native and non‐native populations of C. mutica. These data were used to investigate the invasion history of C. mutica and to test potential source populations in Japan. High diversity (31 haplotypes from 49 individuals), but no phylogeographical structure, was identified in four populations in the putative native range. In contrast, non‐native populations showed reduced genetic diversity (7 haplotypes from 249 individuals) and informative phylogeographical structure. Grouping of C. mutica populations into native, east Pacific, and Atlantic groups explained the most among‐region variation (59%). This indicates independent introduction pathways for C. mutica to the Pacific and Atlantic coasts of North America. Two dominant haplotypes were identified in eastern and western Atlantic coastal populations, indicating several dispersal routes within the Atlantic. The analysis indicated that several introductions from multiple sources were likely to be responsible for the observed global distribution of C. mutica, but the pathways were least well defined among the Atlantic populations. The four sampled populations of C. mutica in Japan could not be identified as the direct source of the non‐native populations examined in this study. The high diversity within the Japan populations indicates that the native range needs to be assessed at a far greater scale, both within and among populations, to accurately assess the source of the global spread of C. mutica.

The toxicity of emamectin benzoate, an aquaculture pesticide, to planktonic marine copepods

The acute and sublethal toxicity of emamectin benzoate to non-target planktonic marine copepods was determined. Emamectin benzoate is the active ingredient in Slice®, an in-feed pesticide formulation used to control parasitic sea lice in salmon aquaculture. The comparative sensitivity of three life stages (nauplii, copepodites, adults) of four common marine copepods (Acartia clausi, Pseudocalanus elongatus, Temora longicornis and Oithona similis) was assessed in 48-h exposures followed by a recovery period in toxicant-free sea water. The calanoid copepods responded similarly to emamectin benzoate and EC50 values were significantly lower than those for the cyclopoid O. similis. Nauplii and copepodite 48-h EC50 values were generally lower than those for the adults. EC50 values ranged from 0.12 μg/l (P. elongatus nauplii) to 232 μg/l (O. similis adults). The primary toxic effect, immobilisation, was generally irreversible. A 7-day sublethal test with adult A. clausi females measured a significant reduction in egg production at higher concentrations. The no-observed-effect-concentration (NOEC) and lowest-observed-effect-concentration (LOEC) values were 0.05 and 0.158 μg/l, respectively. Concentrations causing toxicity to planktonic copepods were considerably higher than Predicted Environmental Concentrations (PEC) in the vicinity of treated salmon farms and suggest that the use of emamectin benzoate for lice control is unlikely to adversely affect planktonic copepods.

Distribution of the introduced amphipod, Caprella mutica Schurin, 1935 (Amphipoda: Caprellida: Caprellidae) on the west coast of Scotland and a review of its global distribution

Caprella mutica Schurin, 1935 was first described from sub-boreal areas of north–east Asia. In less than 40 years C. mutica has spread throughout the northern hemisphere and the first recorded sighting in the southern hemisphere is reported here. Caprella mutica has been introduced to temperate oceanic coasts between latitudes of 25 and 70 °N. Outside its native range, C. mutica has only been found in areas of human activity, including ports, aquaculture facilities and an oilrig; the species has not yet been found in natural habitats. Shipping and aquaculture transfers are the most likely long distance vectors; recreational boating and drifting weed are the most likely short distance vectors. Temperature and salinity do not explain the small-scale distribution of C. mutica on the west coast of Scotland; globally its annual temperature range is 0–22°C. This suggests that the local scale distribution of C. mutica is potentially limited by the availability of suitable transportation vectors during the dispersal phase rather than by physical environmental factors following release.

Survivorship, growth and reproduction of the non-native Caprella mutica Schurin, 1935 (Crustacea: Amphipoda)

Caprella mutica Schurin is an epifaunal amphipod crustacean which originates in north-east Asia and has spread throughout the world, yet very little is known about fundamental aspects of this species biology. This paper examined the survivorship of C. mutica reared under laboratory conditions at 13–14 °C, 14 h light: 10 h dark photoperiod and fed commercial salmon feed, the diatom Cylindrotheca fusiformis Reumann and Lewin, the macroalgae, Fucus vesiculosus L. and given no additional feed. In addition, growth, maturation and reproduction of C. mutica fed C. fusiformis were assessed. No significant difference in survivorship of C. mutica was observed for the diet types over the experimental period. C. mutica was able to survive for upto 20 days without additional food. Average survival time of males and females fed the diatom, C. fusiformis was 68.8 d (range = 62–73 d) and 82.0 d (range = 76–92 d). Juvenile C. mutica emerged from the brood pouch at a body length of 1.33 mm and moulted at 5.0–11.0 day intervals. Males exhibited faster growth rates than females after Instar VII. Females produced their first brood at Instar VII, 24–26 days post-hatching and with an average body length of 8.5 mm. Each female had an average of two broods sequentially and these were released at 20.2 day intervals. Brood size for a single female increased from 11.3 (±9.9) hatchlings at Instar VII to 25.5 (±11.5) at Instar IX and the maximum number of hatchlings produced by a single female was 82. The results suggest that C. mutica exhibits a number of life-history traits that would potentially enable it to withstand global transportation and to rapidly become established in an introduced region, if environmental conditions are suitable.

Dinoflagellate cysts as proxies for palaeoceanographic conditions in Arctic fjords

Abstract The potential of using dinoflagellate cysts as proxies for palaeoceanographic conditions and as monitors of the dynamic marine environment of climatically sensitive Arctic fjords was investigated with sediment traps. Dinoflagellate cysts were analysed from three separate deployments in two high Arctic fjords in the Svalbard archipelago. Two deployments in Kongsfjorden on the west coast of Svalbard occurred during 2002 and 2006–2007 and a deployment in Rijpfjorden on the NE coast occurred during 2006–2007. The cyst production displayed peaks of abundance in the spring and late summer with distinct differences in cyst occurrence in different fjords and in different years. The recorded and identified cyst species were consistent both with the hydrography of the fjords and with changes in cyst composition that are comparable to the seasonal shifts in water mass characteristics. The presence of the heterotrophic species Protoperidinium conicum in Kongsfjorden during 2002 is of note and may reflect the availability of a particular food source possibly associated with the strong influx of Atlantic Water. Cysts recovered from Kongsfjorden during 2006–2007 were dominated by Islandinium minutum, an indicator of cold, polar to subpolar conditions. The temperature and salinity characteristics of the ambient hydrography in this period indicated less influence by Atlantic Water than in 2002, and the cyst production was consistent with regional cyst distribution patterns. In Rijpfjorden, cyst assemblages were dominated by Pentapharsodinium dalei, consistent with the fjord being dominated by full Arctic conditions during the mooring deployment and the possible occurrence of stratified water with high productivity during the spring phytoplankton bloom.

Seasonal population dynamics of the non-native Caprella mutica (Crustacea, Amphipoda) on the west coast of Scotland

Information on the life history and population dynamics of non-native species is essential to understand the process of invasion and impacts on invaded ecosystems. The non-native marine caprellid amphipod Caprella mutica has successfully established populations on coastlines throughout the temperate northern hemisphere and in New Zealand in the southern hemisphere. The introduction mechanism has been surpassed and it is now important to understand its ecology and biology in non-native habitats. The seasonal population dynamics of C. mutica were investigated over 18 months at four sites with different levels of anthropogenic disturbance on the west coast of Scotland. Abundance of C. mutica fluctuated seasonally at all sites, peaking during June to October. The highest abundance recorded on a single mesh collector was 319 000 individuals m-2 in August 2004 at one of the fish farms. Both seasonal and site-specific factors influenced the population dynamics of C. mutica. Both males and females were significantly larger and more abundant at the fish farm sites. Individuals displayed reproductive characteristics at a smaller size at the fish farm sites, indicating earlier maturity. The results suggest that anthropogenic disturbance and artificial resource enhancement contribute to the global establishment success of non-native C. mutica.

A new generation of biocides for control of crustacea in fish farms

Farming of salmon has become a significant industry in many countries over the past two decades. A major challenge facing this sector is infestation of the salmon by sea lice. The main way of treating salmon for such infestations is the use of medicines such as organophosphates, pyrethrins, hydrogen peroxide or benzoylphenyl ureas. The use of these medicines in fish farms is, however, highly regulated due to concerns about contamination of the wider marine environment. In this paper we report the use of photochemically active biocides for the treatment of a marine copepod, which is a model of parasitic sea lice. Photochemical activation and subsequent photodegradation of PDAs may represent a controllable and environmentally benign option for control of these parasites or other pest organisms in aquaculture.

Impacts of mosquitofish, Gambusia affinis, on black mudfish, Neochanna diversus.

Abstract The potential for western mosquitofish, Gambusia affinis, to negatively affect populations of black mudfish in New Zealand wetlands was investigated with annual fishing surveys of the Whangamarino wetland and by laboratory experiments evaluating competition and predation of mosquitofish on mudfish adults and larvae. Abundance of mudfish juveniles was reduced in the presence of mosquitofish at marginal wetland sites close to permanent water, but mosquitofish were not found at ephemeral adult mudfish habitats. In constructed wetland microcosms, mosquitofish reduced both growth and condition of post‐larval mudfish but did not attack or kill mudfish. In laboratory aquaria, mosquitofish rapidly consumed mudfish fry but survival time of the latter was significantly extended by an increase in density of submerged structures and by the presence of an alternative food source for mosquitofish. Because mosquitofish cannot survive in ephemeral wetlands that dry over summer, the impacts of mosquitofish on mudfish are likely to be minimal except in habitats where mosquitofish can survive year‐round owing to the presence of permanent standing water.