STUDIES OF MESOHERBIVORY IN AQUARIA AND IN AN UNBARRICADED MARICULTURE FARM ON THE CHINESE COAST1

The effects upon macrophytic and epiphytic algae of caprellid amphipods, including Caprella irregularis Mayer, and of gammarid amphipods, including Ampithoe lacertosa Bate, Jassa falcata (Montagu) and Pontogeneia rostrata Gurjanova, were studied in aquaria and in a coastal mariculture farm near Qingdao, People's Republic of China. The macrophytic species studied included Enteromorpha linza (L.) J. Agardh, Gracilaria asiatica Zhang & Xia, Gracilaria lemaneiformis (Bory) Weber-van Bosse and Scytosiphon lomentaria (Lyngbye) C. Agardh. These algae and amphipods were selected for study because of their local abundances. Aquarium experiments demonstrated that C. irregularis, J. falcata and P. rostrata feed on ephemeral/epiphytic algae. A. lacertosa (adults and juveniles) ate Gracilaria but preferred E. linza. The different species of amphipods had substantially different patterns of daily activity. Caprellids prevented epiphytic overgrowth of G. asiatica when added to plants in an experimental, openocean, mariculture farm, despite the presence of numerous amphipod predators (e.g. the fishes Hexagrammos otakii Jordan & Starks and Sebastes thompsoni Jordan & Hubbs). Periodic removals of all (naturally colonizing) amphipods from another group of plants in the farm resulted in heavy epiphytic overgrowth. Since these results were obtained in an unbarricaded mariculture farm, we conclude that mesoherbivores may have large effects upon algal community structure in temperate intertidal and subtidal habitats.     

Survivorship,growth and reproduction of the non-native <Emphasis Type="Italic">Caprella mutica</Emphasis> 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.     

Population dynamics of Caprella dilatata and Caprella equilibra (Peracarida: Amphipoda) in a Southwestern Atlantic harbour

We studied the population dynamics and reproductive biology of Caprella dilatata and Caprella equilibra in order to provide the basis for understanding the ecological role of both species in Mar del Plata Harbour. Caprellids and organisms from the fouling community were obtained by sampling in the harbour, monthly from April 2014 to March 2015. Mean density of C. dilatata was homogeneous during most of the study period (ca. 50–200 ind/100?g) and reached their maximum in May (ca. 650 ind/100?g), while C. equilibra did not show any differences during the sampling period (ca. 30 ind/100?g). Juveniles of C. dilatata reached their highest densities in May, while ovigerous females were at their maximum values in late spring, summer and early autumn, and no correlation was found between seawater temperature and monthly density. On the other hand, C. equilibra reached its maximum juvenile and ovigerous female densities in summer, and showed a positive correlation with seawater temperature. Sex-ratio was female biased in C. dilatata, but in C. equilibra it was equal between sexes. The number of eggs carried by females was positively correlated to the size in both species. The present study suggests that the population dynamics of C. equilibra are intimately related to seawater temperature, while for C. dilatata no relationship was found. Future studies of ecology and behaviour traits in caprellid species are needed in order to determine the ecological role and the environmental factors that could affect both species.     

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.     

Mass occurrence of an introduced crustacean (Caprella cf. mutica) in the south-eastern North Sea

The caprellid amphipod Caprella mutica is indigenous to coastal waters of north-east Asia and was first recorded in European waters in 1995. We now detected mass occurrences of > 3000 individuals per m² in harbours of the two islands of Sylt and Helgoland in the German Bight, North Sea. Currently, Caprella mutica seems to be restricted to artificial hard substrata but we expect it to become a new species in natural hard bottom assemblages of that region as well.