Variability In Abundance Vertical-Distribution And Ontogenetic Migrations Of Thysanoessa-Longicaudata (Crustacea Euphausiacea) In The Northeastern Atlantic-Ocean

The vertical distribution, seasonal and ontogenetic migrations and seasonal variability in abundance of Thysanoessa longicaudata (Krøyer) were investigated using the Longhurst-Hardy Plankton Recorder for a 4 yr period (March, 1971 to May, 1975) at Ocean Weather Station “I” (59°00′N; 19°00′W) in the north-eastern Atlantic Ocean. Of 8 species of euphausiids identified at this position, the vast majority were T. longicaudata (for example, 99.5% of the total euphausiids in 1972 belonged to this species). From March to October the majority of calyptopes, furciliae and adults of T. longicaudata were found in the upper 100 m. The major spawning occurred in spring at a water temperature of 9° to 10°C and calyptopes and furciliae appeared in late April, reaching their maximum abundance in May. There was no evidence of large-scale diurnal migrations, although an extensive ontogenetic migration of young developmental stages was observed. The eggs were found from 100 m down to 800 m, the maximum depth of sampling, and the vertical distribution of the three naupliar stages showed a “developmental ascent” as they matured. During the main reproductive period in May, over 70% of all nauplii were below 500 m while more than 94% of Calyptopis Stage I were above 500 m with their maximum abundance in the euphotic zone (0 to 50 m). Calyptopis Stage I is the first feeding stage and it is this stage which shows the largest ontogenetic migration. Brief descriptions of the egg and nauplii are given.

Population-Dynamics And Production Of Euphausiids. III Meganyctiphanes-Norvegica And Nyctiphanes-Couchi In The North-Atlantic Ocean And The North-Sea

Seasonal changes in abundance, size and aspects of the population structure of Meganyctiphanes norvegica (M. Sars) and Nyctiphanes couchi (Bell) are described from samples taken with the “Continuous Plankton Recorder” at 10 m depth over a 2 yr period (1966 and 1967) in the North Atlantic Ocean and the North Sea. M. norvegica lived for a maximum of just over 2 yr, and adults of both year-classes spawned during a limited breeding season in the spring or summer. N. couchi spawned over a prolonged breeding season, giving rise to a complex of cohorts with overlapping size ranges. It was concluded that 3 or 4 cohorts were spawned in each year and that the maximum life span was probably greater than 1 yr, although maturity may be attained in less than a year. Estimated annual production at 10 m depth for M. norvegica ranged from 0.80 to 18.74 mg m-3yr-1 and for N. couchi from 0.67 to 8.23 mg m-3yr-1. P:B ratios ranged from 1.3:1 to 6.3:1 for M. norvegica and 4.0:1 to 5.5:1 for N. couchi.

Calorific Ash Carbon And Nitrogen-Content In Relation To Length And Dry-Weight Of Parathemisto-Gaudichaudi (Amphipoda Hyperiidea) In The North-East Atlantic Ocean

The calorific, ash, carbon and nitrogen content, length and dry weight were determined for the hyperiid Parathemisto gaudichaudi (Guerin). Regression equations for all these variables were determined so that they can be estimated by calculation from measurements of length of the hyperiid. Mean values for total nitrogen and carbon were 7.79±0.85% and 36.80±4.18% of the dry weight, respectively. The carbon to calorific equivalent for P. gaudichaudi was 10.37 kcal g-1 carbon (9.13 kcal g-1 when corrected for nitrogen). The calorific value for ash-free adult P. gaudichaudi was 5.138 kcal g-1±1.309 (4.510 kcal g-1 when corrected for nitrogen). This large variation in the calorific content (coefficient of variation of 25.84%) can be accounted for largely by variation in the ash content (coefficient of variation of 21.84%). The calorific value determined for P. gaudichaudi is similar to that measured for other carnivorous crustaceans and adds support to the hypothesis that animals with high calorific content have a low fecundity and an energy-rich store which can be used as a buffer during unfavourable periods in their life.