Biochemical composition of the isopod Mesidotea entomon (Linnaeus) from the western Arctic

Summary Changes in biochemical composition were determined for the isopod Mesidotea entomon (Linnaeus) from two differing ecological habitats in the western Arctic. Isopods from Pauline Cove, Yukon Territory, showed quantitative differences in total lipid and carbohydrate compared with those of similar body size from Dolomite Lake, Northwest Territories. Total chitin, ash, and protein were similar in isopods from both sites. A seasonal accumulation of protein and lipid was observed in isopods from Dolomite Lake prior to the onset of winter. The roles of ecological habitat, season, parasitism, nutritional and reproductive cycles in the organic composition of M. entomon are discussed.     

Size-selective predation by fourhorn sculpin,Myoxocephalus quadricornis (L.) (Pisces) on Mesidotea entomon (L.) (Crustacea,Isopoda)

During three different seasons Mesidotea entomon specimens from fourhorn sculpin stomachs were analyzed, and compared with the M. entomon population in the field. The field samplings were carried out in the northern Bothnian Sea. Feeding experiments revealed fourhorn sculpins to be highly selective when feeding on M. entomon.The fourhorn sculpin most preferably selected large M. entomon in the field as well as in the laboratory experiments. The preference for large M. entomon remained after correction for availability of differently sized M. entomon. In summer the actual sizes of M. entomon eaten by fourhorn sculpin were smaller than in autumn and winter. During all three seasons the oldest M. entomon were the ones most preferred. Ultimate effects of predation by fourhorn sculpin on the life-history of M. entomon are discussed.     

Effects of large Saduria entomon (Isopoda) on spatial distribution of their small S. entomon and Monoporeia affinis (Amphipoda) prey

We performed laboratory experiments to investigate the effects of predator avoidance and numerical effects of predation on spatial distribution of small Saduria entomon (Isopoda) and Monoporeia affinis (Amphipoda), with large S. entomon as predators. The horizontal distribution and mortality of the prey species, separately and together, were studied in aquaria with a spatial horizontal refuge. We also estimated effects of refuge on mortality of small S. entomon and M. affinis by experiments without the refuge net. In addition, we investigated whether predation risk from large S. entomon influenced the swimming activity of M. affinis, to clarify the mechanisms behind the spatial distribution. Both small S. entomon and M. affinis avoided large S. entomon. The avoidance behaviour of M. fffinis contributed about 10 times more to the high proportion in the refuge than numerical effects of predation. Due to the low mortality of small S. entomon the avoidance behaviour of this species was even more important for the spatial distribution. The combined effect of avoidance behaviour and predation in both species was aggregation, producting a positive correlation between the species in density. M. affinis showed two types of avoidance behaviour. In the activity experiments they reduced activity by 36% and buried themselves in the sediment. In the refuge experiments we also observed avoidance behaviour with the emigration rate from the predator compartment being twice the immigration rate. The refuge did not lower predation mortality in M. affinis, probably due to the small scale of the experimental units in relation to the mobility of the species. Predation mortality in small S. entomon was higher in absence of a refuge and especially high in absence of M. affinis.     

Growth and reproduction of an estuarine population of the colonial hydroidCordylophora caspia (Pallas) in the northern Baltic Sea

Growth and reproduction of the colonial hydroidCordylophora caspia were monitored during the breeding season in natural conditions. In 1987, a life history study was carried out on the upright stems of the main stolon. Mean size of uprights varied cyclically. The first peak coincided with the peak number of sexual hydranths, after which the mean upright length decreased, possibly indicating somatic costs of sexual reproduction. Extrinsic factors like flooding may also have contributed to cyclical changes in upright size. In 1988 and 1989, colonies were reared on experimental plates in the estuary. In 1988, colonies grew until mid July, after which they regressed to a dormant condition and then started growing again in mid August. Predation and space competition are discussed as possible causes for this dormancy in the middle of the growing season. In 1989, colonies grew continually, with the exception of a decline in colony biomass and number of feeding hydranths at the end of July, just following the peak of sexual reproduction. Sexual reproduction started in the early stages of colonial development for all years. During early summer,C. caspia allocated resources simultaneously in colonial growth and sexual reproduction. However, sexual reproduction had a clear peak in mid summer, and thereafter sexual reproduction ceased while colonial growth continued.     

Direct and indirect effects of predation by Saduria entomon (Isopoda) on the size-structure of Monoporeia affinis (Amphipoda)

We performed a 6-month laboratory experiment to investigate the direct and indirect effects of predation by the benthic invertebrate predator Saduria entomon on the growth and survival of Monopreia affinis prey individuals in different age-cohorts at low and high prey densities. The experimental results were compared with changes of growth and abundance in corresponding age-cohorts of M. affinis at sites with different S. entomon and M. affinis densities in the deep sublittoral zone of the Bothnian Sea during the same year. In the experiment, the presence of S. entomon reduced growth rate of M. affinis in the 1-year and 2-year age-cohorts at low amphipod density. Increased refuge use by M. affinis, expressed as a decrease in swimming activity in the presence of S. entomon, is suggested to have reduced feeding rate and therefore growth of the amphipods. The recruitment of M. affinis offspring was reduced in presence of S. entomon. In the field, the growth rate of amphipods in the 1-year cohort increased with increasing S. entomon density at low amphipod density. We found no corresponding increase of M. affinis growth in the 2-year cohort. The positive effect on 1-year amphipod growth indicated that predation reduced intra-cohort competition of M. affinis and increased growth of surviving prey at high predator density. In both the experiment and the field data we found indications of size-selective predation on smaller M. affinis specimens. This was because of the changed ratio between number of individuals in the juvenile age-cohorts and lower recruitment of amphipod offspring connected to S. entomon density. The experimental results and field data suggest that predation by S. entomon may have both direct and indirect effects on the size-structure of M. affinis populations. Received: 22 June 1998 / Accepted: 15 March 1999     

Seasonal abundance and reproduction of clausocalanid copepods in the northern Gulf of Aqaba (Red Sea)

Clausocalanid copepods dominate subtropical mesozooplanktoncommunities. Their life cycles, however, are generally unknown.Here, we follow the seasonal population development and reproductivebiology of Red Sea clausocalanids in the northern Gulf of Aqaba,between February 2002 and December 2003. Monthly vertical haulstaken with a Nansen net (200-µm mesh size) between 100m and the surface revealed four species, including a new record(Clausocalanus minor) for the area. Ctenocalanus vanus abundancespeaked during winter and spring, followed by Clausocalanus farranipeaking in spring and, additionally, in June 2003. In 2002,the abundance of Clausocalanus furcatus showed no distinct seasonaldevelopment of abundance, whereas in 2003, it reached high densitiesin January, July and November. Overall, C. vanus dominated theclausocalanid community during the first half of the year andC. furcatus during the second half of the year, whereas thepercentage of C. farrani remained fairly stable throughout bothyears. The correlation between the environmental parameters(temperature and chlorophyll a concentration) and the proportionof mature gonads was significant only between C. vanus and temperature.Incubation experiments showed that egg production rates variedbetween 0–3.3 and 1.8–9.2 eggs female^–1 day^–1in C. farrani and C. furcatus, respectively. Endoparasitismby dinoflagellates and the occurrence of intersexes were foundin all three species, with C. farrani being the most affected.     

Further observations on flagellates within sea ice in northern Bothnian Bay, the Baltic Sea

To improve our knowledge of flagellates inhabiting the Baltic Sea ice and water column during the winter, material was obtained from northern Bothnian Bay in March/April 1995. Light microscopical observations on live and fixed material and further transmission electron microscopy of whole mounts revealed 47 nanoflagellate taxa. In addition, detached scales of eight taxa were encountered. It is now evident that nearly all nanoflagellate classes are present within Bothnian Bay sea ice. The most common groups were cryptomonads, dinoflagellates, chrysophytes, prasinophytes, choanoflagellates and heterotrophic flagellates of unknown systematic position (Protista incertae sedis). Most flagellates in Baltic Sea ice biota apparently thrive in both the water column and the sea ice, while some, e.g. Paraphysomonas spp. (Chrysophyceae), heterotrophic euglenids, volvocalean chlorophytes, and some taxa of uncertain systematic affinity, are more frequently found within the sea ice. Received: 9 February 1997 / Accepted: 23 September 1997     

Denitrification and N2O effluxes in the Bothnian Bay (northern Baltic Sea) river sediments as affected by temperature under different oxygen concentrations

Denitrification rates and nitrous oxide (N₂O) effluxes were measured at different temperatures and for different oxygen concentrations in the sediments of a eutrophied river entering the Bothnian Bay. The experiments were made in a laboratory microcosm with intact sediment samples. ¹⁵N-labelling was used to measure denitrification rates (Dw). The rates were measured at four temperatures (5, 10, 15 and 20°C) and with three oxygen inputs (<0.2, 5, and 10 mg O₂ l⁻¹). The temperature response was highly affected by oxygen concentration. At higher O₂ concentrations (5 and 10 mg O₂ l⁻¹) a saturation over 10°C was observed, whereas the anoxic treatment (<0.2 mg O₂ l⁻¹) showed an exponential increase in the temperature interval with a Q ₁₀ value of 3.1. The result is described with a combined statistical model. In contrast with overall denitrification, the N₂O effluxes from sediments decreased with increasing temperature. The N₂O effluxes had a lower response to oxygen than denitrification rates. The N₂O/N₂ ratio was always below 0.02. Increased temperatures in the future could enhance denitrification rates in boreal river sediments but would not increase the amount of N₂O produced.     

Growth and reproduction of the wedge clam (Donax trunculus) in the Sea of Marmara, Turkey

Reproduction, growth and mortality of the wedge clam Donax trunculus were studied in an unexploited population in the northern part of the Sea of Marmara. Age determination was based from counting shell increments by inspection of both the external ring structure and the internal structure on thin cross-sections of the shell. Maximum life span was observed as 6 years for the studied population, but 4 years (shell length 40–41 mm) were usually not exceeded. Maximum length was 44.8 mm. Growth parameters were estimated as L _∞   = 44.15 mm, k  =   0.62 year⁻¹, C  = 1 and WP = 0.83 from external ring structure, and L _∞   = 42.44 mm, k  =   0.75 year⁻¹, C  = 1 and WP = 0.79 from internal growth bands (thin section). Natural mortality ( M ) was estimated as 0.98 year⁻¹. Sex ratio was not significantly different from 1 : 1. The monthly maturation process was assessed macroscopically and from variation in the mean total ash-free dry weight per shell weight of adult individuals. Spawning occurred between April and July with a peak between May and June. The recruitment pattern was unimodal.     

Shade-adapted Algae beneath Ice and Snow in the Northern Bothnian Sea

The winter-spring phytoplankton flora in the coastal waters of the northern Bothnian Sea consists mainly of marine cold water species even adapted to low light. These dinoflagellates and diatoms seem to be selectively promoted by the seven months of low light and water temperature. They are able to grow during this period of subsaturated light and have their abundance maxima around ice-break. Solar radiation measured under ice and snow cover was in the same order of magnitude as the compensation points of some of the species. In summer, these algae species vanish from the water, and surely survive in the form of inactive life stages.     

Egg size and composition in Ceratoserolis (Crustacea: Isopoda) from the Weddell Sea

Summary Samples of ovigerous female Ceratoserolis trilobitoides carrying newly spawned (stage A1) eggs in the marsupium were obtained from Borge Bay; Signy Island (South Orkney Islands), the continental shelf near Elephant Island (South Shetland Islands), and two sites in the inner Weddell Sea. The dry mass of a newly spawned egg was greater at the inner Weddell Sea sites even when the larger size of the females from the Weddell Sea and the positive relationship between egg size and female size were taken into account. Larger eggs contained more yolk, and there was a slight but significant tendency for larger eggs to have a lower percentage nitrogen content. Eggs from Ceratoserolis meridionalis were smaller in size than sympatric Ceratoserolis trilobitoides, but of similar composition. The reason for a greater investment per egg by females at higher latitudes is not clear, but it may be related to a slightly longer development period, itself associated with the lower water temperatures in the inner Weddell Sea.Data presented here were collected during the European Polarstern Study (EPOS) sponsored by the European Science Foundation     

Eye function of Mysidacea (Crustacea) in the northern Baltic Sea

Eye spectral sensitivity, [S(lambda)], was measured in seven northern Baltic mysid species using an electroretinogram technique. Their S(lambda) curves were compared with the spectral distribution of underwater light at their normal habitats. In the littoral species Neomysis integer, Praunus flexuosus and Praunus inermis, the S(lambda) maxima, [S(lambda)(max)], were in the wavelength-bands of 525-535, 505-515 and 520-530 nm respectively. The neoimmigrant species Hemimysis anomala had a S(lambda)(max) around 500 nm and high sensitivity at 393 nm, possibly indicating UV-sensitivity. S(lambda) of the pelagic species Mysis mixta and Mysis relicta sp. II was at about 505-520 nm. M. relicta sp. I from Pojoviken Bay and fresh water humic Lake P??j?rvi had S(lambda)(max) at approximately 550 nm and 570 nm respectively. This is in accordance with a similar long-wavelength shift in light transmittance of the respective waters. The eyes of the latter population were also damaged by strong light. The pontocaspian neoimmigrant H. anomala is clearly adapted to waters transmitting more blue light.     

A Red List of terrestrial isopods (Isopoda: Oniscidea) in Flanders (northern Belgium) and its implications for conservation

Journal of Insect Conservation - Although diversity and abundance of arthropods have been shown to decline globally, they are underrepresented in nature conservation efforts and policies....     

Marine reserves along the Sinai Peninsula (northern Red Sea)

The coral world of the northern Red Sea, situated along the shallow waters of the Sinai Peninsula, has been intensively investigated by Israeli scientists during the last decade. Many aspects of these investigations revealed the presence of unique ecosystems which developed mainly after the last postglacial period less than 10,000 years ago! At this time the cooling of the ambient waters swept out most of the neopleistocenic coral formations, and all the richness and diversity of species observed today evolved after those profound events. At present, typical ecoformations, in which the corals comprise the main part, are found in the northern part of the Gulf of Aqaba, around the southern tip (Tiran Straits) of the Sinai Peninsula, and in the shallow parts of the Gulf of Suez. In 1967 teams of our scientists investigated the marine habitats, and a number of marine parks and sanctuaries, protected by law, have been established. Thus destruction of unique faunal elements is being prevented. Today, with the withdrawal of Israel and the return of Egypt to its territories, such parks should receive much attention and remain protected habitats for the benefit of nature and mankind.     

Growth, condition and reproduction in the Impala ram (Aepyceros melampus)

The relationship between reproductive activity, body growth and condition in the male Impala is examined. Body growth is described by the use of the von Bertalanffy equation, and asymptotic values for each parameter are given together with the age at which these are attained. Seasonal changes in body condition are determined by the use of the kidney index and the fat content of the bone marrow, and this is related to body weight and the time of the rut. Growth and development of the reproductive organs with age and season are described in relation to reproductive activity.     

Distribution and abundance of fish larvae in the northern Ionian Sea (Eastern Mediterranean)

The purpose of this paper was to study the spatial distribution, abundance and composition of fish larvae in the northern Ionian Sea. Samples were collected to the 600 m depth with an electronic multinet BIONESS during the “INTERREG Italia-Grecia” oceanographic cruise carried out in March 2000 off the Apulian Italian coast. A total of 46 species of teleost early stages were collected, belonging to 38 genera and 22 families. Over 52% of the larvae identified were mesopelagic species, almost 27% were demersal and about 21% pelagic. A total of 307 myctophids, 69 clupeids and 61 gadid post-larvae dominated the community. Benthosema glaciale (mean 6.1 mm SL) was the most abundant species (21.6%), the most frequent in the samples (28.8%), and dominant in the whole study area (mean 1.4 ind/100 m³). Particular attention was given to the horizontal and vertical distribution and abundance of the three dominant post-larval species: Benthosema glaciale, Sprattus sprattus sprattus and Notoscopelus elongatus. The Pearson coefficient (R = 0.734) showed a high correlation between total zooplankton and fish larval assemblages in terms of spatial distribution abundance values. Regarding the vertical distribution of fish larvae, Sorensen’s index (S = 0.69) showed that fish larvae and total zooplankton abundance peaks co-occurred along the water column.     

Cadmium tolerance and adsorption by the marine brown alga Fucus vesiculosus from the Irish Sea and the Bothnian Sea

Cadmium (Cd) uptake capacities and Cd tolerance of the marine alga Fucus vesiculosus from the Irish Sea (salinity 35 psu) and from the Bothnian Sea (northern Baltic, 5 psu) were quantified. These data were complemented by measurements of changes in maximal photosynthetic rate (P(max)), dark respiration rate and variable fluorescence vs. maximal fluorescence (F(v):F(m)). At concentrations between 0.01 and 1 mmol Cd l(-1), F. vesiculosus from the Bothnian Sea adsorbed significantly more (about 98%) Cd compared with F. vesiculosus from the Irish Sea. The photosynthetic measurements showed that the Bothnian Sea F. vesiculosus were more sensitive to Cd exposure than the Irish Sea algae. The algae from the Irish Sea showed negative photosynthetic effects only at 1 mmol Cd l(-1), which was expressed as a decreased P(max) (-12.3%) and F(v):F(m) (-4.6%). On the contrary, the algae from the Bothnian Sea were negatively affected already at Cd concentrations as low at 0.1 mmol Cd l(-1). They exhibited increased dark respiration (+11.1%) and decreased F(v):F(m) (-13.9%). The results show that F. vesiculosus from the Bothnian Sea may be an efficient sorption substrate for Cd removal from Cd contaminated seawater and this algae type may also have applications for wastewater treatment.