The calanoid copepod Acartia italica Steuer, phenomenon in the small saline Lake Rogoznica (Eastern Adriatic coast)

Lake Rogoznica, near ibenik, Croatia, is a salt coastal lakewith a maximum depth of about 15 m. During most of the year,this small, naturally eutrophied lake is highly stratified,with hypoxia/anoxia occurring in the bottom layer. Total anoxia,with the presence of hydrogen sulphide, was recorded on September27, 1997. At that moment, massive mortality of all planktonicand benthic organisms was observed. After the anoxia, Acartiaitalica, the only planktonic copepod species of the lake, re-establishedquickly. Before anoxia, the population dynamics of the A.italicapopulation depended primarily on predator/prey relationships.However, in the post-anoxic period, nutrient–phytoplankton–copepodrelationships became more important, as there was no longerany predation pressure. From all accounts, it would appear thatonly A.italica is adapted to the extreme conditions which appearfrom time to time in the lake, and that this species has animportant role in the functioning of the lake ecosystem. Acartiaitalica was very important for the gradual normalization oflife in the lake after total anoxia.     

Vertical distribution of protozoan and microcopepod communities in the South Adriatic Pit

The qualitative composition, numerical abundance and verticaldistribution of radiolarians, tintinnines, nauplii and smallcopepod assemblages were studied in the central area of theSouthern Adriatic Pit at three stations during 10 cruises fromOctober 1985 to May 1990. The samples were collected with aplankton net of 53 µm mesh size equipped with a closingsystem in eight vertical layers. Data are presented for 53 radiolarians,61tintinnines and for the first time for 22 poecilostomatoidspecies in the Adriatic Sea. According to the numerical abundanceof assemblages and the frequency of occurrence of the bulk ofthe individual species population in the water column, fourcommunities could be defined: the surface (0–50 m), thesubsurface (50–100m), the midwater (100–600 m) andthe deep-sea community (below 600 m). The euphotic layer wascharacterized by tintinnines, copepod nauplii, cyclopoids andjuvenile calanoid copepods, while radiolarians and poecilostomatoidcopepods dominated in the deeper layers. The highest numericaldifferences between stations and seasons were noted only onthe surface. Towards the deeper layers, the differences wereconstantly smaller, and below400 m there was a uniform distributionof all assemblages. This research, on the basis of the numericalabundance of protozoans and micrometazoans, shows that the centralpart of the South Adriatic Pit is considerably richer than mentionedby earlier authors.     

Mesaiokeras hurei n. sp. (Copepoda, Calanoida, Mesaiokeratidae) from the Adriatic Sea

A new species of Mesaiokeras is described from the hyperbenthosof Veliko Jezero, a marine lake on the island of Mljet, Croatia.This is the first species of this genus and family (Mesaiokeratidae)reported from the Adriatic and Mediterranean seas. It is characterizedby small body length (an average 361 µm for females and337 µm for males), the low number of free segments (21)and the armature of the antennules, very long spine (a₂) ofexopodite I of female right leg 4, the presence of long processeson the ventroposterior area of the female genital double-somite,the form and surface ornamentation of the genital area, theform and ornamentation of male and female leg 5, and the formand armature of caudal rami. This species was found in shallowwater with very stable hydrographic conditions and at a populationdensity from 1 to 26 ind. m^-3.     

Speleohvarella gamulini gen. et sp. nov., a new copepod (Calanoida, Stephidae) from an anchialine cave in the Adriatic Sea

A new copepod genus and species, Speleohvarella gamulini, collectedfrom the anchialine cave iva Voda on Hvar Island (Croatia),is described from both sexes. This is the first record of acalanoid copepod found in an Adriatic anchialine cave. The newgenus is distinguished from other Stephidae by a combinationof the following features: the cephalosome is separate fromthe first pedigerous somite, and the fourth and fifth pedigeroussomites are fused; the female urosome has 4 segments, the genitaldouble-somite is symmetrical and the caudal rami is asymmetricalwith the right longer than the left; antennules of both sexesare symmetrical and 24-segmented, with the fusion of ancestralsegments II–IV, X–XI and XXVII–XXVIII; theexopod of antenna is 7-segmented; 2 setae are present on thebasal exite of maxillule; in the male the right leg 5 is shortand 3-segmented, and the left leg elongate and 5-segmented.     

Gelatinous invertebrate zooplankton of the South Adriatic: species composition and vertical distribution

The species composition and vertical distribution of gelatinousinvertebrate zooplankton were investigated from April 1993 toJune 1994 in the 0–1000 m water column at a deep-sea stationin the northern part of the South Adriatic Pit. Fifty-sevenspecies were identified: 11 hydromedusae, 13 calycophores, 3ctenophores, 3 heteropods, 10 pteropods, 8 polychaetes and 9chaetognaths. The pteropod Desmopterus papilio and the heteropodProtatlanta mediterranea were recorded for the first time inthe Adriatic Sea. Data from this study differed from those ofprevious investigations in the South Adriatic as regards thenumerically dominant polychaete and pteropod species. All investigatedgroups generally were more abundant in the upper 100 m and decreasedwith depth. Different vertical distributions of life stageswere observed for those species that occupy a wide depth range:Persa incolorata, Solmissus albescens, Limacina inflata, Cymbuliaperoni, Pelagobia longicirrata, Sagitta lyra and Sagitta decipiens.     

Little known species of small Oncaeidae (Cyclopoida) from the South Adriatic

In the present paper the three poorly known species of smallOncaeidae (Oncaea longipes, O. minima, O. vodjanitskii are redescribed.The male O. minima is described for the first time.     

The family Xystonellidae (Ciliophora, Tintinnina) in the Adriatic Sea

This paper reports quantitative, horizontal and vertical distributiondata of the 11 species of the family Xystonellidae found inthe Adriatic Sea and in the Strait of Otranto. The samples werecollected in coastal and open waters, with a plankton net equippedwith a closing system, in the period from 1973 to 1986. At thedeeper stations of the South Adriatic Pit, hauls were takenin eight vertical layers, while at other stations sampling dependedon the respective depth of each station. Xystonellidae are oceanictintinnines, mainly present in the South Adriatic and the Straitof Otranto throughout the year. They are characteristic of SouthAdriatic and Eastern Mediterranean water masses. Horizontaldistribution of lower mesopelagic species is limited by the200 m isobath. Only sparse individuals of the upper mesopelagicand epipelagic species were found in the Jabuka Pit, probablydue to the late autumn and winter current. These species werenot registered to the north of this region. They were registeredbelow the 200 m depth as dominant tintinnines, while in summerthey represented an average of 81% of the total tintinnine population.     

Changes in the microzooplankton assemblages in the northern Adriatic Sea during 1989 to 1992

Microzooplankton were sampled at five fixed stations in theopen waters of the northern Adriatic during four cruises in1989, nine in 1990, six in 1991 and 12 in 1992. Changes in thequalitative-quantitative composition, together with the spatial-temporaldistribution of the microzooplankton assemblages in the northernwaters of the open Adriatic, were the result of atypical oceanographicand productivity conditions in the entire region of this sea.Owing to low values of ciliated protozoa, which comprised only26% (1989) and 36% (1991) of the total number of microzooplankton,primary production cannot be controlled through grazing. Thismay possibly explain the occurrence of marine snow. The presenceof the larger mucous aggregates in the later phase causes asignificant decrease in the density of the naupliar copepodpopulation. Therefore, the usual dominance of copepods in summerdoes not occur and their development cycle is displaced to lateautumn. Consequently, only Olihona nana, a species of widerecological tolerance, comprised up to 73% of the total numberof postnaupliar copepods during the presence of mucous aggregatesin 1989. Thus, this small copepod plays an important role inthe processes of remineralization in the northern Adriatic.     

A new type of zooplankton sampler

This paper describes a new, simple zooplankton sampler for quantitativesampling and studying the microdistribution of the mesozooplankton.