Dominant Crustacean Research Articles

Tropodiaptomus lateralis Kiefer, 1932 (Copepoda: Calanoida) in Oguta Lake, southeastern Nigeria

Tropodiaptomus lateralis is the dominant crustacean zooplankter of lake Oguta, in the Lower Niger delta of Nigeria. A redescription, will illustrations is given. Its apparently rare occurrence elsewhere in the River Niger system is discussed. Biotic (fish predation pressure), as well as abiotic (low conductivity, low turbidity) factors seem to be involved.

The 1980s – a decade of change in the Benguela ecosystem

Changes that occurred in sea surface and some deeper temperatures, surface winds, currents, plankton and some dominant crustacean (rock lobster Jasus lalandii), molluscan (squid Loligo vulgaris reynaudii and abalone Haliotis midae), fish (anchovy Engraulis capensis, pilchard Sardinops ocellatus, Cape hakes Merluccius spp., sole Austroglossus pectoralis, kingklip Genypterus capensis and various species of linefish) and seabird (Cape gannet Morus capensis) resources in the Benguela ecosystem in the 1980s are documented. Although fishing had a clear influence on changes in some of the resources, a wide spectrum of organisms, from plankton to top predators, were influenced directly or indirectly by the abiotic environment. Concurrent changes in many of the resources suggest that the same environmental change may impact on more than one. Simultaneous change throughout the Benguela system indicates that environmental forcing sometimes takes place over wide geographic areas. At the northern and southern extremities of the Benguela system, responses to environmental change may be different because processes through which the change is mediated are different.

Seasonality and abundance of some dominant crustacean zooplankton in Lake Awasa, a tropical rift valley lake in Ethiopia

The zooplankton of a Rift Valley lake in Ethiopia, Awasa, was sampled at 3 stations for 2 years (1986 and 1987) concurrently with various meteorological and limnological measurements. The spatial and temporal variation in abundance of some numerically dominant crustaceans, Mesocyclops aequatorialis similis (Copepoda), Thermocyclops consimilis (Copepoda) and Diaphanosoma excisum (Cladocera) is discussed. Temporal (months, sampling dates) rather than spatial (station) variability accounts for more than 50% of the total variance in zooplankton abundance but horizontal patchiness exists during periods of high zooplankton density. Sampling errors were generally low, except for counts of cyclopoid nauplii (subsampling) and Diaphanosoma (inter-replicate variance).

Zooplankton associations in Zimbabwe

The specific composition and diversity of the zooplankton in 18 impoundments in Zimbabwe were analysed on the basis of samples taken in July and August 1983. All the lakes lay at altitudes over 1200 m, with the highest at 2270 m.Thirty species of Rotifera and 20 species of Crustacea were identified, but the mean numbers of species per lake were 5·7 rotifers and 4·5 crustaceans. Some records represent considerable extensions of known ranges. Daphnia laevis was the most widespread and frequently dominant crustacean, while among the rotifers Keratella cochlearis was most frequently dominant, particularly in the lakes at the upper part of the altitudinal range.Ordination and cluster analysis of the associations revealed a group of lakes with closely interrelated similarities which could be attributed to their lying on tributaries of the same river system and receiving trout from the same hatchery. These analyses also picked out the lowest locality as the most divergent and the one showing the most typically tropical zooplankton association. Although all the lakes were well within the tropics, their altitudes seem to have excluded some of the widespread tropical African zooplankters.The possibility that these associations could be formed by random colonization is discussed and dismissed.The momentary species composition of these Zimbabwean zooplankton associations was similar to that given by Pennak (1957) for the world average, although the mean number of species of Copepoda was significantly lower than the world average. Comparisons with data from Brazil and Lake Maggiore indicate the need for a further geographical analysis.A comparative study of the species diversity in impoundments of different sizes indicates that, over several orders of magnitude of area, the number of species of Ciadocera and Copepoda shows a small increase, but the number of species of Rotifera shows a much larger and more variable increase.

POPULATION DYNAMICS OF THE SPONGE-DWELLING ALPHEID SYNALPHEUS LONGICARPUS, WITH OBSERVATIONS ON S. BROOKSI AND S. PECTINIGER, IN SHALLOW-WATER ASSEMBLAGES OF THE EASTERN GULF OF MEXICO

Investigations were conducted on species composition, population dynamics, and ecological interactions of alpheid shrimps associated with the loggerhead sponge Spheciospongia vesparia in shallow-water assemblages of the eastern Gulf of Mexico. Three species, Synalpheus brooksi, S. pectiniger, and the numerically dominant S. longicarpus were found in coexistence. Biomass and numbers of all three species found within the sponge were directly proportional to increasing sponge volume. Dominance of S. longicarpus, a eurythermal tropical species, is attributed to successful year-round reproduction. S. brooksi and S. pectiniger are fugitive species in this particular association. The latter species are able to colonize the habitat, but seasonal temperature minima by depressing egg production limit their ability to coexist in greater abundance. Coexistence of the three shrimp species appears to coincide with a wide degree of niche overlap. Potential competition for limited available space within the host may be intense and, combined with the differing reproductive success of each species, may be of considerable importance in determining population size and species composition of the associates. Sponges provide a unique habitat for a wide array of cryptic marine organisms. Previous studies have revealed the species composition of associates of various sponge species (Pearse, 1932, 1950; Fishelson, 1962; Dauer, 1973; Riitzler, 1976; Westinga and Hoetjes, 1981) and have examined the importance of sponge size, structure, and location (Long, 1968; Riitzler, 1976; Uebelacker, 1977; Westinga and Hoetjes, 1981) as factors affecting associated species composition. Many sponge species harbor abundant and consistently similar associations, yet little is known of the life history and dynamic role of many of these cryptic species within their particular host sponge. Loggerhead sponges, Spheciospongia vesparia (Lamarck) have been reported to harbor large populations of snapping shrimps of the genus Synalpheus (Decapoda: Alpheidae) (Coutiere, 1909, 1910; Pearse, 1932, 1950; Hoetjes et al., 1977; Westinga and Hoetjes, 1981; Dardeau, 1984). With the exception of Dobkin's (1965) description of the larvae of S. brooksi, the life history of most species of Synalpheus is poorly known. We report the population dynamics of three species of snapping shrimps: Synalpheus brooksi Coutiere, 1909, S. longicarpus (Herrick, 1891), and S. pectiniger Coutiere, 1907, which are dominant decapod crustacean inhabitants of the loggerhead sponge Spheciospongia vesparia in the eastern Gulf of Mexico. Relationships among associates and between associates and host were examined to obtain additional information regarding the life histories of these cryptic shrimps. DESCRIPTION OF STUDY AREA The coastal fauna of the Gulf of Mexico exhibits affinities of both warm temperate and tropical origin. Northern gulf fauna is Carolinian warm temperate, whereas the fauna of the southern Gulf is primarily Caribbean tropical in nature (Briggs, 1974; Lyons and Collard, 1973). Establishment of a distinct zoogeographic boundary is hampered by wide ranging temperatures and seasonally changing

Competition in zooplankton communities: Suppression of small species by Daphnia pulex1

The hypothesis that a large zooplankton herbivore, Daphnia pulex, can competitively reduce the abundance of resident zooplankton when colonizing a community of small species was tested in two lakes. When introduced to enclosures in eutrophic Larimore Pond, D. pulex decreased phytoplankton abundance by an order of magnitude, resulting in drastically reduced densities of Tropocyclops prasinus and Mesocyclops edax, the two dominant crustaceans in the pond. Daphnia pulex was also added to enclosures in oligo‐mesotrophic Dynamite Lake, along with nutrients, in a factorial design. Three Dynamite Lake zooplankters were reduced in density by D. pulex under both enriched and unenriched conditions: Bosmina longirostris, Trichocerca multicrinis, and copepod nauplii. Nutrient additions allowed these taxa to overcome some effects of competition with D. pulex. Daphnia pulex reduced the densities of copepods and rotifers common to both lakes more in eutrophic Larimore Pond than in unenriched Dynamite Lake enclosures.These results show that a large herbivore can reduce the density of some small zooplankton species and therefore contribute to the scarcity of small species in lakes dominated by large herbivores. Furthermore, the results suggest that the competitive effects of a large herbivore on rotifers and copepods may be more pronounced in eutrophic systems because the large species can attain a higher population density, and subsequently alter the resource base to a greater extent, in eutrophic systems.

Dynamics of a subtropical plankton community, with emphasis on the copepod Mesocyclops edax

The zooplankton community of a subtropical, eutrophic lake was studied over an annual cycle. Mesocyclops edax, the numerically dominant crustacean, exhibited a stationary age distribution for most of the year (July–March). Per capita growth rates (r) of M. edax approximated zero throughout most of the study, indicating a close correspondence between birth and death rates. High death rates in the spring and summer probably were due to intense predation, since physiological mortality was low and predators were abundant. Multiple regression analyses indicated that much of the variation in M. edax birth rates could be explained by abundance of their animal prey. Other plankton in this lake exhibited considerable seasonality, but not to the marked degree characteristic of temperate populations. The number of zooplankton species was low and cladocerans were scarce, as is characteristic of many eutrophic Florida Lakes.

Seasonal succession and vertical distribution of zooplankton in Lake Hayes and Lake Johnson

Seasonal variations in the species composition, abundance, biomass, and vertical distribution of zooplankton in two eutrophic, warm‐monomictic lakes are described for the period December 1969 to February 1972. In Lake Hayes, Boeckella dilatata was the dominant crustacean and Ceriodaphnia dubia was subdominant. Lake Johnson was dominated by Ceriodaphnia and Bosmina meridionalis and Boeckella were subdominant. Daphnia were common in spring in Lake Hayes, but very rare in Lake Johnson. Chydorus and Asplanchna appeared in summer in both lakes. Zooplankton were slightly more abundant in both lakes in 1971 than in 1970; the annual mean was 1.7 times higher in Lake Johnson than in Lake Hayes in both years. Biomass was highest in spring. In Lake Hayes it ranged from 0.7 to 4.6 g.m‐2 dry weight; in Lake Johnson it fluctuated in 1971 from 0.3 g.m‐2 in March to 7.4 g.m‐2 in November. Animals occurred at all depths during holomixis, but were nearer the surface during stratification. Vertical distribution was often bi...

The relation between the scattering layer and the Euphausiacea.

The source of the scattering effect is not, at present, susceptible of direct proof, but if an organism could be found whose characteristics agreed with those of the layer on a sufficient number of points, then there would be a high probability that this is the actual source of the effect. From the diurnal migration of the layer there seems no room for doubt that it is caused by an animal. Of the animal population of the sea, three groups seem considerably more probable than any others, namely, fish, squid, and crustacea. There are certain arguments which make the latter the most likely, and if experimental tests now in progress show that the crustacea meet the acoustical requirements, then there will be little reason to consider either fish or squid.Of the crustacea, the small copepods may prove to be the source of shallow reverberation and possibly some very shallow layers. Euphausid shrimps are the dominant crustacean at the depth of the main scattering layer. These and large red prawns are the dominant crustacea at the depth of a still deeper layer which is briefly referred to. Euphausids occupy the same day level as the main layer, and execute a similar diurnal migration. The dominant species of euphausid varies geographically, and each species has a characteristic day level. Where it has been possible to make a comparison, there is reasonably good agreement between the geographical trend of the daytime depth of the layer and dominance of deep- or shallow-living euphausids. The euphausid population is generally a complex of a number of species. The recording instrument used does not give sufficient definition to show a number of separate layers under such conditions. Certain areas were examined where there was a simpler euphausid population with only two abundant species, and these had different characteristic levels. The bathygrams from this area showed two distinct layers on a number of occasions. The scattering layer is usually confined to deep water, and disappears or is replaced by one with different characteristics in shallow water. This parallels the distribution of oceanic euphausids, but would probably apply equally well to other oceanic animals. The same is true of the correlation found in the Mediterranean between the decrease eastwards of the scattering effect and the similar decrease of the total plankton, including euphausids. The relation found between the level of the scattering layer and illumination, and the modification of this by temperature, is that which would be predicted for euphausids, but also for other planktonic animals. In one type of scattering layer, a reversed type of diurnal migration has been recorded, the layer descending in the evening and ascending in the morning. It is believed that certain euphausids behave in this way. Such reversal is rare in zooplankton and we do not, at present, know of any other organism which makes as extensive a reversed migration as this particular layer. The characteristics required in an organism which could be the source of the scattering effect are met, in all cases in which they have been tested, by euphausids. They are met in only some cases by other planktonic forms. There seems, therefore, to be a considerable probability that it is euphausids which cause the effect.In the section on the biology of euphausids, a summary of relevant information for the North Atlantic area is made. On the basis of analyses of the bathygrams, a theory is proposed to explain the limiting action of temperature and illumination as environmental factors. It was found that, subject to the limitations of data at present available, the geographical distributions of various euphausid species, as predicted from hydrographic observations, agreed fairly well with that observed in net hauls. Most previous work on zooplankton has been confined to the shallower-living forms, so attention is drawn to the considerable differences in environmental conditions to which such deeper-living forms as euphausids are subject.Actual measurements of illumination at these depths have yet to be made. The attempt to compute the illumination and its changes under different conditions is discussed in the Appendix.