Changes In Size Frequency Distribution Research Articles

First record of the non-indigenous jellyfish Blackfordia virginica (Mayer, 1910) in the Baltic Sea

Marine invasions are of increasing concern for biodiversity conservation worldwide. Gelatinous macrozooplankton contain members, which have become globally invasive, for example the ctenophore Mnemiopsis leidyi or the hydromedusae Blackfordia virginica. B. virginica is characterised by a large salinity tolerance, with a brackish-water habitat preference, and by a metagenic life history strategy with an alternation between sexually reproducing planktonic medusae and asexually reproducing benthic polyps to complete the life cycle. In this study we analysed 8 years of ichthyoplankton survey data (2010–2017) from the Kiel Canal and 14 ichthyoplankton summer surveys in the central Baltic Sea (2008–2017). We report the first presence of B. virginica in northern Europe, namely from the southwestern Baltic Sea and the Kiel Canal. In the Kiel Canal, B. virginica was first sporadically sighted in 2014 and 2015 and has developed persistent populations since summer 2016. Changes in size-frequency distributions during summer 2016 indicate active recruitment in the Kiel Canal at salinities between 7 and 13 and temperatures > 14 °C. Close vicinity to and direct connection with the southwestern Baltic Sea, where B. virginica was observed during 2017, indicate that the Baltic Sea and other brackish-water habitats of Northern Europe are at risk for colonisation of this non-indigenous species. Our results highlight that monitoring activities should consider gelatinous macrozooplankton for standard assessments to allow for the detection of non-indigenous species at an early stage of their colonisation.

Life history characteristics of the fluvial shrimp Macrobrachium yui (Holthuis, 1950) (Decapoda, Palaemonidae) spawning in the cave streams in northern Laos

This study aims to understand the reproductive and larval characteristics and the migratory patterns of the shrimpMacrobrachium yui(Holthuis, 1950). We conducted monthly samplings of the adult, juvenile and larval shrimp at fixed points in the Xuang River system in northern Laos. We determined the seasonal changes in size frequency distribution, difference in size among sampling sites, occurrence of drifting larvae, and physiological condition of the shrimp. The size distributions ofM. yuidiffered significantly throughout the year among sections of the river system: small-sized juveniles occurred in the Xuang River, various size classes in the Pho Stream, and larger adults in the Bokengsakang cave stream. The gonadosomatic index of females is the highest in the Bokengsakang cave stream and the gonadosomatic index of males is the highest in the Pho Stream. Drifting larvae that had already completed morphological development for settlement on the substrate occurred only in the Bokengsakang cave stream, although the hatched larvae have a free-swimming larval period. The overall results indicate thatM. yuifemales spawn in the Bokengsakang cave stream after mating with males during or before migration to the cave stream, and the hatched larvae remain in the cave stream until settling on the bottom. The life history migration ofM. yuiis attributed to the early stages of the life cycle, depending strongly on the cave stream.

Invasion of a naticid predator and associated changes in death assemblages of bivalve prey in northern Japan: implications for palaeoecological studies

The recent invasion of a naticid predator (Laguncula pulchella) and associated changes in the death assemblages of bivalve prey (Ruditapes philippinarum) provide a baseline for interpreting predator–prey interactions in the fossil record. This article presents quantitative data on size-frequency distributions (SFDs) of living and death assemblages, prey size selectivity and drillhole site selectivity from the Tona Coast, northern Japan. Before the appearance of the predator, the SFD of the death assemblage exhibited a right-skewed platykurtic distribution, and there were very few predatory drillholes. Once the predator appeared, frequencies of predatory drillholes increased, particularly in the smallest size class (2–10 mm shell length). Furthermore, juvenile peaks in the SFDs of death assemblages sharpened, and thus, SFDs exhibited strongly right-skewed leptokurtic distributions. These changes suggest that intense naticid predation precluded juvenile clams from growing to adulthood, and thus, many dead shells of juvenile clams were introduced into the sediment. The changes in SFDs may also indicate intensification of predation pressure in the fossil record. No temporal shifts in prey size selectivity and drillhole site selectivity were noted, despite substantial changes in the demographics of Ruditapes philippinarum. This suggests that lack of specific size classes of preferred prey species is unlikely to be a primary factor accounting for size mismatches between predator and prey, because, in such situations, naticid predators probably attack other prey species. Therefore, such a factor is unlikely to primarily explain the less stereotypical predatory behaviour (i.e. low prey size selectivity and low drillhole site selectivity), which has been frequently recognized in fossil assemblages. Such less stereotypical predatory behaviour in fossil assemblages is likely to be explained by other factors, such as the existence of multiple predator taxa and lack of specific size classes of all available prey.

Postsettlement growth of two estuarine crab species, Chasmagnathus granulata and Cyrtograpsus angulatus (Crustacea, Decapoda, Grapsidae): laboratory and field investigations

The estuarine grapsid crabs Chasmagnathus granulata and Cyrtograpsus angulatus belong to the most typical and dominant inhabitants of brackish coastal lagoons in southeastern South America. In a combined laboratory and field investigation of juvenile growth, we measured the increase in body size in these species under controlled conditions as well as in field experiments (in Mar Chiquita lagoon, Argentina), seasonal changes in size frequency distribution of a natural population, and growth related changes in selected morphometric traits of male and female juveniles (relations between carapace width, carapace length, propodus height and length of the cheliped, and pleon width). At 24°C, Cy. angulatus grew faster than Ch. granulata; it reached the crab-9 instar (C9; 13 mm carapace width) after 92 days, while Ch. granulata required 107 days to reach the C8 instar (7.4 mm). At 12°C, growth ceased in both species. The pleon begins to show sexual differences in the C5 (Cy. angulatus) and C8 instar (Ch. granulata), respectively, while the chelae differentiate earlier in Ch. granulata than in Cy. angulatus (in C4 vs C6). In the field, growth was maximal in summer, and was generally faster than in laboratory cultures. However, there is great individual variability in size (about 25% even in the first crab instar) and in size increments at ecdysis, increasing throughout juvenile growth. Our data indicate that, in the field, small-scale and short-term variations in feeding conditions, temperature, and salinity account for an extremely high degree of variability in the absolute and relative rates of growth as well as in the time to sexual differentiation.

Follicular dynamics and germinal bed activity during the annual ovarian cycle of the lizard, Calotes versicolor.

Changes in size frequency distribution of extrastromal follicles, atretric follicles (AF), and the number of oogonia, oocytes, and primordial follicles in the ovaries are studied in Calotes versicolor during its annual reproductive cycle. Extrastromal follicles were graded into stages I to VI based on their diemeter. Stage I (0.5-0.75 mm) follicles are found throughout the year. The recruitment of stage II (0.76-1 mm) and stage III (1.10-2 mm) follicles occurs during December and March, respectively. Follicles of stage I-III are found in greater number in May. Stage IV vitellogenic follicles (2.10-3 mm) are recruited in April. Advanced vitellogenic follicles (stage VI) are formed between May and August. From April to August, the ovaries of lizards contain vitellogenic follicles of stages IV or V or VI suggesting that once a set of follicles enters vitellogenic phase there is no recruitment of another set of vitellogenic follicles from previtellogenic follicles until the former ovulates. The presence of vitellogenic follicles and at least two sets of CL in July-August suggest that C. versicolor may oviposit at least three clutches of eggs per season. The clutch size in this lizard varies from a maximum 24 eggs in May to a minimum of 13 eggs in September. The previtellogenic AF are found throughout the year. Atresia is more prevalent in stage III suggesting that these follicles are more prone to become atretic. Interestingly, atresia of vitellogenic follicles occurs rarely. Each ovary in C. versicolor has two germinal beds. The germinal beds contain a greater number of oogonia (536-696), primary oocytes (40-71), and primordial follicles (32-55) during prebreeding and early breeding phases of the ovarian cycle. © 1993 Wiley-Liss, Inc.

Seasonal changes in size frequency distribution and estimated age in the marine copepod Acartia hudsonica during a winter-spring diatom bloom in Narragansett Bay

Seasonal changes in length frequency and estimated age distributions indicated that Acartia hudsonica adult females are dominated by successive age groups during the winter–spring bloom in Narragansett Bay. The biomass peak during March and April was composed of over-wintering, late autumn-spawned copepods. Winter-spawned copepods entered the adult population during a brief period in late April to early May, and the influx of spring-spawned copepods began during the second week of May. Concurrent studies of egg production and feeding suggested senescence of the adult population prior to the transition between the autumn-spawned and the winter–spring-spawned copepods. Thus population productivity may reflect not only environmental conditions, but also the age-dependent physiological condition of the adults. Modeling indicated that small interannual variations in temperature (±1°C) will significantly affect development rate and maturation of A. hudsonica during winter and spring. The 2°C temperature range corresponded to a 3-week shift in the timing of peak maturation and could significantly alter the intensity of grazing and degree of coupling between primary producers and herbivores during the spring bloom.

Distribution, abundance and size-structure of cerithiid gastropods in sediments at One Tree Reef, southern Great Barrier Reef

The patterns of abundance of molluscs in sediments at One Tree Reef, southern Great Barrier Reef were determined for three adjacent habitats in October 1985: a shallow subtidal sandflat, a deep channel, and the sloping, unstable edge separating the two. Deposit-feeding cerithiid gastropods, especially Rhinoclavis aspera (Linnaeus, 1758), R. fasciata (Bruguière, 1792) and R. vertagus (Linnaeus, 1758), were the most abundant molluscs present but these species were predominantly found in the coarse sandy sediments of the sandflat. The abundances and sizes of these three species were monitored seasonally from October 1985 to January 1988 on the sandflat. Densities fluctuated during the three years of the study and varied at a number of spatial scales. The density of R. aspera was generally greater at the beginning of the year, after recruitment, then gradually declined until the next period of recruitment. This pattern was not as evident for R. fasciata or R. vertagus. Changes in size-frequency distributions through time suggest that movement of animals, either by migration and/or passive transport in the shifting sediments may contribute to the observed patterns. Comparisons are made between temperate and tropical soft-sediments habitats, especially in relation to the distribution of deposit-feeding organisms.

Effectiveness of size frequency distributions in regulating intraspecific spatial overlap of stream insects

Spatial niche breadth and overlap of size groups of four species of epilithic stream insects were studied to determine if broad size frequency distributions serve to reduce intraspecific competition for space. Mean niche overlap decreased with greater breadth of size frequency distributions for only one species (Baetis intercalaris) and did not vary in relation to population density. Similarly, the ratio of the probabilities of intergroup and intragroup encounter did not vary as a function of the breadth of size frequency distributions. Therefore, it was concluded that changes in size frequency distribution have a minimal effect on intraspecific competition for space among epilithic species. It was suggested that observed size frequency distributions may be more a function of extant environmental conditions (temperature and flow) than of previous or extant intraspecific competition.