Abundance Of Early Life Stages Research Articles

Early life stages of the invasive Atlantic blue crab Callinectes sapidus in the Western Mediterranean Sea

The early life cycle of the Atlantic blue crab Callinectes sapidus includes seven zoeal stages that develop in coastal waters, and a later megalopal stage that colonizes estuaries. Although these stages have been largely studied in native ecosystems, very little is known about larval patterns in smaller-scale, invaded, estuarine environments such as those available in the Mediterranean Sea. The general aim of this study is to assess the distribution and abundance of early life stages of C. sapidus in the communication channels of the Albufera lagoon with the Mediterranean Sea, and in adjacent coastal waters. Different sampling methods were employed to target each life stage. (1) For zoeae, planktonic tows were conducted using a 300 μm manta net along 200 m transects parallel to the coastline at distances of 300, 1000 and 3000 m from the shore. (2) A small and manageable passive collector model was used to capture megalopae and juveniles in estuarine areas. This system was first tested from 2020 to 2021 in a single channel, with a weekly sampling frequency, and two more channels were added in 2022. Additionally, intensive daily sampling was conducted in one of the channels from September to November 2022 during the settlement peak. Results showed that zoeae of C. sapidus were more abundant in August 2021, at 1000 m from the coast, and appear to have a disjoint temporal distribution with zoeae of other crab species. Megalopae and juveniles were more abundant from September to November at all sampling sites and times. In 2022, collectors featured a dominance of megalopae at two of the sites (ca. 73%), while the site with the lowest salinity showed a dominance of juveniles (84%). For megalopae, comparative results from the intensive and the regular sampling campaigns showed that time of residence within collectors is just a single day. For juveniles, higher numbers were detected with increased deployment time, suggesting a need for enhanced habitat complexity.

Influence of environmental conditions on spatial distribution and abundance of early life stages of Antarctic silverfish,Pleuragramma antarcticum(Nototheniidae), in the Ross Sea

AbstractThe Antarctic silverfishPleuragramma antarcticumBoulenger is the dominant fish species in the high Antarctic zone, playing a key role in the Ross Sea midwater shelf ecosystem. Unlike other notothenioids, it is holoplanktonic species, spending its entire life cycle in the water column. Early life stages ofP. antarcticumare generally found in the upper 200 m and their spatial distribution is largely affected by water masses and general circulation. To understand better the mechanisms involved in the geographical distribution of the Antarctic silverfish within the western Ross Sea, an analysis of abundance and distribution was carried out in relation to oceanographic conditions. Samples were collected in summer during the 1998, 2000 and 2004 Italian cruises, covering the majority of the western sector of the Ross Sea. Overall 127 stations were sampled using standard plankton nets for biological samples and CTD and XBT to record abiotic parameters. Although all surveys were in December–January, the yearly results differed in terms of relative abundance of larval developmental stages and of oceanographic characteristics. The 1997–98 samples were characterized by very low abundance overall and by the virtual absence of early larvae. In summers 1999–2000 and 2003–04 the abundance ofP. antarcticumwas one order of magnitude higher than in the earlier season. In 1999–2000 catches were mainly composed of pre-flexion larvae and late postlarvae, while in 2003–04 catches were made up of pre-flexion larvae and juveniles. In January 2000 the Ross Sea summer polynya was fully open as the pack ice was almost completely melted, whereas in January 1998 and 2004 the opening of the polynya was considerably delayed. As a consequence, a delay in phytoplankton blooms and a decrease in primary production were observed in the summer seasons 1998 and 2004 with respect to 2000. The spatial distribution of early life stages, that were confined to the continental shelf and shelf break of the Ross Sea, generally appeared to be positively influenced by transition zones (oceanographic fronts). In addition, most of catches were recorded on or in close proximity to the banks (Pennell, Mawson, Ross and Crary) that characterize the continental shelf of the Ross Sea. On the basis of present findings and literature data, a link between the general circulation in the western Ross Sea and the distribution pattern of the early life stages ofP. antarcticumhas been developed.

Distribution and abundance of early life stages of <i>Sardina pilchardus</i> in the Gulf of Tunis (Central Mediterranean Sea) in relation to environmental and biological factors

Four seasonal surveys were carried out in the Gulf of Tunis between summer 2002 and spring 2003 to study the abundance and distribution of Sardina pilchardus eggs and larvae in relation to environmental parameters. In the Gulf of Tunis, Sardina pilchardus begins spawning in autumn (23 eggs/10 m²) and attains its peak in winter (257 eggs/10 m²) when the mean SST is lowest (13.4°C). Sardine reproduction seems to be triggered by the decrease in the SST. In winter, the main spawning areas were located to the south of Zembra Island and the north of Cape Bon. Larvae were more abundant in winter (38 larvae/10 m²), while lower densities were collected in autumn and spring (1 larva/10 m²). The highest abundance of larvae (288 larvae/10 m²) was recorded southwest of Zembra Island. Eggs and larvae were mainly concentrated in the relatively warmer and saltier waters with high zooplankton abundance and, inversely, with a low concentration of nitrate and chlorophyll a and a low diatom abundance.

High levels of spatial and temporal recruitment variability in the temperate sparid Pagrus auratus

Knowledge of spatial and temporal variation in the abundance of early life stages is important to developing an understanding of juvenile recruitment processes and, ultimately, the dynamics and demographics of fish populations. In Victoria, south-eastern Australia, snapper, Pagrus auratus, supports an important fishery characterised by high variability in year-class strength. We investigated spatial and temporal variation in the recruitment of small juvenile (0+) snapper by monitoring their abundance in four bay and inlet nursery areas during four consecutive summer/autumn recruitment periods (2000–2003). We found considerable spatial variability in the abundance of recruits, both within and among inlets. Interannual recruitment variation, however, differed among inlets. Recruitment into the largest nursery area and most important fishery, Port Phillip Bay, varied by ~10-fold across years, whereas variation for the other inlets was low or not significant. There were also clear differences in size distributions of recruits among both inlets and years. Strong recruitment in Port Phillip Bay during 2001 was related to a longer period of spawning and successful larval settlement and was associated with above average water temperatures. Future monitoring of 0+ recruitment in Victoria and studies of the recruitment processes should be specific to individual nursery areas.

Population decline off the Japanese sardine Sardinops melanostictus owing to recruitment failures

The Japanese sardine Sardinops melanostictus started to decline after 1989. Recruitment to age 1 population was small in four year-classes from 1988 to 1991. The population decline after 1989 resulted from recruitment failures in 4 consecutive years. Egg production was high in the years of poor recruitment. The recruitment failures were caused not by a reduction in reproductive output but by low survival between egg stage and age 1 recruitment. Abundance of post first-feeding larvae positively correlated with egg and yolksac larval abundance. Mortality at the first-feeding stage was not so variable as to destroy correlations between the abundance of early life stages. The population of age 1 recruits did not correlate with the abundance of post first-feeding larvae. Recruitment of the sardine was not fixed by the end of the first-feeding stage. Cumulative mortality through the early life stages, rather than relatively instantaneous mortality at the first-feeding stage, is thought to be responsible for the recruitment success or failure and eventual population fluctuations of the sardine.

Relationships among Early Life Stages of Morone americana and Morone saxatilis from Long-Term Monitoring of the Hudson River Estuary

Annual abundances of eggs, yolk-sac larvae (YSL), post-yolk-sac larvae (PYSL), and young-of-the-year (YOY) stages of Morone americana and Morone saxatilis are summarized from a 17-yr monitoring program in the Hudson River Estuary. Variability in temperature and freshwater flow in the Hudson River explained little of the interannual variation of early life stages of either species. Year class strength as indicated by the abundance of early life stages does not appear to be strongly influenced by environmental conditions. YSL were positively related to the abundance of eggs, but these relationships were weak, reflecting the high uncertainty in egg abundance estimates. There were positive relationships between the abundances of YSL and PYSL for both species. Our analysis implies that interannual variability in mortality is less important in determining recruitment to PYSL than the abundance of the prior life stages. There was no relationship, however, between the abundance estimates of PYSL and YOY. Differential mortality among years during the larval stage may result in juvenile recruitment being independent of larval abundance. A second possibility is that YOY are poorly sampled so that the monitoring programs currently provide inadequate estimates of the abundance of YOY.

Distribution and abundance of early life stages of squid (Illex argentinus) in the south-west Atlantic

A joint research cruise (Japan-Argentina-Uruguay) was carried out in the South-western Atlantic during August-September 1989 in order to study the winter-spawning and hatchery areas of Illex argentinus, and also the migration pattern of the juveniles towards the continental shelf. A few Rhynchoteuthion larvae were found in subtropical waters of the Brazil Current, next to the Brazil-Malvinas confluence, and in the frontal zone with shelf water, but never at temperatures below 14°C. Large numbers of juveniles found in subantarctic waters (6–10°C) on the shelf were probably migrating southward from their hatchery grounds following the zooplankton concentrations on which they were feeding.