Early life resources assemblage structure and succession to the marine Osteichthyes in the Laizhou Bay of Bohai Sea

Habitats distributed in the Laizhou Bay were critical for the accomplishment of the life cycles of fish and productive fisheries, in the Bohai Sea or even in the Yellow Sea. Based on a pooled analysis of the historical data available for almost 40 years, and combined with the field survey of current fish habitat conditions, a long-term data set of early life resources surveys to marine Osteichthyes, carried out in the Laizhou Bay was built. Mathematical statistics and time series analysis were used to interpret the recruitment characteristics and long-term trends in early life resources assemblage structure, biodiversity, and synchrony. The analysis showed that the early life resources assemblage structure in the Laizhou Bay changed continuously. The seasonal differences in community composition, abundance index, predominant taxa, and species diversity to eggs and larvae fish assemblage were evident. The abundance index and taxa number of egg and larval fish assemblages declined to an all-time low around the early 2010s, after which it showed signs of recovery recently. The taxa number of egg and larval fish decreased from 44 in the 1980s, 34 in the early 1990s, 40 in the late 1990s, and 35 in the 2000s to 24 in the early 2010s; from the middle and late 2010s, it showed a certain degree of recovery, and recently increased to 38 species. The recent number of the pelagic eggs taxa is only sixty percent of that in the 1980s, and with its abundance less one-third of the 1980s. The number of the pelagic eggs taxa had fell to an all-time low around the early 2010s, with taxa number less than half of the 1980s; while, the abundance of the pelagic eggs fell to an all-time low around the late 2000s, with its abundance only one-twentieth of the 1980s. The number of larvae fish taxa decreased first and then increased in each season (except in winter), while the abundance of fish larvae first increased and then decreased, however, both showed an upward trend in winter. The recent number of the larvae fish taxa is only three-fourths of that in the 1980s, and with its abundance less than ninety percent of the 1980s. The number of the larvae fish taxa fell to an all-time low around the early 2010s, with the number of taxa only half of the 1980s; while, larvae fish abundance reached a historical peak around the late 2000s, with its abundance about 1.9 times as much in the 1980s. Small pelagic and benthopelagic taxa with short life span, rapid maturation, strong coupling to lower trophic levels, were the main components by relative abundance detected in the eggs and fish larvae collected across different survey periods. The dominant taxa substitution was obvious, otherwise, the substitution rate was significantly accelerated in recent years. A significant amount of interannual and decadal variability remained in the species biodiversity index during the same survey season. Habitat and temperature adaptation studies of the spawning stock showed that the number of taxa with different habitat types and different temperature adaptation types took on a tendency of first decreasing and then increasing, profiling in the survey seasons across different survey times; annual percentage of the continental shelf pelagic-neritic fish taxa increased, combined with the continental shelf demersal and benthopelagic taxa decreased. Compared with the survey result in the1980s, the taxonomic composition and abundance of the egg and larval fish assemblage changed considerably. These variations were determined by a complex array of continuously changing conditions interacting with the demographic variables of each species, which was the concrete embodiment of high turnover in fish community structure and decline of fishery resources under long-term effects of overfishing and environmental change. Systematically summarizing long term trends in early life resources assemblage structure, biodiversity, and synchrony in the Laizhou Bay, and looking at how communities have changed in the past can help us understand the mechanism of spawning habitats stability, which could provide scientific evidence on laying down certain measures for the conservation and management of fishery resources in the Laizhou Bay, and the following impact assessment. Such as fishing, pollution, mariculture, and large-scale coastal engineering projects on the relative effects of climate and anthropogenic-induced factors on marine fish populations.