RESUMEN
In recent decades, economic activity has sharply increased in the Pechora Sea, one of the most hydrologically unique areas of the Barents Sea. Hence, the information about the current state of its ecosystems is quite important for assessing their possible changes in the future. The aim of the present study was to analyze the distribution of macrobenthos and assess its ecological quality in the southeastern part of the Pechora Sea at the beginning of the 21st century (based on data collected in 2012-2013). The results showed that since 1920s there have been no serious changes in the macrobenthos in the studied area. The weak shifts detected in the benthic fauna were either within the natural range of fluctuations in population of common species, or may be associated with differences in the methodological approaches of different researches. Heterogeneity in the macrobenthos distribution, the most significant abiotic factors identified in relation to it, quantitative indicators of biota, and species dominating in communities were similar to those revealed in previous studies. As of 2013, the characteristics of benthic communities in the southeastern part of the Pechora Sea, including their ecological quality, allow us to refer them as undisturbed biosystems.
Asunto(s)
Biota , EcosistemaRESUMEN
Phylogenetic relationships and the timing of evolutionary events are essential for understanding evolution on longer time scales. Cheilostome bryozoans are a group of ubiquitous, species-rich, marine colonial organisms with an excellent fossil record but lack phylogenetic relationships inferred from molecular data. We present genome-skimmed data for 395 cheilostomes and combine these with 315 published sequences to infer relationships and the timing of key events among c. 500 cheilostome species. We find that named cheilostome genera and species are phylogenetically coherent, rendering fossil or contemporary specimens readily delimited using only skeletal morphology. Our phylogeny shows that parental care in the form of brooding evolved several times independently but was never lost in cheilostomes. Our fossil calibration, robust to varied assumptions, indicates that the cheilostome lineage and parental care therein could have Paleozoic origins, much older than the first known fossil record of cheilostomes in the Late Jurassic.
RESUMEN
Pattern generation by foundation species (FS) is a primary structuring agent in marine and terrestrial communities. Prior research, focused on single-species or guild-dominated habitats, stressed the role of facilitation in maintaining community structure. However, many habitats are developed by multiple FS from different guilds. Competition between these FS may provide an additional agent potentially responsible for spatial and temporal patterns. In the White Sea, epibenthic patches formed by barnacles (Balanus crenatus) and solitary ascidians (mainly Styela spp. and Molgula spp.) on small stones and empty bivalve shells (mainly Serripes groenlandicus) produce microhabitats for different sessile taxa. We hypothesized that: (1) several FS would provide habitats for most of other species in the community; (2) different FS promote different assemblages of sessile organisms; (3) the interplay of facilitation and competition best explains observed patterns of abundance and demography in FS; and (4) these interactions shape the whole community, increasing the diversity compared to less heterogeneous patches constituted by single FS. We examined 459 patches and the results generally supported this hypothesis. The number of FS in a patch positively affected species diversity. Most sessile species (72% of individuals) resided on barnacles, ascidians and red algae, except barnacles that dominated the primary substrate. The size structure of barnacles (live individuals and empty shells) and ascidians were interrelated, suggesting long-term patch dynamics whereby ascidians regularly replace barnacles. Following this replacement, we expect consequent changes to the entire dependent assemblage. Evidence for these changes exists in the spatial pattern: most sessile and motile taxa demonstrated significant associations with either FS. Our results indicate that the small-scale patterns observed in patches formed by multiple FS are primarily generated by facilitation of dependent taxa by FS, and facilitation and competition between different FS.