Macrobenthic Faunal Abundance, Distribution and Diversity in the Bakkhali River, East Coast of Bangladesh

The study aimed to assess the macrobenthos abundance and distribution from the Bakkhali River, East Coast of Bangladesh. Macrobenthic and water samples were collected from the upper, middle and lower part of the river during post-monsoon. Several indices were used to find macrobenthos abundance and distribution and their correlation with water parameters were also assessed. Present study identified a total of 628 macrobenthos individuals representing 10 major taxa at three stations where 9 taxa were reported in both upper and middle parts whereas only 7 taxa were observed at lower stream of the river. The highest abundance of macrobenthos (301.04 indivs/m2) was recorded at the lower stream and the lowest abundance (166.3 indivs/m2) was found at the upper part of the river. Macrobenthos distribution showed that the number of Oligochaetes was higher (220 indivs) followed by Nemertinas (169 indivs) and Polychaetes (145 indivs). Study findings reveal that macrobenthos abundance and distribution were comparatively higher at the lower stream than the upper and middle part because of higher level of pollution and sendimentation rate that might influence the macrobenthos abundance and diversity in the upper and middle part. The study also found macrobenthos abundance was proportionally increased with increasing salinity and pH. However, macrobenthos abundance was decreased with increasing temperature. Simpson index (D) was the highest (0.32) at middle and lower part and the lowest (0.23) was in the upper part. Shannon-wiener index (H) was also higher (1.68) at the upper part. Both the indices showed higher diversity at the upper part because of having maximum taxa in the station. Based on the H value, this study reported that Bakkhali River was moderately polluted since H value was in the range of 1.44 to 1.68. These might be because of anthropogenic sources of pollution in the vicinity of the river. This study suggests to take proper management strategies to control aquatic pollution and conserve aquatic biodiversity. The Dhaka University Journal of Earth and Environmental Sciences, Vol. 10(1), 2021, P 47-55

Spatial variation in the structure of overwintering, remnant Saccorhiza polyschides sporophytes and their associated assemblages

Understanding the structure and richness of natural communities is a fundamental goal of marine ecology, and foundation species such as large macroalgae have a disproportionate role in structuring biodiversity. However, high-resolution information on assemblages associated with macroalgae is lacking for many species and regions. Saccorhiza polyschides is a warm-temperate kelp with a relatively short lifespan (12–18 months), large thallus and bulbous holdfast offering habitat for diverse assemblages. In the UK, S. polyschides populations are thought to have proliferated recently. Here, we quantified the density and habitat structure provided by S. polyschides along a gradient of wave exposure within Plymouth Sound, and examined the composition and diversity of associated faunal assemblages. Density varied significantly between sites but not by wave exposure, while biometric measurements were generally highly variable. Senescing holdfasts from sporophytes offered valuable habitat, with high abundance and richness of associated assemblages, although these varied markedly between sporophytes and sites. Faunal abundance, taxon richness and diversity were significantly higher at fully exposed sites than at moderately exposed sites. Internal volume of holdfasts was positively correlated with faunal abundance and taxon richness. We recorded more than 27 distinct taxa and up to ~600 individuals within a single holdfast. Taxa included three fish species, including a novel observation of the pipefish Nerophis lumbriciformis. Further work is needed to examine seasonality in habitat structure and associated diversity patterns but our study demonstrates that even remnant holdfasts from decaying sporophytes represent a valuable microhabitat that may provide shelter, protection and food during winter.

Megafaunal Community Structure From the Abyssal to Hadal Zone in the Yap Trench

Hadal trenches remain one of the unexplored ocean ecosystems due to the challenges of sampling at great depths. It is still unclear how a faunal community changes from the abyssal to the hadal zone, and which environmental variables are the key impacting factors. In this study, nine dives of the Human Occupied Vehicle (HOV) “JIAOLONG” were conducted from abyssal to hadal depths (4,435–6,796 m) in the Yap Trench on the southeastern boundary of the Philippine Sea Plate in the western Pacific, divided into 48,200 m video transects, to describe the megafaunal communities and reveal their relationship with environmental factors. A total of 1,171 megafauna organisms was recorded, 80 morphospecies (msps) from 8 phyla were identified based on the video data, most of which were reported for the first time in the Yap Trench. Arthropoda was the most abundant phylum and Echinodermata was the most diverse phylum of the megafaunal community. The faunal abundance increased with depth, whereas the Shannon diversity index decreased with depth. Cluster analysis suggested seven assemblages, with five abyssal groups, one mixed group, and one hadal dominant group. Although megafaunal communities changed gradually from abyssal zone to hadal zone, both PERMANOVA and PERMDISP analyses revealed that the communities are significantly different between abyssal zone and hadal zone, indicating 6,000 m as the boundary between the two depth zones. Depth, substrate, slope, and latitude were identified as four important environmental factors with significant influence on megafaunal community structure. This study proposed a transition pattern from the abyssal to hadal zone in the Yap Trench, highlighted the importance of habitat heterogeneity in structuring megafaunal community in a hadal trench.

Do beds of subtidal estuarine seagrass constitute a refuge for macrobenthic biodiversity threatened intertidally?

Biodiversity differentials between macrobenthic assemblages associated with adjacent intertidal and subtidal areas of a single seagrass system were investigated for the first time. Assemblage metrics of conservation relevance—faunal abundance and its patchiness, faunal richness, and beta diversity—were examined at four contrasting dwarf-eelgrass localities in the Knysna estuarine bay, part of South Africa's Garden Route National Park but a system whose intertidal areas are heavily impacted anthropogenically. Faunal assemblages were significantly different across all localities and between subtidal and intertidal levels at each locality although their taxonomic distinctness was effectively constant. Although, as would be expected, there were clear trends for increases in overall numbers of species towards the mouth at all levels, few generalities relating to the relative importance of the subtidal seagrass habitat were evident across the whole system—magnitude and direction of differentials were contingent on locality. Shore-height related differences in assemblage metrics were minor in the estuarine and lagoonal zones but major in the marine compartment, although the much greater subtidal faunal abundance there was largely consequent on the superabundance of a single species (the microgastropod Alaba pinnae), intertidal zones then displaying the greater species diversity due to greater equitability of species densities. Along its axial channel, the Knysna subtidal seagrass does not support richer versions of the intertidal polychaete-dominated assemblages fringing it; instead, it supports different and more patchily dispersed gastropod-dominated ones. At Knysna at least, the subtidal hardly constitutes a reservoir of the seagrass biodiversity present intertidally.

A combined approach in determining late Quaternary fluctuations in deep water masses derived from neodymium isotopes, faunal variations and d13C in foraminifera along the western continental slope of South Africa

<p>The Meridional Overturning Circulation is crucial in regulating Earth‘s climate and is composed of various ocean currents, playing an important role in heat exchange and the distribution of water masses. The transfer of water masses also affects regional carbon storage, nutrient contents, temperature, evaporation and precipitation balances in the oceans. The advancement in our understanding of the interaction between these water masses can contribute to our current knowledge on the state of the oceans. The use of foraminiferal isotope geochemistry and faunal analyses has greatly contributed to understanding the changes our oceans have undergone in the Quaternary. The purposes of this study are to determine what the timescales were at which the bottom water masses were changing and to determine at which periods the influence of these water masses were the strongest. A combination of neodymium and δ<sup>13</sup>C isotopes, as well as faunal abundance records in this study, were derived from foraminifera in cores recovered at 3522 m and 3631 m water depths along the western margin of South Africa to investigate deep water mass variability in the southeast Atlantic Ocean during the last two glacial terminations. The neodymium isotope composition (<sup>143</sup>Nd/<sup>144</sup>Nd), expressed as εNd, were measured in planktic foraminifera from the western continental slope of South Africa. This isotopic tracer is useful in tracking deep water masses on the sub-millennial scale owing to the short residence time of Nd in seawater. Foraminifera (single-celled protists) microfossils acquire the bottom water Nd signature upon burial that can be useful in providing insight into the variability of deep water masses. In addition to the εNd records, the foraminiferal δ¹³C results also support the results of the neodymium isotopes. These records in this study are largely correlative with the abundances of benthic species <em>Cibicidoides wuellerstorfi</em>, reflecting shifts between the southern-sourced Antarctic Bottom Water (AABW) and the northern-sourced North Atlantic Deep Water (NADW) during the last two glacial terminations at ~130 ka and ~18 ka. The εNd, δ¹³C results and <em>C. wuellerstorfi</em> relative abundances indicate an intensified inflow of southern-sourced water masses and weakened NADW inflow along the margin during peak glacial periods MIS 6 and MIS 2. The terminations of these peak glacials were more beneficial to stronger penetration of NADW into the southeast Atlantic.</p>

Relationship of biological communities to habitat structure on the largest remnant flat oyster reef (Ostrea angasi) in Australia

Oyster reef restoration is a growing field in Australia, yet formal descriptions of associated biological communities for reefs created by native flat oysters (Ostrea angasi) do not currently exist. Native flat oysters once formed extensive and complex three-dimensional habitats in bays and estuaries across southern Australia until indiscriminate fishing, sedimentation and disease led to their near disappearance. To determine the diversity and abundance on naturally occurring oyster reefs, we sampled four sites on the last known naturally occurring oyster reef ecosystem, which resides in north-eastern Tasmania, and compared them to the surrounding soft sediment regions. Assemblages were related to environmental variables to determine whether consistent patterns were present. Oyster reef sites contained three times the faunal abundance of the surrounding soft sediment regions. Abundance among echinoderms, arthropods, molluscs and fish was much elevated, whereas annelids showed similar levels of abundance but differed in terms of species composition. These results show that oyster reefs do support abundant and diverse assemblages, emphasising the probable loss of community-level biodiversity associated with their historical decline around southern Australia.

Benthic faunal assemblages in seagrass meadows in Albany, Western Australia

Title (Bahasa Indonesia): Kumpulan fauna bentik di hamparan lamun di Albany, Australia Barat In order to compare benthic fauna assemblages in four locations of seagrass beds in Albany (Princess Royal Harbour, Oyster Harbour, Two People Bay and Frenchman Bay), a research had beenconducted between 18 and 21 April 2017. There were two aims of this study. First, to investigate six sites within four locations with various degree of anthropogenic impact in order to understand the faunal richness and abundance in those locations. Second, to measure and record the environmental factors which are assumed to be important regulators of the observed patterns between the sites. The result showed that the highest faunal abundance (227 Faunal) was found at Frenchman Bay, a less anthropogenically impacted area, while the lowest abundance (26 Faunal) was at Oyster Harbour-Emu Point which was an anthropogenically affected site. However, in terms of faunal diversity, there was no significant difference among all sites. The environmental factor which had significant relationship with the difference in benthic faunal assemblages at each site was found to be coarse sand.Satu kegiatan penelitian pada tanggal 18 hingga 21 April 2017 telah dilakukan untuk membandingkan kumpulan fauna bentik di empat lokasi padang lamun di Albany (Pelabuhan Princess Royal, Pelabuhan Oyster, Teluk Two People, dan Teluk Frenchman). Penelitian inimempunyai dua tujuan, yaitu: 1) menyelidiki enam titik penelitian yang beradadalam empat lokasi dengan berbagai tingkat dampak antropogenik untuk memahami kekayaan dan kelimpahan fauna di lokasi tersebut; dan 2) mengukur dan mencatat faktor-faktor lingkungan yang dianggap berperan sebagai pengaturdari pola yang diamati pada semua lokasi. Hasil penelitian menunjukkan,bahwa kelimpahan fauna tertinggi (227 fauna) ditemukan di Teluk Frenchmanyang merupakandaerah yang kurang terdampak gangguan antropogenik;sedangkan kelimpahan terendah (26 individu) ditemukandi Oyster Harbour-Emu Point yang merupakan lokasi yang terpengaruh secaraantropogenik. Namun, dalam hal keanekaragaman fauna, tidak ada perbedaan yang signifikan di antarasemua lokasi. Faktor lingkungan yang memiliki hubungan signifikan dengan perbedaan kumpulan fauna bentik di masing-masing lokasi ialah pasir kasar.

Benthic macro-faunal abundance and diversity and sediment distribution in Akhziv submarine canyon and the adjacent slope (eastern Levant Basin, Mediterranean Sea)

The Israeli coastline is generally characterized by a broad and shallow continental shelf. Akhziv submarine canyon (ASC), in its northern reach, creates a locally unique marine ecosystem. The present study is the first to investigate the benthic macro-fauna of ASC, in order to assess its importance as a potential productivity ‘hotspot’ within its ultra-oligotrophic surroundings. Seven research cruises were conducted during 2010-2013, along ASC’s two channels and at iso-bathic control sites on the adjacent slope (AS), encompassing 8 sampling stations, at depths of 40-450 m. Bottom samples were collected by a Van Veen Grab, gravity corer and a GOMEX box corer. The infauna (≥500 µm) were counted and identified to the lowest possible taxonomic level. Sediments were analysed for grain size & composition and total organic carbon concentration. Mean benthic macro-faunal abundance (individuals/500ml ± SD) was higher inside the canyon (13.0±19.4) compared to the AS (2.9±3.3) (p=0.004), as was estimated true taxon richness (Chao1): 42.2 versus 10, respectively. Sediments’ mode grain size was found to be significantly higher in ASC’s eastern channel compared to AS (p=0.028), along with sand enrichment of up to 36%. The higher macrofaunal abundance and taxon richness may relate to a more heterogeneous sea bed provided by the higher diversity in grain size existing inside ASC. A relatively rich benthic realm, such as that observed in the ASC, may serve as a refuge for certain species and by hosting a relatively diverse assemblage, stands a better chance of adapting to changing conditions such as climate change.