Quantifying the Response of an Estuarine Nekton Community to Coastal Wetland Habitat Restoration

Globally coastal habitats are experiencing degradation and threatening the production of critical ecosystem services such as shoreline stabilization, water filtration, and nursery grounds for marine fauna. To combat the loss of these ecosystem services, resource managers are actively restoring coastal habitats. This study compares samples collected from non-restored sites, sites restored in 2011, and sites that underwent restoration in 2019. Restoration sites are impacted wetlands with high elevation mounds that were leveled to increase the areal extent of intertidal habitats, enabling the recruitment of intertidal flora and fauna. Fyke nets were used to sample nekton within the upper intertidal zone. To quantify restoration success, nekton abundance, biomass, diversity, and indicator species were quantified. Sites restored in 2011 had a greater abundance compared to non-restored sites. Common snook, clown gobies, silversides, juvenile mullet, and Gulf killifishes were indicator species at successfully restored sites, while salinity, site type, and Secchi depth played important roles in predicting abundance and diversity. These findings are consistent with recent studies suggesting it can take years to see quantifiable differences in nekton communities following habitat restoration. Additionally, this work provides new insight regarding the benefits of restoring coastal wetland elevation to maximize intertidal habitat, thereby positively impacting nekton communities.

Checklist, Indeks Ekologi, dan Status Konservasi Komunitas Fauna Akuatik di Kawasan Sungai Unda dan Sekitar Pantai Jumpai, Kabupaten Klungkung, Provinsi Bali

Aquatic organisms or nekton have an important role in supporting the stability of the aquatic environment and human life. This study aims to determine the nekton type community, ecological index, and their conservation status in the Unda River area and around Jumpai Beach, Klungkung Regency, Bali. The study was conducted in July - August 2020. The study was conducted in 2 communities, namely Macrozoobenthos and Nekton. Macrozoobenthos samples were collected using the quadratic method in the Jumpai Beach area and the direct observation method along the Unda River. Nekton communities are collected through primary data using "survey methods" and secondary data through interviews with fishermen and local communities. The ecological index data were analyzed using the Shannon-Weiner diversity index (H'), dominance index (C), and uniformity index (E), while the data on Nekton type and conservation status were analyzed descriptively. The nekton species community in the waters of the Unda River and Jumpai Beach areas was obtained as many as 26 species in 21 families which were dominated by Kepala Timah (Aplocheilus panchax) and sepat rawa (Trichogaster trichopterus), while Nautica sp for the Macrozoobenthos community. The ecological index of the aquatic community is the Shannon-Weiner Diversity Index (H') value of 2.98 (moderate), the wealth index (R) of 3.95 (moderate), and the evenness index (E) of 1.21. (High). The highest percentage ratio of nekton communities was obtained by the Macrozoobenthos community, namely 53%, while the nekton species was 46%. Conservation status shows that 13 species are included in the LC (Least Concern) category, 12 species are included in the NE (Not Evaluated) category, and 1 species are included in the VU (Vulnerable) category.

«Wrong fish» or wrong hypotheses: what happens to nekton of the Pacific waters at Kuril Islands?

A phenomenon of undulating fluctuations of nekton abundance in the Kuroshio system is discussed on example of japanese sardine Sardinops melanostictus, as the most abundant and the most fluctuating species. The so-called «sardine epochs» are distinguished according to this species abundance. The last such epoch ended in the early 1990s. Since 2014, structural changes occurred again in the nekton communities of the Pacific waters off Kuril Islands, caused by expansion of southern fish and squid species, primarily japanese sardine and chub mackerel Scomber japonicus, and decreasing in abundance of japanese anchovy Engraulis japonicus and saury Cololabis saira. The scope of these changes allowed Russian fishermen to resume the fishery on japanese sardine and chub mackerel in the Russian exclusive economic zone since 2016. Annual catch of Japanese sardine increased steadily from 6,700 t in 2016 to 315,500 t in 2020. Over these 5 years, Russian fishermen landed 531,700 t of sardine and 167,900 t of chub mackerel. However, many Russian fishery forecasters believe that these reconstructions is only a «rehearsal» of the upcoming «sardine epoch», being based on formal climatic indices, without delving into the mechanisms of abundance fluctuations. The authors note that new «sardine epochs» cannot be predicted as completely similar to the previous ones. Several hypotheses on causes of the beginning and end of japanese sardine blooms are considered critically, and the conclusion is made that mechanisms which determine its year-classes strength are still unclear, as well as the reasons of undulating fluctuations of this species and some other nekton species abundance, because of high complexity of this problem.

Identifying patterns in the multitrophic community and food-web structure of a low-turbidity temperate estuarine bay

Food web dynamics outline the ecosystem processes that regulate community structure. Challenges in the approaches used to capture topological descriptions of food webs arise due to the difficulties in collecting extensive empirical data with temporal and spatial variations in community structure and predator–prey interactions. Here, we use a Kohonen self-organizing map algorithm (as a measure of community pattern) and stable isotope-mixing models (as a measure of trophic interaction) to identify food web patterns across a low-turbidity water channel of a temperate estuarine-coastal continuum. We find a spatial difference in the patterns of community compositions between the estuarine and deep-bay channels and a seasonal difference in the plankton pattern but less in the macrobenthos and nekton communities. Dietary mixing models of co-occurring dominant taxa reveal site-specific but unchanging food web topologies and the prominent role of phytoplankton in the trophic base of pelagic and prevalent-detrital benthic pathways. Our approach provides realistic frameworks for linking key nodes from producers to predators in trophic networks.

Nekton communities as indicators of habitat functionality in Philippine mangrove plantations

In the present study, we investigated the changes to nekton communities with increasing mangrove forest age and relationships between nekton and the mangrove vegetation, mangrove sediments and environmental variables. The nekton community was assessed as a potential indicator for evaluating habitat functionality of mangrove planting programs. In all, 99 species from 52 families were captured, including crabs, shrimp, squid and fish. The crustacean assemblage was dominated by Portunidae and Penaeidae, whereas the fish assemblage was dominated by Atherinidae, Apogonidae, Hemirhamphidae, Tetraodontidae, Congridae, Sphyraenidae, Murraenidae, Ambassidae, Gerreidae, Clupeidae, Platycephalidae, Gobiidae, Mullidae and Plotosidae, with these families accounting for 90% of all individuals collected. The species composition, abundance and biomass of the nekton community were not significantly correlated with mangrove vegetation and sediment variables, but were significantly associated with environmental variables, particularly proximity to reef and tidal inundation. The lack of correlations suggests that the whole nekton assemblage was not a useful indicator in evaluating the progress of restoring habitat functionality in these planted mangroves. However, a significant interaction with mangrove vegetation was found for non-fish components of the nekton. As such, crustaceans, particularly of the Portunidae and Penaeidae families, were useful indicators for determining the habitat functionality of planted mangroves.