Large Infaunal Bivalves Determine Community Uptake of Macroalgal Detritus and Food Web Pathways

Investigating adult reproduction as a potential barrier to recovery of wild Manila clam (Venerupis philippinarum) populations impacted by the Nathan E. Stewart oil spill, Central Coast, B.C

Understanding the chronic effects of environmental disasters, such as oil spills, is critical to assessing long-term impacts on marine ecosystems and guiding recovery efforts. We assessed the reproductive potential of adult Manila clams (Venerupis philippinarum) from sites impacted by the Nathan E. Stewart oil spill (Central Coast, British Columbia, Haíɫzaqv Territory, October 2016) to determine if reduced reproductive capacity may be driving a delayed population recovery among the impacted clam populations. Clams from both reference and impacted sites were conditioned under controlled laboratory settings, with reproductive metrics (gonadosomatic index, progression of gamete development, fertilization success, spawning success) showing no significant differences between sites, suggesting that reproductive output in adults is not currently limiting recovery. Adult clams from all sites successfully spawned under controlled laboratory conditions. However, despite successful spawning and fertilization, larval survival was uniformly low across sites; this low survival may be attributable to methodological factors, such as temperature or handling stress rather than direct impacts of the oil spill. Findings suggest factors other than adult reproductive capacity are causing continued delay of population recovery, warranting further investigation.

Effects of stock enhancement on the macrobenthic community and ecological health in the intertidal zone of the estuarine wetland in Nanhui, China

Nanhui Dongtan Wetland is an important part of Yangtze Estuary Wetland, and its species diversity has been affected by reclamation in recent years. To increase the diversity of species in reclamation areas, stock enhancement was implemented in the Nanhui Dongtan Wetland in May 2020 as a method of ecological restoration. We investigated macrobenthos before and after release, analysed changes in the macrobenthos and evaluated the ecological health of the sampled area. The diversity index showed species were more abundant and community structure were more diversified after release. Functional groups and redundancy analysis showed that the effects of stock enhancement on macrobenthos in Nanhui Dongtan wetland may be based on changes in secondary productivity. Stock enhancement may promote the resistance of macrobenthic communities to organic pollution without negatively affecting ecological health. As a method of ecological restoration, stock enhancement will play a positive role in the restoration of macrobenthic communities.

Resource partitioning of a Mexican clam in species-poor Baltic Sea sediments indicates the existence of a vacant trophic niche

Invasive species are often generalists that can take advantage of formerly unexploited resources. The existence of such vacant niches is more likely in species-poor systems like the Baltic Sea. The suspension feeding wedge clam, Rangia cuneata, native to estuarine environments in the Gulf of Mexico, was sighted for the first time in the southeastern Baltic in 2010 and a few years later in the northern Baltic along the Swedish coast. To explore possible competition for food resources between R. cuneata and the three native clams inhabiting Baltic shallow soft bottoms, stable isotope and fatty acid analyses were conducted. There was no overlap between R. cuneata and any of the native species in either stable isotope or fatty acid niches. This suggests efficient partitioning of resources; multivariate analyses indicate that separation was driven mainly by δ13C and by fatty acids reflecting diatoms and cyanobacteria, respectively (e.g. 16:1ω7 and 18:3ω3). R. cuneata reflected seasonal variation in phytoplankton more than other clams reflecting higher trophic plasticity. In conclusion, the addition of R. cuneata to the Baltic shallow soft bottoms suggests the existence of a vacant trophic niche in these sediment habitats, however the long-term effects on other species and nutrient cycling requires further studies focusing on the population dynamics of R. cuneata and its impact on the Baltic Sea ecosystem.

Baseline Inventory of Benthic Macrofauna in German Marine Protected Areas (2020-2022) before Closure for Bottom-Contact Fishing

The response of benthic habitats and organisms to bottom-contact fishing intensity is investigated in marine protected areas (MPAs) of the German EEZ in the North and Baltic Seas. We examined the current state of macrofauna biodiversity in 2020-2022. Comparative analysis for macrofauna (in- and epifauna) inhabiting nine Natura 2000 MPAs constitutes a baseline to assess the effects of bottom-contact fishing exclusion in the future. Aspects of spatial and temporal variability are briefly summarized and discussed. We provide a species list for each region, including 481 taxa, of which 79 were found in both regions, 183 only in the North Sea, and 219 only in the Baltic Sea. The Baltic Sea dataset surprisingly included higher numbers of taxa and revealed more Red List species. The share of major taxonomic groups (polychaetes, bivalves and amphipods) in species richness showed peculiar commonalities between the two regions. In the North Sea, multivariate analysis of community structure revealed significantly higher within-similarity and stronger separation between the considered MPAs compared to the Baltic MPAs. Salinity, temperature and sediment fractions of sand were responsible for over 60% of the variation in the North Sea macrofauna occurrence data. Salinity, mud fraction and bottom-contact fishing were the most important drivers in the Baltic Sea and, together with other considered environmental drivers, were responsible for 53% of the variation. This study identifies aspects of macrofauna occurrence that may be used to assess (causes of) future changes.