Invasive bivalves continue to spread and negatively impact freshwater ecosystems worldwide. As different metrics for body size and biomass are frequently used within the literature to standardise bivalve‐related ecological impacts (e.g. respiration and filtration rates), the lack of broadly applicable conversion equations currently hinders reliable comparison across bivalve populations. To facilitate improved comparative assessment among studies originating from disparate geographical locations, we report body size and biomass conversion equations for six invasive freshwater bivalves (or species complex members) worldwide: Corbicula fluminea, C. largillierti, Dreissena bugensis, D. polymorpha, Limnoperna fortunei and Sinanodonta woodiana, and tested the reliability (i.e. precision and accuracy) of these equations. Body size (length, width and height) and biomass metrics of living‐weight (LW), wet‐weight (WW), dry‐weight (DW), dry shell‐weight (SW), shell free dry‐weight (SFDW) and ash‐free dry‐weight (AFDW) were collected from a total of 44 bivalve populations located in Asia, the Americas and Europe. Relationships between body size and individual biomass metrics, as well as proportional weight‐to‐weight conversion factors, were determined. For most species, although inherent variation existed between sampled populations, body size directional measurements were found to be good predictors of all biomass metrics (e.g. length to LW, WW, SW or DW: R² = 0.82–0.96), with moderate to high accuracy for mean absolute error (MAE): ±9.14%–24.19%. Similarly, narrow 95% confidence limits and low MAE were observed for most proportional biomass relationships, indicating high reliability for the calculated conversion factors (e.g. LW to AFDW; CI range: 0.7–2.0, MAE: ±0.7%–2.0%). Synthesis and applications. Our derived biomass prediction equations can be used to rapidly estimate the biologically active biomass of the assessed species, based on simpler biomass or body size measurements for a wide range of situations globally. This allows for the calculation of approximate average indicators that, when combined with density data, can be used to estimate biomass per geographical unit‐area and contribute to quantification of population‐level effects. These general equations will support meta‐analyses, and allow for comparative assessment of historic and contemporary data. Overall, these equations will enable conservation managers to better understand and predict ecological impacts of these bivalves.

The invasive European green crab (Carcinus maenas) poses a significant ecological threat due to its rapid global spread and disruptive impact on coastal ecosystems. In the southwestern Atlantic, the northernmost population was recently recorded in the San Matías Gulf, offering a unique opportunity to study its demographic and life-history traits at the leading edge of its range. We assessed the sex ratio, population density, size distribution, and size at which 50% of females were ovigerous (SM₅₀) in the intertidal zone. Our findings revealed a male-biased sex ratio (1.50 males per female) and low population density (0.42 crabs m⁻²), suggesting early-stage establishment. A size-structure analysis showed a well-structured population with clear cohort separation in both sexes and evidence of two recruitment events. The carapace width at which 50% of females were ovigerous was estimated at 61.48 mm. Although egg-bearing females exhibited a well-marked seasonality, with the highest prevalence from May to July, their presence nearly year-round suggests an extended reproductive period and adaptability to local conditions, which may be advantageous in recently established populations, facilitating invasion success. These traits, combined with the species’ ongoing range expansion, highlight the invasive potential of C. maenas and its possible ecological impacts on the San Matías Gulf.