Micronekton biomass estimation from digitized images

Abstract

Quantifying the biomass of micronekton in the ocean typically requires tedious and time-consuming analytical procedures involving manipulation of samples. To address this issue, it is essential to develop methods that accurately estimate biomass avoiding long-time processing of samples to provide it in almost real time This study proposes an approach to measure individual biomass from digitized individual body area recorded by an optical counter or camera. By developing and implementing these methods, it may be possible to balance the need for accurate biomass estimates with the preservation of samples for further taxonomic studies. In this study, we compared individual dry weight and body area measured using an image processing from various groups of micronekton captured in tropical and subtropical waters. Micronekton samples, including meso- and bathypelagic fish, cephalopods, decapods, and gelatinous organisms were captured in different locations of the North and Equatorial Atlantic Ocean, and Mediterranean Sea. The specimens were photographed, and their morphological parameters, such as length and body area, were obtained from the images. The relationship between the body area and wet and dry weight was then analyzed to estimate the biomass from the images. The results showed a rather high correlation between body area and dry weight for the studied groups. Regression analysis revealed correlation coefficients (r) of 0.965, 0.974, 0.965, and 0.863 for cephalopods, crustaceans, gelatinous organisms, and mesopelagic fish, respectively. The statistical significance of the relationships between dry weight and body area was confirmed, with p-values less than 0.001 for all groups. Zonal differences in mesopelagic fish and some families were observed. This method of using digitized body area to estimate biomass will provide rapid estimation of biomass compared to traditional techniques, preserving samples for future taxonomic and ecological studies. However, there is also a need for increasing the sample size for certain groups, mainly gelatinous organisms, to improve our estimation of biomass as a viable alternative to traditional methods.