The Impact of Microorganisms Transported in Ships’ Ballast Water on the Fish of the Estuarine Waters and Environmental Sustainability in the Southern Baltic Sea

Abstract

Ballast water represents a significant vector for the transfer of aquatic organisms and chemical pollutants. Although various groups of transported microorganisms can have a negative impact on native species of aquatic fauna, the available literature usually focuses on larger organisms. This is important because microorganisms cause changes in the balanced aquatic environment, including a stable trophic pyramid. The objectives of this study were twofold: (i) to determine the seasonal changes in the microbiota of the ballast water of long- and short-range ships entering the southern Baltic port, with a focus on fish pathogenic microorganisms and (ii) to potentially assess the threat to the ichthyofauna caused by the introduction of these microorganisms into the aquatic environment. The analytical results demonstrated notable variability in microbial density across the samples, contingent on the distance traversed by the ships. The samples of ballast water collected in autumn exhibited the highest microbial density compared to those collected in spring and summer. The samples contained yeast (1.00–2.98 log cfu/mL), mold (1.30–3.26 log cfu/mL), and bacteria (2.18–4.61 log cfu/mL), including amylolytic bacteria (0.95–3.53 log cfu/mL), lipolytic bacteria (0.70–2.93 log cfu/mL), and proteolytic bacteria (0.70–2.39 log cfu/mL). The most prevalent were the Pseudomonas bacteria (0.48–4.40 log cfu/mL), including Pseudomonas fluorescens (0.20–2.60 log cfu/mL. The port waters in spring and summer were primarily characterized by the presence of bacteria belonging to the genus Bacillus. Additionally, the samples exhibited the presence of Intestinimonas, Oceanobacillus, and Virgibacillus bacteria. The short-range vessel samples were populated primarily by bacteria belonging to the genus Bordetella, accompanied by Oligella, Brackiella, and Basilea oraz Derxia, while the ballast water of long-range ships contained mainly Acholeplasma and Clostridium, accompanied by Bacillus, Peptosteptococcus, Intestinibacter, Terrisporobacter, Anaerobacillis, Anaerofustis, Oxobacter, and Listeria. A phylogenetic analysis of the bacteria recorded in the ballast water revealed the presence of species, including Bordetella and Acholeplasma, which can facilitate the colonization of aquatic organisms by pathogenic entities. The results of this study showed that despite the use of water treatment systems on ships, ballast waters carry microorganisms that can negatively impact new environments, including local fish populations (e.g., P. fluorescens). These observations point to the need for further research on the effectiveness of ballast water management systems used to date to minimize the environmental impact of organisms carried in ships’ ballast water to preserve natural resources and environmental sustainability in port waters.