Final answer:
Ballast water contains a wide range of organisms such as bacteria, algae, invertebrates, and fish. These species are transported globally as ships take in and discharge ballast water, despite the challenging conditions and the BWE process designed to flush out coastal organisms. Hence, all the listed options are correct.
Step-by-step explanation:
Organisms present in ballast water include a variety of aquatic species. These organisms encompass bacteria, algae, invertebrates, and even fish species. Ballast water serves as a significant vector for the global transport of these organisms as ships move around the world, taking in and discharging ballast water in various ports. Notably, the majority of species transported in ballast water are invertebrates. These include not only adult forms but also microscopic stages such as larvae and eggs that are resistant to the stresses of transport. Phytoplankton and zooplankton are frequently found, and species of fish, although less common, are also transported in ballast tanks. Some bacterial groups and various algae (eukaryotic organisms) are also present, flourishing even in the challenging conditions within the ship's tanks.
The process of Ballast Water Exchange (BWE) attempts to reduce the risk of introducing non-native species by exchanging coastal ballast water for mid-ocean water. However, some species still survive the journey despite the osmotic stress caused by this process. The survival of these organisms is a testament to their resilience and their ability to withstand a range of environmental conditions, including darkness and changes in salinity and temperature.
Therefore, the correct answer to the question, "What organisms are present in ballast water?" would be 4) All of the above, which includes bacteria, algae, invertebrates, and fishes.