The Polynesian voyaging canoe Hikianalia is on a 2,400 mile return journey from Aotearoa to Hawaii. Crewmembers will be sending frequent updates so that educators and students can track her progress in conjunction with the Worldwide Voyage Tracking Map.
We can tell that we are now getting close to Tahiti and tropical islands by the warm water temperature (28° Celsius / 82° Fahrenheit) and a house fly that visited us two days ago on deck. We had a few rough days with some strong to variable winds and lots of squalls. Before that we had a few days of light winds where at times we sailed at slow enough speeds (less than 2 knots) to tow the plankton net twice for about 20 minutes each. Since we left Aotearoa (New Zealand) the water has lost its green color and become dark blue suggesting less primary production by phytoplankton. The lower production is also confirmed by the lower oxygen concentrations we have been measuring and is reflected in lower phytoplankton abundance and diversity in our plankton tow.
In general we can see that most are transparent with minimal pigments and many long spines and appendages. Even though most zooplankton are consumers of phytoplankton or other zooplankton, they are still low in the marine food chain and easily become prey for bigger animals. The lack of pigments and transparent appearance helps zooplankton to be less visible to predators. The other challenge zooplankton has is to stay close to the own prey, mostly phytoplankton, which stays relatively close to the surface of the water column as it needs sunlight to grow via photosynthesis. Plankton, generally defined as organisms, not able to swim against currents (plankton is derived from a Greek word that means drifting), are not good swimmers and therefore need other means of buoyancy to stay close to their food source. One option to increase buoyancy is to have lots of spines or appendages, another one is to have enclosed oil droplets – sometimes lightly yellow or orange in color.
Fish embryos or even hatched fish larvae are very hard to identify as they often look nothing like their adult form. Most of them however have white muscle tissue and often black pigment spots like the one in the picture below. Maybe one of our readers can tell us what this fish might be?