Although it might not feel like it, winter is finally over. The days are getting longer and as I mentioned in last month’s column, our local waterways are coming alive. Phytoplankton populations have now reached densities that will support the next level of the food web, the zooplankton.
The word zooplankton is derived from Greek words zoon meaning animal and planktos meaning wanderer. As “wandering animals,” zooplankton are similar to phytoplankton as they are not capable of swimming great distances, rather they drift where the currents take them. But unlike phytoplankton, zooplankton cannot produce their own food and must receive nourishment by feeding on other organisms.
Zooplankton are divided into two groups, holoplankton and meroplankton. Holoplankton are those animals that remain planktonic for their entire lives. Of these organisms, copepods are by far the most abundant and can be found living in every aquatic habitat on the planet. A type of crustacean, there are over 21,000 described species of copepod ranging in size from .2 mm to 10 mm in length. Their name comes from the Greek words Kope and Podos meaning “oar-footed,” which refers to a pair of swimming legs that propel them through the water like a pair of oars.
Copepods are known as primary consumers because they feed on phytoplankton, which are known as primary producers (synthesize their own food through the process of photosynthesis). Larger zooplankton, small fish, crustaceans, and even giant baleen whales feed upon copepods, creating a crucial link in marine food webs by transferring the energy produced by phytoplankton to organisms at higher trophic levels. Every local species of fish we enjoy to target depends on copepods as a food source during their larval stages. In fact, research has shown that striped bass will have a strong recruitment in years when spawning events coincide with high concentrations of copepods.
The second type of zooplankton, meroplankton, are organisms that spend part of their lives as plankton. This includes the larval stage of most fish, crustaceans, mollusks and polychaetes (worms). As part of the planktonic soup, they will feed on other zooplankton until they grow large enough to swim against the ocean’s currents or settle to a benthic lifestyle. At this point they will begin the adult stage of their life and will no longer be considered plankton.
A perfect example of this scenario is the tropical fish that arrive to the northeast every summer. After being spawned in the tropics, some of these larvae will be carried north via the Gulf Stream (an ocean current originating in the Gulf of Mexico and moving north along the east coast of the U.S.). By the time these larvae reach our area, they are fully developed and leave the “soup” to take on an adult existence. Unfortunately, many of these fish will perish when water temperatures drop at the onset of autumn as they are unable to migrate the great distance needed to return to warmer waters.
A positive aspect of an organism being part of the meroplankton is the ability for them to disperse their population to surrounding areas. This is how new shipwrecks or artificial reefs become colonized, as well as areas that have been decimated by overfishing to be repopulated.
Not all zooplankton are microscopic in size. Jellyfish, comb jellies and siphonophores (man o’ war) are some of the largest animals in the ocean (some attaining lengths greater than 100 feet). Even though they are capable of some basic swimming, they are not strong enough to swim against the currents, hence their classification of being part of the zooplankton. They are further categorized as meroplankton due to their alternating life stages. The adult stage, known as a medusa, is what we are most familiar with when discussing jelly-type organisms. After reproducing sexually, the resulting larva, known as a planula, will remain in the plankton until it comes in contact with a hard substrate. At this point, it leaves its planktonic life and becomes a benthic organism known as a polyp and looks very much like a sea anemone. From this stage, it will reproduce asexually, budding itself and returning to the plankton.
There might not be too many fish “biting” right now, but as zooplankton populations continue to boom, that will soon change. A smorgasbord of zooplankton will draw the attention of hungry baitfish. These baitfish ultimately attract all the fish species that we enjoy catching while fishing the waters of the North Fork.
With a degree in marine biology from LIU/Southampton, Chris Paparo is the manager of Stony Brook Southampton’s Marine Sciences Center. Additionally, he is a member of the Outdoor Writers Association of America and the NYS Outdoor Writers Association. You can follow Paparo on Facebook and Instagram at @fishguyphotos