The Secret Life of The Ocean by Maria Gonzalez

THE SECRET LIFE OF THE OCEAN

THE SECRET LIFE OF THE OCEAN Compiled by M. A. Gonzรกlez

Left: Obelia sp.

CONTENTS Introduction

05 Marine Gastropods

11 Copepods

Taxonomy:

06 Chaetognatha

Living in Groups:

01 Nanoplanktonic Flagellates 09

07 Tunicates

Apaptations

02 Cnidarians

08 Cladocera

Night Swimming

03 Phylum Rotifera

09 Krill

Communities of Zooplankton

04 Polychaeta

10 Insect Larvae

Colphon

Left: Obelia sp.

INTRODUCTION By Marine Biologist M. E. Skeel Zooplankton are the tiny animals that float around on the surface of the ocean and feed on the microscopic plants that make up the phytoplankton, or on each other. They are so small that they cannot easily be seen and so for most people they donâ&#x20AC;&#x2122;t even exist. But what would happen if they didnâ&#x20AC;&#x2122;t? We have clues from the fossil record. At the end of the Permian there was a huge extinction event that took out an estimated 95% of all living species at the time. Again, at the end of the Cretaceous, there was another massive extinction event which took

out not only all the dinosaurs but many other species as well, including the majority of large marine species. The causes of these extinction events are still debatable although there is strong evidence for a meteor strike at the end of the Cretaceous. What does seem evident is that whole ecosystems collapsed because the food chains collapsed. When the plants and animals at the bottom of the food chain died in their millions or even billions, animals further up the food chain died out for lack of food. Even if they survived the initial catastrophe, they starved in the years of dearth following.

This is what would happen to the marine ecosystems if something were to happen to the zooplankton. Even now, this can be seen in the phenomenon known as El Nino, when the currents off South America change. Normally there are areas of upwelling off Peru where nutrient-rich cold waters rise to the surface, which leads to plankton blooms which feed the fish. When an El Nino event occurs, the currents change, the upwelling does not occur, the plankton blooms fail and the fish either starve or move elsewhere. Other animals such as penguins and seals are also affected and many chicks and

pups unlucky enough to be born in such years will starve. Half the whales of the world are baleen whales and they are totally dependent upon phyto and zooplankton for their food. These whales are migratory, going to warm tropical waters to raise their babies. Then they travel great distances to areas of upwelling in colder waters such as the Subantarctic Convergence where plankton thrive on rising nutrients. It takes millions of planktonic organisms in each mouthful to sustain a humpback whale. To sustain an entire population of even 2

one species of baleen whales takes billions of plankton every year. Each whale has to eat enough to sustain itself not only for the six months of feeding but a further six months of travel, breeding and child rearing in nutrient and food-poor tropical waters. Are phytoplankton enough to sustain the whales? Apparently not. What they need are krill; millions and millions of tiny crustaceans that resemble shrimp. These animals are the basis of the entire Antarctic food chain, supporting the fish, the sharks, penguins, seals and whales. Remove these tiny

animals and potentially the entire ecosystem would collapse, with dire consequences to all these life forms. So are the zooplankton of the worldâ&#x20AC;&#x2122;s oceans in any danger? It doesnâ&#x20AC;&#x2122;t look like we are going to be hit by a meteor any time soon but there is a danger closer to home: ourselves. As we deplete the oceans of the larger fish, we are fishing lower and lower on the food chain. Now large factory ships are beginning to take krill. Some of it goes for fertilizers and a lot of it ends up in pet food. A few people are making a large profit on these

tiny animals. But if we overfish the zooplankton communities, we risk the collapse of the oceans ecosystems and then we will find out just how important zooplankton are.

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ZOOPLANKTON: (zoh-plankton)

Zooplankton are tiny animals found in all ocean zones, particularly the pelagic and littoral zones in the ocean, but also in ponds, lakes, and rivers.

They are a key component of marine ecosystems.

TAXONOMY Information by marinebio.org

Zooplanktons are classified by size and by developmental stage. Size categories include: picoplankton that measure less than two micrometers, nanoplankton measure between two to 20Âľm, microplankton measure between 20Âľm up to 200 Âľm, mesoplankton measure between 0.2mm up to 20mm, also macroplankton measure between 20mm to 200mm, and the megaplankton, which measure over 200mm (almost 8 inches). There are two categories used to classify zooplankton by their stage of development: meroplankton and holoplankton. Meroplanktons are actually larvae that eventually change

into worms, mollusks, crustaceans, coral, echinoderms, fishes, or insects. Holoplankton remain plankton for their entire life cycle, and include pteropods, chaetognaths, larvaceans, siphonophores, and copepods. Meroplankton and holoplankton are components of almost every taxonomic group. However, the most common plankton are protists, nanoplanktonic flagellates, cnidarians, ctenophores, rotifers, chaetognatha, veliger larvae,

base of marine food webs as primary producers. Protozoa are also protists and are similar to animals. Protozoa make up a huge part of micro and nanozooplankton, such as amoebas, ciliates, and flagellates. These animals do not photosynthesize energy. Some amoebas such as those classified as Foraminifera and Actinopoda have hard skeletons, usually larger than 2 millimeters in diameter, that help form deep-sea sediment.

copepods, cladocera, euphausids, krill and tunicates. Protists produce energy by photosynthesis and form the 7

Protozoa with mixed Ciliates

NANOPLANKTONIC FLAGELLATES Zooplankton also include the nanoplanktonic flagellates that help keep bacteria populations under control. They are characterized by either a long tail used for swimming (flagellates) or by hair-like structures called cilia (ciliates). Some dinoflagellates have a net-like structure called a protoplasmic net— used to capture and eat prey that are typically larger in size than bacteria. Some dinoflagellate species are also responsible for harmful fish kills and the infamous red tides. Ciliates are capable of catching bacteria, other protists and phytoplankton.

CNIDARIANS

Mixotrophs are an amazing organism that are half plant and half animal. Mixotrophs have the ability to ingest other organisms through phagocytosis (phago: “to eat” + cytosis: “cells” = the process of engulfing other cells for ingestion) but also contain functional photosynthetic structures.

Cnidaria is a phylum that contains the colonial siphonophores and the scyphozoans—also known as the true jellyfish. Both of these animals are predators and have stinging tentacles. They are not found often in fresh water and in the ocean they inhabit the layers closer to the surface. Comb jellies or ctenophores were previously classified under Cnidaria but have recently been distinguished from other jellyfish because they lack the characteristic stinging cells of other jellyfish known as nematocysts. Comb jellies keep copepod zooplankton levels in check through predation.

Cnidarians

PHYLUM ROTIFERA There are about 2,375 species of rotifers in freshwater and only 125 in the ocean. Most of the rotifers are non-motile (not able to move) but about 100 species are holoplanktonic. They usually eat bacteria, detritus, other rotifers, algae or protozoa. Rotifers are highly efficient reproducers. They are able to reproduce asexually (without a mate) when environmental conditions are good, and sexually when environmental conditions are stressful. This ability allows rotifers to conserve energy in good conditions and adapt to their environment in stressful conditions. Adaptation is possible through sexual reproduction because a variety of

POLYCHAETA offspring are produced, allowing the individuals best suited to the environment to survive. These tiny animals are quite unique because they demonstrate incredible complexity in comparison with organisms of a similar size. The distinguishing feature of a rotifer is its corona, a collection of cilia shaped like a wheel around the head end of the organism. As the cilia move, they create a current which sucks in food for the rotifer and helps it to navigate.

The Polychaeta or polychaetes are a class of annelid worms, generally marine. Each body segment has a pair of fleshy protrusions called parapodia that bear many bristles, called chaetae, which are made of chitin. Polychaeta means “many-bristled” (as opposed to the Oligochaeta which are “fewbristled”), and indeed the polychaetes are sometimes referred to as bristle worms. More than 10,000 species are described in this class. Common representatives include the lugworm (Arenicola marina) and the sandworm or clam worm Nereis. 11

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MARINE GASTROPODS

CHAETOGNATHA

Another type of zooplankton include the larvae of benthic mollusks usually found in coastal waters, such as marine gastropods including heteropods or pteropods.

The chaetognatha or Arrow worms are mostly holoplanktonic and are abundant worldwide. These transparent worms are approximately 3 cm long and have fins on the sides of their bodies.

Some tunicates are planktonic, such as the holoplanktonic classes Appendicularia and Thaliasia. Both are filter feeders; Appendicularia consumes small food particles using a mucous filter. Other types of tunicates are benthic and are only planktonic during their larval stages.

TUNICATES

Heteropods

Arrow worm

Thalia democratica

(Phylum Arthropoda, Subphylum Crustacea, Order Copepoda)

(Euphausia superba)

Claudocera are found in coastal waters. They swim using an antenna, like copepods, but instead of using their first antenna—they use the second antenna. They appear to have two sections to their body but it’s only an illusion caused by a folded outer shell. Cladocerans eat phytoplankton and other zooplankton. Like many species of zooplankton, cladocerans migrate to the surface at night. This is referred to as “diurnal migration”.

Krill, classified under Euphausids, are found all over the world. They can be 3 cm large and are an important source of food for many types of whales. In cold waters, krill often feed on diatoms, a type of phytoplankton. In warmer water they eat other animals.

CLADOCERANS

KRILL

INSECT LARVAE The larvae of the midge Chaoborus is the only widely known insect larvae classified as plankton. Chaoborus comes up during the night to float with other plankton and eats many types of zooplankton in lakes.

Rotifers

Krill

Ciliates

COPEPODS (Phylum Arthropoda, Subphylum Crustacea, Order Copepoda)

Most macrozooplankton are copepods found in marine and freshwater ecosystems. Copepods swim using an antenna and frontal structures on their bodies. They eat phytoplankton and detritus, and occasionally other zooplankton smaller in size.

LIVING IN GROUPS

ADAPTATIONS All species of plankton have been forced to develop certain structural adaptations to be able to float in the water column. Adaptations include: flat bodies, lateral spines, oil droplets, floats filled with gases, sheaths made of gel-like substances, and ion replacement. The flat body and spines allow some species of plankton to resist sinking by increasing the surface area of their bodies while minimizing the volume. All other adaptations keep plankton from sinking quickly to the bottom. Zooplankton have also adapted mechanisms to deter fish (their heaviest predator) including:

transparent bodies, bright colors, bad tastes, red coloring in deeper water, and cyclomorphosis. Cyclomorphosis occurs when predators release chemicals in the water that signal zooplankton, such as rotifers or cladocerans, to increase their spines and protective shields.

NIGHT SWIMMING

Many types of zooplankton migrate deeper into the water during the day and come up at night. The migration of species appears to be dependent on location rather than particular species types. All plankton migrate differently based on factors like age, sex and the season. The amount of light is probably the major factor in the extent of migratory behavior. It seems that zooplankton move around most in low light and least in higher light situations. Itâ&#x20AC;&#x2122;s possible that zooplankton migrate to lower levels during the day so they are less visible to predators relying on vision. At Copepods

night, zooplankton can sneak up to the surface and snack on phytoplankton relatively safely. The lower metabolism occurring in colder waters during the day may also be a factor in the migration of zooplankton. This way, zooplankton can save energy by feeding in the cooler, night waters. The fact that different species of zooplankton have varying migration times seems to be the result of a partitioning of resources.

COMMUNITIES OF ZOOPLANKTON Specific species of zooplankton occupy particular marine habitats. Each species is uniquely adapted to factors like light, temperature, turbulence, and salinity in its environment. Zooplankton on one side of the Gulf Stream are different species from those on the other side. These characteristics of different species of zooplankton can sometimes help scientists distinguish one water mass from another.

change. Zooplankton are highly responsive to nutrient levels, temperatures, pollution, food that is not nutritious, levels of light, and increases in predation. As well as providing an essential link in the marine food chain (which is an understatement), the diversity of species, amount of biomass and abundance of zooplankton communities can be used to determine the health of an ecosystem.

Zooplankton are also sensitive to their environment and like phytoplanktonâ&#x20AC;&#x201D;a change in zooplankton concentration can indicate a subtle environmental

There are other factors that influence the distribution of zooplankton like predation, reproduction, community interactions and the amount of 21

available resources. Zooplankton can also be predators of algae or protozoa causing the sizes of these organisms to change through evolution. When light concentrations in boreal or temperate areas increase in spring, phytoplankton communities increase in number. Because zooplankton feed on smaler planktons like phytoplankton, the numbers of zooplankton increase in response during the spring. However, the reaction of zooplankton is dependent on the species type as well, so sometimes the zooplankton numbers increase only in the summer with other spike in the fall. 22

Chaoborus

Zooplankton are also affected by levels of pH, heavy metals, calcium, and aluminum. Nutrients like nitrogen and phosphorus will affect the prey of zooplankton (like algae, protozoa and bacteria), indirectly affecting zooplankton survival. Scientists are still putting together pieces of the zooplankton puzzle. Some questions include how nutrient levels found in algae can influence the growth and behavior of zooplankton. Other questions considered important to marine and human life is how toxins and pollution is affecting this crucial link in the food chain.

Marinebio.org References Dinoflagellates - Andrew MacRae, Palynology at The University of Calgary Dept. of Geology and Geophysics Krill: Chesapeake Bay Program Zooplankton Project Zooplankton Ecology - Department of Fisheries and Aquatic Sciences, University of Florida Robert W. Sanders, “Zooplankton”, in AccessScience@McGraw-Hill, http://www.accessscience.com, DOI 10.1036/1097-8542.756950 Podon sp

COLOPHON Graphic Design and Silkscreen Parsons The New School for Design Professors: Katarzyna Gruda William Morrisey Design: Maria A. Gonzalez Typefaces: Akzidenz Grotesk Bodoni Old Face BE. Software: InDesign CS4 Text: marinebio.org M.E. Skeel (www.helium.com) Images: Flickr Guide to the Marine Zooplankton of south eastern Australia. (http://www. 24

tafi.org.au/zooplankton/index.html) Noctiluca scintillans