April 20, 2006

Peacocks of the Sea

It was a busy day with two MOC 1 nets launched and recovered, a MOC 10 deployed, an open water dive, and ring net tows. I was busy helping launch and recover nets, as well as process samples. Much of my day was spent at the sorting station. When cod end buckets are removed from the plankton nets they are hauled to the sample sorting station. One of the first tasks is to dump the contents into a white tray so the jellyfish, vertebrates, decapods, and euphausids (krill) can be removed. These trays are teaming with little crimson crustaceans, clear gelatinous water crawlers, and the remains of dead fish, primarily from the genus Cyclothone. While watching the organisms swim about, flecks of color shine in the water that resemble what Rainbow Fish scales floating in water might look like. Colors of blue, pink, purple, and red reflect in these containers teaming with little vigorously swimming animals. These tiny flat flashes of color remind me of flakes of mica that appear in sediments along a streambed. These colors are not from a mineral however, but instead they are reflections coming from the exoskeleton of Sapphirina, a marine copepod. Some of these copepods are parasites that live inside the siphon chamber of salps. Each species comes in a different color and it has been suggested that these colors may play a role in mate choice. This genus of copepods exhibits sexual dimorphism. That is, the males are physically different from the females. In this case the males are flashy and brightly colored, whereas the females are more translucent. These guys may be the little peacocks of the sea. See the following web link for an image and description:


Despite the abundant brilliance of these little copepods, the samples we are collecting are sparser than samples from colder waters. It appears the Sargasso Sea is not only a desert to man, but deserted of marine zooplankton as well. The northern waters are much more productive and have a greater biomass of zooplankton than this tropical station. One reason for this is that this part of the ocean is relatively oligotrophic, devoid of nutrients. The ocean in this region is more stratified. The upper waters do not mix well with the lower nutrient rich waters due to a strong thermocline created from the constant warm temperatures. In northern seas the surface water cools each season and sinks, helping mix the lower nutrient rich waters with the upper layer. These upper layers are the source of the primary production. The tropical waters do not get the same mixing, especially the Sargasso Sea which has weak currents. The nutrients like iron and nitrate tend to be low in the epipelagic zone and trapped in the organisms themselves. Very little production occurs and the amount of sugar, by-products of photosynthesis, is low. This low amount of food trickles down into the deeper zones, resulting in low zooplankton abundance. Similar affects can be seen in tropical lakes such as Lake Tanganyika. Although Lake Tanganyika receives a high amount of light, most of the nutrients for plant production are trapped in the cold deep water. The surface is lacking in nutrients and therefore produces little food. The biomass of animals in this lake is low compared to lakes in colder areas. In northern lakes the surface water cools below 4 degrees Celsius each year and sinks. The lakes turn over and the nutrients from deeper waters are mixed in the column. These lakes tend to be more productive and have a higher abundance of organisms.

Daily question: What is the organism depicted in the picture below and what makes it different from a cnidarian? (Hint: the common name refers to something you would use on your hair.)


(Photo from www.CoML.org/Images and Video)


Picture 1: Nancy Copley from WHOI on her birthday photographing a crimson crustacean.

Picture 2: Video microscopy image of a shrimp collected from CMarZ census.

Picture 3: Jellyfish collected from blue water dive.

Picture 4: Sargassum algae. This algae is endemic to the Sargasso Sea.

Picture 5: ARMADA Teacher-at-Sea, Joe Catron, splitting samples.