About agreer35

I am a biological oceanographer at the University of Southern Mississippi interested in the application of imaging technology to study ocean life

Polychaetes: ocean “crawlers”

The name for these worms literally means “many bristles,” which refers to the “legs” that they use to move through the water. These surprisingly fast animals are predators of copepods, appendicularians, and even small larval fishes. Most polychaetes are meroplankton, meaning that they are plankton only for their egg and larval stages. When they reach a certain size, they settle out of the water column and spend their adult lives associated with some kind of substrate (e.g., reefs, sand, mud, rock, etc.). A few species are holoplanktonic, spending their entire lives drifting in the ocean currents.

One genus of holoplanktonic polychaete that we have encountered in the ISIIS images is Tomopteris. These 2-5 cm polychaetes feature several adaptations that are favorable for life in water column. First, they are highly transparent, allowing them to blend into the surrounding water. If they could be easily seen, polychaetes would be tasty little snacks for fish. One thing that limits their transparency is a gut that runs down the middle of the body. When this gut is full, the polychaete is easier to see because it cannot hide a stomach full of food! Someone might hypothesize that polychaetes that have recently eaten might be more susceptible to visual predators, such as fish, but to date, no one has explored this question. Second, their “legs” have paddle-shaped ends with two lobes, which improve their swimming ability compared to other groups of polychaetes (Todd et al. 1996).

AllPoly

Many of these polychaetes (Tomopteris spp.) are actively swimming. The gut runs down the center of the animal between the legs, but it is difficult to see in these images.

Although polychaetes are relatively rare plankton, we did manage to see a good number of them near Stellwagen Bank, Massachusetts, USA. The graph shows the vertical distribution of the Tomopteris polychaetes along two ISIIS transects. As you can see, Tomopteris polychaetes were predominantly found in deeper waters. In the images taken, it is difficult to see the gut, which would show up as a white line running down the middle of the body. This means that these individuals had not eaten recently, so what are they doing in the deep waters? Possibly hiding from predators in waters with less light? Or could this behavior be related to mating? Only with further research can we find out what influences the distributions of these and other planktonic animals.

PolyProfs

Near Stellwagen Bank, Massachusetts, USA, many of the polychaetes tended to reside deeper in the water column. They are virtually absent from the top 20 m.

Unidentified polychaete larvae imaged by ISIIS in the Gulf of Mexico

Unidentified polychaete larvae imaged by ISIIS in the Gulf of Mexico.

References:

Todd CD, Laverack MS, Boxshall GA (1996) Coastal Marine Zooplankton: A practical manual for students (2nd ed.) Cambridge University Press, New York.

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Plankton blooms: Causes and Consequences

As organisms that cannot swim against the currents, plankton are intimately connected to their physical environment. Many species are quite sensitive to the temperature, salinity, and nutrient levels that either lead to their proliferation or demise. Physical conditions and nutrient levels can lead to high abundances of particular plankton types. These plankton “blooms” are common throughout the world’s oceans and can be composed of phytoplankton, zooplankton, or gelatinous zooplankton, depending on the environmental conditions.

Generally phytoplankton (plankton that use photosynthesis like plants) need nutrients and light to grow at very high rates. Since light is readily available in the surface ocean, nutrient availability is the most important driver of phytoplankton blooms. Phytoplankton blooms of most concern to environmental monitoring groups are often described as Harmful Algal Blooms (HABs). Some HABs composed of diatom species Pseudo-nitzschia spp. or the dinoflagellate Karenia brevis can produce toxins harmful to copepods, fish, and higher trophic levels like dolphins and humans. “Red tides” are actually blooms of Karenia brevis that sometimes lead to massive fish dieoffs. Other phytoplankton blooms are harmful not because of the toxins that they produce, but because of the processes that happen when the blooms die off: massive amounts of phytoplankton die and sink to the bottom where they are decomposed by bacteria. These bacteria use oxygen to consume the dead phytoplankton, creating large portions of the water column that are low in oxygen. Fishes and some zooplankton avoid these low oxygen zones, but gelatinous zooplankton seem to be able to withstand low oxygen conditions. These low oxygen regions are often referred to as “dead zones” because very few animals can live there. A dead zone occurs regularly in the summertime in the northern Gulf of Mexico and has been expanding in recent years. Reducing nutrient/fertilizer runoff from farmlands and cities is therefore crucial to limiting the growth of phytoplankton and maintaining healthy coastal ecosystems.

A bloom of Karenia brevis viewed from the air. This "crimson tide" is only composed of small dinoflagellates, but it can have devastating consequences for a coastal ecosystem. Source: http://microbewiki.kenyon.edu/index.php/File:Red_tide_genera.jpeg

A bloom of Karenia brevis viewed from the air. This “crimson tide” is only composed of small dinoflagellates, but it can have devastating consequences for a coastal ecosystem.
Source:
http://microbewiki.kenyon.edu/index.php/File:Red_tide_genera.jpeg

Blooms of zooplankton can form via two different mechanisms 1) currents from different water masses merge to create a dense patch of organisms, or 2) consistently favorable conditions allow the zooplankton to reproduce faster than their predators can consume them. These two mechanisms are distinguished in the scientific literature as “apparent blooms” and “true blooms” (Graham et al. 2001). Apparent blooms can result from converging currents such as fronts, or the behavior of zooplankton aggregating along some kind of physical discontinuity, such as a thermocline. True blooms are typically the result of high food concentrations, high survival of larvae/juveniles, or a combination of multiple factors. For scientists, it is sometimes difficult to know what mechanism led to a zooplankton bloom, and they need to consider the history of the water masses where the zooplankton are found to figure out how the bloom formed (Greer et al. 2013). Zooplankton blooms associated with copepods are generally considered to be healthy for the ecosystem. The timing of copepod peak abundances with the first feeding of larval fishes is thought to be an important factor contributing to the variation in fish population abundances (Cushing 1975). Blooms of jellyfish, on the other hand, are often associated with ecosystems that are environmentally degraded through high nutrient input or consistent overfishing (Jackson et al. 2001), but there are some scientists who think jelly blooms are simply a characteristic of their life histories (Condon et al. 2013). More data on jellyfish abundances over longer time periods will help scientists understand relationships between the environment and the frequency of jellyfish blooms. You can also report jellyfish sightings at http://www.jellywatch.org.

Here is avideo of one ISIIS downcast through the water column of near a frontal feature offshore of San Diego, CA, USA. It shows a bloom of Solmaris spp. jellies concentrated near the surface. Convergent currents that are commonly seen at fronts likely contributed to the formation of this bloom.

References:

Condon RH, Duarte CM, Pitt KA, Robinson KL, Lucas CH, Sutherland KR, Mianzan HW, Bogeberg M, Purcell JE, Decker MB, and others (2013) Recurrent jellyfish blooms are a consequence of global oscillations. Proc Natl Acad Sci U S A 110:1000-1005

Cushing DH (1975) Marine ecology and fisheries. Cambridge University Press, London

Graham WM, Pagès F, Hamner WM (2001) A physical context for gelatinous zooplankton aggregations: A review. Hydrobiologia 451:199-212

Greer AT, Cowen RK, Guigand CM, McManus MA, Sevadjian JC, Timmerman AHV (2013) Relationships between phytoplankton thin layers and the fine-scale vertical distributions of two trophic levels of zooplankton. Journal of Plankton Research 35:939-956

Jackson JBC, Kirby MX, Berger WH, Bjorndal KA, Botsford LW, Bourque BJ, Bradbury RH, Cooke R, Erlandson J, Estes JA, and others (2001) Historical overfishing and the recent collapse of coastal ecosystems. Science 293:629-637

Arrow worms: voracious plankton predators

You may think orcas or great white sharks are the most voracious predators in the oceans, but based on their abundance and ability to consume a wide range of prey items, chaetognaths (a.k.a. “arrow worms”) give those big animals a run for their money. Large predators like sharks are extremely rare, but scoop up a bucket of seawater almost anywhere in the world and you are likely to find a few chaetognaths (if you have a microscope handy). Chaetognaths are transparent worms that often remain motionless in the water column, apparently relying on the element of surprise to capture a wide variety of plankton, including copepods, appendicularians, small fish larvae, and smaller chaetognaths. Chaetognaths are thought to be generalist feeders because their stomach contents often reflect the community captured by plankton nets. They use a mass of chitinous hooks around their mouths to capture prey – which gives them their name (“chaetognath” translates from Latin to mean “hairy jaw”) and a notoriously menacing appearance.

Chaetognaths are often straight in the ISIIS images but can also swim rapidly for short distances. The camera typically cannot resolve the tiny chitinous hooks on the chaetognath's mouth.

Chaetognaths are often straight in the ISIIS images but can also swim rapidly for short distances. The camera typically cannot resolve the tiny chitinous hooks on the chaetognath’s mouth.

Chaetognaths comprise about 100 species that are all typically 1-2 cm long. They are most abundant along the coasts, with some species being so sensitive to salinity that oceanographers can identify discrete water masses based solely on the community of chaetognath species. Similar to many other types of zooplankton, chaetognaths are hermaphrodites, first being male then changing into female as they get larger. Fertilized eggs can be attached to vegetation or encased in a gelatinous web. Eggs then hatch into juvenile chaetognaths, and thus they have no larval stage. This is called direct development because there is no process of metamorphosis.

A clear image of the chaetognath's mouth on the cover of Current Biology.

A clear image of the chaetognath’s mouth on the cover of Current Biology.

The chaetognath’s body is streamlined and adapted to feeding with minimal visual input. The have sensory cilia that can detect small vibrations in the water that tell the chaetognaths that prey is within striking distance. With a quick flick of its tail, the chaetognath surges forward to capture the prey in its chitinous hooks used for grasping. It then transfers the prey to its mouth where it is swallowed whole. Some deeper water chaetognaths (>700 m deep) can even use bioluminescence to create a cloud of light that scientists think can be used to escape predation (Haddock and Case 1994).

The most handsome chaetognath found by our citizen scientists!

The most handsome chaetognath found by our citizen scientists!

References:

Haddock SHD and Case JF (1994) A bioluminescent chaetognath. Nature 367:225

Johnson WS and Allen DM (2005) Zooplankton of the Atlantic and Gulf coasts: A guide to the identification and ecology. Johns Hopkins University Press, Baltimore, MD

Lalli CM and Parsons TR (1997) Biological oceanography an introduction. Elsevier Butterworth-Heinemann, Burlington, MA

Copepods: Rice of the Sea

Of all plankton groups, probably most is known about the copepods. They represent a critical link in the food chain and are consumed by diverse animal community ranging in size from small fish, chaetognaths, and ctenophores all the way up to large whales (the right whale is a voracious copepod feeder). Because of their small size and importance as food, copepods are affectionately known as “the rice of the sea.” Copepods are effectively captured by plankton nets because they have hard exoskeletons, and scientists have good estimates of their abundances and distributions. Although copepods are all relatively small (0.5 mm – 5 mm in length), they comprise over 200 families and 10,000 different species.

CopepodsTogether

Examples of typical copepods. Note to the two large appendages on the top of the head with small sensory hairs

Copepods consume both phytoplankton and microzooplankton in two different ways: suspension feeding and raptorial feeding. Suspension feeding is relatively passive and performed by beating small appendages that draw a current through a feeding chamber. Copepods then select which particles encountered are food and discard others. Raptorial feeding is used to actively capture prey. Many copepods have small sensors on their first appendages to detect water disturbances produced by prey and also predators. They can use these relatively large appendages to “hop” through the water and capture an unsuspecting prey item or to quickly escape a predator.

Copepod reproductive strategies vary greatly and are adapted towards the ability to withstand the variable conditions that characterize the ocean environment. For example, many copepod eggs have the ability to enter a phase of diapause where they remain viable on the bottom for several months or even years, only hatching with conditions are favorable (high concentrations of food). Some copepods carry their eggs, allowing them to develop a bit before releasing them into the water column. The timing of copepod reproduction is especially important for the life cycle of fishes because most fish larvae depend on the recently hatched copepod nauplii for food. If there are not enough copepod nauplii present when fish larvae are abundant, there could be mass starvation events causing few fish larvae to reach their juvenile stage. Because of this, the copepod life cycle is extremely important to fish populations and overall ocean ecosystem health.

This image was taken from a thin layer near Stellwagen Bank offshore of Massachusetts, USA. Each one of the white particles is a copepod. The concentration of organisms in this image corresponds to ~400,000 individuals per cubic meter! That is some good eating for a right whale!

This image was taken from a thin layer near Stellwagen Bank offshore of Massachusetts, USA. Each one of the white particles is a copepod. The concentration of organisms in this image corresponds to ~400,000 individuals per cubic meter! That is some good eating for a right whale!

One of the most remarkable characteristics of copepods is their tendency to aggregate in discrete thin layers within the water column. Sometimes >90% of the copepod biomass will be confined these thin layers, which are a maximum of 5 m thick. ISIIS and other systems that sample on small scales are ideal for detecting these layers of copepods, and the function of the formation and dissipation of copepod thin layers is not well understood. Copepods have been shown to be attracted to strong changes in current direction and speed, potentially allowing them to feed at a faster rate within these zones (Woodson et al. 2005). The changes in environmental variables associated with aggregations of copepods are of great interest to marine ecologists. With your help, we can better understand how these extremely important organisms are distributed throughout our oceans!

References:

Johnson WS, Allen DM (2005) Zooplankton of the Atlantic and Gulf coasts: A guide to their identification and ecology. Johns Hopkins University Press. Baltimore, MD.

Woodson CB, Webster DR, Weissburg MJ, Yen J (2005) Response of copepods to physical gradients associated with structure in the ocean. Limnol Oceanogr 50:1552-1564

Salps and Doliolids

Salps and doliolids (class Thaliacea) are interesting animals because they are in the phylum Chordata, which includes all animals with a notochord during development (e.g., humans, fish, cats), but thaliaceans have a vastly different appearance and feeding strategy compared to most vertebrates. A salp or doliolid body is essentially a giant pumping muscle that forces water through a mucous net filter that collects phytoplankton and is ingested periodically. Both groups have limited mobility, with salps using muscular contractions to scoot through the water, while doliolids use tiny beating cilia to propel themselves.

salpsolo

A salp in the process of forming a new chain of clones for asexual reproduction (see white coil)

The life history of salps and doliolids is remarkable and complex. Similar to plants, their life cycle alternates between sexual and asexual generations. The solitary phase reproduces asexually by budding off clones of itself. On salps, a chain of these clones develops on the solitary animal that is then released and reproduces sexually with other salp chains. The chains first mature as female and then change sexes to become male when they are larger! These chains release small solitary salps that then begin asexual budding once they are a certain size. Doliolids on the other hand produce short-lived tadpole larvae that are not seen in salps. When you consider that a chain of salps contains an average of ~28 individuals, it is no surprise that these organisms are capable of extremely fast reproductive rates and can double their populations in hours (Heron 1972). Some scientists think their remarkable reproductive rates can overwhelm other phytoplankton grazers, which could explain the fact that large salp aggregations are often associated with low biomass of other grazers (Alldredge and Madin 1982).

Doliolids images offshore of Monterey Bay showing asexual budding

Doliolids imaged offshore of Monterey Bay showing asexual budding

Because of their ability to reproduce quickly, salps are often very abundant near steady supplies of phytoplankton, such as at ocean fronts (zones where two water masses with differing physical properties meet) and eddies (Deibel and Paffenhöfer 2009). However, these organisms cannot tolerate extremely dense aggregations of phytoplankton because their mucous filters will become clogged with prey, which severely decreases their feeding efficiency. Salps and doliolids can “bloom” like other jellies, and when these blooms die off the dead salp bodies can export a large amount of carbon into deeper waters. Because of salps and doliolids close evolutionary relationship to vertebrates, scientists are also very interested in their developmental biology. Scientists are trying to use salps as a model organism to study the development of complex nervous systems in all vertebrate animals (Lacalli and Holland 1998).

Check out this video from Plankton Chronicles on these remarkable animals!

Plankton Chronicles Project by Christian Sardet, CNRS / Noe Sardet and Sharif Mirshak, Parafilms. See Plankton Chronicles interactive site: planktonchronicles.org

References:

Alldredge AL and Madin LP (1982) Pelagic tunicates: Unique herbivores in the marine plankton. Bioscience 32:655-663

Deibel D and Paffenhöfer GA (2009) Predictability of patches of neritic salps and doliolids (tunicata, thaliacea). J Plankton Res 31:1571-1579

Heron AC (1972) Population ecology of a colonizing species: The pelagic tunicate Thalia democratica – I. individual growth rate and generation time. Oecologia 10:269-293

Lacalli TC and Holland LZ (1998) The developing dorsal ganglion of the salp Thalia democratica, and the nature of the ancestral chordate brain. Philosophical Transactions of the Royal Society B: Biological Sciences 353:1943-1967

Why do we need Citizen Science?

In many fields of science, new technology is leading to unprecedented data production. This, in turn, requires extensive analysis with minimal sub-sampling to detect as much detail as possible. In biological oceanography, imaging systems have become more useful with increasing computer speed and storage capabilities, and image data address some of the fundamental problems with traditional sampling methods that are destructive to fragile organisms (i.e., jellyfish and marine snow). On a given tow with our system, the In Situ Ichthyoplankton Imaging System (ISIIS), we produce approximately 400,000 images in 7 hours with many different species across a range of sizes present in each image (500 μm to 13 cm). This is an incredible amount of information that would take years for one person to fully analyze. When we are out at sea, we typically sample for WEEKS and come back to land with millions of images. Computer algorithms can perform basic tasks of extracting specimens that look similar, but human brains are extremely adept at interpreting an organism in 3D and providing context in the image data that a computer cannot. The amazing abilities of people to recognize patterns that computer algorithms may see as unimportant cannot be underestimated.

Shrimp photograph taken from under a microscope

Shrimp photograph taken from under a microscope (photo credit: Cedric Guigand)

Another reason we are using Citizen Science is so that you, the citizen scientist, can participate in the process of discovery. After all, most oceanographic research is funded at least in part by taxpayer money, and these novel plankton images combined with Citizen Science are a great way to engage those who fund the research. We think it is far more effective to cultivate interest in science through the discovery process itself, rather than the production of jargon-filled reports and papers only understood by other oceanographers (don’t worry, those will come later). In addition, this online format provides an opportunity for us to educate people about life in the oceans, potentially inspiring the next generation of ocean scientists. With Citizen Science, there is the potential for new discoveries arising from simply allowing many people to look at the images.

This larva of a deep water shrimp was captured in the Gulf Stream near South Florida (Photo credit: Cedric Guigand)

This larva of a deep water shrimp was captured in the Gulf Stream near South Florida (photo credit: Cedric Guigand)

We believe our research with ISIIS is particularly applicable to Citizen Science and the process of discovery because this new imaging technology provides a huge amount of data and a unique glimpse into ocean life. I have spent the last 5 years of my graduate school career at the University of Miami examining hundreds of thousands of plankton images, and every time I flip through the images, I always have the feeling that I could see something that no human has ever seen before. I try to instill this sense of wonder and hope for discovery in all people that work with the images, because when you see something interesting, like an elaborate siphonophore or a dense patch of copepods, you are likely the first person to see that species in its natural environment. When we get enough eyes on these images and discussions facilitated through the Plankton Portal website, the sky’s the limit for the discoveries that can be made with Citizen Science!

Why use images to study plankton?

Although ocean science has made many great advances, many biological processes are still poorly understood. In the sciences generally, a common theme is using new technology to examine patterns on smaller, more fundamental scales (e.g., DNA technology in biology, nanoparticle physics), with the goal of revealing underlying mechanisms. Plankton imaging is a method to examine patterns of organisms on a smaller scale, giving insight into how these organisms live and interact with each other. In addition, many planktonic animals are fragile and easily destroyed by plankton nets: the traditional tool to study plankton distributions. These plankton nets also suffer from the problem of having to sample over large portions of the water column, so an oceanographer might use a single net to capture copepods and shrimps and assume that these organisms co-occur if they appear in the same sample. However, it is entirely possible that the organisms are confined to discrete thin layers that do not overlap spatially. An imaging system can distinguish between these two scenarios, while a plankton net cannot. Images also provide information about the natural orientation of plankton, which can allow us to make predictions about their movement and feeding strategies.

 The bongo net is a traditional tool of biological oceanographers but is biased toward plankton with a hard exoskeleton (crustaceans) (Image source: NOAA Cruise DE 10-09 Report).

The bongo net is a traditional tool of biological oceanographers but is biased toward plankton with a hard exoskeleton (crustaceans) (Image source: NOAA Cruise DE 10-09 Report).

When we think about the future of our planet, climate change and predicting its effects are of great concern. In order to make meaningful predictions about a system, you need to create a mathematical model. One of the most important aspects of any model is the initial conditions and baseline variability. For many planktonic animals, especially jellyfish, we do not know their abundance, variation, or how they interact within the oceanic food web, which is all crucial information for predicting the future of our oceans under climate change conditions. Using an imaging system like ISIIS can lead to better population estimates of many different plankton types, and this information can complement many types of oceanographic studies. Fine-scale data can improve estimates of feeding and encounter rates for planktonic organisms, which is critical to our understanding of the oceanic food web.

A colony of salps such as this one would be destroyed or broken up into individuals if sampled with a net system. The in situ image in this situation gives information on the asexual budding of this fast reproducing phytoplankton grazer.

A colony of salps such as this one would be destroyed or broken up into individuals if sampled with a net system. The in situ image in this situation gives information on the asexual budding of this fast reproducing phytoplankton grazer.

When compared to plankton samples preserved in ethanol or formalin, image data provide distinct advantages in data processing and collaboration. For one, oceanographers can tackle age old questions like what are the biological and physical drivers of plankton aggregations and dispersal, and how do plankton aggregations impact the populations of wild fish, a multi-billion dollar global industry? The ‘digitization’ of biological data improves the ability to share data, fostering collaboration among ocean scientists with differing expertise. Having these images available on the internet (through a database server) increases the accessibility of biological oceanography to students, teachers, and the public. It is our hope to one day have these images available to the public, so everyone can gain an appreciation for the diversity of life in the ocean and perhaps use them to supplement science classes. The Zooniverse and Citizen Science is a great start to achieving these goals of making ocean science more “open access,” and we are so appreciative of your help!