ISIIS in the field: OSTRICH cruise in progress

Hi Plankton Portal!

The Science Team is currently out in the field in the Straits of Florida, on the R/V Walton Smith, sampling with both ISIIS and MOCNESS (Multiple Opening Closing Net and Environmental Sampling System), on an 18-day cruise titled OSTRICH (Observations on Subtropical TRophodynamics of ICHthyoplankton).

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The overall goal of this NSF-sponsored project is to quantify the patterns and consequences of the fine-scale to sub-mesoscale distributions of larval fishes, their prey, and their predators near and across a major western boundary current passing through the Straits of Florida. By sampling a series of water masses at very high resolution, this study addresses specific hypotheses concerning: i) the drivers of aggregations and patchiness, and ii) the biological consequences of predator-prey interactions at fine scales.

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Sample ISIIS images showing diversity of plankton from multiple coastal sites (including the Southern California Bight!)

Sampling involves a novel combination of detailed in situ sampling of the horizontal and vertical distributions of plankton, targeted fine-scale net sampling, and analyses of individual-level recent daily larval growth to enable the identification of the biological and physical processes driving fine-scale plankton distributions.

Follow along on the ISIIS facebook page as we periodically post updates (via our terrible internet connection at sea!) and also check out this cool video made by one of our cruise participants, Chris Muiña:

 

 

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What’s the goal of this research project?

The underlying objective of this research project is centered on a small-scale front and its associated biological activity. A front is a meeting of two water masses, and oceanic fronts are generally broken up into several broad categories, depending on the physical environment and phenomenon that cause these water masses to converge. Oceanographers have been interested in fronts for a long time, because they tend to be areas of high productivity. The elevated productivity at fronts is a result of the converging water masses physically aggregating many marine organisms.

Small-scale fronts are, as the name suggests, smaller in spatial scale: they tend to occur on the order of tens of kilometers instead of hundreds to thousands of kilometers like some of the other major fronts. Small-scale fronts occur frequently, but have also been harder to describe because they are more ephemeral than large fronts.

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Sampling region in the Southern California Bight (SCB)

We set out to study one particular small-scale front in the Southern California Bight (SCB, see map for study region) because it was in an area that has received long-term oceanographic investigation – it is always good to do studies where there is lots of baseline data. We were primarily interested in exploring what biota was out there and seeing if there was biological aggregation at the front.  Indeed there was! We saw a large aggregation of our now favorite jellyfish, Solmaris rhodoloma, at the front and described it in a 2012 research paper. You don’t have to worry about reading it. It basically says what I just told you: we found a lot of Solmaris at this small-scale, salinity-driven front.

Solmaris rhodoloma aggregation

Solmaris rhodoloma aggregation

One of the interesting things about Solmaris is that they are part of a family of medusae that predate exclusively on other gelatinous zooplankton. They have been known to eat arrow worms and doliolids, but now, because of our images, we also think they are eating larvaceans and small siphonophores as well. So finding the large aggregation of Solmaris actually generated another research question for us: what’s going on with the rest of the gelatinous zooplankton at and around this front? What are the main processes driving their distribution? Is predation pressure from Solmaris affecting them in any way?

It turns out that the second question is much harder to answer than you would think. Not knowing exactly what Solmaris is eating, and how long they’ve been accumulating at the front makes it difficult for us to tell if they’re just happening upon a patch of prey or they have already eaten everything around them. One approach is to determine the movements and directions of the organisms, which is why we’re asking you to measure their orientation. We hope that knowing their orientation (and that of their potential prey) can help us model their movement patterns and “age” the Solmaris aggregation, so to speak. Of course, it’s possible that even with this data we will still not be able to determine how long Solmaris has been aggregating at the front. However, this kind of orientation information has never been acquired for jellyfish of this size and at this scale, so any data we gather will be new and interesting!

This is just one of many questions that Plankton Portal can help answer.  The biological data contained within these images can bring us closer to a greater understanding of zooplankton ecology in general.  Understanding the abundance, distribution and biomass (that’s where the size measurements come in) of this extremely understudied group of organisms – the small gelatinous zooplankton – can help us assess their broader impact in the marine food web, contribution to carbon cycling, and even help us learn how to identify hotspots of marine productivity in the future. This is how research grows and develops: it starts from a small, initial question (“hmm, I wonder if there is anything interesting at a small offshore front?”), which leads us to additional questions, and down the road, will hopefully help mankind appreciate and better protect its precious marine resources.

Thank you for your help and participation in Plankton Portal – you are contributing to a more knowledgeable future and hopefully one where we can better care for the sea around us.

How do we get the images?

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Since the 1800’s, plankton has been studied and collected using simple nets with very fine mesh. The process of analysis of these plankton ‘samples’ is tedious, labor intensive, confined to laboratory, and can only be done on relatively small areas of the ocean. By sampling in this manner, it is difficult to get a good understanding of how planktonic organisms are distributed and how they interact with each other. Yet plankton represents a very important part of a global system feeding larger animals like fish, whales and many others. The In Situ Ichthyoplankton Imaging System (ISIIS) is one of a few systems in the world capable of improving the way we study plankton to better understand their life and function in the marine environment. Instead of using an actual net to capture plankton, ISIIS captures the images of the organisms and information about their immediate surroundings. ISIIS samples continuously, resulting in a collection of digital images that record the exact location of the various plankton organisms in relation to each other and the environment in which they live. Further, the images are recorded onto a simple hard drive instead of slurry of plankton all mixed together in a sample jar with formaldehyde (yech!).

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ISIIS is an underwater imaging system developed to capture real time images of plankton that are relatively rare, small, and fragile such as fish larvae and delicate gelatinous organisms (like jelly fish). ISIIS is composed not only of a macro-camera system with its own illumination but it also is integrated into an underwater vehicle with a variety of additional sensors to measure the depth, salinity and temperature of the water, as well as such properties as dissolved oxygen, light level, and even how much chlorophyll a (measure of primary production) is present. Together, the camera and sensors provide detailed profiles and tracks of what plankton are where and what the ocean environment around them is like.

isiis schematic

The vehicle, and associated imaging system and sensors, moves up and down through the water column using side-mounted, user-controlled dive fins (like an underwater glider) while being towed behind an oceanographic ship moving at 5 knots. The vehicle frame is divided into four compartmentalized enclosures with imaging and optical equipment seamlessly integrated into ISIIS’s ventral housings and environmental sensors and electronics in the dorsal housings. ISIIS is designed to undulate in a zigzag fashion between the surface and a maximum depth of 200 meters.

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The ISIIS system utilizes imaging technology very similar to an office scanner flipped on its side. The imaged parcel of water passes between the forward portions of two streamlined pods where it is “scanned” and transformed into a continuous image. The resulting very high-resolution image is of plankton in their natural position and orientation. When a sufficient volume of water is imaged this way, quantification of concentration (individuals per unit volume) and fine scale distribution is possible. ISIIS is capable of imaging a maximum of 162 Liters (43 gallons) of water per second (when moving at 5 knots) with a pixel resolution of 70 µm (the thickness of a human hair).

The imaging data and associated oceanographic data are sent to the surface ship via a fiber optic cable and recorder onto a main computer for later viewing and analysis.