Assessing marine ecosystems health requires multiple tools to study in an integrative way environmental pollution and impacts across different biological levels. One of the main challenges is to link physical, chemical and biological components in large-scale ecosystems when little information is available. For example, the Deepwater Horizon oil spill in 2010, contaminated the water column in the Gulf of Mexico from the epipelagic (0-200 m) to the mesopelagic (200 -1000) and bathypelagic (>1000 m) habitats; but assessment of the impact to the deep-pelagic GoM was hampered due to a lack of comprehensive data regarding diversity, abundance, distribution, and pollutants baseline-content of pelagic fauna. Several programs since the spill (e.g. DEEPEND Consortium) have improved our knowledge and understanding of the deep-pelagic ecosystem, the largest habitat in the Gulf of Mexico, and on Earth. However, information regarding the source, composition and inputs of chemical contaminants to deep pelagic fauna is still absent. Chemical contaminants can alter biological diversity and ecosystem functioning, therefore are key for linking long-term population dynamics and environmental stressors.
As part of the DEEPEND Consortium, my role is to establish a time series of chemical composition in deep-pelagic fauna (fishes, shrimps, cephalopods) collected after the Deepwater Horizon spill. For this study, the analysis of polycyclic aromatic hydrocarbons (PAHs) was chosen because: 1) these compounds are common in crude oil; 2) are persistent in the environment; 3) their composition can be used to broadly detect the source of contamination; and 4) can be toxic to fauna. PAHs are a large group of organic compounds organized in multiple aromatic rings typically found as complex mixtures. They are present in petroleum, coal, wood, and their combustion products. When present in high amounts, for example after an oil spill in the ocean, PAHs can cause lethal and sub-lethal effects on fauna like juvenile and adult fishes, potentially increasing mortality, skeletal malformations, genetic damage, immunotoxicity, etc.
Recently, with the collaboration of different programs, we were able to establish a decadal assessment of PAHs in mesopelagic fish tissues as indicators of environmental contamination in the deep-pelagic ecosystem. The results generated from this study indicate deep-pelagic fishes were exposed to elevated concentrations of PAHs after the Deepwater Horizon spill (2010-2011). In 2015-2016, PAH concentrations were close to the levels measured in 2007; but only for muscle tissues, because elevated concentrations were found in ovaries containing eggs. The high concentrations of PAHs found in 2010-2011 (muscle tissue), and 2015-2016 (eggs) are within the range of PAH concentrations found to cause lethal and sublethal effects on fishes. These results suggest a long-term sink for oil in deep pelagic organisms, potentially greater than shallower counterparts. Our findings demonstrate the importance of monitoring the persistence of organic contaminants in deep pelagic organisms. However, our study also indicates the need for more extensive ecosystem-based efforts of the deep-pelagic ocean (> 10 years) to better understand the long-term impacts across multiple levels of biological organization.
Here are some of the animals I am examining for PAH contamination:
1) Cyclothone obscura; 2) Onychoteuthis banksii,; 3) Histioteuthis corona
For DEEPEND, I am one of the taxonomists that identify the cephalopods (squid and octopus) that are collected from the MOCNESS nets. I am also collecting two other mollusc groups, pteropods (Sea Butterflies) and heteropods (Sea Elephants). Once animals are identified, tissue could go to one or more of the following places for further DEEPEND study: Stable isotope analysis (examples food web interactions among fauna), PAH (studying possible contaminants), or genetic barcoding for species identification verification and genetic diversity analysis.
Photo 1: A Sea Elephant, Carinaria sp.
Photo 2: A sample of Sea Butterflies (pteropods)
One of the advantages of using the MOCNESS is that we can collect organisms at discreet depths to analyze patterns on a fine scale. All focus animals: fishes, crustaceans, gelatinous organisms, and cephalopods are examined to piece together a more complete picture of the midwater column dynamics as they all contribute to the carbon moving from the surface waters to the deep-sea floor.
Team Mollusca are looking at vertical migration patterns for our three groups. Past studies on cephalopod vertical migration involve very few individuals per species so it is important to make the most of the large collection we have to further analyze these patterns. Our findings suggest that there is no one set vertical migration pattern by group but the patterns differ by species. For example, deep-sea pelagic octopods and the Vampire Squid are not found above 600m in the water column while the Moon Squid and Firefly squid move from the mesopelagic (200-1000m) to the epipelagic (0-200m) nightly, presumably for feeding purposes. We are noticing similar patterns in the heteropods, some migrate upwards and some do not. Pteropod analysis is underway at this time, stay tuned!
Here are some of the molluscs that are migrators and non-migrators,
Non-migrators: Japetella diaphana and Vampyroteuthis infernalis
Migrators: Selenoteuthis scintallins and Pterygioteuthis sp.
In the DEEPEND, we apply many techniques to learn about the animals that live in the depths of the twilight zone. One of the types of equipment we use is called an echosounder. While this may sound like a strange instrument, its actually quite common and in fact is on most fishing boats, and often called the ‘fish finder’ or the ‘bottom machine’. We use a similar type of fish finder that is powerful enough to send and receive sound to the depths of the ocean and use the data we collect to study the patterns of the animals in the deep scattering layers (DSLs). In the figure, the daily migration event can be seen with many of the animals within the DSL moving from the depths into the surface at night. Interestingly, not all animals move up at night and some remain at depth and the use of the acoustic devices helps us to better understand how the DSLs change in space and time.
Photo 1: Output from the echosounder of the DSL layer moving up at dusk
Photo 2: Examples of collected animals in the MOCNESS that the echospunder attempts to pick up. Interestingly, squid and octopods don't create a strong enough signal for the echosounder to pick up.
While the echosounder provides important data about the timing, extent and intensity of the migration patterns and the DSL in general, acoustics are limited in their ability to discriminate among species. Because of this limitation, we use net to collect samples to identify the community of organisms which also permits us to describe the diversity of species that we encounter. The mesopelagic community in the Gulf of Mexico is hyperdiverse with greater than 800 species of fishes, crustaceans and other invertebrates.
Indeed, the most prominent piece of equipment that we rely on is the MOCNESS which allows us to collect specimens at through the water column.
The echosounders on the ship provide a picture of large patterns in the ocean so we can learn about the processes that are important at broad scales. However, it is often useful to be able to zoom into the layers and see the individuals that live in those deep areas and to look at them one-on-one. To achieve this, we have attached an autonomous battery-powered echosounder onto the frame of the MOCNESS and added two transducers that collect acoustic data very close to the individuals (~20-40m). By placing the echosounder closer to the animals at depth, we can actually count and measure individuals and learn about their behavior in the dark without the need for any lights. We are learning a tremendous amount from the data we have collected on these animals and are excited to see what tonight’s sampling event shows us!!
Photo: Echosounder attached to the MOCNESS and output screen of individual animals
Hi! My name is Natalie Slayden, and I am a Master’s student at Nova Southeastern University working as a Research Assistant in Dr. Tracey Sutton’s Oceanic Ecology Lab. This DEEPEND cruise is my first research cruise!
Photo: Natalie and Nina prepping the MOC
On this DEEPEND cruise, I am a part of the fish processing team. The process begins with the boat pulling the MOCNESS which is a net system consisting of six nets. One net fishes open the entire time, while the other five nets open and close at different depths allowing us to determine where we catch certain species by depth in the water column. Once the nets are pulled out of the water, the fishes are brought into the lab per net. Dr. Tracey Sutton sorts and identifies each fish to species. I then weigh, measure, and preserve the fishes based on how they will be utilized. All this information is entered into the DEEPEND database by my partner in crime, Nina Pruzinski. Several universities use these fishes for varying projects.
For my thesis project, I am looking at the otoliths (ear stones) of non-vertically migrating deep-pelagic fishes to determine their age. I will also describe the otolith patterns and correlate those patterns to the life history of the fishes. Fishes have otoliths to help them orient themselves within the water column and detect sound. The otoliths have rings that can be counted to determine age. The rings can represent days, months, years, or a single meal. The fishes I will use for my project are frozen so that I can remove and analyze the otoliths once I get back to the lab at Nova Southeastern University. Below are some pictures of the fishes that I will be using for my age and growth study!
Photo 1: Nannobranchium lineatum (Lanternfish species)
Photo 2: Chauliodus sloani (Viperfish species)
On DEEPEND cruises we spend most of our time doing science-related activities that you may have read about in previous blogs. Believe it or not, we do occasionally have down time and we have to figure out how to fill it. There is a TV in the galley that is quite popular to hang around and watch during meal times and late at night. My favorite DEEPEND pastime however, is fishing!
Photo: Max on the hunt for his first tuna
DEEPEND researchers assemble a stack of rods and reels before every cruise in the hopes we will stumble across some good fishing action. This is not guaranteed and I have been skunked on previous DEEPEND cruises. On afternoons when the net is not in the water and we are in transit to another station trolling is the go-to method of fishing. We have already landed on small tuna on this cruise while trolling.
Photo: The rod and reel assemblage area of the lab
Typically the best fishing takes place when a school of fish or some sort of floating structure (like sargassum or floating boards) is spotted. Floating structure often attract small baitfish, which in turn attract larger predators. Already this cruise we have stumbled across a school of Chicken (small) Mahi and Little Tunny. I have landed two Mahi and a Little Tunny, which was my first ever tuna species caught on a rod and reel!
Phptps: Ocean Triggerfish; Travis with a Little Tunny; Bpttom photo: Little Tunny