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Gulf of California 2015, Leg 2 – Midwater Ecology – Log 7

Gulf of California 2015, Leg 2 – Midwater Ecology – Log 7

Food Web Ecology

As we near the end of the midwater ecology leg, scientists onboard are beginning to piece together a unique collection of observations and data gathered from ROV dives and midwater trawls. A synthesis of these observations will provide us with new insights regarding how deep-water animals of the Gulf of California interact with one another to create a vibrant and interesting ecosystem. Within our science party, areas of expertise include cephalopod biology, deep-sea fish ecology, physiology, evolutionary biology, molecular taxonomy, and what I consider to be my specialty–oceanographic food web ecology.

Marine food webs encompass feeding interactions between organisms within an environment. These interactions dictate energy flow and the production of top predators, which are important to the human food supply. The environment of interest on this expedition is the deep sea, a vast and fluid habitat characterized by constant darkness, extremely cold temperatures, high pressure, and a somewhat sparse distribution of animal life. Collectively, these characteristics make the deep sea difficult to access without technologically advanced instruments such as ROV Doc Ricketts and the MiniROV.

Like in other deep-sea ecosystems, animals in the Gulf of California thrive far beneath sunlit surface waters where photosynthesis occurs. Despite this distance from the surface, deep-sea animals ultimately depend on photosynthesis-derived production reaching the deep sea as marine snow sinking through the water column. Some small animals feed directly on marine snow, while some animals are specifically equipped to filter and ingest marine snow from the water column (e.g., the worm Poebius, pyrosomes, and larvaceans). These animals then can become the prey of larger animals. Some deep-sea animals are also capable of making regular vertical migrations from surface to mesopelagic waters, serving as vectors of energy transfer to the deep sea.

Tracing a series of predator-prey interactions from small marine plants photosynthesizing at the surface up to large predatory fish (such as tunas and marlins) can be a complex endeavor. For example, we have been seeing an abundance of Stomias atriventer, a scale-less dragonfish with vicious teeth, a delicate chin lure, and astounding bioluminescent abilities. Visual observations confirm that Stomias use their lure to attract and ingest myctophids, or lanternfish, which are known to eat zooplankton. Tracing predator-prey interactions ultimately leads us back to phytoplankton, the primary food of small zooplankton like copepods, in the food web.

Close-up of the head and chin lure of Stomias atriventer. Photo by Karen Osborn.

As a postdoctoral research fellow in the Midwater Ecology Group, I am focusing on identifying the primary predator-prey interactions framing deep-sea food webs. Traditional methods, such as looking directly into the stomachs of predators and identifying their prey items, do not work well with deep-sea animals because they are difficult to collect.

Thus, I will be measuring naturally occurring biomarkers in deep-sea animals which integrate diet over time in a broad sense. Guided by MBARI’s unique video record of the deep sea and decades of keen observations by biologists, a biomarker perspective will aim to unveil the mysteries of often-marveled yet little-known pelagic food webs more closely.

Anela sits at the science camera controls in the Western Flyer control room.

– Anela Choy