Bioluminescence Cruise: Defense in the Deep: Blog 8

Good evening, science enthusiasts!

My name is Ryan Bos and I am a graduate student in Dr. Tamara Frank’s deep-sea biology lab at Nova Southeastern University. Currently, I am undertaking a trophic study emphatic of microplastics in deep-sea shrimps and fishes. My study aims to demonstrate the connectivity between deep pelagic assemblages and the epipelagic while elucidating the transfer of microplastics in marine food webs.

I am writing to you from the R/V Walton Smith. As our net plunges into the light deprived depths of the mesopelagic (200m-1000m), we are reminded of how hostile the deep sea can be. As such, denizens of the deep must be equipped anatomically and physiologically with the tools to outlast their competitors.

Today’s topic of interest is ‘defense in the deep sea’, as in how can prey defend themselves, avoiding being consumed by predators. Given that the deep sea is characterized by high faunal diversity, there is an eclectic array of adaptations for defense.

1. Camoflauge: Countershading and Counterillumination

Simply put: countershading is possessing a dark dorsal portion of the body, while having a lighter or what ventral portion. This strategy is effective because predators looking down from above will have trouble discerning a prey item from a dark background. Moreover, predators looking up from below will have trouble distinguishing prey from downwelling light.

Counterillumination is an effective form of camoflauge in which an animal can utilize light producing cells called photophores to precisely match the intensity of downwelling light thereby breaking up its silhouette.

2. Shells and spines

Possessing and maintain a shell is an effective way to bolster defense in the deep sea. Not only do predators face the challenge of penetrating a shell, but also spend time in doing so. Having the added benefit of spines decreases the likelihood of being predated on as well as doing some damage to any attacker. In the pelagic realm, shelled species have a tendency of having thinner shells relative to benthic species. This is because pelagic species have to counteract continually sinking due to gravity as opposed to benthic species that can maneuver easily on the sea floor.

3. Bioluminescent spew

Bioluminescent spew or glowing vomit used for defense is commonly seen in deep-sea shrimps. Deep-sea shrimps can use this brightly glowing spew to not only stun predators, but also as a ‘burglar alarm’ in which a secondary predator in the vicinity can target the now glowing initial attacker. After spewing its bioluminescent fluids onto an attacker, a shrimp can tail-flip away to safety.

4. Nutritionally poor/unpalatable

It is crucial to conserve and expend energy appropriately in the deep sea, as meals may be few and far between. When encountering a prey item that is nutritionally poor, perhaps primarily made of water, coupled with stinging cells, a predator is more likely to avoid consuming this prey species, as it would cost energy to predate on it, and the reward would not be worthwhile. An excellent example of an animal that is nutritionally poor/unpalatable is a siphonophore. Not only do siphonophores consist largely of water, but also have stinging cells called nematocysts that pack a punch to any unfortunate enough to come into contact with them.