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Posts from the ‘Marine Mysteries’ category

What on earth . . . and its tail is a snorkel!

Here’s one of the best mysteries I’ve been gifted recently.

It started with videos sent to me from Leesa Flynn that she had taken at Cordova Bay, southern Vancouver Island, British Columbia. Just look! What powers of observation Leesa has. This animal is less than 6 cm long and what’s with that tail?!

I did NOT know what this animal was and how my interest was piqued. I did suspect it might be an organism found in non-marine environments since it was so high up in the intertidal zone. Likely the water was not very salty where it was found.

The mystery had to be solved
I am very fortunate to have quick access to expertise far greater than my own. Those I reached out to included Rick Harbo, author of many ID guides for marine life of the Pacific Northwest. Rick did not recognize this animal, so off the videos went further into the web of expertise, intriguing many biology experts along the way.

To the relief of all, the identification came back through Hugh MacIntosh of the Royal BC Museum and Kevin Kocot of the University of Alabama. They recognized that this was a larval stage of a species of Hover Fly. The larvae are not known to be in marine environments so the water near this organism must have been from a creek flowing on the beach or highly diluted by rain.

One of the many species of Hover Fly – an Orange-spotted Drone Fly, Eristalis anthophorina.
Photo by Jimmy Dee via Wikimedia

Larva of a bee-like insect
The long tail of these larvae functions like a snorkel. It’s a breathing tube whereby larvae of Hover Flies can be underwater feeding while breathing from the surface. What a remarkable adaptation!

There are MANY species of Hover Fly and they are really important to the environment. The adults are important pollinators and the larvae recycle nutrients and some feast on pests like aphids (which parasitize on plants / crops).


But what species of Hover Fly specifically was the larva that Leesa observed? I think this mystery organism is a species of Drone Fly of genus Eristalis. I provide detail about that at the end of this blog. First let me address . . . Rat-tailed Maggots.

Rat-tailed Maggots and Bum Breathers?
I learned that the broad grouping of larvae in the family of Hover Flies appears to be referenced as “Rat-tailed Maggots”.

There’s an increased chance that you’re cringing now – right? Many of us have negative associations with the words “maggot” and “rat”.

That wonderful adaptation of the long breathing tube allows these larvae to live and feed in environments that may poor water quality e.g. sewage. As described by Real Monstrosities: “Since Rat-tailed Maggots breathe air, they have no use for gills, which in turn means they’re not particularly reliant on water quality. Thus, there’s many a Rat-tailed Maggot that lives in the squalor of cesspits, pools of sewage, watery manure or carcasses.

The one featured in this mystery is not likely to have been in water of poor water quality. It’s just that they could live and feed in those environments. They can also be terrestrial. They do tend to lay eggs in nutrient rich environments.


Here you have colourful text from IFLScience about this broad group of larvae to accompany the video above of a different species of Hover Fly larvae (not the species in this mystery).

“Rat tailed maggots are the larval form of some species of hoverfly, which can be terrestrial or aquatic. They start out life as a blob with a breathing tube, later dragging themselves onto land to pupate and turn into certain flies. Rat tailed maggots enjoy feeding on decaying organic matter which is why you’ll often find them in dank ponds and rotting trees, as well as anywhere there’s an open source of feces (including, one time, Glastonbury Festival).

They have a long breathing tube called a siphon attached to their rear end which is why some entomologists affectionately refer to them as “bum breathers”. They bulk up in their larval, rat tailed maggot form before pupating in soil or other dry material and emerging as several species of hoverfly.

You might think the rat tailed maggot is a little ugly, but they are champions for the environment both in their larval and adult forms. As rat tailed maggots, they encourage the turnover of nutrients by eating decaying matter and pooping it out again. They also predate on common plant pests such as aphids.

As adults, they’re hugely important pollinators which facilitate gene flow across isolate plant populations as they are big travelers. So, if you see a rat tailed maggot, do your bit by simply letting it do its thing.”

Screen grab from Leesa’s video.

But which larvae is this specifically?
I think that the larva in this mystery is a species in a subgrouping of Hover Flies (family Syrphidae), known as Drone Flies (genus Eristalis).

In what I was able to learn from the contributions to iNaturalist.ca, it appears there are 6 species of Drone Fly that have been found on Vancouver Island. I am hopeful that an etymologist reading this blog will be able to narrow down which one this larvae is.

The six are:
Common Drone Fly Eristalis tenax
Dusky Drone Fly Eristalis obscura
Orange-legged Drone Fly Eristalis flavipes
Orange-spotted Drone Fly – Eristalis anthophorina
Orange-spined Drone Fly 
Eristalis nemorum


Thank you so much for your interest in all creatures great and small, furred and maybe what some human brains interpret as a little freaky. These species are perfection with adaptations that ensure success in the web of life. A web to which we, of course, belong. 💙


Sources:

Screen grab of larvae from Eristalis genus from this source.

Above: Comic by UnderdoneComics.com which included the text: “Ever spend time outside and notice an insect that looks like a bee but has wings like a fly hovering near you? Well sir, that’s a hoverfly. And my favorite kind is the drone fly—because, as you can see from the comic—it has an amazing lifecycle.

Before they become bee-lookalikes, their larval stage resembles a deep sea diver. They breathe through a tube that comes out of their butt and they laze around eating plant particles. How crazy is that?”

The Creature Below the Floathouse?

How I enjoyed receiving the following mystery this week.

Be sure to have your sound on when you read and listen to the clip below.

Yes, it’s a male Pacific Harbour Seal! So many people do not realize that the male Harbour Seals establish and defend territory in the water (unlike species of sea lion and elephant seal who defend territory on land).

From Discovery of Sounds in the Sea . “Harbor seals were thought to be the least vocal of the pinnipeds. Recent studies have shown, however, that males produce underwater vocalizations during the mating season to attract females or to compete with other males. Males establish territories in the waters offshore of haul-out sites. Using underwater vocalizations, they defend their territories against other males and display to females traveling through the area. Their underwater vocalization is described as a roar with a peak frequency at approximately 1.2 kHz. Harbor seals also produce a wide variety of in-air vocalizations, including short barks, tonal honks, grunts, growls, roars, moans, and pup contact calls.”

It is remarkable isn’t it that these sounds were not known to be made by male Harbour Seals until ~1994.? This is the most common marine mammal on so many coasts and yet . . . we know so little.

Note: The person who sent me the mystery preferred to remain anonymous and that the location of the recordings not be provided. I can share that it was in the Sunshine Coast area of British Columbia. However, this underwater sound could be from ANYWHERE male Pacific or Atlantic Harbour Seals wish to pass on their genes. 🙂

See below for some of the research into Harbour Seal vocalizations.


From the research of Leanna Matthews:

“Similar to other aquatically mating pinnipeds, male harbor seals produce vocalizations during the breeding season that function in male-male interactions and possibly as an attractant for females. I investigated multiple aspects of these reproductive advertisement displays in a population of harbor seals in Glacier Bay National Park and Preserve, Alaska. First, I looked at vocal production as a function of environmental variables, including season, daylight, and tidal state. Vocalizations were highly seasonal and detection of these vocalizations peaked in June and July, which correspond with the estimated time of breeding. Vocalizations also varied with light, with the lowest probability of detection during the day and the highest probability of detection at night. The high probability of detection corresponded to when females are known to forage. These results are similar to the vocal behavior of previously studied populations.

However, unlike previously studied populations, the detection of harbor seal breeding vocalizations did not vary with tidal state. This is likely due to the location of the hydrophone, as it was not near the haul out and depth was therefore not significantly influenced by changes in tidal height.

I also investigated the source levels and call parameters of vocalizations, as well as call rate and territoriality. The average source level of harbor seal breeding vocalizations was 144 dB re 1 μPa at 1 m and measurements ranged from 129 to 149 dB re 1 μPa. Analysis of call parameters indicated that vocalizations of harbor seals in Glacier Bay were similar in duration to other populations, but were much lower in frequency.

During the breeding season, there were two discrete calling areas that likely represent two individual males; the average call rate in these display areas was approximately 1 call per minute.

The harbor seal breeding season also overlaps with peak tourism in Glacier Bay, and the majority of tourists visit the park on a motorized vessel. Because of this overlap, I investigated the impacts of vessel noise on the vocal behavior of individual males. In the presence of vessel noise, male harbor seals increase the amplitude of their vocalizations, decrease the duration, and increase the minimum frequency. These vocal shifts are similar to studies of noise impacts on other species across taxa, but it is unknown how this could impact the reproductive success of male harbor seals.

Finally, I looked at the role of female preference for male vocalizations. Using playbacks of male vocalizations to captive female harbor seals, I found that females have a higher response to vocalizations that correspond to dominant males. Females were less responsive to subordinate male vocalizations, which had a shorter duration and a higher frequency. Given that male harbor seals decrease the duration and increase the frequency of vocalizations in the presence of noise, it is possible that these vocalizations become less attractive in noise.


Click here for Harbour Seal vocal samples from Discovery of Sound in the Sea.

Sources:

Discovery of Sound in the Sea (DOSITS) – Harbor Seal Sounds (Phoca vitulina).

Hanggi, E. B., & Schusterman, R. J. (1994). Underwater acoustic displays and individual variation in male harbour seals, Phoca vitulina. Animal Behaviour, 48(6), 1275–1283. 

Matthews, Leanna. (2017). Harbor Seal (Phoca vitulina) Reproductive Advertisement Behavior And The Effects Of Vessel Noise. SURFACE.

Nicholson, T. E. (2000). Social structure and underwater behavior of harbor seals in southern Monterey Bay, California.

Sabinsky, P. F., Larsen, O. N., Wahlberg, M., & Tougaard, J. (January 01, 2017). Temporal and spatial variation in harbor seal (Phoca vitulina L.) roar calls from southern Scandinavia. The Journal of the Acoustical Society of America, 141, 3.)

Van, P. S. M., Corkeron, P. J., Harvey, J., Hayes, S. A., Mellinger, D. K., Rouget, P. A., Thompson, P. M., … Kovacs, K. M. (January 01, 2003). Patterns in the vocalizations of male harbor seals. The Journal of the Acoustical Society of America, 113, 6, 3403-10.