A new study published in the Marine Ecology Progress Series highlights a resilient sea sponge’s response to its changing environment. The rare footage was captured by Ocean Networks Canada (ONC) seafloor cameras off the BC coast for over four years, marking the longest continuous recording of these ancient but remarkably active animals in the wild.
The baseball-sized sponge, nicknamed Belinda by the researchers, was recorded by an eight-camera array and scientific instruments deployed at Folger Pinnacle, a site within ONC’s NEPTUNE (North-East Pacific Time-series Undersea Networked Experiments) subsea observatory off the British Columbia coast.
Researchers at the University of Alberta, University of Victoria (UVic), and ONC, a UVic initiative, observed Belinda’s daily, yearly, and seasonal changes in size, shape and colour. The cameras were rolling for the sponge’s sometimes daily “sneeze-like” contractions; as it shrank prior to the winter hibernation; as well as during the marine heatwave (aka the Blob) in the Pacific Ocean off North America between 2013 to 2016.
Long-term monitoring of sedentary animals like sponges is rare and the study provides pivotal insight into the impact of environmental conditions such as water quality and temperature, both of which are affected by climate, according to the research team.
Timelapse of Belinda’s daily, yearly, and seasonal changes over four-years of video data from 2012 to 2015.
‘Responsive and dynamic’
“Sponges provide a vital service for marine ecosystems by filtering the water and recycling nutrients – yet this is the first-ever long-term monitoring dataset,” said Dominica Harrison, lead author of the publication and a UVic graduate student. “Our study reveals how responsive and dynamic sponges are in their natural habitats but beyond that, these data are helping us explore how environmental changes tied to climate change might impact the vital ecosystem functions that sponges provide.”
The hundreds of hours of video from the research site 23 m deep off the Vancouver Island coast was coupled with even more high-frequency, long-time series datasets collected by multiple ONC scientific instruments deployed as part of the experiment.
Photosynthetically available radiation, oxygen, chlorophyll, turbidity, current speed, salinity, temperature and pressure, were all uploaded into Oceans 3.0 and later analyzed by the research team for a fulsome look at changes to the sponge’s appearance and behaviour.
“We see through this dataset massive changes in the colour, texture and shape of the sponge over time but it’s actually very resilient and rebounds back to its original form,” said Sally Leys, principal investigator of the paper, and a professor in the Department of Biological Sciences at the University of Alberta.
Winter dormancy observed
Each winter, Belinda contracted to half its size, despite lacking muscles and a nervous system, as it entered a dormant state. Researchers believe the innate behaviour triggered internally by the sponge is a response to decreased available food sources, such as phytoplankton, zooplankton, and detritus (organic matter).
During the summer months, phytoplankton blooms at Folger Pinnacle increase particulates in the water as the sponge regained its shape. Similar to a human coughing, Belinda was seen performing regular “sneeze-like” contractions lasting upwards of a day at a time to clear debris that accumulated while filter feeding.
“While the sponge contractions appear fast in the video recordings, each one actually takes 11 hours, and in the winter it contracts for several months,” said Leys.
“Such slow behaviour is on a similar timeline of weather and climate patterns, so sponges are in many ways excellent sentinels of the environment because they respond very slowly to changes.”
Belinda and the Blob
In August 2014, the long time-series monitoring of the camera array allowed researchers to observe the onset of significant changes in Belinda’s appearance during ‘the Blob’; the sponge’s colour darkened from a healthy pale orange-yellow to a deep orange and it took on a lumpy texture.
“Folger Pinnacle experiences surface warming conditions even though it’s 23 metres down. Early in the experiment, the sponge was tall and had vigorous contractions, but in 2014 it was shorter, darker coloured, and the contractions were sluggish. That change in shape may be correlated with the Blob,” said Leys. “We also noticed that lots of shelly material landed on the sponge in 2014 as though barnacles and other animals had died nearby.”
Belinda at Folger Pinnacle in April 2023, captured by Pelagic Technologies Inc.
Benefits of long-term monitoring
According to the researchers, the observation between 2012 and 2015 provided insights not only into Belinda’s itself but also the surrounding diverse ecosystem, including interactions with animals like sea stars, snails, and crabs.
“The sponge had so much character, twitching and flinching to some hidden cues and yet tolerating sea stars draping their arms over it for hours on end. Some sea stars seemed to visit the sponge several times, and tiny snails, crabs and even anemones walked around and over it,” said Leys.
The ONC camera array used in this study was designed for an underwater 3D imaging project.
“Observatories equipped with cameras enable us to document in-situ species behaviour and monitor environmental changes over both short and long terms. They are a key resource to support ecosystem health assessment and develop strategies for protecting marine environments” says ONC staff scientist Paulo Corrêa, a co-author of this publication along with ONC senior staff scientist, Fabio De Leo.
Although the camera array was removed in 2015 with the conclusion of the project, divers have confirmed as recently as two months ago that Belinda remains at Folger Pinnacle, healthy and back to its original colour.
Ongoing monitoring could reveal even more about how sea sponges like Belinda respond to changing ocean conditions.
“Eyes in the water tell you a lot. Long-term monitoring is essential to document both the warming changes and how they affect the seafloor, but also, how animals are resilient to change and may come back if they can adjust,” said Leys.
