Understanding cold-water corals

This post is a contribution from our guest Dr Katleen Robert, at the Fisheries and Marine Institute of Memorial University, St John’s, NL, Canada.

From May 15th to June 8th, I was lucky enough to participate in my 10th expedition at sea.  As part of the TOSCA Expedition composed of an international team of scientists, I boarded the RV Celtic Explorer in Galway, Ireland, and we left for the Charlie-Gibbs Fracture Zone, approximately 1,500 km away in the middle of the Norther Atlantic.  The main goal of the expedition was to understand the geology of the area, but I was really there to study the environmental conditions which affect the distribution of megabenthic species (organisms which live on the seafloor and are large enough to be captured in imagery from cameras).

A common concept in ecology is the idea of a species’ niche.  Very briefly, this represents the set of environmental conditions and resources which are needed for individual species to survive and reproduce.  Hence by looking at where species occur and do not occur, we can start to understand what kind on conditions are most suitable for each species.  For example, species attached to the seabed and which rely on food being delivered by currents (suspension- or filter- feeders such as cold-water corals or sponges), may prefer steep or elevated structures where currents may be slightly higher (Figure 1).  On the other hand, other species are deposit-feeders (such as sea cucumbers), and feed on food which ‘snowed’ down from the surface and accumulated at the surface of sediment.  These species will tend to occur in areas dominated by soft sediments (Figure 2).  Of course, it gets much more complicated than that and many other factors (e.g. temperature, salinity, pressure, orientation, type and frequency of food available, …) need to be taken into account to fully understand why species occur where they do.


Figure 1: Cold-water corals on small boulder on top of a ridge


Figure 2: Sea cucumber on soft sediment at ~2000m in depth

As part of my research, I am particularly interested in understanding the factors controlling the distribution of cold-water corals.  These are similar to tropical corals that can bee seen while snorkeling or scuba diving.  They are long-lived large colonies made up of many individual polyps, but instead of having symbiotic organisms that allow them to use the energy of the sun, cold-water coral polyps catch tiny food particles suspended in the water column, and as such, can occur in much deeper waters where there is no sunlight.  We often find many other species in close proximity to cold-water corals, and we believe that cold-water coral presence leads to higher biodiversity, possibly at it provides complex habitats for other species to utilize (e.g. protection for small fish or hard substrate for sea anemones to get higher up from the seafloor where more food might be available).  However, cold-water corals are at risk from activities such as trawling and potential impacts from climate change (e.g. ocean acidification).  The former removes large colonies which can take 100s of year to replace, while the latter is likely to affect the ability of corals to build their calcium carbonate skeleton.  Hence, my aim is to help understand where these species occur so we can minimize impacts and monitor responses to potential changes.

Katleen Robert

Fisheries and Marine Institute of Memorial University
St John’s, NL, Canada

 

Here are some pretty images from the seafloor during the TOSCA expedition (provided by the ROV Holland 1).

Crinoide standing over a bunch of rocks.
A shrimp next to a soft coral. The two red/pink dots by the right bottom corner is apart from 10 cm.
A bunch of corals and sponges on a rock.
In some areas, dozen of fish were swimming around the ROV.
This is a deep-water black coral, and its age is probably by several hundreds years old!

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