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Questions from the Audience

Are the soft type corals on Cape Cod as threatened by coral bleaching and ocean acidification as hard corals?

The soft corals you might find around Cape Cod (like Alcyonium) do not have symbiotic dinoflagellates living in their tissues like the hard coral Astrangia or their tropical relatives. They normally live in deep water where there is not enough light for photosynthesis. They also don’t have a solid hard skeleton but rather have lots of microscopic pieces called sclerites that add some toughness to the coral and protection from predators, but allows the coral to be flexible. They are made from calcium carbonate, just like the skeletons of hard corals, and so can be impacted by ocean acidification, but basic physiology like respiration can be negatively impacted by decreases in pH and so many animals, especially mobile invertebrates like squid, are most at risk by the greater threat of acidification in higher latitudes like Woods Hole.

Is any other sea life attracted to the artificial reef?

attached to the blocks or flitting around in the holes and crevices. We deployed the reef in summer 2019 and within a week we already saw fishes especially juvenile black sea bass and cunner hanging around, as well as lots and lots of periwinkle snails. Later we saw algae, a number of bryozoans, and hydroids. This summer we hope to survey the ARMS () we added to the reef structure last fall and look forward to discovering more sea life!

What are some other species of cold water corals?

Surprisingly, there are quite a few species of corals that thrive in cold water. However, these species are usually found in the deep sea. The Smithsonian Institution that contains a lot of information on their biology, research, and conservation. Astrangia is the only hard coral you are likely to encounter in Woods Hole, but in deep water you can find more branching types like Oculina and Lophelia. Scientists have actually only recently discovered many of these reefs, as we know so little about the deep sea, but they can be extensive and just as beautiful as their more tropical cousins. NOAA has a about a survey done to document deep-sea coral habitats off the northeastern United States.

What's the furthest north corals can grow?

Hard corals have actually been found in both the Arctic and Antarctic Oceans, but these are very slow growing, deep water species like Lophelia. Astrangia in Woods Hole is probably the highest latitude (41°N) where corals with symbiotic dinoflagellates have been found. However, if we look at solely tropical species that form reefs, the furthest north you can find them are in Japan, Mexico (Sea of Cortez, 29°N), and Israel (Eilat, 29°N). The northernmost reef was recently discovered off of Tsushima Island, Japan at a latitude of 35°N. While temperatures there do not vary as widely as they do in Woods Hole, the corals at this high latitude site experience a range of 13 °C to 27 °C on average. Pretty impressive!

How selective is Astrangia for the species of symbiont? Is it the same species throughout its range? Great question! That is exactly what we want to figure out! Can different species of dinoflagellates grow in Astrangia? How do the different species impact growth rates or temperature sensitivity in the coral? Can multiple species live together in the same colony? This is something we know for a handful of coral species but has been poorly studied in Astrangia. We don’t even know if they harbor the same species of symbiont throughout its range, or if they change seasonally like some corals do on northerly reefs like on Bermuda. We have had some success in reinfecting bleached Astrangia with two different types of symbionts, but we need to do more testing including genetic confirmation that the symbionts are who we think they are.

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