A Five-Year, In Situ Growth Study on Shallow-Water Populations of the Gorgonian Octocoral Calcigorgia spiculifera in the Gulf of Alaska

Abstract

Gorgonian octocorals are the most abundant corals in Alaska where they provide important structural habitat for managed species of demersal fish and invertebrates. Fifty-nine gorgonian species have been reported from Alaska waters but little is known about their life history characteristics to help us gauge their ability to recover from seafloor disturbance. Colonies of the holaxonian Calcigorgia spiculifera were tagged beginning in 1999 at three sites in Chatham Strait, Southeast Alaska, using scuba and their growth measured annually for up to 5 years. Colonies were video recorded, and computer image analysis tools provided calibration of video images for measuring the length of several branches. Growth data indicate that C. spiculifera grows much slower (6.0 mm yr-1) than other gorgonians in Alaska for which there are data and that intraspecific growth is highly variable. We fit a Bayesian linear mixed-effects model that showed that average colony growth was significantly reduced with warmer temperature and presence of necrosis. The model further indicated that growth may slow among larger (older) colonies. Based on these results and previous studies, we propose that gorgonian growth rates are taxonomically constrained at the Suborder level and that holaxonians grow the slowest followed by scleraxonians and calcaxonians (2–3 times as fast). Findings of this study indicate that it would take approximately 60 years for C. spiculifera to grow to its maximum size and depending on the location and size of the parental standing stock, at least one and possibly 10 additional years for recruitment to occur. Our results further indicate that colonies that are injured, perhaps chronically in areas of frequent disturbance, grow at slower rates and if the current trend of ocean warming continues then we can expect these corals to grow more slowly, and the habitats they form will require more time to recover from disturbance.

Understanding growth and age of red tree corals (Primnoa pacifica) in the North Pacific Ocean

“…In this species of gorgonian coral, the growth rates declined logarithmically with age such that younger corals grew faster than older corals. This is consistent with other species of gorgonians [ 32 , 40 , 41 ].…”

“…This information could be used by coastal managers to identify which aggregations are most vulnerable to disturbance from human activities, and which should be highlighted for protection. If age and growth characteristics are phylogenetically constrained, as has been suggested for some taxa [ 40 ], then the techniques developed and insights gained in this study could have broader application in the North Atlantic Ocean where another Primnoa species (e. g. P . resedaeformis ; [ 13 , 45 ]) also forms ecologically important habitats.…”

In situ growth of deep-sea octocorals after the Deepwater Horizon oil spill

“…Growth rates were low compared to other studies, ranging from an average total linear growth (of all branches) of 0.14 (±0.24 SD) cm/year per colony for Paramuricea biscaya colonies at MC344 to 2.5 (±3.2 SD) cm/year for Paramuricea sp B3 at AT357. Image-based studies of shallow-water octocorals have found substantially higher growth rates, up to an average of 2 cm/year per individual branch (Brazeau and Lasker, 1992;Coma et al, 1998;Lasker et al, 2003;Matsumoto, 2004;Stone et al, 2017). Coma et al, (1998) reported that the average growth rate of Paramuricea clavata in the Mediterranean varied between 0.5 and 0.8 cm/year per branch depending on their size, which translated to an average increase of 1.8 cm in colony height every year.…”

“…The proportion of new branches (growth proportion), the amount of linear growth (growth proportion*total coral size), and both the number of branches that increased in length and the number of newly-formed branches between every consecutive year or between 2012 and 2017 were then estimated for each coral. As very few branches grew on each coral colony, all growth rates indicated in this study represent the total amount of growth detected on each colony, and not the average growth per branch as in several other studies (Brazeau and Lasker, 1992;Coma et al, 1998;Lasker et al, 2003;Matsumoto, 2004;Stone et al, 2017).…”

“…Non-destructive methods to measure growth rates have been developed for shallow-water octocorals with a planar morphology. In several studies, the linear growth of individual branches was measured from images of coral colonies that were, in some instances, compressed between sheets of clear acrylic glass to align branches and photographed against a grid (Brazeau and Lasker, 1992;Coma et al, 1998;Lasker et al, 2003;Matsumoto, 2004;Stone et al, 2017). However, due to the technical limitations associated with working in the deep sea, these methods have not been used for deep-sea octocorals.…”