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

Abstract

Although the role of deep-sea corals in supporting biodiversity is well accepted, their ability to recover from anthropogenic impacts is still poorly understood. An important component of recovery is the capacity of corals to grow back after damage. Here we used data collected as part of an image-based long-term monitoring program that started in the aftermath of the Deepwater Horizon oil spill to develop a non-destructive method to measure in situ growth rates of Paramuricea spp. corals and characterize the impact of the spill on growth. About 200 individual coral colonies were imaged every year between 2011 and 2017 at five sites (three that were impacted by the spill and two that were not). Images were then used to test different methods for measuring growth. The most effective method was employed to estimate baseline growth rates, characterize growth patterns, estimate the age of every colony, and determine the effects of impact and coral size on growth. Overall growth rates were variable but low, with average annual growth rates per site ranging from 0.14 to 2.5 cm/year/colony. Based on coral size and growth rates, some colonies are estimated to be over two thousand years old. While coral size did not have an influence on growth, the initial level of total impact in 2011 had a significant positive effect on the proportion of new growth after 2014. However, growth was not sufficient to compensate for branch loss at one of the impacted sites where corals are expected to take an average of 50 years to grow back to their original size. The non-destructive method we developed could be used to estimate the in situ growth rates on any planar octocoral, and would be particularly useful to follow the recovery of corals after impact or assess the effectiveness of Marine Protected Areas.

Spatial distribution and habitat characterization of marine animal forest assemblages along nine submarine canyons of Eastern Sardinia (central Mediterranean Sea)

“…Because of their demography (Bramanti et al, 2019;Girard et al, 2019) and tridimensional structure, these animal forests are particularly vulnerable to mechanical injuries inflicted by anthropogenic pressures, such as direct fishing activities (bottom trawling, longlines and trammel nets) and their indirect consequences (Derelict Fishing Gears -DFGs, sediment resuspension and consequently silting), as well as the accumulation of marine litter (Puig et al, 2012;Clark et al, 2016;D'Onghia et al, 2017;Hinz, 2017;Giusti et al, 2019;Gori et al, 2019;Puig and Gili, 2019). Beside fishing activities, other aspects are further impacting…”

Effects of Petroleum By-Products and Dispersants on Ecosystems

“…As a result of the intentional mitigation efforts, the offshore water column and deep benthos received large amounts of oil and dispersants. That decision doomed many deepsea communities, including deep coral assemblages, some of which are estimated to be over 2,000 years old (Girard et al, 2019). Coral colonies themselves were covered to varying degrees in the flocculent material derived from marine oil snow produced by the DWH spill.…”

“…Coral colonies themselves were covered to varying degrees in the flocculent material derived from marine oil snow produced by the DWH spill. Colonies that were lightly impacted have shown signs of recovery, while those with more extensive injury have continued to decline and have lost entire branches of their colonies (Girard et al, 2019). Reductions in the numbers and sizes of colonies at the impact sites will affect total reproductive output because their fecundity is dependent on the number of reproductive polyps in the colony.…”

A Synthesis of Deep Benthic Faunal Impacts and Resilience Following the Deepwater Horizon Oil Spill

“…with some individual colonies requiring more than 100 years to recover (Girard et al, 2019;Montagna and Girard, 2020).…”