361
still higher than at the reference sites between 2016 and 2017. All these results indicate an ongoing, long-term non-acute effect of the DWH oil spill on deep-sea corals
(Girard and Fisher 2018).
Results from the long-term monitoring of corals impacted by the spill showed
that the fate of these corals was still uncertain 7 years after the spill. In order to plan
for future monitoring, a study used a modeling approach to assess the recovery of
impacted corals over the longer term (Girard et al. 2018). In this study, an impactdependent matrix model was parameterized based on data collected as part of the
long-term monitoring program. This model was then used to estimate the time necessary for every impacted coral colony to reach a state where all branches are visibly healthy (time to recovery) and branch loss. Results from the model indicated
that, depending on their initial level of impact, the majority of impacted coral colonies will have recovered within 10 years. However, the most heavily impacted corals could take up to 30 years to reach a state where all branches appear healthy.
Moreover, some of these impacted colonies are projected to lose a large number of
branches, leading to a 10% reduction in coral biomass at some impacted sites by the
time all corals will have visibly recovered. Based on these results, Girard et al.
(2018) suggested that corals should be monitored every 2 years (sufficient as recovery is slow) until 2021 and then less frequently for a further 20 years to assess
potential non-acute effects and follow the potential recovery of the most heavily
impacted corals.
High-resolution images of individual coral colonies were also used to measure in
situ growth rates Girard et al. 2019). Growth rates were estimated for both
Paramuricea biscaya and Paramuricea sp. B3, providing important baseline information on the biology of these coral species. Additionally, the impact of the DWH
oil spill on growth was characterized. No negative long-term impact of the spill was
detected on growth. On the contrary, the level of total visible impact had a significant positive effect on growth after 2014 at two of the impacted sites (MC 294 and
MC 297). However, this positive effect was not sufficient to compensate for the high
levels of branch loss experienced by impacted corals as growth rates were extremely
slow (average growth rates for healthy P. biscaya ranged from 0.14 to 1.2 cm/year/
colony) (Girard et al. 2019). As a result, impacted coral colonies at MC 294 are
expected to take over 50 years on average to grow back to their original size, and
some impacted colonies could even take hundreds of years.
Results on the recovery and growth rates of P. biscaya not only suggested that
this coral species has a low resilience to anthropogenic impact but also showed that
its resilience differs between sites. Overall, corals at MC 297 and MC 294 tended to
head toward recovery, while the health of corals at MC 344 tended to deteriorate
(Girard and Fisher 2018). Moreover, healthy MC 344 corals had lower growth rates,
and none of the impacted corals at this site visibly grew between 2011 and 2017
(Girard et al. 2019). These differences in coral’s response to the spill show that historical and environmental variables inherent to each site can have a significant influence on the recovery potential of coral communities after impact.
No apparent long-term effect of the spill was observed on the ophiuroid A.
clavigerum, the most common associate observed on P. biscaya. Several individuals
22 Deep-Sea Benthic Faunal Impacts and Community Evolution Before, During…
still higher than at the reference sites between 2016 and 2017. All these results indicate an ongoing, long-term non-acute effect of the DWH oil spill on deep-sea corals
(Girard and Fisher 2018).
Results from the long-term monitoring of corals impacted by the spill showed
that the fate of these corals was still uncertain 7 years after the spill. In order to plan
for future monitoring, a study used a modeling approach to assess the recovery of
impacted corals over the longer term (Girard et al. 2018). In this study, an impactdependent matrix model was parameterized based on data collected as part of the
long-term monitoring program. This model was then used to estimate the time necessary for every impacted coral colony to reach a state where all branches are visibly healthy (time to recovery) and branch loss. Results from the model indicated
that, depending on their initial level of impact, the majority of impacted coral colonies will have recovered within 10 years. However, the most heavily impacted corals could take up to 30 years to reach a state where all branches appear healthy.
Moreover, some of these impacted colonies are projected to lose a large number of
branches, leading to a 10% reduction in coral biomass at some impacted sites by the
time all corals will have visibly recovered. Based on these results, Girard et al.
(2018) suggested that corals should be monitored every 2 years (sufficient as recovery is slow) until 2021 and then less frequently for a further 20 years to assess
potential non-acute effects and follow the potential recovery of the most heavily
impacted corals.
High-resolution images of individual coral colonies were also used to measure in
situ growth rates Girard et al. 2019). Growth rates were estimated for both
Paramuricea biscaya and Paramuricea sp. B3, providing important baseline information on the biology of these coral species. Additionally, the impact of the DWH
oil spill on growth was characterized. No negative long-term impact of the spill was
detected on growth. On the contrary, the level of total visible impact had a significant positive effect on growth after 2014 at two of the impacted sites (MC 294 and
MC 297). However, this positive effect was not sufficient to compensate for the high
levels of branch loss experienced by impacted corals as growth rates were extremely
slow (average growth rates for healthy P. biscaya ranged from 0.14 to 1.2 cm/year/
colony) (Girard et al. 2019). As a result, impacted coral colonies at MC 294 are
expected to take over 50 years on average to grow back to their original size, and
some impacted colonies could even take hundreds of years.
Results on the recovery and growth rates of P. biscaya not only suggested that
this coral species has a low resilience to anthropogenic impact but also showed that
its resilience differs between sites. Overall, corals at MC 297 and MC 294 tended to
head toward recovery, while the health of corals at MC 344 tended to deteriorate
(Girard and Fisher 2018). Moreover, healthy MC 344 corals had lower growth rates,
and none of the impacted corals at this site visibly grew between 2011 and 2017
(Girard et al. 2019). These differences in coral’s response to the spill show that historical and environmental variables inherent to each site can have a significant influence on the recovery potential of coral communities after impact.
No apparent long-term effect of the spill was observed on the ophiuroid A.
clavigerum, the most common associate observed on P. biscaya. Several individuals
22 Deep-Sea Benthic Faunal Impacts and Community Evolution Before, During…