Response to sedimentation stress of the gorgonian coral Primnoella chilensis from the Chilean fjord region

Sedimentation is one of the main disturbance factors influencing benthic communities and coastal reef organisms through a variety of mechanisms. In Chilean Patagonia, rising anthropogenic intrusions such as coastal road projects and aquaculture installations threaten the local biodiversity causing increased sedimentation with even more to be expected. Primnoella chilensis (Philippi, 1894) is an important habitat-forming gorgonian coral, abundant in this region, but significant abundance decreases were reported for the last decade. The present study aimed to describe physiological and behavioural stress responses of P. chilensis to increased sedimentation. Therefore, two laboratory experiments were conducted measuring colonies' responses in respiration for 18 hours as well as documenting polyp activity and mucus secretion for 15 days under sediment exposure. No significant differences in oxygen consumption were measured, presumably due to the low number of test organisms. Further, no mucus secretion or changes in colonies' overall activity were detected. However, an analysis on single polyp level revealed a significantly increased percentage of open polyps when exposed to high sedimentation. This increased activity may be explained by intensified filter-feeding behaviour and active sediment rejection. In addition, a spawning event was detected as a possible stress reaction. All in all, the results suggest that P. chilensis is able to tolerate the simulated sedimentation loads of 225 and 450 mm/y due to its morphology and compartmentalized behaviour. This goes along with previous findings on gorgonian corals. Nonetheless, anthropogenic disturbances may by far exceed and alter natural ones due to their extent and persistence causing unpredictable, dangerous conditions for the benthic community

Activity states of Primnoella chilensis colonies under sediment exposure of 15 days, Treatment 2, X-Huinay

To determine behavioural stress, polyp activity states of Primnoella chilensis colonies and the frequency of these states were observed under turbid seawater in an experimental setup for 15 days (Treatment 1: equals sedimentation rate of 225 mm/y; Treatment 2: equals sedimentation rate of 450 mm/y; control group: ambient seawater). A visual overview analysis of colonies of Primnoella chilensis was conducted with the image-viewing program IrfanView. In a defined sector the overall colony activity was assessed and categorized: category 0 = > 50 % of polyps closed; category 1 = > 50 % of polyps semi-open; 2 = > 50 % of polyps open ; x = no data

Percentage of Primnoella chilensis polyps activity states under sediment exposure of 15 days, observation period 21 h, Control, Punta Gruesa

To determine behavioural stress, polyp activity states of Primnoella chilensis colonies were observed for 21 hours after eleven days under turbid seawater exposure in an experimental setup (Treatment: equals sedimentation rate of 450 mm/y; control group: ambient seawater). Image analysis was conducted by drawing a segmented selection line along the centre of the colonies' internal axis using the image-processing program ImageJ. This line was moved to the side by 175 % of the internal axis' width measured in pixels and 250 % respectively, resulting in two lines that were named selection A and B. These distances were chosen because fully expanded polyps showed a horizontal spread of about two times the internal axis' diameter and fully closed polyps less than one time respectively. For both lines, a plot profile was created showing grey values of all pixels under the segmented selection line. Lighter pixels of the extended polyps in comparison to the black background resulted in countable peaks. Therefore, the plot was divided by the highest and lowest grey values and bisected horizontally using the vector graphics editor Adobe Illustrator. The number of peaks in the upper part of the divided plot-image was then counted in ImageJ using the function 'analyze particles'. Lastly, the number of polyps of a category was calculated: category 0 (closed): = total polyps observed minus counted peaks for selection line A; category 1 (semi-open): = counted peaks for selection line A minus counted peaks for selection line B; category 2: = counted peaks for selection B

Activity states of Primnoella chilensis colonies under sediment exposure of 15 days, Treatment 1, Punta Gruesa

To determine behavioural stress, polyp activity states of Primnoella chilensis colonies and the frequency of these states were observed under turbid seawater in an experimental setup for 15 days (Treatment 1: equals sedimentation rate of 225 mm/y; Treatment 2: equals sedimentation rate of 450 mm/y; control group: ambient seawater). A visual overview analysis of colonies of Primnoella chilensis was conducted with the image-viewing program IrfanView. In a defined sector the overall colony activity was assessed and categorized: category 0 = > 50 % of polyps closed; category 1 = > 50 % of polyps semi-open; 2 = > 50 % of polyps open ; x = no data

Mass values of two sediment samples collected in the intertidal zone of the estuary of Río Lloncochaigua

Sediment was sampled on 22nd of May 2019 by removing the uppermost 2 cm sediment. In the laboratories the sediment was wet-sieved to gain a grain size of < 125 µm (test sieve, Gilson, Columbus, USA). Sediment was heated for 30 minutes to 40 °C in a drying oven (UT 6, Heraeus, Hanau, Germany). Afterwards, they were dried for 36 h at 50 °C in a drying oven (UT 6, Heraeus, Hanau, Germany), weighed again to determine dry mass and then ashed for 24 h at 500 °C in a muffle furnace (LV 5/11/B 170, Nabertherm, Lilienthal, Germany) and weighed again to determine ash-free dry mass

Activity states of Primnoella chilensis colonies under sediment exposure of 15 days, Treatment 1, X-Huinay

To determine behavioural stress, polyp activity states of Primnoella chilensis colonies and the frequency of these states were observed under turbid seawater in an experimental setup for 15 days (Treatment 1: equals sedimentation rate of 225 mm/y; Treatment 2: equals sedimentation rate of 450 mm/y; control group: ambient seawater). A visual overview analysis of colonies of Primnoella chilensis was conducted with the image-viewing program IrfanView. In a defined sector the overall colony activity was assessed and categorized: category 0 = > 50 % of polyps closed; category 1 = > 50 % of polyps semi-open; 2 = > 50 % of polyps open ; x = no data

Photographs, biomasses, morphological parameters and activity states of Primnoella chilensis colonies used in an experiment for sediment exposure of 15 days

Colonies of P. chilensis were sampled via self-contained underwater breathing apparatus (SCUBA) diving on 14th and 15th of May 2019 at two different sites in Comau fjord. At each site, 20 colonies of a length between 20 cm and 30 cm were collected at a depth between 16 m and 20 m by cutting the terminal tips of the colonies with scissors. To determine behavioural stress, polyp activity states of Primnoella chilensis colonies and the frequency of these states were observed under turbid seawater in an experimental setup for 15 days (Treatment 1: equals sedimentation rate of 225 mm/y; Treatment 2: equals sedimentation rate of 450 mm/y; control group: ambient seawater). A visual overview analysis of colonies of Primnoella chilensis was conducted with the image-viewing program IrfanView. In a defined sector the overall colony activity was assessed and categorized: category 0 = > 50 % of polyps closed; category 1 = > 50 % of polyps semi-open; 2 = > 50 % of polyps open ; n.d. = no data. After the experiment, each coral colony was carefully blotted dry using delicate task wipers and weighed to determine the wet mass. Furthermore, the respective lengths and polyp diameter of a single, representative polyp were measured. Afterwards, they were dried for 36 h at 50 °C in a drying oven, weighed again to determine dry mass and then ashed for 24 h at 500 °C in a muffle furnace and weighed again to determine ash-free dry mass