Admiralty Anchor UnderSea Explorer-NW Osprey reef Latitude: 13.53.244S Longitude: 146.33.435E Date: 1-3-4 and 17-3-4 Florent Cade SITE DESCRIPTION Admiralty Anchor is located on the north-west side of Osprey Reef. It is a sheltered site that is regularly visited by a small number of divers. Its habitat commonly comprises bommie fields with canyons and swimthroughs, and steep walls on the west side. Located in the Coral Sea more than 25 km from the shore, Osprey Reef is a deep-sea mount with steep drop-offs which fall below 1 m. It is considered pristine and is a popular dive site with a growing live-aboard dive industry. Osprey Reef is not currently managed. Since Osprey reef is 25 km from shore, the site experiences little anthropogenic impact. Tourism and the occasional recreational fishing would be considered their main anthropogenic pressure. During the survey season of 24 a bleaching event occurred at Osprey Reef which is reported in a separate document although the data is outlined here. Surveys have been conducted at this site since 22 and this year there were two survey periods on the 1 st and 17 th March due to the bleaching event, of which only the substrate data was collected. There is therefore no invertebrate data for the second survey.
SUBSTRATE SURVEY The substrate is dominated by hard corals and rocks. There is between 51.88% and 56.88% of hard coral cover on the two surveys but no dominant hard coral growth form (branching, encrusting, columnar or submassive). Rock comprises between 3.63% and 36.88% of the substrate and is mainly Corraline Algae. There are small amounts of other substrate categories (figure 1). In two weeks, the percentage of bleached hard corals increased from 3.75% to 16.9% of the substrate. 3% of the hard corals found in the second survey, on the 17 th of March, were bleached. There was a high amount of variability between the bommies. Close to the survey some areas presented a highly colourful display due to fluorescent corals, whereby fluorescent pigments remain during expulsion of zooxanthellae (Pic 2). Limitations: There may be slight differences in both survey periods even though they are only 16 days apart but this is most likely due to variability due to the position of the transect. Along the same lines although an increase in bleaching was observed some of this may be attributed to this variability. Ideally more replicates are required to attain greater accuracy. Percent cover 6 5 4 3 2 1 Comparison of Percent Cover Substrate for Admiralty Anchor, between the 1st and the 17th of March 24 (5m depth) HC 1-3-4 HC 17-3-4 SC 1-3-4 SC 17-3-4 RKC 1-3-4 RKC 17-3-4 NIA 1-3-4 NIA 17-3-4 SP 1-3-4 SP 17-3-4 RC 1-3-4 RC 17-3-4 RB 1-3-4 RB 17-3-4 SD 1-3-4 SD 17-3-4 SI 1-3-4 SI 17-3-4 OT 1-3-4 OT 17-3-4 Substrate type Figure 1: The percentage of bleached hard corals (HCB) increases from 3.75% to 16.9% OT SI SD RB RCCA RCTA RC SPE SP NIA RKCTA RKCNIA RKC SCB SCZ SCL SC HCB HCP HCE HCM HCF HCBR HC
Substrate Monitoring 22-24: There has been a significant increase in hard coral cover from 22 to 24 although this difference is not significant over the last year (see overlapping standard error bars). There has been a significant increase in the percent cover of Rock. Nutrient Indicator Algae was reported in 22 and there has been no further reports since (figure 2) Percent cover +/- SE 6 5 4 3 2 1 Percent Cover of Benthic Communities at Admiralty Anchor 5m depth 22 to 24 24/3 and 14/5/22 13/1/23 1/3 and 17/3/24 HC SC RKC NIA SP RC RB SD SI OT Substrate type Figure 2: There is a slight increase in HC and RC and a decrease in NIA and SP at Admiralty Anchor over the period 22-24.
INVERTEBRATE SURVEY Giant clams were found with a mean abundance of 16 per 1m 2. A few number of Drupella were noted (Figure 3 and 4). Mean Abundance of Invertebrates at Admiralty Anchor 6m depth 1-3-4 Mean Abundance +-SE 2 18 16 14 12 1 8 6 4 2 Banded coral shrimp Diadema Pencil urchin T. ananas S. chloronotus H. nobilis H. fuscopunctata S. variegatus Crown of Thorns Giant clam Tripneustes Triton shell Lobster Trochus Drupella Figure 3: The dominant invertebrate at Admiralty Anchor is the Giant Clam Distribution of Giant Clams by Size, Mean abundance per 1 9 8 7 6 5 m2 4 3 2 1 Admiralty Anchor 1-3-4 <1 cm 1-2 cm 2-3 cm 3-4 cm 4-5 cm >5 cm Giant clams size Figure 4: Tthe sizes of the Giant Clams found at Admiralty Anchor are mostly between 1 and 2cm in length. No Giant Clams greater than 3cm were found along the transect.
IMPACT SURVEY The main impacts were Drupella snails and other scars (Figure 5). Mean Abundance per 1 m2 1.2 1.8.6.4.2 Boat/Anchor damage Mean Abundance of Impacts at Admiralty Anchor 5m depth 1-3-4 Dynamite damage Other damage Trash: Fish nets Trash: General Drupella scars Crown of Thorns scars Other scars Figure 5: The main impacts reported are unidentified scars and scars caused by the Drupella snails
BLEACHING SURVEY 24 High numbers of bleached corals were found on this site. 2% of the living corals were estimated to be bleached (figure 6). Bleaching particularly concerned the fire corals Millepora sp. and Acropora sp. which were often 1% bleached. Among all these bleached corals, we observed an average of 8% of the surface colony affected, which indicates a high intensity of bleaching (figure 7). Percentage of coral population affected by bleaching Bleached Corals (%), 2 Nonbleached Corals (%), 8 Figure 6: Bleaching was estimated to affect 2% of the coral population within the belt transect Mean surface affected by bleaching within bleached corals Colony surface nonbleached (%), 2 Colony surface bleached (%), 8 Figure 7: Bleaching intensity was high with many completely bleached corals
PICTURES Pic 1: Millepora tenella, a species for which most of the colonies were entirely bleached (Admiralty Anchor). Florent Cade Pic 2: Corymbose plate Acropora sp. that appear to be very sensitive to bleaching were in most cases entirely bleached with fluorescent pigments remaining (Admiralty Anchor). Florent Cade Pic 3: Caulerpa algae and Halimeda were abundant (Admiralty Anchor) Jos Hill