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Using photography to monitor changes in sub-Antarctic epibenthic communities following 25 years of non-sampling

By Grant van der Heever and Dr Charles von der Meden, SAEON Egagasini Node
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Grant van der Heever prepares to deploy SAEON’s deep-sea camera system, the SkiMonkey III

Marine benthic ecosystems are understudied and we know relatively little about large parts of our offshore environments.

This is particularly true in the Southern Ocean, where information on offshore benthic fauna is limited to a handful of studies.

In a quest to gain more information on the benthic communities around the Prince Edward Islands, a monitoring study was launched by SAEON’s offshore node in 2013 using their newly acquired deep-sea camera system, the SkiMonkey III. This study was the first of its kind, and an attempt to better understand long-term changes in the benthic communities around the island.

By re-photographing the sites sampled by Prof. George Branch and colleagues in 1988, the present study aims to examine changes in the benthic communities following the 25-year interval.

Within the larger study area, a biennial monitoring study was launched by SAEON’s postdoctoral research fellow, Dr Charles von der Meden in 2013, with aims to re-sample the sites in 2015 and 2017. The finer-scale sampling is necessary in order to characterise short-term variability in the benthic assemblages. This step will help to distinguish patterns of possible long-term change from natural variability.

To date, photographic data from the years 2013 and 2015 have been analysed, and some interesting results have come to light, including some significant temporal differences in the composition of benthic assemblages around the islands, with notable changes in the density of bryozoans, tube-building polychaetes (Lanice marionensis) and several other suspension feeding groups.

2017 voyage to the Prince Edward Islands

Armed with the SkiMonkey III camera system, newly appointed offshore instrumentation technician, Grant van der Heever, joined the 2017 annual relief voyage to the Prince Edward Islands to collect the final year’s photographic data.

After spending three days in the harbour due to unforeseen circumstances, the SA Agulhas II finally departed in the early hours of the morning on 9 April 2017. With engines at full steam the SA Agulhas II arrived at the island on 12 April 2017, a record two days later!

Owing to the nature of this voyage, oceanographic science was intermittent, with ship-based science only being conducted on days when the weather was not suited for flying cargo to the island. Despite these limitations, Grant managed to conduct successful camera tows across 13 of the 20 proposed stations.

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Figure 1: Association between starfish and sponges

Figure 2: Association between basket stars and octacorals

Figure 3: Association between hermit crabs and anemones

A number of different habitat types were observed (sand, gravel and rocky habitats), with the general changes in species composition occurring in response to changing habitat. Interesting associations between species were noted as well, with Grant managing to capture images of starfish attached to sponges (Figure 1), basket stars attached to octacorals (Figure 2) and anemones attached to the shells of hermit crabs (Figure 3).

The recent attachment of the plankton net and cone dredge to the towed camera system proved to be successful, with in-situ sediment samples and near-bottom plankton and larval samples collected from each of the 13 camera stations.

Ultimately, the cruise was a huge success, with Grant managing to obtain good images and videos from all the highest and high priority stations. These new images will need to be processed and analysed in conjunction with the full dataset before conclusions can be drawn about the extent to which short-term variability affects patterns of benthic communities at the islands.

The outcomes from this study will most certainly shed light on how the composition and abundance patterns of benthic biota have changed around the island over the last 25 years.

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