Twilight Reefs of Kimbe Bay

In recent years, technological advances such as remotely-operated and autonomous underwater vehicles and closed circuit rebreather diving have provided researchers with unprecedented access to coral reef ecosystems beyond the depths accessible using traditional techniques such as open-circuit SCUBA diving. These ‘mesophotic’ reefs, defined as occurring from depths of between 30-150 m, are attracting increasing scientific interest in recognition of their unique biodiversity

ER_PNG_2016-110_THUMBNAIL.jpgFigure 1: A wealth of biodiversity including octocorals and scleractinians as one decends into mesophotic depths. Images (including the banner image above) by TE. Roberts of Tethys Images ©. 

In Kimbe Bay, the transition from hard corals to octocorals (gorgonian sea fans and soft corals), as well as sponges and black corals exist at 40-50 m depth. Here the reefs begin to thrive in a completely new way, with forests of sea fans peppering the walls and ledges. These twilight reefs yield new and unusual gorgonians, the subject of SJR's research. ER_PNG_2016-1_THUMBNAIL.jpgFigure 2: Shallow colony of the ubiquitous gorgonian Annella mollis (Nutting, 1910). Image by TE. Roberts of Tethys Images ©. 

Out of the 23 dives that SJR used electronically-controlled closed circuit rebreather technology, 39 transects were conducted and approximately 200 specimens were collected, 131 of which taken from over 50 m depth, 36 from 90-120 m depth. 

DSC04722_PNG_Kimbe_Is_Bebryce_60m_13_11_2016.JPG_THUMBNAIL.jpgFigure 3. A new species of the gorgonian sea fan Bebryce n.sp., at 60 m depth. Image by SJ. Rowley.

It is expected that several new species of gorgonians were discovered during this exploratory research, with taxonomic and molecular analyses currently underway. The seamounts of Kimbe Bay are the most intriguing habitats, with deep geomorphological characteristics supporting an endless abundance and diversity of species with increasing depth. 

DSC00167_PNG16_KH8_Acanthogorgia_cf_100m_21_11_2016_THUMBNAIL.jpgFigure 4. The gorgonian sea fan at 100 m depth. Image by SJ. Rowley.

Much remains to be discovered here at Kimbe Bay, and we hope to secure funding to further investigate these unexplored reefs and observe the beautiful sharks and fish, which seem to lurk at these mysterious depths.

Adapted from Bridge TL, Rowley SJ, Roberts TE. 2017. Twilight Reefs of Kimbe Bay. Karai Bilong Solwara, Mahonia Na Dari, 2-3. Link