Estimating larval recruitment in the deep sea

Overview

The first deployment of settlement frames used to investigate larval recruitment in the deep sea has been completed. The settlement frames were attached to the BOP (blow out preventer) on the Paul B Loyd Jr drilling rig, west of Shetland of the UK. Initial examination of the frames show animals have settled on all the substrates during the four month deployment. This work is part of the international deep-sea research programme INDEEP

 

Larval Recruitment

Benthic invertebrates play a major role in carbon cycling through the world’s oceans. Most of these invertebrates have complex life cycles. The adults are either sessile or show limited motility and live on or in the seafloor. Their larvae are planktonic and can spend weeks to years in the water column before finding suitable substratum to settle, assume a benthic existence and recruit to the adult population. Larval dispersal allows these species to maintain existing populations, re-colonize areas that have been disturbed (such as from exploration of natural resources) and colonize new areas as habitat becomes available by natural (e.g. wood falls or whale falls) or anthropogenic (e.g. artificial reefs) processes. While the rates of recruitment have been widely measured for many shallow-water species and habitats, they are mostly unknown for the deep sea. The limited existing information suggests that these rates, and thus population recovery from perturbation, are much slower than in shallow water, but much remains to be learned.

 

INDEEP

INDEEP (www.indeep-project.org) is an international project that combines the expertise of 100s of scientists worldwide to develop and synthesise our understanding of deep-sea global biodiversity and functioning. Through collaboration with SERPENT the project aims to make preliminary estimates of larval recruitment in deep-water habitats across several ocean basins. Using a simple device that can be easily deployed and recovered on oil rigs during exploration drilling members of the pool of larvae (as possible recruits) in the region of the rig are being collected.

 

Collaboration with Science and Industry


Collaboration like this is mutually beneficial to the research community and the industry. From the research perspective, although the simplicity of the device prevents a comprehensive evaluation of the larval pool, the extensive spatial coverage across ocean basins provides an unprecedented opportunity to obtain first estimates of possible dispersal distances and recruitment rates in a remote habitat. The industry can benefit by obtaining estimates of recruitment rates of species available to re-colonize areas that have been disturbed by exploration in situ (and thus of direct relevance), as well as of potentially fouling species.
 One of the main goals of INDEEP is to provide a framework to bridge the gap between scientific results and society and aid in the formation of sustainable management strategies. A partnership with industry can directly address this goal. The success of the project relies on the international nature of both INDEEP and Transocean, alongside the successful history of SERPENT in collaboration with industry.


The Frame

The device used is a frame (~33 x 33 cm) made of PVC (3 cm diameter) on which 9 blocks made of 3 different materials are attached. Each block is 5 x 5 x 5 cm and is attached to the frame by nylon threaded rod. A block of wood (7 x 5 x 33 cm) is attached lengthwise on one of the sides of the frame. The different materials “represent” different types of habitats (e.g. carbonate rocks) or structures (PVC) that larvae may recruit to.

Frame on BOP

Above: An image of one of the prototype frames in place on the BOP before deployment. This original metal frame has been replaced with PVC.

The first deployment

The first deployment of settlement frames used to investigate larval recruitment in the deep sea has been completed. Two settlement frames were attached to the BOP (blow out preventer) on the Paul B Loyd Jr drilling rig, west of Shetland of the UK prior to its deployment at the seabed. As part of their routine monitoring the ROV team working on the rig checked the frames regularly during the deployment. They remained in place for the duration of the drilling programme and were removed from the structure and the samples preserved when the BOP was recovered to the surface in December 2012. The samples were then sent to NOC in Southampton for analysis. Initial examination of the frames show animals have settled on all the substrates during the four month deployment.

Indeep frame

Above: A ROV image of the prototype frame on the BOP at the seabed West of Shetland.

The first frames have now been recovered and returned to the laboratory in Southampton. The inital inspection has revealed hydroids have settled on the structures. There were also several small molluscs. There are likely several other species to be found when the full investigation is carried out.

Some of the intial images are shown below:

indeep blocks