Abstract
BackgroundOceanographic moorings (OMs) are standard marine platforms composed of wires, buoys, weights and instruments, and are used as in situ observatories to record water column properties. However, OMs are also comprised of hard substrates on which a variety of invertebrates can settle when they encounter these structures along their dispersal routes. In this contribution, we studied the fouling communities found on two OMs deployed in the Ross Sea (Antarctica). Furthermore, a cage containing the Antarctic scallop Adamussium colbecki (E. A. Smith, 1902) was incorporated in the OM. The growth of the caged A. colbecki were evaluated after 1 year and their shells used as biological proxy for seawater temperature and salinity.MethodsA variety of settlers were collected from two different OMs deployed in the Ross Sea (Antarctica) and species identified using a combination of morphological and genetic (mainly through DNA barcoding) characteristics. Caged scallops were individually marked with permanent tags and their growth studied in terms of size-increment data (SID). Cages were specifically designed to prevent damage to individuals due to water drag during OM deployment and retrieval. Growth parameters from the caged individuals were applied to the A. colbecki juveniles that had settled on the mooring, to trace the likely settlement period.ResultsThe growth performance of caged A. colbecki was similar to that from previous growth studies of this species. The remarkable survival rate of caged specimens (96.6%) supports the feasibility of caging experiments, even for a species with a fragile shell such as the Antarctic scallop. Some of the new recruits found on the mooring were A. colbecki, the same species we put into special cages fixed to it. The settlement of the A. colbecki juveniles started during the Austral spring with a peak in summer months and, remarkably, coincided with seasonal changes in water temperature and flow direction, which were recorded by the mooring’s instruments. Genetic data from other settlers provided new information about their larval ecology and connectivity.DiscussionOceanographic moorings are expensive and complex experimental platforms that, at present, are strictly used for the acquisition of physical and biogeochemical data. Their use for in situ ecological experiments on model organisms suitable for caging and to study fouling species has yet to be fully explored. We present the outcomes of a study, which represents a baseline for the characterization of Antarctic fouling biodiversity. We hope that in the near future an internationally coordinated systematic study of settlers could be initiated around the Antarctic continent. This could utilize “new generation OMs” equipped with standardized settlement structures and agreed sampling protocols for the study of fouling communities.
Highlights
Biological monitoring, or biomonitoring, is based on the use of model species or “bioindicators” to assess changes in the environment
A total of 58 of the 60 individuals added to the cages were healthy and, of these, only six specimens were excluded from size-increment data (SID) calculations because their shell edges were too damaged
The two dead specimens were found as loose valves and possibly died shortly after mooring deployment
Summary
Biological monitoring, or biomonitoring, is based on the use of model species or “bioindicators” to assess changes in the environment. Whenever an indicator species is not naturally present in the area to be monitored, biomonitoring studies have involved translocating specimens from a source population (which is usually used as control site) to the impacted area. The bivalves are contained in submerged cages, generally positioned in shallow waters (1–10 m depth) (Andral, Galgani & Blottiere, 2007) by divers and eventually retrieved by grapple hooks (Roméo et al, 2003; Gorbi et al, 2008) This “caging approach” can be used in deep waters, with cages attached to lines moored with weights and stabilized by mid-water and surface buoys. Discussion: Oceanographic moorings are expensive and complex experimental platforms that, at present, are strictly used for the acquisition of physical and
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