Restoration of fish nursery functions with artificial habitats

Gilles Lecaillon

Ecocean, France

The Biohut’s latest advancements

Biohut is a small artificial habitat that reproduces fish nursery functions for port and coastal infrastructures (Figure 1). Since the confirmation of Biohut’s ecological functions in Mediterranean waters with the GIREL and NAPPEX projects (MERCES Newsletter 04, May 2018), more than 3000 Biohuts have been installed, thus creating a network of 27 French marinas equipped with Biohut (between 20 to 90 units per marina), along with commercial ports such as Calais, Port-Vendres and Rotterdam. 

Figure 1. Pontoon Biohut immersed in a marina. Port Hercule, Monaco, ©Rémy Dubas/Ecocean

Figure 2. Juvenile dusky grouper (Epinephelus marginatus) hiding among the shell substrate of a Biohut. 50mm, La Ciotat, France, ©Rémy Dubas/Ecocean

The Biohut habitats are monitored 2 to 3 times per year to analyze their colonization by fish and mobile invertebrates. Analysis of the Biohut monitoring data has improved our understanding of several aspects of the Biohut’s functions. We recorded the presence of juveniles of several patrimonial species in the Biohut nurseries, such as dusky grouper (Figure 2), royal grouper, cod, European eel and seahorses. In total, 105 different fish species have been observed in the Biohut, most of which present in their juvenile stage. The Biohut is colonized mainly by juvenile fish by which to enhance their survival, although this efficacy can vary among species (Figure 3).

Figure 3. Average and standard deviation of individuals abundance, all species combined, per habitat and monitoring action, in 3 different areas of Marseille Commercial Port.

Some species can benefit greatly from such artificial habitats. Juveniles of species such as Annular seabream, which normally rely exclusively on seagrass meadows as nurseries, were observed in large numbers in the Biohut (Figure 4). Studies have also shown that there are no significant differences in the physical condition and growth of demersal juvenile fish growing in ports and those growing in natural environments.

Figure 4. Juvenile seabream (Diplodus spp.) feeding and sheltering on a Biohut mesh. 20mm, ©Rémy Dubas/Ecocean

Ecocean and its partners have started to study the different assemblages of invertebrate species found in the Biohut. New monitoring protocols have since been developed. A scientific publication from the University of Exeter characterizes the assemblages of invertebrate mobile fauna in the Biohut and the dependence of their evolution on immersion time. More than 170 species of invertebrate organisms have been observed in Mediterranean Biohut systems (Figure 5).

Figure 5. Summary of repartition of species richness and abundance of the different invertebrate taxonomic groups in the Biohut installed in the Mediterranean.

To broaden the spatial application of the Biohut, Ecocean had the opportunity to install Biohut in the port of Helsingør in Denmark. This allowed us to analyze the behavior of different local fish communities.  The density and species richness of fish in Helsingør exceeded that in the Mediterranean, with up to 90 juvenile fish representing 11 species occurring simultaneously in a single Biohut. Many North Sea fish species, such as cod, saithe and pollack, were observed feeding and sheltering in the Biohut.

As an exciting development with huge commercial potential, Ecocean will be the first to install artificial habitats on floating offshore wind turbines. Ecocean is involved in the on-going EFGL (Floating wind turbines of the Gulf of the Lion) consortium that will deploy three 10-MW floating turbines in the Gulf of the Lion (Leucate) in 2021. To better determine habitat shapes, materials and optimum fixation, Ecocean has developed a 15m buoy equipped with different types of Biohut (Figure 6) in order to adapt to the biodiversity that will settle on a floating structure. Installed in mid-2019, 16 km offshore at 70 m depth, the buoy is being monitored by the University of Perpignan using visual census and acoustic monitoring.

Figure 6. Biodiversity observation Buoy (BoB) aims to study fish and invertebrate colonization in offshore conditions, ©Rémy Dubas/Ecocean

References

Bouchoucha et al., 2016. Potential use of marinas as nursery grounds by rocky fish: insights from four Diplodusspecies in the Mediterranean. MEPS 547, 193–209.

Bouchoucha et al., 2018. Growth, condition and metal concentration in juveniles of two Diplodusspecies in ports. Marine Pollution Bulletin 126, 31-42.

Mercader et al., 2016. Observation of juvenile dusky groupers (Epinephelus marginatus) in artificial habitats of North-Western Mediterranean harbors. Marine Biodiversity. DOI 10.1007/s12526-016-0498-x

Mercader et al., 2017. Small artificial habitats to enhance the nursery function for juvenile fish in a large commercial port of the Mediterranean. Ecol. Eng. 105, 78-86.

Mercader et al., 2019.Is artificial habitat diversity a key to restoring nurseries for juvenile coastal fish? Ex situ experiments on habitat selection and survival of juvenile seabreams. Restoration Ecology. https://doi.org/10.1111/rec.12948 

Richardson et al., in prep. Composition of mobile invertebrate assemblages in artificial habitats determined by duration of immersion in commercial harbors

Selfati et al., 2018. Promoting restoration of fish communities using artificial habitats in coastal marinas. Biol. Cons. 219 (2018) 89-95.

Further information about Biohut® projects around the world (including pictures and videos): www.nappex.fr. General information about Ecocean: www.ecocean.fr.Gilles Lecaillon (gilles.lecaillon@ecocean.fr).