Assessing the effectiveness of restoration actions for Bryozoans: the case of the Mediterranean Pentapora fascialis

Ecological restoration is increasingly implemented worldwide to protect and recover ecosystems that have been degraded, damaged or destroyed. Traditionally, most conservation efforts in marine systems have focused on the creation of marine protected areas. However, rapid rates of ecosystem degradation highlight the need to apply and develop active management actions together with the establishment of protected areas to conserve and manage biodiversity. Restoration efforts in marine ecosystems have focused on charismatic taxa, such as corals and seagrasses, overlooking other groups, such as bryozoans. Bryozoans are one of the most abundant and common structural groups in marine benthic ecosystems distributed worldwide. Due to their rigid skeleton, they are considered habitat-forming species, which increases ecosystem complexity and provides shelter for other species. Moreover, due to their fragility, some species have been used as ecological indicators for anthropogenic threats, such as recreational diving. However, there is a lack of knowledge of many ecological aspects of bryozoans, and the effects of restoration action on these aspects have not been explored previously. Within MERCES project, we have developed for first time effective protocols to restore these abundant organisms.

Restoration techniques tested

Our study was carried out within the Marine Protected Area of the Montgrí, Medes Islands and Baix Ter Natural Park in the north-western Mediterranean Sea. Restoration actions were focused on Pentapora fascialis (Pallas, 1766) (Figure 1), a common and dominant Mediterranean bryozoan in rocky benthic communities. We tested two types of previously restoration methodologies applied effectively to restore other benthic species: the installation of different types of surfaces to enhance the recruitment of the target species (Figure 1) and the transplantation of adult colonies through a study of the best methodology for adult transplantation.

Figure 1. Types of recruitment surfaces for the enhancement of the recruitment of P. fascialis: A) 5×5 cm plain-surface natural rock/stone plates B) Structural 10×10 cm plastic grids.

Plastic grids offer the best recruitment surfaces to enhance the recruitment of P. fascialis

The recruitment and growth of P. fascialis was high in the experimental conditions highlighting the capacity of bryozoans to recover after perturbations. Structural plastic grids were the best recruitment surfaces to enhance the recruitment of P. fascialis (Figure 2). By contrast, we did not observe any recruitment on plain-surface settlement plates. This is in agreement with the globular shape and vertical growth of P. fascialis, which prefers to settle in complex interstices of substrates, rather than on flat surfaces.

Figure 2. P. fascialis recruitment enhancement experiment. Detail of one of the recruitment grids during monitoring: April, July and October 2017 and July and October 2018.

The best technique for adult transplantation

The best technique to transplant adult colonies was to attach the colony to a plastic screw on the boat (ex situ)using a nylon threadand then attach the screw to the substrate with epoxy (Figure 3E). Due to the fragility of the calcified P. fascialisskeleton, higher survival rates were reached when the colonies were manipulated on the boat where the manipulation could be done more carefully and precisely. By contrast, underwater manipulation resulted much lower survival rates of the colonies. Moreover, we transplanted adult colonies collected from a ghost fishing net trapped on the bottom and six months later their survival rate was at 50%, which is similar to successful transplantation actions of other benthic groups.

Figure 3. Pilot action to find the best methodology for adult transplantation P. fascialis colonies. A) Restoration area; B) Manipulation of the colonies in situ ; C) Transport of adult colonies from the sea bottom to the boat to tying ex situ the colonies to the plastic screws; D) Methodology of manually tying the colonies to the plastic screws on the boat; E) Colonies attached do the plastic screws on the boat; F) Colony attached directly to the bottom using two-component epoxy putty; G) Colony attached to the bottom using a flange and plastic screw; and H) Colony attached to the bottom using a nylon thread and plastic screw

Conclusions

Recruitment enhancement is the most effective restoration technique for the studied bryozoan species as it offers a non-invasive methodology and yields high recruitment and growth rates. By contrast, adult transplantation should be considered only in cases such as the detection of lost fishing nets detached at the bottom with epibiotic bryozoans.Despite the high economic costs of restoring marine habitats, our study represents a low-cost and low-tech approximation, encouraging non-scientists and managers of marine protected areas to implement these techniques at larger scales.

Reference

Pagès‐Escolà, M., Linares, C., Gómez‐Gras, D., Medrano, A., & Hereu, B. (2019). Assessing the effectiveness of restoration actions for Bryozoans: The case of the Mediterranean Pentapora fascialis. Aquatic Conservation: Marine and Freshwater Ecosystems.