Resilience of Zostera marina habitats and response of the macroinvertebrate community to physical disturbance caused by clam harvesting

ABSTRACT

The consequences of physical disturbances to seagrasses depend on disturbance frequency relative to the capacity for recolonization and recovery following fragmentation. In a subtidal seagrass meadow of Zostera marina L., following a season of clam harvesting, we compared the temporal change of shoot density and biomass of this seagrass together with the community structure of the associated macroinvertebrates, at two sites differing in the intensity of the physical disturbance. The impacted site showed significantly lower shoot density and total biomass than the non-impacted site initially. The increase in above-ground biomass over four months (May to September) of this species was significantly higher (46%) at the impacted site than in the area not affected by the disturbance. Four months after cessation of the extraction activity, the biomass and density values of Z. marina reached similar values to those measured in the non-impacted site. The sexual reproductive effort of the seagrass population affected by the disturbance (4%) was significantly lower than at the non-impacted site (10%), which could influence genetic diversity and the seed bank. The community structure of molluscs showed 54% similarity between sites at the beginning of the study. Four months later, mollusc communities increased to a similarity of 74%. The current closure season (four months annually) established for the recovery of the exploited stocks of bivalves allowed the recovery of Z. marina density and biomass. Nevertheless, other population properties, such as those related to reproductive patterns, remained altered by the disturbance.

RESPONSIBLE EDITOR:

• Margot Hessing-Lewis

KEYWORDS:

• Physical disturbance
• seagrass
• resilience
• Zostera marina

Acknowledgements

The authors would like to thank the reviewer Dr Jennifer Ruesink and an anonymous reviewer for their thorough and constructive review; their comments have considerably improved this article. We would also like to acknowledge Aida Ovejero for help to prepare Figure 1, the Estación de Ciencias Mariñas de Toralla of the University of Vigo for their technical support, Carmen B. de los Santos and Francisco Arenas for their logistic support in the field and Fernando Aneiros for assistance during the identification process of the macrofauna.

Disclosure statement

No potential conflict of interest was reported by the authors.