Interactions between climatic variables and human pressures upon a macroalgae population: Implications for management

Abstract

The combined effects of human pressures (e.g., exploitation and wastewater discharges) and environmental variables (e.g., light, waves, temperature) have been studied only minimally in terms of sublittoral macroalgae resources. Using a long-term series (1993–2012) of cover and biomass of Gelidium corneum macroalgae, along the Basque coast (Bay of Biscay), the effects of human pressures and changes in climate have been studied. The biomass and the percentage of samples with <25% of algae cover have decreased significantly (p < 0.002), over time. Sunlight hours are responsible for producing biomass, but the reduction is mainly due to an increase of waves >5 m height. However, there are differences between sectors, with Gelidium biomass and cover being a function of the exploitation of this alga and wastewater discharges. In areas where these human pressures are present, the resource is more vulnerable to environmental changes, than in a sector in which human pressures are absent. Human pressures have reduced the resilience of these macroalgae beds, exacerbating the loss of biomass and macroalgae cover, under such climate changes. The implications of these findings, for the management of the resource in a sustainable way within the Water Framework Directive and the Marine Strategy Framework Directive, are discussed. There is a need for increasing resilience for macroalgae restoration along the Basque coast.