Effect of trampling and digging from shellfishing on <em>Zostera noltei</em> (Zosteraceae) intertidal seagrass beds

Abstract

Summary: Seagrass beds are among the most valuable ecosystems in the world but they are also among the ones most affected by human activities, and they have decreased significantly in recent decades. In many areas, such as in the Basque Country (northern Spain), seagrass beds occupy areas that are also of interest for human activities such as recreation and shellfishing. They may therefore face a number of pressures that cause damage or irreversible states. Taking into account the limited distribution of seagrass beds in the Basque Country and the interest in their conservation, an eight-month field experiment focusing on the Zostera noltei growing season was carried out to evaluate the effect of shellfish gathering. We used generalized linear models to assess different intensities of trampling and digging, as the most important pressures of shellfishing applied to Zostera noltei beds. The results indicated that shoot density of Z. noltei was negatively altered by trampling treatments and positively affected (as a recovery) by digging treatments. This finding suggests that shellfishing adversely affects seagrass abundance and is potentially responsible for its low density in the Oka estuary. Our findings are important for management and should be taken into account in seagrass conservation and restoration programmes.Keywords: Zostera noltei; seagrass; tidal flats; invertebrate harvesting; impact; field experiment. Efecto del pisoteo y excavación del marisqueo sobre las praderas intermareales de Zostera noltei (Zosteraceae)Resumen: Las praderas marinas se encuentran entre los ecosistemas más valiosos del mundo; sin embargo, también se encuentran, al mismo tiempo, entre los más afectados por las actividades humanas, por lo que han sufrido un importante declive en las recientes décadas. En algunas zonas, como por ejemplo en el País Vasco (Norte de España), las praderas marinas ocupan superficies que también son de interés para varias actividades humanas (p.ej. paseo, marisqueo); por ello, se enfrentan a diversas presiones que provocan daños o situaciones irreversibles. Teniendo en cuenta la reducida distribución de las praderas marinas en el País Vasco y el interés por su conservación se realizó un experimento de campo de 8 meses de duración, centrado en el periodo de crecimiento de Zostera noltei, para evaluar el efecto del marisqueo. Se aplicaron distintas intensidades de pisoteo y excavación (consideradas como presiones más importantes ejercidas por el marisqueo) sobre una superficie de pradera marina. Los resultados obtenidos mediante modelos mixtos lineales generalizados indican que la densidad de hojas de Z. noltei respondió negativamente en los tratamientos de pisoteo y positivamente (reflejando una recuperación) en el experimento de excavación. Esto sugiere que el marisqueo afecta negativamente a la abundancia de la pradera marina, y que es potencialmente responsable de su baja densidad en el estuario del Oka. Estas aportaciones resultan relevantes para la gestión de estas zonas y deberían tenerse en cuenta...

Socioeconomic Determinants of Mangrove Exploitation and Seagrass Degradation in Zanzibar: Implications for Sustainable Development

“…Mangrove resources extracted were used for charcoal making, boat making, building poles, and fuel wood [45]. Quinn et al [37] reported similar findings in Brazil and Vietnam, whereas the resources extracted from seagrass included bivalve and bait collection [19,43] and seaweed [22,42] through seaweed farming and fish by using fishnets and traps. The resources obtained from both mangrove forest and seagrass meadows were collected by economically active ages ranging from 26 to 50 years old.…”

“…Moreover, assessment done by Watson et al [42] revealed that the global catch of bivalves is approximately 121,000 tonnes per annum with a retail value of m5.5 billion. This increase comes with physical disturbance in seagrass meadows; for example, Garmendia et al [43], Watson et al [42], and Eckrich and Holmquist [44] reported the effect of trampling and digging during bait collection in Zostera noltii (Zosteraceae) and Thalassia testudinum. The present study revealed that substantial numbers of respondents (48%) in all sites studied engage in seaweed farming, and they contribute unknowingly to seagrass degradation.…”

Seagrass beds provide habitat for crabs, shrimps and fish in two estuaries on the South Island of New Zealand

“…obs. ), although intensive and repeated trampling associated with fishing and digging obviously have stronger and more lasting impacts (Eckrich and Holmquist 2000, Alexandre et al 2005, Skilleter et al 2006, Travaille et al 2015, Garmendia et al 2017.…”

Characterization of a resilient seagrass meadow during a decline period

“…Cochón et al 2005, Martin et al 2010, Garmendia et al 2017, in the Bay of Santander the decline was followed by a fast recovery characterized by patches of vegetation alternating in space and time. Today, Z. marina and Z. noltei occupy most of the shallow tidal flats in the Bay of Santander (Ondiviela et al 2015), and the high recovery rate observed suggests that resilient meadows played an important role in this process.…”