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The effect of seagrass bed habitat quality on selected ecosystem services

Periodic Reporting for period 1 - PIONEER (The effect of seagrass bed habitat quality on selected ecosystem services)

Reporting period: 2018-01-08 to 2020-01-07

Seagrass meadows serve many important ecosystem functions and services in coastal waters. Most notably, through their role as nursery and feeding areas they support a great abundance and diversity of fish and invertebrates, making them important for fisheries and local economies. In spite of their ecological and socio-economic importance, seagrass meadows worldwide have been experiencing declines and habitat degradation through fundamental changes in their structural complexity. Currently only limited knowledge exists of how these configurational changes influence the functioning and the ecological and cultural services provided by seagrasses. PIONEER takes an interdisciplinary approach to examine the following objectives:
• To examine the influence of anthropogenic pressures on seagrass (Posidonia oceanica) habitat structure
• To evaluate the influence of seagrass habitat structure on fish assemblages and nursery and foraging areas for fish
• To study fishers’ perception of the importance of seagrass for the recreational fishing sector.
PIONEER provides relevant and timely information for the implementation of the EU Marine Strategy Framework Directive, which aims to achieve Good Environmental Status in all water bodies across EU member states by 2020.
Twenty seagrass meadows from inside Marine Protected Areas (3 MPAs Reserva Marina del Freu de sa Dragonera, Reserva Marina de la Badia de Palma, Reserva Marina del Migjorn de Mallorca) and at varying distances from anthropogenic activity hubs such as harbours and marinas were studied along the southern coast of Mallorca, Balearic Islands, Spain. A total of 4 ecological surveys and one hydro-acoustic survey were carried out to collect data on seagrass habitat structure and complexity and fish communities associated with this habitat. Estimates of recreational fishing pressure, anchoring pressure and water quality were used to examine the influence of anthropogenic pressures on seagrass habitat structure. We found a significant negative association between anchoring pressure and seagrass patch size suggesting that high anchoring pressure results in smaller and more fragmented meadows. Water nutrient concentration (represented by the δ15N in seagrass leaves) also affected seagrass and fish species living in this habitat. High nutrient concentrations resulted in seagrass meadows of low shoot density and shoot biomass, which were favoured by populations of Diplodus annularis, but not by Symphodus ocellatus. The annular seabream (D. annularis) is a resident fish species of Posidonia oceanica and a species of socio-economic importance to the Mallorcan recreational fishery. Therefore, further studies into how seagrass habitat structure affects D. annularis population structure (density and biomass), growth and body condition were carried out. Body condition was higher at higher shoot density and lower conspecific density suggesting that release from competition among conspecifics for resources might influence D. annularis body condition. The mean daily growth for juveniles during the early settlement phase in seagrass (30 days post-settlement) was higher for juveniles in areas with low shoot density, high predator & conspecific density, high water nutrient content, and high recreational fishing pressure. Variation in seascape composition can affect access to food resources and/or predators, possibly influencing post-settlement growth and mortality, and subsequently adult population structure. Understanding how the surrounding seascape affects individual-based measures of habitat quality, like condition or growth, provides useful information regarding optimal fish habitat.
Contributions beyond the state-of-art:
• A review of published studies dealing with the response of fish communities to structural and configurational changes in seagrasses revealed that only 5% out of 90 studies examined measured functional aspects, the rest examined structural aspects (density and species richness). The work carried out under this MC project improves on the current state-of-the-art knowledge by examining the importance of seagrass for functional properties (size spectra, fish growth, fish body condition), thus addressing Good Environmental Status (GES) that maintain that both structure and function of ecosystems should be safeguarded.
• A comparison of stereo-remote underwater video (SRUV), diver survey and beam trawl survey techniques for fish population studies has been carried out as part of this work. This contributes towards a better understanding of survey techniques for studying aspects and drivers of marine fish population dynamics and for better informing science-based management.
• An examination of the spatio-temporal patterns and the quantification of anchoring pressure using Automatic Identification System (AIS) has been carried out during this project. This work provides important data for marine habitat conservation and marine spatial planning in the Balearic Islands. This will provide managers and practitioners with an essential tool to mitigate threat and to put adequate management measures in place to protect threatened habitats. Furthermore, the methodology developed during this work has wide applicability regionally and globally and can be adapted to other regions of the work to assess habitat vulnerability to boat anchoring.
SCUBA diver survey for measuring seagrass characterisitcs
Micro-otolith analysis for aging of juvenile fish