The study carried out in Gran Canaria by researchers from the BIOCON group at the University Institute of the ULPGC, resulting from work conducted within the framework of the international ‘ReefRUV Global Network’, identifies the negative effects caused by human activities such as overfishing on these essential functions
Research by the Biodiversity and Conservation (BIOCON) group at the ECOAQUA University Institute of the University of Las Palmas de Gran Canaria (ULPGC), carried out off the coast of Gran Canaria, reveals that the biomass and intensity of ecological functions (such as herbivory) in reef fish communities decline significantly as a result of human pressure. The study, therefore, highlights the significant impact of human pressures on trophic interactions mediated by reef fish.
The research, published in the international journal Estuarine, Coastal and Shelf Science under the title ‘High dominance renders reef fish trophic interactions vulnerable to human pressures in oceanic islands’, notes that “the observed decline in feeding pressure, which generally exceeds that of biomass, suggests that fishing activities may exert additional and hidden negative effects on these interactions, beyond what changes in biomass can reveal”.
These patterns were driven primarily by the target species of the fishery, which accounted for 87% of the fish biomass and 93% of the fishing pressure.
An example image of a fish community in the Canary Islands surveyed using the ReefRUV Global Network methodology, which quantifies both the species present and their trophic impact.
The biomass of omnivores and herbivores fell by a factor of 19 and 3, respectively, whilst the feeding pressure exerted by these groups decreased by a factor of 6 and 4, respectively. For the researchers, given the crucial role these groups play in the transfer of energy and materials from primary producers to higher trophic levels, these data highlight the “urgent” need to promote their sustainable management and conservation within these oceanic island ecosystems.
Human influence on fish-mediated trophic interactions has traditionally been investigated through indirect indicators, such as the biomass of trophic groups. However, according to the researchers behind this study, fish biomass alone may not adequately reflect the nuanced responses of these groups to different levels of human pressure, such as changes in the nature and intensity of trophic interactions.
In this regard, it is worth noting that some trophic groups exhibited more pronounced declines in feeding pressure than would be expected solely from a reduction in their biomass; this highlights potential compensatory mechanisms that need to be studied in greater detail to understand the role humans play in mediating trophic interactions in the marine environment.
Therefore, in this research, conceived and led by researcher Néstor E. Bosch, together with master’s student Iris Barroso, with the collaboration of other members of the BIOCON group, visual counts and remote video surveys were combined to assess how human pressures influence the spatial patterns of reef fish biomass, but also on feeding pressure on an oceanic island in the eastern Atlantic (Gran Canaria).
Photo of Dr Néstor E. Bosch, a researcher with ECOAQUA’s BIOCON group, during a campaign to implement the ReefRUV Global Network methodology in the Chinijo archipelago in the Canary Islands.
International monitoring network
This study, in which more than 6,000 fish of 37 species were surveyed to study the impact on biomass and almost 2,000 individuals of 19 species were surveyed for the study on feeding pressure, is the result of work carried out within the framework of the scientific initiative entitled ‘ReefRUV Global Network: a network for monitoring reef ecosystems using remote underwater video’.
This is an international research network bringing together scientists and research centres from around the world (Brazil, Australia, the USA, Spain) – including the principal investigator of the study, Dr Néstor E. Bosch, a member of the BIOCON group at ECOAQUA – to study variations in the biodiversity and behaviour of reef organisms at macroecological scales using standardised Remote Underwater Video Systems (RUVs), which enable the collection of non-invasive data, minimising the impact on marine fauna.
The network, led by principal investigator Sergio Floeter (Federal University of Santa Catarina, Brazil) and which has recently launched a new website (https://reefruv.ufsc.br/), aims to generate comparable observations across regions and continents, enabling an assessment of how marine ecosystems respond to different environmental and human pressures on a global scale. Thanks to a common methodology, the network is building one of the largest audiovisual databases on marine biodiversity currently in existence.
An overview of the locations where the standardised ReefRUV Global Network methodology is used.
The Canary Islands are one of the main nodes of the ReefRUV Global Network in the eastern Atlantic. Over the last three years, researcher Dr Néstor E. Bosch and other colleagues at ECOAQUA have systematically implemented this methodology across the islands, incorporating both seasonal variability (four annual surveys) and interannual variability, with nearly 32 hours of video footage analysed and more than 4,000 interactions between organisms quantified. This scientific infrastructure has enabled the generation of fundamental information on the dynamics of Canarian reef ecosystems.
ECOAQUA researchers have led the implementation of the ReefRUV methodology in the Canary Islands, including the design of sampling programmes, the execution of field campaigns, the analysis of underwater videos, and the development of studies aimed at understanding how human activities and climate change affect the biodiversity and functioning of reef ecosystems.
They have also actively contributed to the consolidation of the international network by generating high-quality time series and developing new ecological applications of the methodology. A study is currently underway on the impact of marine heatwaves on the behaviour and feeding pressure of reef fish.
You can read the full study via the following link:
https://www.sciencedirect.com/science/article/pii/S0272771425001830?via%3Dihub