This work package is geared to understanding how EN induced changes affect the structure and dynamics of Chilean-Peruvian intertidal and subtidal communities and the resources they offer. This will be done by retrieving, compiling and standardizing existing data on communities (species composition, abundance, diversity, biomass) and selected biological features (growth, reproduction, recruitment, feeding) followed by integrative analyses and interpretation.

The relative influence of nutrient availability ('bottom-up') vs. predator ('top-down') as the main forces controlling community structures and dynamics has been debated for a variety of habitats. The different primary producers supporting coastal food webs may be benthic microalgae, macroalgae or phytoplankton or nutrient input through watersheds. Studies of coastal community responses to nutrient enhancement showed inconsistent results, apparently because their trophic connections include a higher diversity of primary producers and consumers. Thus, coastal food webs may be more resilient to changes in sources of primary production or predation level (and hence harvesting). EN changes the availability of nutrients, and thus it is likely that community control (and production of commercial marine resources) switch from being bottom-up to be top-down controlled. Therefore information from recent moderate and strong EN events (e.g. 1982/83, 1987/88, 1991-93, 1997/98) as well as LN events (like the strong and longer than usual 1998-2001 event) will be analyzed to study differences within the respective community related to resilience. Based on population dynamic data (recruitment, growth, natural and fishing mortality), the production and productivity of commercial species under non-EN and EN conditions will be calculated using all the existing data and results from the ongoing monitoring programmes of several participants. Obvious gaps for the understanding of EN impacts on the coastal resources will be filled by studying biological mechanisms. Experiments will also favour aquaculture of species with high local and export value and thus increase the income and livelihood for humans relying on aquatic resources. Additionally, changes of the energy flux prior, during and after EN and LN events will be analysed.

Larval supply to coastal communities is another major structuring force, which is highly affected by EN. Also LN impacts recruitment by decreased water temperature and thus growth and reproductive output and/or changing larval transport. We will focus on understanding the role of larval supply across the area affected by EN.

A third force is ecosystem engineering (EE), which refers to the changing of habitats by organisms. Shells and structures of macroalgae are good examples, which modify the mortality rate of many species. Given that one characteristic manifestation of EN is the proliferation of local molluscs (A. purpuratus, T. chocolata), we expect EE effects to be locally important in EN main areas. To study this process is another target, which will also be useful to explore possibilities of using shells or artificial substrates to improve recruitment of commercially important species.

The results of CENSOR will further serve to identify biological indicators for EN. Management strategies for benthic resources of the coastal Humboldt Current ecosystem will be derived based on our findings.

Contact

Workpackage Leader: Juan Tarazona