SIBER SPIS sept 2011.pdf - IMBER

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SIBER Science Plan and Implementation Strategy Human activities on the ocean also have direct impacts on the marine environment. Aquaculture industries are growing in many countries around the IO rim. How does aquaculture influence coastal water quality What will be the impact of the growing aquaculture industry (e.g. deforestation of coastal mangroves, eutrophication, etc.) on coastal marine communities and biogeochemical processes Will the frequency and intensity of HAB events change due to increased anthropogenic nutrient inputs associated with aquaculture Fish aquaculture typically involves substantial inputs of organic matter in the form of feed. How does aquaculture demand for feed affect wild-caught fisheries in the IO How will these human activities influence rates of species evolution and extinction For example, will introduction of genetically altered farm species impact the gene pools of wild populations Many human activities are likely to impact sensitive coral reef environments in the IO. What are the anthropogenic (climate change, land use) impacts (SST, pH, sediment and nutrient loading due to runoff, etc.) on coral reefs What are the important contaminants (oil, pesticides, radionuclides, heavy metals, organics, etc.) and their sources and sinks in the IO, and how do the inputs of these contaminants change over time (seasonal, interannual) How are these contaminants processed/recycled in the ecosystem, and what are their residence times Th e m e 6: Th e r o l e o f h i g h e r t r o p h i c l e v e l s in e c o l o g i c a l p r o c e s s e s a n d b i o g e o c h e m i c a l c y c l e s To what extent do higher trophic level species influence lower trophic levels and biogeochemical cycles in the IO, and how might this be influenced by human impacts (e.g. commercial fishing) Ba c k g r o u n d Assessing the role of pelagic consumers on ecosystem dynamics and biogeochemical cycles (and vice versa) and developing an end-to-end food web understanding are important considerations for IMBER. Trophic networks comprised of protists, metazooplankton, nekton and top predators (tuna, squid, sharks) are important in both the epipelagic and mesopelagic zones, with many of the larger animals bridging and influencing both habitats. In addition, turtles, seabirds and mammals, even fishermen may be important to consider in the context of some science issues. Questions of relevance relate to the physiologies and behaviors of the organisms themselves, but even more so to the impacts of top-down versus bottom-up controls and the interactions between ecosystem processes and biogeochemical cycles. For example, the well-known ecological relationship between environmental stress and reduced species diversity is relevant to potential future climate impacts on the OMZ as well as to coastal eutrophication issues facing both the AS and the BoB. Despite their size range differences, micro- and mesozooplankton are both functionally diverse assemblages with multiple trophic levels, complex feeding relationships and broadly overlapping prey resources. For instance, appendicularians feed efficiently on prey as small as bacteria (Scheinberg et al., 2005), while some large dinoflagellates are notable selective consumers of large diatoms (Strom and Buskey, 1993). According to a synthesis of JGOFS results by Landry (2009), micro-herbivores consume 71% of daily primary production in the AS, with little evidence of substantial differences in seasonal averages. At finer spatial scale, the rates of microzooplankton grazing on phytoplankton tend to follow production, decreasing from the coast to offshore for most of the year, but with high rates extending well offshore during the deep convective mixing associated with the NEM. Microzooplankton grazing rates can be high in the upwelling region during the SWM, and they generally account for the utilization of ~50% of diatoms (Brown et al., 2002), a role often attributed entirely to larger mesozooplankton in ecosystem models. Carbon estimates of food web fluxes through microzooplankton suggest 42
SIBER Science Plan and Implementation Strategy that 7-24% of daily primary production can be transferred to mesozooplankton through a protist grazing chain of one or two steps (Landry, 2009), which provides a steady and important supplement to direct phytoplankton consumption by larger consumers. Grazing rate studies of the mesozooplankton were not conducted as intensively as those of the microzooplankton during JGOFS; hence, what is known from direct experimental studies is presently inadequate to fully support (or refute) the hypothesis that they play a major role in controlling phytoplankton standing stock and production, especially during SWM upwelling (e.g. Barber et al., 2001; Smith, 2001). The available rate data do, however, suggest that mesozooplankton consume about 25% of daily primary production on average from direct feeding on phytoplankton, while indirect estimates from empirical production models based on size-structured biomass and temperature put mean total consumption of mesozooplankton (including microzooplankton, detritus and carnivory) at ~40% of primary production, with relatively modest seasonal variability (Landry, 2009; Roman et al., 2000). Overall, mesozooplankton production (i.e. the flux of carbon that passes through zooplankton to support higher trophic levels) in the AS is ~12% of primary production (Roman et al., 2000), or about 0.15 tons C km-2 d-1. Water column studies of mesozooplankton in the AS during the 1990s produced several significant discoveries (Smith, 2005). The apparent paradox of high standing stocks of zooplankton coinciding with low standing stocks of phytoplankton during the NEM was resolved; the high biomass of mesozooplankton is sustained by primary productivity stimulated by convective mixing and by an active microbial food web. Another important observation is that the SWM (upwelling) season supports a burst of mesozooplankton growth. At the end of that season, diapause causes at least one very abundant copepod (Calanoides carinatus) to leave the epipelagic zone. The JGOFS observations also illuminated a potential linkage between mesozooplankton speciation associated with OMZ conditions. One copepod that withstands the conditions in the OMZ (Pleuromamma indica) appears to have increased in abundance over the past 30 years suggesting that the OMZ may have grown in size or intensity in that time. Finally, abundance of the cyclopoid copepod genus Oithona during fall intermonsoon and the NEM seasons were much higher in the 1990s than in collections made with comparable nets 60 years previously (John Murray Expedition), suggesting a possible long-term alteration of the base of the food web. Long-term changes in copepod species abundance have also been observed elsewhere in the IO. Specifically, dominant coastal upwelling copepod abundances have declined off the SW coast of India (R. Stephens, personal communication). This may indicate long-term ecological change in coastal waters during the SWM, potentially attributable to climate effects on the physical system or to a more proximate cause, such as hypoxia. Among the higher-level consumers that feed on mesozooplankton and above, mesopelagic myctophids have been characterized as “annual fish” because of their fast growth rates and short (i.e. 1-year) lifespan. Squid exhibit similar life strategies. Population biomass levels of these groups should therefore respond quickly to climate variations. While longer-lived top predators, such as sharks and tunas generally have slower population response to climate variability, changing conditions can cause them to significantly alter behavior. For example, migrations of tunas in equatorial waters are strongly influenced by climate phenomena like the IOD (Marsac et al., 2006). Behavioral changes may provide early indications of adjustments to degrading or evolving environmental circumstances, and are important to understand for both short- and long-lived key species. As discussed in Themes 3 and 4, the NW IO contains one of the three major OMZs of the open ocean (Naqvi et al., 2006a). Strong OMZs have substantial impacts on the abundance and distribution of mesopelagic organisms. OMZ species are typically diurnal vertical migrators, 43
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