Resource base of blue cod Parapercis colias subpopulations in marginal fjordic habitats is linked to chemoautotrophic production

Abstract

Metapopulations are often distributed across habitat patches with distinct differences in nutritional resources. We investigate individual variability in diet among subpopulations of blue cod Parapercis colias across productivity gradients within Fiordland, New Zealand. δ 13C and δ 15N of basal organic matter, including phytoplankton, macroalgae, terrestrial detritus and the chemosymbiont-harbouring clam Solemya parkinsonii, were collected. P. colias from inner and outer fjord sites within 5 fjords were analysed for proportion of diet comprising S. parkinsonii, and δ 13C and δ 15N of muscle tissue. Relative abundance of photoautotrophic organic matter was quantified from surveys of chl a and abundance of common kelp Ecklonia radiata. Information on mussel beds was collected to characterise potential for benthic-pelagic coupling. A mass balance model using δ 13C and δ 15N was used to estimate trophic level and proportion of organic matter from chemosynthesis for individual blue cod. Blue cod from the inner fjords had more variable use of organic matter originating from photoautotrophic versus chemoautotrophic sources than those from outer fjord regions. This was consistent with greater occurrence of S. parkinsonii in stomachs of blue cod from the inner fjords. Abundance of phytoplankton and occurrence of mussels statistically explained 87% of the variability in proportion of organic matter originating from chemosynthesis. These data provide an important example of variation in basal organic matter sources among subpopulations within a marine metapopulation. Our results demonstrate the importance of organic matter produced from chemosynthesis in coastal food webs providing a mechanism for maintenance of high trophic level consumers in marginal habitats. © Inter-Research 2012.