Understanding patterns of body size variation is a fundamental goal in ecology, but although well studied in the terrestrial biota, little is known about broad-scale latitudinal trends of body size in marine fauna and much less about the factors that drive them. We conducted a comprehensive survey of interspecific body size patterns in coastal cephalopod mollusks, covering both hemispheres in the western and eastern Atlantic. We investigated the relationship between body size and thermal energy, resource and habitat availability and depth ranges. Both latitude and depth range had a significant effect on maximum body size in each of the major cephalopod groups (cuttlefishes, squids and octopuses). We observed significant negative associations between sea surface temperature (SST) and body size. No consistent relationships between body size and either net primary productivity (NPP), habitat extent (shelf area) or environmental variation (range of SST and NPP) were found. Thus, temperature seemed to play the most important role in structuring the distribution of cephalopod body size along the continental shelves of the Atlantic Ocean, and resource availability, seasonality or competition only played a limited role in determining latitudinal body size patterns.KEY WORDS: Body size · Ectotherms · Cephalopods · Thermal energy · Resource availability · Latitude · Temperature-size rule
Resale or republication not permitted without written consent of the publisherMar Ecol Prog Ser 464: [153][154][155][156][157][158][159][160][161][162][163][164][165] 2012 hypotheses suggest that ambient energy (temperature) is the best environmental explanatory variable for the latitudinal-size trends, both lack a convincing mechanistic explanation. The resource availability (primary productivity) hypothesis assumes that body mass must be maintained by a sufficient food supply and predicts greater body sizes in more productive areas (Rosenzweig 1968). However, it is worth noting that cephalopods are voracious carnivores with many different feeding strategies that enable them to feed opportunistically on a wide range of prey , and their growth seems to be primarily limited by predation rather than food shortages (Wood & O'Dor 2000).Some also argue that species adopt smaller body sizes in more equatorial areas because of increased inter-and intra-specific competition for resources (McNab 1971, Ashton et al. 2000. Because the feeding, behavior and reproduction of neritic cuttlefish, octopuses and squids are closely associated with seabed characteristics, one may argue that the larger continental shelves near the poles (i.e. greater habitat availability) could affect cephalopod body size variation by reducing competition. Moreover, variation in oxygen availability has been suggested to explain polar gigantism (Chapelle & Peck 1999) and size increase in the deep sea (McClain & Rex 2001, but also see Spicer & Gaston 1999 for a rebuttal of this idea). Seasonality (or fasting endurance) has also been advocated to explain latitudinal...