Sizing ocean giants: patterns of intraspecific size variation in marine megafauna

Abstract

What are the greatest sizes that the largest marine megafauna obtain? This is a simple question with a difficult and complex answer. Many of the largest-sized species occur in the world’s oceans. For many of these, rarity, remoteness, and quite simply the logistics of measuring these giants has made obtaining accurate size measurements difficult. Inaccurate reports of maximum sizes run rampant through the scientific literature and popular media. Moreover, how intraspecific variation in the body sizes of these animals relates to sex, population structure, the environment, and interactions with humans remains underappreciated. Here, we review and analyze body size for 25 ocean giants ranging across the animal kingdom. For each taxon we document body size for the largest known marine species of several clades. We also analyze intraspecific variation and identify the largest known individuals for each species. Where data allows, we analyze spatial and temporal intraspecific size variation. We also provide allometric scaling equations between different size measurements as resources to other researchers. In some cases, the lack of data prevents us from fully examining these topics and instead we specifically highlight these deficiencies and the barriers that exist for data collection. Overall, we found considerable variability in intraspecific size distributions from strongly left- to strongly right-skewed. We provide several allometric equations that allow for estimation of total lengths and weights from more easily obtained measurements. In several cases, we also quantify considerable geographic variation and decreases in size likely attributed to humans.

Demography alters carbon flux for a dominant benthic suspension feeder, the giant barrel sponge, on Conch Reef, Florida Keys

“…Specifically, changes in carbon flux are primarily influenced by three processes: (1) the growth of sponges in all stages, (2) the survival of the largest sponges (stages IV and V), and (3) the input of new recruits by the largest sponges (stage V). Given their size, which can exceed 1 m in height and diameter (McClain et al., ), the largest sponges have a proportionally high contribution to total population biomass, and hence, carbon flux, through the processes of reproduction and survival. These results highlight the need for increased conservation of the largest X. muta , as they are particularly susceptible to mortality from vessel groundings, dredging and marine debris (McMurray & Pawlik, ).…”

Evolutionary pathways toward gigantism in sharks and rays

“…For instance, the largest sharks ever recorded (both ∼18 m in length) are the ectothermic, filter‐feeding whale shark ( Rhincodon typus ), and the extinct megalodon († Otodus megalodon ), a presumed mesotherm and the largest marine macropredator to ever live (McClain et al. ; Pimiento and Balk ; Ferrón ; Ferrón et al. ).…”

A giant squid (Architeuthis dux) off Reunion Island, western Indian Ocean: the greatest giant ever?

“…We focused on the DML and the TL reconstruction since the former is a 'reference' length for cephalopod measurements (Roper & Voss, 1983) while TL is commonly used for demonstration of extreme size of the giant squid among cephalopods (e.g. McClain et al, 2015;Paxton, 2016). The most robust allometric equations were selected from the literature based on the following three criteria: statistical significance (if provided by the authors), large sample size, and the A. dux size range covering extreme sizes of reference parts and entire squid.…”

“…The total length was extrapolated from the DML based on the following relationships: Paxton (2016) (3) and McClain et al (2015) (4):…”

“…Anecdotal reports of total length (TL) often approach extreme values of several tens of metres (Heuvelmans, 1968;Paxton, 2016); however, scientific literature documents considerably smaller sizes. Even scientific records of A. dux that ranged within 15-20 m TL (Kirk, 1888;Berzin, 1971Berzin, , 1972 are commonly challenged (Grist & Jackson, 2007;McClain et al, 2015;Paxton, 2016). There is also disagreement on giant squid lifespan: estimates of longevity range from 2-3 years (Gauldie et al, 1994;Lipiński, 1997;Lordan et al, 1998;Grist & Jackson, 2007) to over 35 years (Landman et al, 2004).…”