BHL Biodiversity Heritage Library https://www.biodiversitylibrary.org/ Malacologia [Ann Arbor,Institute of Malacology]1962- https://www.biodiversitylibrary.org/bibliography/12920 v.41 (1999): https://www.biodiversitylibrary.org/item/47254 Page(s): Page 455,Anderson, et al., Page 456, Page 457, Page 458, Page 459, Page 460 Holding Institution: Harvard University, Museum of Comparative Zoology, Ernst Mayr Library Sponsored by: Harvard University, Museum of Comparative Zoology, Ernst Mayr Library Generated 2 July 2021 5:54 AM https://www.biodiversitylibrary.org/pdf4/1332081i00047254.pdf This page intentionally left blank. MALACOLOGIA, 1999, 41 (2): 455-460 DETERMINATION OF THE DIET OF OCTOPUS RUBESCENS BERRY, 1953 (CEPHALOPODA: OCTOPODIDAE), THROUGH EXAMINATION OF ITS BEER BOTTLE DENS IN PUGET SOUND 1 2 3 4 Roland C. Anderson , Paul D. Hughes , Jennifer A. Mather & Craig W. Steele ABSTRACT Den middens have been used to determine the diet of several species of octopuses, but are not available for the red octopus ( Octopus rubescens Berry, 1953). As a result, its diet in the wild is poorly known. To determine their diet, 0. rubescens were collected in beer bottle dens, evicted from the bottles for measurement, and released. The shell contents of the bottles were then sieved, identified and compared to those from bottles not containing octopuses. The shell con­ tents of bottles containing octopuses had significantly more species and significantly more shells than bottles without octopuses. In this mud/sand area, the octopuses were consuming predom­ inantly the gastropod Olive/la baetica. Beer bottle trash on the sea floor is a non-polluting den re­ source for 0 . rubescens, and is shown here to be a valuable tool for diet analysis. Key words: Octopus, diet, habitat, Puget Sound, beer bottles. INTRODUCTION mation about feeding, because many octo­ puses leave middens of prey remains in front The small red octopus, Octopus rubescens of their dens (Mather, 1991 ; Hanlon & Mes­ Berry, 1953, is the most common octopus in senger, 1996). The dens of 0. rubescens the nearshore area on the west coast of the have only been inferred from their being United States (Hochberg & Fields, 1980), but trawled up in empty giant barnacle shells, its habits are not very well known. Several in­ beer bottles, and other hard containers of ap­ dications of prey preference have been given propriate size (Dorsey, 1976). A female guard­ for 0. rubescens, mostly from laboratory stud­ ing her eggs was even found in a cast-off ies. For example, Warren et al. (1974) delin­ shoe (Anderson, 1994). Other than beer bot­ eated its color changes while attacking prey, tles (Anderson, 1994, 1997), natural dens and Dorsey (1976) described its natural his­ have not been described for 0. rubescens tory and social behavior. Anderson (1997) and from observations in the wild. Octopuses Boyle (1991) described methods for its aquar­ have used discarded human trash as dens for ium husbandry and laboratory maintenance. millennia (Lane, 1957; Cousteau & Diole, Hochberg (1997) listed the diets observed in 1973). Fishermen have taken advantage of the laboratory, which included a variety of the octopuses' propensity to inhabit shelters species of molluscs and crustaceans. There is by lowering strings of jars; the octopuses little information on the feeding of 0. ru­ crawl into them and can be harvested when bescens in the wild, although Hochberg & the jars are retrieved. This behavior has been Fields ( 1980) stated that 0. rubescens prefers used to assess octopus populations by Voight small crabs, and Laidig et al. (1995) observed (1988), who placed 325 ml beer bottles on in­ them eating small euphausiids. This limited in­ tertidal sand flats as shelters. Such collection formation on the natural diet of 0. rubescens succeeded because octopuses prefer shelter inspired the present study. that is dark and has a small entrance (Mather, Many species of octopuses take refuge in a 1982; Aronson, 1986). A routine collection of den over a period of days or weeks (Mather, 0. rubescens in bottles revealed the shell re­ 1982, 1991; Ambrose, 1983; Hartwick et al., mains of likely prey items and suggested beer 1984; Voight, 1988; Cigliano, 1993). The dens bottles could serve a further purpose, as a of octopuses are a conspicuous aspect of tool for analyzing the previously unknown their natural history, and are a source of infor- prey choice of 0. rubescens. 1The Seattle Aquarium, 1483 Alaskan Way, Seattle, Washington 98101 , USA; [email protected] 2University of Washington, Seattle, Washington, USA 3University of Lethbridge, Lethbridge, Alberta, Canada 4 Edinboro University of Pennsylvania, Edinboro, Pennsylvania, USA 455 456 ANDERSON ET AL. MATERIALS AND METHODS prey species. We also compared the number of shell species in bottles with octopuses to Sixteen Octopus rubescens were found in those without, using a niche breadth index de­ "aged" 355 ml beer bottles with a mouth open­ veloped by Cardona (1991 ). This index looks ing size of 18.0 mm inside diameter by scuba at frequencies of occurrence of the different divers during the fall and winter of 1997 - 1998 prey species to calculate a niche breadth in 20-25 m deep water at Federal Way, 30 km index, and we considered unoccupied bottles south of Seattle, Washington State, USA. and occupied ones as representatives of two Long duration in the sea was indicated by a predator "species". dense covering of barnacles (Ba/anus crena­ tus) and/or sea anemones (Metridium gigan­ teum). Sixteen aged bottles unoccupied by RESULTS octopuses were also collected. Octopuses in their bottles were placed into zippered plastic All octopuses found at the site during the bags and transferred to the Seattle Aquarium day were within bottles, possibly because no using the methods of Anderson (1997). Octo­ suitable dens other than Polinices shells, al­ puses were removed from the bottles by hold­ ways occupied by hermit crabs (see Jensen, ing the bottles mouth downward over a pail of 1995), were available. Significantly more oc­ water. Remaining bottle contents were rinsed topuses were found in aged brown bottles (16 out thoroughly into the pail. The octopuses occupied, 7 unoccupied) than in clear ones (0 were sexed, weighed, measured for mantle occupied, 9 unoccupied) when tested with a length (ML), and released into the water near two-way Chi-square test (X2 = 16.358; p < the Aquarium, a known habitat for 0. ru­ 0.001 ). The octopuses' mean weight was 8.26 bescens (Jeff Christiansen, pers. comm.). g, and their mean mantle length was 19 mm. The contents of the bottles were then strained Possible prey remains consisted of mollus­ through a sieve with a 2.0 mm openings, and can shells and barnacle fragments and were the shells collected were kept and identified. found in nearly all bottles. They came from a The labels were removed from 30 new bot­ large number of species, but predominantly tles (short, brown 355 ml Budweiser® bottles, from the molluscs Olive/la baetica, Alia sp., with a mouth opening size 18.0 mm inside di­ Kurtziella sp., and Nassarius mendicus, and ameter) and they were painted black, because the barnacle Ba/anus crenatus (Table 1 ). octopuses prefer dark dens (Mather, 1982; Comparisons of number of shells between oc­ Voight, 1988). The bottoms of the bottles were cupied and unoccupied bottles could only be left unpainted so octopuses inside could be made for these five species because of the seen with the aid of a dive light. They were laid small numbers found of the other species. out on the bottom about 100 m from where the Chi-square analyses revealed that each of previous octopuses were collected. After 66 these five species were found significantly days, all bottles were retrieved and any octo­ more often in bottles that had been occupied puses inside were measured, weighed, and by an octopus (Table 2). released. Any shells inside were sieved, re­ The niche breadth index developed by Car­ trieved and identified. The taxonomy of some dona (1991) applied to the shells found in the of the small gastropods examined is in a state bottles (Table 3) uses occurrence frequen­ of flux (Ronald L. Shimek, pers. comm.), so cies, that is, in how many individuals collected they were not identified beyond genus, using of each species of shell a certain food type the guides of Abbott (1974), Kozloff (1987), was found. Cardona's index is an improve­ and Rice (1971 ). ment/extension of the Gladfelter-Johnson An 0. rubescens found in a bottle at the Index (Gladfelter & Johnson, 1983) in that it same site was taken to the Seattle Aquarium, looks at numbers of occurrence rather than where the interior of its bottle was cleaned out relative percentage of total volume or weight and the octopus allowed to re-occupy the bot­ of the collected food items. By using these tle. It was placed in an aquarium with 39 live niche-breadth calculations, we found a niche Alia sp., collected from the same area from breadth for the occupied bottles to be B' = eelgrass. The octopus was ejected from the 0.2417 and for the unoccupied bottles B' = bottle after 10 days and the bottle's contents 0.1275. The occupied bottles had about twice examined. the niche breadth of the unoccupied bottles, Comparisons of the number of likely prey which is a clear indication of octopus activity. species between occupied and unoccupied After 10 days, the octopus in captivity had bottles were made for the five most common consumed 14 of the 39 Alia sp. available in its 0 m -l m JJ -s: TABLE 1. Mean number of molluscan and crustacean prey remains per bottle found on mud/sand habitat in Puget Sound. z ~ Octopus-occupied old Unoccupied old - Octopus-occupied Unoccupied new 0 bottles (N = 16) bottles (N = 16) new bottles (N = 2) bottles (N = 28) z Olive/la baetica 27.