File:American malacological bulletin (1988) (18153063762).jpg

Title: American malacological bulletin
Identifier: americanmal6719881990amer (find matches)
Year: 1983 (1980s)
Authors: American Malacological Union
Subjects: Mollusks; Mollusks
Publisher: (Hattiesburg, Miss. ?) : (American Malacological Union)
Contributing Library: Smithsonian Libraries
Digitizing Sponsor: Biodiversity Heritage Library

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ARONSON: OCTOPUS ECOLOGY 53 briareus merits further attention. REPRODUCTION: EGGS AND EGG BROODING In censuses from March 1982 to July 1983, females guarding eggs were recorded in Sweetings Pond in each month except June and July 1983, with annual peaks in February and March (Aronson, 1986). In southeastern Florida, Octopus briareus seem to display a more strongly seasonal maturation and breeding cycle (Hanlon, 1983); the degree of synchrony may therefore vary from population to population. The mean egg length, computed from eggs at develop- ment Stage IV (Wells and Wells, 1977) or earlier was 10.50 ± 0.68 SD mm (range 9.0 - 12.0 mm, n = 99; based on 11 eggs each from nine females). The mean mantle length of females guarding eggs was 6.1 ± 0.92 SD cm (n = 25). Two egg broods, followed from stage IV or earlier to hatching, gave a development time range of 50-67 days. The first female brooded her eggs for 50 days (11 May-30 June 1982; 23.5-32.0°C) and the second for 67 days (18 January-26 March 1983; 20.5-23.5°C). The value of 36 days quoted by Hanlon (1983) for development time in Sweetings Pond was an early minimum estimate. Clutch sizes were determined from egg strands col- lected within two days of hatching. For each egg strand, the number of empty attached capsules and the number of egg stalks from which the capsule had been separated were counted. This procedure avoided the destruction of clutches, which would have been necessary had the eggs been counted prior to hatching. The error caused by possible loss of hatched strands was minimal. The mean clutch size was 267.3 ± 99.2 SD eggs (range 97 - 414 eggs; n = 8). There was no correla- tion between clutch size and the mantle length of the brooding female (product-moment correlation coefficient, r = -0.20, n = 8, p > 0.90; Sokal and Rohlf, 1969). Hatching success was high: 1453 of 1471 eggs (from 6 females) hatched, for a success rate of 98.8%. The egg sizes, clutch sizes, develop- ment times, hatching success and average size of brooding females were similar to previous findings for Octopus briareus (Hanlon, 1983). INJURIES Two classes of injury were noted for Octopus briareus in Sweetings Pond: arm injuries and scars. Arm injuries con- sisted of severed or regenerating arms. Arm injuries can result from cannibalism, and O. briareus can also lose or autotomize (Lange, 1920) arms in fights. In a fight staged by divers be- tween a female of mantle length 4.0 cm and an 8.0 cm female, the smaller one lost three arms. However, neither octopus lost any arms in the only fight observed under natural conditions. In this case two males, 4.5 and 5.5 cm in mantle length, were struggling underneath a brown sponge. The larger individual clearly had the advantage in both fights. It was impossible to tell whether these were territorial or predator-prey en- counters, or both. Scars occurred in a number of forms (Fig. 4). They were usually on the head, or dorsal or ventral mantle, although they occurred on the arms as well. Many scars were rings. In other cases, white lesions of varying sizes appeared on
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Fig. 4. Sample of Octopus briareus dorsal mantle scar patterns. All scars are drawn in negative. A, sucker marks and a triangular skin lesion; B, sucker marks and lines; C, sucker marks, perhaps from a single O. briareus arm; D, extensive skin lesions. the mantle, arms or webbing where patches of skin had been removed. Still other scars were dark or light lines. From the second observation of copulation, it is ob- vious that the dark ring scars were sucker marks. Skin lesions could arise from the suckers or beak bites of other octopuses; they could also result from infections or from scraping against rough surfaces. Linear scars, rarer than the other two categories, are of unknown origin. Scars can be acquired dur- ing mating, in encounters with cannibals and during fights. There was no evidence of injuries caused by in- terspecific interactions (in contrast to Hartwick et a/., 1988). The only animals common enough and large enough to have posed a threat to Octopus briareus were spider crabs, Mithrax spinosissimus, which reached at least 20 cm in carapace width. However, these herbivorous crabs became quite alarmed and retreated when O. briareus were placed near them. Larger Octopus briareus displayed the results of injuries more frequently than did smaller ones (Table 3). The most obvious explanation is that the probability of an older in- dividual having interacted with aconspecific is greater. Males and females not guarding eggs showed about the same fre- quency of injury. Females guarding eggs showed a high rate of arm loss and scarring, possibly due to cannibalism by copulating males and the effects of their suckers, and to the general deterioration associated with egg-brooding. It would be interesting to see whether O. briareus in low-density coastal populations, which presumably encounter conspecifics less

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