Impact of temperature on juvenile growth and age at first egg-laying of the Pacific reef squid Sepioteuthis lessoniana reared in captivity

Cephalopod mollusks exhibit highly plastic life cycle traits influenced primarily by the interactive effects of food availability, light cycle and temperature, with the latter perhaps the most influential. Hatchlings of the tropical reef squid Sepioteuthis lessoniana were hatched from field-collected eggs in the laboratory and cultured at different temperatures to evaluate the effect of temperature on growth rates. All groups showed rapid, sustained growth rates from hatching to a size of 10–25 g. Beyond this size range, growth was slower and not clearly exponential in form. Growth rate was closely linked to temperature. Squids grown at approximately 27 °C attained a size of 10 g in as little as 45 days at sustained growth rates of 12.2% body weight day⁻¹ (%bw day⁻¹), while squids cultured at 20 °C required almost 100 days to attain the same size at rates of 5.7%bw day⁻¹. At an age of 55 days and approximately 1 g body weight, juvenile squids cultured at 20 °C were able to accelerate growth rates from 5.7%bw day⁻¹ to over 12%bw day⁻¹ when temperature was raised to 27 °C. They maintained this growth rate to a size of about 10 g and an age of at least 75 days post-hatching, indicating that body size and not age is the limiting factor for this rapid post-hatching growth. By comparison, conspecifics cultured near 27 °C from hatching had shifted out of the rapid post-hatching growth phase by day 50 at sizes between 10 and 50 g. The hatchlings from temperate to subtropical Japan had consistently higher growth rates at comparable temperatures than hatchlings from tropical Okinawa. When plotted as growth rate versus temperature, the Japanese group had a clearly higher slope to the relationship than the tropical populations, equivalent to a 2%bw day⁻¹ difference in growth rate at 25 °C. Age at first egg-laying was decreased at higher culture temperatures; however, overall life span was not. Received: 21 February 2000 / Accepted: 6 September 2000     

Egg-capsule deposition and how behavioral interactions influence spawning rate in the squid<Emphasis Type="Italic"> Loligo opalescens</Emphasis> in Monterey Bay,California

Recent evidence suggests that, contrary to what was believed previously, most Loligo spp. females spawn multiple times and do not die immediately following a single spawning event. The present study used sustained focal observations of male/female pairs of the opalescent inshore squid Loligo opalescens Berry to examine the structure and behavior of near-bottom spawning groups. The study was carried out in a small area (10 km²) of Monterey Bay, California (36°36.1N; 121°53.4W), at depths of 25–45 m, using video cameras mounted on remotely operated vehicles. Behavioral observations were made primarily during daylight hours over known spawning beds in April and November 2000, and August 2001. Squid formed large aggregations in the water column where pairing occurred. Most commonly, only small numbers of active spawners were found at the substrate depositing egg capsules, and the mean operational sex ratio in the spawning groups was 1.87 males:1 female (range=1.0–8.5), although the ratio fluctuated rapidly as roving lone males joined and departed from the small spawning groups. On average, females (n=40) deposited 2.67 capsules (range 2–7) per focal observation at an average interval of 8.47 min between depositions (n=67). Following deposition of the capsules, females broke away from their consort males and jetted upwards to rejoin large schools located many meters above the substrate. Egg-capsule deposition was often interrupted by lone males seeking a mate, or by the approach of predators including fish and marine mammals. The results suggest that most of the communal egg beds in southern Monterey Bay are built up slowly through daily intermittent spawning, not in large big bang reproductive events as often depicted for L. opalescens.Communicated by J.P. Grassle, New Brunswick     

Assessment of potential groundwater contamination sources in a wellhead protection area

Determining the human health dangers from potential contamination sources, within a wellhead protection area (WHPA), requires that a risk analysis be undertaken. In this study, a desktop geographic information system and spreadsheet software are used to implement an EPA risk screening methodology for WHPAs called 'Managing Ground Water Contamination Sources in Wellhead Protection Areas--A Priority Setting Approach'. The methodology was applied to a WHPA in Gaston County, North Carolina. Results indicate that the risk of well contamination from an interstate highway and gas station with old steel underground storage tanks were comparatively high. Medium risks included a thoroughfare and highway, while low risks were assigned to machine shops, a body shop, septic systems and a gas station with new underground storage tanks and secondary containment. A sensitivity analyses of the Priority Setting Approach indicated that risk scores were extremely sensitive to hydrogeologic variables such as hydraulic conductivity. It is recommended that risk assessors utilize a range of hydrogeologic parameters to assess overall risk from each potential contamination source.     

Effect of temperature on laboratory growth,reproduction and life span of Octopus bimaculoides

Laboratory culture of 40 Octopus bimaculoides from April 1982 to August 1983 through the full life cycle at 18°C vs 23°C provided information on the growth, reproductive biology and life span of this California littoral octopus. At 18°C, the cephalopods grew from a hatchling size of 0.07 g to a mean of 619 g in 404 d; the largest individual was 872 g. Octopuses cultured at 23°C reached their highest mean weight of 597 g in 370 d; the largest individual grown at this temperature was 848 g after 404 d. Growth data revealed a two-phase growth pattern: a 5 mo exponential phase followed by a slower logarithmic (power function) phase until spawning. At 5 mo octopuses grown at 23°C were over three times larger than their 18°C siblings. However, beyond 6.5 mo, growth rates were no higher at 23°C than at 18°C. At 13.5 mo, the mean weight of the 18°C group surpassed that of the 23°C group. The slope of the length/weight (L/W) relationship was significantly different for the two temperature regimes, with the 23°C octopuses weighing 18% less than their 18°C siblings at a mantle length of 100 mm. Females weighed more than males at any given mantle length. Males grew slightly larger and matured before females. The L/W relationship indicated isometric body growth throughout the life cycle. Higher temperature accelerated all aspects of reproductive biology and shortened life span by as much as 20% (from approximately 16 to 13 mo). O. bimaculoides has one of the longest life cycles among species with large eggs and benthic hatchlings. Extrapolations to field growth are made, and the possible effects of temperature anomalies such as El Niño are discussed.