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The distributions of marine ectotherms are governed by physiological sensitivities to long-term trends in seawater temperature and dissolved oxygen. Short-term variability in these parameters has the potential to facilitate rapid range expansions, and the resulting ecological and socioeconomic consequences may portend those of future marine communities. Here, we combine physiological experiments with ecological and demographic surveys to assess the causes and consequences of sudden but temporary poleward range expansions of a marine ectotherm with considerable life history plasticity (California market squid, Doryteuthis opalescens). We show that sequential factors related to resource accessibility in the core range-the buildup of large populations as a result of competitive release and climate-associated temperature increase and oxygen loss that constrain aerobic activity-may drive these expansions. We also reveal that poleward range expansion alters the body sizeand therefore trophic role-of invading populations, with potential negative implications for socioeconomically valuable resident species. To help forecast rapid range expansions of marine ectotherms, we advocate that research efforts focus on factors impacting resource accessibility in core ranges. Determining how environmental condi-tions in receiving ecosystems affect body size and how body size is related to trophic role will help refine estimates of the impacts of future marine communities.

The productivity of a small tropical temple pond was studied by the light‐and‐dark bottle method and by following the natural changes in carbon dioxide and oxygen. Production varied from 6.0 g C/m2 per day in December 1962 to 11.0 g C/m2 per day in June 1962. The apparent photosynthetic yields were usually greater when the carbon dioxide and oxygen changes in natural waters were used to calculate production. A daytime reduction in methyl orange alkalinity in upper strata and an increase in phenolphthalein alkalinity, attributed to precipitation of carbonate, were significant features of this shallow eutrophic biotope. The dominant plankton community in this pond was of bluegreen algae. Growth of fish was found to be good. There was a conversion of 1.65% of the primary production to fish.