In a field population of the protogynous red grouper Epinephelus morio in the eastern Gulf of Mexico, females with oocytes at all stages of development were collected during the spawning season suggesting that several batches of oocytes may be released over the spawning period. Plasma oestradiol (E 2 ) levels were highest in ripe females whose gonads contained both cortical alveoli and vitellogenic oocytes during the breeding season. Males were still spermiating as late as August, although levels of androgens 11-ketotestosterone (11-KT) and testosterone (T) had declined from their peaks in March. A few red grouper with either perinucleolar or cortical alveoli stage oocytes were undergoing sex change both during and after the spawning period. Low levels of E 2 , T and 11-KT were detected in transitionals. Proliferation of male tissue was not restricted to any specific area of the gonad but occurred in pockets within the ovarian lumen. The sequence of an increase in gonial cells along the periphery of the lamellae, increase in interstitial tissue, degradation of female elements, and formation of a sperm duct seemed to be concurrent with spermatocyte proliferation and the process of preparing the gonad to function as a testis. 1998 The Fisheries Society of the British Isles

Fish often aggregate to spawn, feed, rest, or avoid predation. Direct observations of very high counts of large‐bodied grouper on deep shipwrecks, however, do not fit into typical descriptions of spawning‐, resource‐, or predation‐driven aggregations. To investigate whether these observations are rare or part of an underlying pattern, we synthesized four decades (1979–2019) of direct observations of groupers on deep‐water (50–300 m) habitats along the southeastern United States (Cape Hatteras, NC to Cape Canaveral, FL). The direct observations, which included 439 remotely operated vehicle transects, 235 human‐occupied vehicle transects, and 881 hook‐and‐line drops, revealed six hotspots of deep‐water groupers on three shipwrecks, two artificial reefs, and one boulder field. Grouper counts at these hotspots (0.10–5.40 grouper per linear m surveyed) exceeded counts of grouper outside of hotspots (<0.01–0.02 grouper per linear m surveyed) by multiple orders of magnitude. Commonalities among the sites with grouper hotspots included that all are relatively isolated structures surrounded by unconsolidated sediments and located in shelf‐edge to upper‐slope depths. Thus, it appears that these isolated habitats, despite their small spatial footprint, represent a disproportionate abundance of deep‐water groupers. Future research efforts should determine how groupers derive sufficient resources from, and thus co‐occur on, these small habitats and how these aggregations relate to the large‐scale dynamics of these populations.

Ecological metrics derived from habitat surveys can provide information necessary to understand population, community, and ecosystem processes. Here, we present a case study on the feasibility of extracting ecological metrics from archeological studies of shipwrecks. Even though shipwrecks that are the focus of archeological surveys also form habitat for diverse flora and fauna, shipwrecks are often studied separately by archeologists and ecologists. Conducting joint archeological and ecological surveys promises to maximize research resources and outputs, yet this cross-disciplinary approach is rare. Here, we test the feasibility of extracting ecological metrics from archeological surveys of two historically significant and deep (200 m) shipwrecks, the German U-boat U-576 and the Nicaraguan freighter SS Bluefields, which sank in close proximity to one another on the continental shelf of North Carolina, USA during World War II. First, we assessed fish density, community composition, behavior, and spatial distribution on these shipwrecks using video and laser-line scanning data collected from human-occupied submersibles during archeological surveys. Second, we examined the ecological benefits and biases of pairing laser-line scanning and video surveys designed for archeological specifications. Our approach allowed us to pinpoint locations of fish around the shipwrecks and to identify these fish to fine taxonomic levels. The extracted ecological data revealed that both shipwrecks hosted high densities (U-576 38.2 AE 4.0; SS Bluefields 32.0 AE 18.0 per along-ship transect) of demersal fishes, including grouper species, and that fish concentrated around high-relief shipwreck features. More broadly, our findings demonstrate the utility and benefits of collecting multipurpose and cross-disciplinary data and provide a proof-of-concept for conducting joint archeological and ecological studies.

Graceful kelp crabs (Pugettia gracilis) are abundant consumers in shallow subtidal ecosystems of the Salish Sea. These dynamic habitats are currently experiencing multiple changes including invasion by non-native seaweeds and warming due to climate change. However, little is known about P. gracilis’ foraging ecology, therefore we investigated their feeding preferences between native and invasive food sources, as well as feeding rates at elevated temperatures to better assess their role in changing coastal food webs. To quantify crab feeding preferences, we collected P. gracilis from San Juan Island, WA and conducted no-choice and choice experiments with two food sources: the native kelp, Nereocystis luetkeana, and the invasive seaweed, Sargassum muticum. In no-choice experiments, P. gracilis ate equal amounts of N. luetkeana and S. muticum. However, in choice experiments, P. gracilis preferred N. luetkeana over S. muticum. To test effects of warming on these feeding rates, we exposed P. gracilis to ambient (11.5 ± 1.3°C) or elevated (19.5 ± 1.8°C) temperature treatments and measured consumption of the preferred food type, N. luetkeana. Crabs exposed to elevated temperatures ate significantly more than those in the ambient treatment. Our study demonstrates the diet flexibility of P. gracilis, suggesting they may be able to exploit increasing populations of invasive S. muticum in the Salish Sea. Warming ocean temperatures may also prompt P. gracilis to increase feeding, exacerbating harmful impacts on N. luetkeana, which is already vulnerable to warming and invasive competitors.