Barry C. Smith

Cultivation of eastern oysters using aquaculture gear increases habitat for temperate reef fish. Cunner ( Tautogolabrus adspersus ), scup ( Stenotomus chrysops ) and tautog ( Tautoga onitis ) inhabit a variety of complex natural and manmade habitats, including oyster aquaculture cage farms. Underwater video was recorded on two cage farms and a rock reef during May–September 2018 to quantify fish behavioural interactions and to assess ecological services provided by aquaculture gear, relative to natural structured seafloor. To collect video, action cameras were mounted on four study cages at a high‐density farm of 40–100 commercial cages (dense farm), on four single cages interspersed on low relief seafloor (sparse farm) and adjacent to four boulders on a rock reef (rock reef), within an embayment off Milford, Connecticut in Long Island Sound (NW Atlantic). Video was recorded hourly in 8‐min segments from 7 AM to 7 PM. Behaviours associated with habitat provisioning (e.g., courtship/reproduction, escape from predators, foraging, sheltering, schooling/grouping, territoriality) were observed for all three fish species on cages and boulders. Foraging and sheltering activity in cunner was significantly higher on cages than boulders while territorial behaviour occurred more frequently on boulders. Instances of escape from predators, foraging and sheltering behaviours in scup and tautog were significantly higher on cages than on boulders. Courtship/reproduction, grouping and territoriality were also higher on cages than boulders in tautog. Our results suggest that oyster cages confer ecological services that fulfil the basic biological and functional requirements of reef‐oriented fish, and provide habitat attributes afforded by natural rock reefs.

Objective: Black Sea Bass Centropristis striata are a temperate reef finfish that occupy natural and artificial structured habitats. This study used fish behavior, condition indices, and production estimates to evaluate how oyster aquaculture cages serve as artificial reefs for Black Sea Bass in central Long Island Sound, USA. Methods: Underwater video was recorded on oyster farms and a natural rock reef to identify and quantify the behavior of Black Sea Bass that is associated with oyster aquaculture cages and boulders. Juvenile Black Sea Bass were sampled from farms and reefs in Clinton and Milford, Connecticut, to assess individual energy density and relative condition factor as measures of habitat quality. Proximate analysis was conducted to develop a predictive regression for percentage of dry weight and energy density in juvenile Black Sea Bass, which was then applied to estimate energy density in fish that were collected from farms and reefs. The abundance of young-of-the-year Black Sea Bass was used to quantify fish production on the oyster farms. Results: Significantly greater shelter and grouping activity were observed on cages than were observed among boulders. Instances of courtship/reproduction in mature fish, escape, foraging, and territorial behavior were statistically similar across the cage and boulder habitats. The condition metrics of energy density and relative condition factor showed no difference in the physiological status of juvenile fish that inhabited farms versus reefs. The enhanced production of Black Sea Bass was estimated to be 4.1 kg/100 cages per year based on higher abundance of young-of-the-year fish on farms relative to the rock reef reference habitat. Conclusions: Our results suggest that aquaculture gear provides valuable habitat services that are similar to those obtained via other man-made structures that are considered essential fish habitat for Black Sea Bass throughout their life history.

One hitherto unstudied aspect of differences between sexual and asexual life stages in large‐scale transport and accumulation is density (mass per unit volume) of cells in each life stage. The specific density was determined for Scrippsiella lachrymosa cells in medium with and without nitrogen (N) enrichment through density gradient centrifugation. Growth medium without N addition is often called “encystment medium” when used for the purpose of resting cyst formation in cyst‐forming dinoflagellates; mating gametes are usually seen after two to three days. Significant differences in specific density were found after two days in encystment medium simultaneously with the observation of typical gamete swimming behavior and mating. The specific density of cells in encystment medium was 1.06 g · cm^‐3; whereas, the specific density of cells in growth medium was 1.11 g · cm^‐3. Cells in encystment medium were found to have significantly increased lipid content, reduced chlorophyll content, and reduced internal complexity. The findings may explain differential transport of less dense and chemotactically aggregating gametes into surface blooms in contrast to denser vegetative cells which perform daily vertical migration and do not aggregate. Passive accumulation of non‐migrating gametes into layers in stagnant water also can be explained, as well as sinking of zygotes when the storage of highly‐dense starch increases. Resting cysts had a density of over 1.14 g · cm^‐3 and would sink to become part of the silt fraction of the sediment. We suggest that differences in behavior and buoyancy between sexual and asexual life stages cause differences in cell accumulation, and therefore large‐scale, environmental transport could be directly dependent upon life‐cycle transitions.