Posts Tagged 'laboratory'

Effects of ocean acidification on the larval settlement and metamorphosis of marine invertebrates

Future Ocean acidification (OA) has the potential to negatively affect marine ecosystems and the organisms they support, with the early life-history stages particularly sensitive to reduced seawater pH and carbonate saturation states. Most marine organisms reproduce through an indirect lifecycle, which includes a free-swimming larval stage. In benthic or sessile taxa, the lifecycle is marked by the larval settlement and metamorphosis processes. Here, at the end of the free-living (generally planktonic) stage, larvae selectively search for a preferred settlement substrate for attachment, with metamorphosis occurring before or after it. Larval settlement and metamorphosis are arguably the most important processes in the life cycle of marine invertebrates, since they determine and optimize the final location of the organisms. Altered larval settlement rates will therefore influence the ecology, abundances and distributions of future coastal communities.

The aim of this thesis was to investigate whether OA could affect the larval settlement success of marine invertebrates, and whether these impacts would be mediated through direct, indirect or carry-over mechanisms. Three key New Zealand coastal marine invertebrates were used as model organisms: the sea urchin Evechinus chloroticus, the black-footed abalone (Haliotis iris) or pāua and the serpulid polychaete Galeolaria hystrix.

Continue reading ‘Effects of ocean acidification on the larval settlement and metamorphosis of marine invertebrates’

Ocean acidification interacts with variable light to decrease growth but increase particulate organic nitrogen production in a diatom

Highlights

• Variable light decreased growth rate and pigmentation contents in both LC and HC.

• Cells grown under variable light appeared more tolerant of high light.

• HC and varying light decreased carbon fixation rate but increased POC and PON.

• HC and varying light lead to less primary productivity but more PON per biomass.

Abstract

Phytoplankton in the upper oceans are exposed to changing light levels due to mixing, diurnal solar cycles and weather conditions. Consequently, effects of ocean acidification are superimposed upon responses to variable light levels. We therefore grew a model diatom Thalassiosira pseudonana under either constant or variable light but at the same daily photon dose, with current low (400 μatm, LC) and future high CO2 (1000 μatm, HC) treatments. Variable light, compared with the constant light regime, decreased the growth rate, Chl a, Chl c, and carotenoid contents under both LC and HC conditions. Cells grown under variable light appeared more tolerant of high light as indicated by higher maximum relative electron transport rate and saturation light. Light variation interacted with high CO2/lowered pH to decrease the carbon fixation rate, but increased particulate organic carbon (POC) and particularly nitrogen (PON) per cell, which drove a decrease in C/N ratio, reflecting changes in the efficiency of energy transfer from photo-chemistry to net biomass production. Our results imply that elevated pCO2 under varying light conditions can lead to less primary productivity but more PON per biomass of the diatom, which might improve the food quality of diatoms and thereby influence biogeochemical nitrogen cycles.

Continue reading ‘Ocean acidification interacts with variable light to decrease growth but increase particulate organic nitrogen production in a diatom’

Vulnerability of Tritia reticulata (L.) early life stages to ocean acidification and warming

Ocean acidification and warming (OA-W) result mainly from the absorption of carbon dioxide and heat by the oceans, altering its physical and chemical properties and affecting carbonate secretion by marine calcifiers such as gastropods. These processes are ongoing, and the projections of their aggravation are not encouraging. This work assesses the concomitant effect of the predicted pH decrease and temperature rise on early life stages of the neogastropod Tritia reticulata (L.), a common scavenger of high ecological importance on coastal ecosystems of the NE Atlantic. Veligers were exposed for 14 days to 12 OA-W experimental scenarios generated by a factorial design of three pH levels (targeting 8.1, 7.8 and 7.5) at four temperatures (16, 18, 20 and 22 °C). Results reveal effects of both pH and temperature (T °C) on larval development, growth, shell integrity and survival, individually or interactively at different exposure times. All endpoints were initially driven by pH, with impaired development and high mortalities being recorded in the first week, constrained by the most acidic scenarios (pHtarget 7.5). Development was also significantly driven by T °C, and its acceleration with warming was observed for the remaining exposure time. Still, by the end of this 2-weeks trial, larval performance and survival were highly affected by the interaction between pH and T °C: growth under warming was evident but only for T °C ≤ 20 °C and carbonate saturation (pHtarget ≥ 7.8). In fact, carbonate undersaturation rendered critical larval mortality (100%) at 22 °C, and the occurrence of extremely vulnerable, unshelled specimens in all other tested temperatures. As recruitment cohorts are the foundation for future populations, our results point towards the extreme vulnerability of this species in case tested scenarios become effective that, according to the IPCC, are projected for the northern hemisphere, where this species is ubiquitous, by the end of the century. Increased veliger mortality associated with reduced growth rates, shell dissolution and loss under OA-W projected scenarios will reduce larval performance, jeopardizing T. reticulata subsistence.

Continue reading ‘Vulnerability of Tritia reticulata (L.) early life stages to ocean acidification and warming’

Short-term effects of hypoxia are more important than effects of ocean acidification on grazing interactions with juvenile giant kelp (Macrocystis pyrifera)

Species interactions are crucial for the persistence of ecosystems. Within vegetated habitats, early life stages of plants and algae must survive factors such as grazing to recover from disturbances. However, grazing impacts on early stages, especially under the context of a rapidly changing climate, are largely unknown. Here we examine interaction strengths between juvenile giant kelp (Macrocystis pyrifera) and four common grazers under hypoxia and ocean acidification using short-term laboratory experiments and field data of grazer abundances to estimate population-level grazing impacts. We found that grazing is a significant source of mortality for juvenile kelp and, using field abundances, estimate grazers can remove on average 15.4% and a maximum of 73.9% of juveniles per m2 per day. Short-term exposure to low oxygen, not acidification, weakened interaction strengths across the four species and decreased estimated population-level impacts of grazing threefold, from 15.4% to 4.0% of juvenile kelp removed, on average, per m2 per day. This study highlights potentially high juvenile kelp mortality from grazing. We also show that the effects of hypoxia are stronger than the effects of acidification in weakening these grazing interactions over short timescales, with possible future consequences for the persistence of giant kelp and energy flow through these highly productive food webs.

Continue reading ‘Short-term effects of hypoxia are more important than effects of ocean acidification on grazing interactions with juvenile giant kelp (Macrocystis pyrifera)’

Near-future ocean warming and acidification alter foraging behaviour, locomotion, and metabolic rate in a keystone marine mollusc

Environmentally-induced changes in fitness are mediated by direct effects on physiology and behaviour, which are tightly linked. We investigated how predicted ocean warming (OW) and acidification (OA) affect key ecological behaviours (locomotion speed and foraging success) and metabolic rate of a keystone marine mollusc, the sea hare Stylocheilus striatus, a specialist grazer of the toxic cyanobacterium Lyngbya majuscula. We acclimated sea hares to OW and/or OA across three developmental stages (metamorphic, juvenile, and adult) or as adults only, and compare these to sea hares maintained under current-day conditions. Generally, locomotion speed and time to locate food were reduced ~1.5- to 2-fold when the stressors (OW or OA) were experienced in isolation, but reduced ~3-fold when combined. Decision-making was also severely altered, with correct foraging choice nearly 40% lower under combined stressors. Metabolic rate appeared to acclimate to the stressors in isolation, but was significantly elevated under combined stressors. Overall, sea hares that developed under OW and/or OA exhibited a less severe impact, indicating beneficial phenotypic plasticity. Reduced foraging success coupled with increased metabolic demands may impact fitness in this species and highlight potentially large ecological consequences under unabated OW and OA, namely in regulating toxic cyanobacteria blooms on coral reefs.

Continue reading ‘Near-future ocean warming and acidification alter foraging behaviour, locomotion, and metabolic rate in a keystone marine mollusc’

Characterization of marine teleost ionocytes in the gill, skin, and inner ear epithelia and their implications for ocean acidification

Ionocytes are specialized epithelial cells that excrete or absorb ions across an epithelium to regulate ionic, osmotic and acid-base levels in internal fluids. These ionocytes perform a wide range of functions (e.g. osmoregulation, pH regulation, and calcification) across various organs (e.g. gill, skin, inner ear). As atmospheric CO2 levels rise and oceanic pH levels fall, teleosts may increase their investment on ionocytes to survive in future ocean conditions. But generally speaking, the gill, skin, and inner ear ionocytes within marine teleost are not well characterized. This dissertation contains research spanning five southern Californian teleosts: the Blacksmith Chromis punctipinnis, the Yellowfin Tuna Thunnus albacares, the White Seabass Atractoscion nobilis, the Pacific Mackerel Scomber japonicus, and the Splitnose Rockfish Sebastes diploproa. In Chapter II, I investigated the individual and group behavioral responses of the Blacksmith, a temperate damselfish, after exposure to CO2-induced low-pH conditions. In Chapter III, I describe a novel technique used to quantify skin ionocytes in larval fishes. In Chapter IV, I applied the Chapter III’s technique to document developmental patterns in the skin and gill ionocytes of larval Yellowfin Tuna. In Chapter V, I investigated larval White Seabass response to hypercapnia by monitoring oxygen consumption rate and quantifying ionocyte abundance and relative ionocyte area across development. In Chapter VI, I characterized two types of inner ear ionocytes responsible for otolith calcification in the Pacific Mackerel. In Chapter VII, I investigated whether future CO2 /pH conditions would affect the gill and inner ear ionocytes of Splitnose Rockfish. Altogether, this work across the multiple teleosts demonstrates that ionocytes 1) have the plasticity to respond to external pH stress, 2) are sufficient to maintain internal homeostasis despite significant differences in CO2/pH levels, and 3) differ greatly in protein, morphology, and function depending on the tissue in question.

Continue reading ‘Characterization of marine teleost ionocytes in the gill, skin, and inner ear epithelia and their implications for ocean acidification’

Biochemical and physiological responses of two clam species to Triclosan combined with climate change scenario

Highlights

• Triclosan bioaccumulation was enhanced under forecasted climate change conditions.

• Triclosan strongly affected clams’ antioxidant defences.

• Cellular damage was prevented by enzymatic and behaviour defence mechanisms.

• Greater response of the Manila clam to TCS exposure combined with climate change scenario.

Abstract

Ocean acidification and warming are among the man-induced factors that most likely impact aquatic wildlife worldwide. Besides effects caused by temperature rise and lowered pH conditions, chemicals of current use can also adversely affect aquatic organisms. Both climate change and emerging pollutants, including toxic impacts in marine invertebrates, have been investigated in recent years. However, less information is available on the combined effects of these physical and chemical stressors that, in nature, occur simultaneously. Thus, this study contrasts the effects caused by the antimicrobial agent and plastic additive, Triclosan (TCS) in the related clams Ruditapes philippinarum (invasive) and Ruditapes decussatus (native) and evaluates if the impacts are influenced by combined temperature and pH modifications. Organisms were acclimated for 30 days at two conditions (control: 17 °C; pH 8.1 and climate change scenario: 20 °C, pH 7.7) in the absence of the drug (experimental period I) followed by a 7 days exposure under the same water physical parameters but either in absence (unexposed) or presence of TCS at 1 μg/L (experimental period II). Biochemical responses covering metabolic, oxidative defences and damage-related biomarkers were contrasted in clams at the end of experimental period II. The overall picture showed a well-marked antioxidant activation and higher TCS bioaccumulation of the drug under the forecasted climate scenario despite a reduction on respiration rate and metabolism in the exposed clams. Since clams are highly consumed shellfish, the consequences for higher tissue bioaccumulation of anthropogenic chemicals to final consumers should be alerted not only at present conditions but more significantly under predicted climatic conditions for humans but also for other components of the marine trophic chain.

Continue reading ‘Biochemical and physiological responses of two clam species to Triclosan combined with climate change scenario’


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Ocean acidification in the IPCC AR5 WG II

OUP book