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Comparing Salinity Tolerance of Kelp species local to Burrard Inlet: Saccharina latissima, Costaria costata, and

Nereocystis luetkeana

As climate change continues to alter the environment, salinity levels along coastlines are expected to

decrease during spring freshets as greater snowfall accumulates over the winter contributing to a greater amount of water runoff. To estimate the potential effects of climate change on kelp species in

coastal British Columbia, mesocosm experiments were designed to manipulate salinity levels and measure growth rate. Overall, low salinity treatments experienced significant reduction in growth in

comparison to high salinity treatments in the kelp species Saccharina latissima. Nereocystis luetkeana and Costaria costata were also observed to have a lower amount of tolerability to salinity levels in

comparison to Saccharina latissima.

Abstract

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Nicole Stamnes BISC 498 – Spring 2014

INTRODUCTION

Kelp rely on many abiotic factors to control their development within their community.

Light, sedimentation, nutrients, water motion, substrata, temperature, and salinity are all

abiotic factors that influence development (Dayton 1985; Steneck et al. 2002). These factors

may limit abundance and dispersal of different kelp species as abiotic factors are variably

distributed in nature; species found in a broad range of habitats may be shown to not be as

affected by abiotic changes in comparison to species which are narrowly distributed into

specific habitats. Kelp distribution has often been correlated with various oceanographic

parameters in which enhance growth and development (Druehl 1977).

Changes in salinity in near-shore waters indirectly result from global warming because

salinity is directly related to changes in precipitation, evaporation, river run off, and ice melt.

Freshwater input into the Fraser River Basin (FRB) is dominated by snow accumulation and the

melt process (Shrestha et al. 2012); the most significant temporal change could include earlier

onset of snowmelt, or driving peak discharges. It has been projected that the FRB will

encounter an increased winter runoff, and decreased summer runoff forecasting potential

hazards associated with larger spring freshets (Shrestha et al. 2012). The total snow cover area

within North America has been increasing within the months of November, December, and

January, while also shifting maximum snow cover from February to January (IPPC 2007).

Winters are becoming colder increasing total snow covered area, and warmer weather follows

draining snow covered mountains into local river basins. There has also been a reduction in

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total snow covered area in the spring seasons in the Northern Hemisphere as warmer

temperatures are causing quicker snowmelts (IPCC 2007). As climate change alters the physical

environment, species may be required to adapt in order to cope with environmental conditions.

This stress may also require species to disperse into new habitats that are more favourable. As

salinity changes occur along the coast of British Columbia (BC), species living adjacent to river

channels may be exposed to unfavourable environmental conditions and required to overcome

the stress. If species are not able to tolerate the stress, species may be limited to habitats due

to ranges in environmental conditions.

Saccharina latissima, Costaria costata, and Nereocystis luetkeana are local kelp species

inhabiting coastal BC. These species may be forced to adapt to environmental changes as

salinity levels decrease to lower levels during spring seasons in BC. Kelp usually produce young

sporophytes in the spring while growth occurs during the summer, and reproduction proceeds

in the fall. As climate change is predicted to alter spring freshets, juveniles must be able to

adapt to possible changes as they will be exposed to lower salinity levels at earlier stages of

their development. Unfavourable salinity levels increase osmotic and ionic stress in kelp species

(Kirst 1990); this may be a factor which limits the total distribution and survival of kelp,

therefore, it is important to define the tolerability of local kelp species to forecast the future of

kelp communities along BC’s coastline.

The purpose of the present study was to compare tolerability of kelp species to a range

of salinity levels in which they may encounter in nature. Mesocosm experiments were

performed to assess the short-term tolerance to salinity of Saccharina latissima, Costaria

costata, and Nereocystis luetkeana. The main questions to be answered were: (1) How does

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salinity affect S. latissima; does developmental stage affect the ability to tolerate changes in

salinity? and (2) Do higher abundant local species exhibit greater salinity tolerability?

MATERIALS AND METHODS

Study sites and collection

Burrard Inlet opens up into the Strait of Georgia, which is located between Vancouver

Island and the mainland of British Columbia, Canada. The Burrard Inlet is partially blocked from

the Pacific Ocean by Vancouver Island, but receives salt water through channels and straits

(Figure 1). However, it also receives an inflow of freshwater from the FRB, the largest river

basin in BC, releasing large amounts of snowmelt from the coastal mountains in the spring

season (Shrestha et al. 2012).

To assess kelp growth rate in the laboratory, specimens were collected in Burrard inlet

in late January and early March 2014 (Figure 1), and were transported directly to the

Department of Fisheries and Oceans West Vancouver Laboratory (Figure 1) and placed in

outdoor flow-through tanks. The lab facility was located on the coast of BC within Burrard Inlet,

and specimens were exposed to natural sunlight, temperature, and weather throughout the

day and night.

Salinity Treatments and Set-Up

To investigate the relationship between growth and salinity level, lab tanks received an

inflow of varying amounts of salt and freshwater. Salt water was directly pumped into the tanks

from Burrard Inlet, along with Cypress Creek freshwater runoff; this set-up mimics what may

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naturally occur as Cypress Creek runoff flows directly into Burrard Inlet where it encounters a

freshet during the spring season. By having an inflow of salt and freshwater, rate of flow can be

manipulated to obtain a range of salinity levels. Eight Tanks were used in total; all having

plumbed natural salt and freshwater.

To test the effects of freshwater run-off on growth of adult S. latissima (N = 31, 3.2 –

68.6 cm in length), individuals were randomly distributed across eight tanks (n = 3 - 4

individuals per tank) of varying salinities. Four tanks received constant flow-through from

Burrard inlet and were considered ‘high salinity’ control tanks (Average 29.2ppt). The remaining

four tanks were treatment groups and received a constant flow-through from both salt water

from Burrard Inlet and freshwater from Cypress Creek at the same rate, and were considered

‘low salinity’ (Average 22.1ppt) tanks. The salinity and temperature readings were recorded

twice weekly for each individual tank using a YSI salinity meter. To measure total new growth of

the kelps, the hole-punch method (Mann 1973) was employed: each individual was hole-

punched above the meristem and the migration of that hole was measured as new growth.

Growth has been used as a response variable for measuring how kelp react to environmental

conditions as it integrates the interactions and trade-offs among many physiological processes

(Kirst 1990; Boden 1979; Lyngby & Mortensen 1996). Kelp remained in the salinity treatments

for a week and the migration of the hole-punch from the meristem after one week was

recorded as new growth (measured to the nearest 0.1 cm).

A second experiment was conducted on juveniles of common local kelp species to

assess (1) differences among species in tolerance of juveniles to freshwater input events and (2)

differences in salinity tolerability in life history stage of S. latissima. Juvenile S. latissima (N =

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20), N. luetkeana (N = 9), and C. costata (N = 5) where distributed at random in eight tanks. All

eight tanks received an inflow of salt and freshwater to manipulate salinity from a range

between 14.2 - 28.2ppt. The salinity and temperature readings were also recorded twice

weekly with a YSI Salinity meter, and the hole-punch method (Mann 1973) was employed to

measure new growth among different species of kelp. Kelp remained in the salinity treatments

for one week where after growth measurements were recorded as the migration of the hole-

punch (measured to the nearest 0.1 cm).

Response of Adult S. latissima

Decreased growth was observed of adult S. latissima in the low salinity treatments,

although this effect was not statistically significant, owing to a single outlier with high leverage

(F1, 6 = 0.618, P = 0.462) (Figure 2). Further inspection of this outlier revealed that the salinity in

this tank was intermediate to the salinity of tanks in the other treatments (26.2ppt). After

removing this tank from the analysis, the decreased growth among individuals in low salinity

was statistically supported (F1, 5 = 9.79, P = 0.026; Figure 3). Because this outlier suggested a

nonlinear response, with a possible optimal salinity level where S. latissima experiences

maximum growth intermediate to the two treatments, growth was reanalysed as a function of

mean tank salinity (Figure 4). This figure predicts that S. latissima are tolerable to a higher level

of salinity as the growth was greatly reduced on left hand side (22.1 – 26.2ppt), in comparison

to the growth on the right side (26.2 – 29.2ppt) of the optimal salinity value for growth.

Response of Juvenile and Adult S. latissima

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Higher growth rates were observed in Juvenile S. latissima treatments in comparison to

adult treatment groups (Figure 5). However, both juveniles and adults displayed little difference

in growth across the range of salinity levels. Juveniles also had a larger amount of variance in

growth per tank in comparison to adult individuals.

Response of Juvenile S. latissima, C. costata, and N. luetkeana

Juvenile C. costata, S. latissima, and N. luetkeana had a varied range of tolerability to

salinity levels (Figure 6). All three species seem to show greatest growth in the intermediate

salinity treatments; however, the difference in growth across the range of salinity treatments

varied among species. Juvenile S. latissima had relatively constant growth in all tested levels of

salinity in comparison to C. costata and N. luetkeana. On the other hand, Costaria costata and

N. luetkeana experienced an incline of growth between 14.2 – 20ppt, and a decline of growth

between 23 – 28.2ppt. Likewise, the nonlinear, quadratic model displayed strong predictive

power for growth of C. costata (R² = 0.732) and N. luetkeana (R² = 0.610).

DISCUSSION

Growth rate of S. latissima, C. costata, and N. luetkeana were affected to varying

degrees by changes in salinity levels. Growth change between high and low salinity groups for

adult S. latissima were statistically different; individuals had greater growth in higher salinities.

All three juvenile species had the greatest growth at the same, intermediate salinity levels.

However, the species differed in their tolerability to suboptimal salinities. Adult and juvenile S.

latissima individuals both had a broad tolerability to salinity, with juveniles having consistently

greater growth across salinities than adults. Juvenile S. latissima was also observed to have a

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greater tolerability to salinity than Juveniles of C. costata and N. luetkeana; the two latter

species exhibited sharp declines in growth from the intermediate, optimal salinity level, to low

and high salinities.

This study shows that different kelp species experience different ranges of tolerability; it

can help predict how species may shift in the future if BC’s coastline experiences a shift in

salinity levels. Costaria costata and N. luetkeana will be more susceptible to salinity changes as

their tolerability is much narrower in comparison to S. latissima. The distribution of S. latissima

includes a wide range of temperature and salinity conditions (Druehl 1967), which correlates

with our tolerability result, and may explain their ability to be broadly distributed in different

types of habitats. Although, as they show a high tolerability, individuals do stop growing

between 10-13ppt, and become bleached below 10ppt (Sprukland & Iken 2011). Even with

their broad range of tolerability, Saccharina latissima are dependent upon salinity level as there

comes a point when they can no longer withstand low salinity.

Adult Saccharine latissima experienced a greater variance in growth in high

salinity treatments in comparison to low salinity treatments (Figure 4). This result may suggest

that kelps allocate their resources similarly when in unfavorable conditions but exhibit an array

of resource allocation strategies when conditions are favourable. Allocation of resources during

stress has not been studied in our kelp of interest, however, it has been extensively looked at in

other organisms. During periods of high resource availability all competing physiological

demands can be maintained at optimal levels, however, in conditions of limiting resource

availability, resources must be directed between competing physiological demands, minimizing

allocation to less essential functions (Ewenson et al. 2003; Kilpimaa et al. 2004). Kelps may

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switch into survival mode during abiotic stress; in low salinity conditions all resources may be

allocated into processes which overcome the osmotic and ionic stress caused by low salinity.

This process may be more important than maximizing growth, but when conditions are

favourable and abiotic conditions are optimal, individuals can invest resources per their own

needs (e.g. reproduction, structural support, etc.) in addition to growth.

As growth can be an indicator for how well a population is thriving off environmental

conditions (Boden 1979; Mortensen 1996) persistence of populations also rely on abiotic

factors for reproduction and other life history processes. Results of growth from one life history

stage may not adequately predict changes in populations affected by abiotic stressors. In S.

latissima we observed no difference in salinity tolerance between juveniles and adults.

However, a difference may occur in other species which generally show less tolerance.

Furthermore, other life history processes not tested in this study (e.g. spore production,

gametogenesis, and germination) are known to be impacted by salinity change (Bushmann et

al. 2004). As C. costata and N. luetkeana have a narrower tolerance then S. latissima, their

different life stages are likely to differ as well in salinity tolerability. Salinity manipulation

experiments have not extensively been applied to many kelp species, however, other abiotic

factors have been tested. Temperature and irradiance have influenced fertility and growth

differences among sporophytes and gametophytes species of C. costata (Gang et al. 2010),

inferring abiotic tolerability differences among different life history stages. In order for an

organism to live in a given environment it must be able to grow, survive, and reproduce (Krebs

2001), therefore, important to understand abiotic tolerability at all life history stages.

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As climate change is becoming a major threat to certain species, it is important to

understand how directly associated species may be affected to understand how the ecosystem

structure may change. The kelp forest ecosystem is diverse and productive hosting a variety of

organisms (Mann 1973). These ecosystems are made up of interactions among species in their

community, limiting species local distribution. Interactions can be mutualistic, communalistic,

antagonistic, or even competitive, which combine forming the “web of life”; if one interaction is

broken, the community may break down by cascading effects (Krebs 2001). Disrupting a

community can be caused by abiotic factors through bottom-up processes affecting organisms

directly and indirectly. Results have shown that climate change can cause a shift in some

species’ spatial distribution of suitable habitat (Alexander et al. 2012, Harley et al. 2012).

Therefore, if salinity affects local kelp species, and changes their distribution and or biomass

within a community, it will likely impact interacting species.

When coastal waters experience decreased salinity from freshwater runoff, they most

often also experience decreased temperature. This is due to the spring freshet; freshwater is

running off mountains from glacial snow melt, a colder temperature than observed in the

ocean. This relationship was also seen in the laboratory experiment; as more freshwater was

added to decrease the salinity, the temperature also decreased. Abiotic factors can interact

synergistically (Fredersdoff et al 2009; Demes & Graham 2011; Harley et al. 2012) so our

inferences are not limited to changes in salinity, per se, but instead to freshwater runoff events.

The salinity manipulation we used does not disentangle the effects of temperature and salinity,

but does mimic natural events, increasing our ability to forecast change in local kelp

communities.

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With knowledge on salinity tolerance per given species, it can also be studied in the field

by observational work. Shelford’s law of tolerance states “The distribution of a species will be

controlled by that environment factor for which the organism has the narrowest range of

tolerance” (Krebs 2001). We can expect to see decreased abundance of C. costata and N.

luetkeana, with unchanged populations of S. latissima, if climate change shifts their habitats

environmental conditions beyond the tolerability level. By determining the difference in salinity

ranges in different areas within Burrard inlet and the Strait of Georgia, predictions can be made

stating where certain species will have a higher chance of inhabiting, and/or have a higher

density than kelp species which perform poorer at that level of salinity.

ACKNOWLEDGMENTS

This study was financially supported by Hakai Network, and provided a laboratory by

Departments of Fisheries and Oceans Canada. I thank my co-supervisors Dr. Anne Salmon and

Dr. Hannah Stewart for their guidance and support. For collecting samples and assistance on

site another thank you goes to Dr. Kyle Demes, and also Beth Piercy for site set-up and

maintenance of the lab facility. Another thank you goes to the CMEC lab and SFU for support

throughout the project.

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FIGURES

Figure 1. Circles represent collection sites in Burrard Inlet and the triangle represents the Department of Fisheries and Oceans Canada Lab facility.

Figure 2. Growth of S. latissima adults: Low salinity (average of 4 tanks: 23.1ppt), and high salinity (average of 4 tanks: 29.1ppt) treatment.

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Figure 3. Growth change of S. latissima: Removal of outlier, low salinity (average of 3 tanks: 22.1ppt), and high salinity (average of 4 tanks: 29.1ppt) treatment.

Figure 4. S. latissima average growth change (cm) per tank inresponse to salinity (ppt).

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Figure 5: Juvenile (R2 = 0.036) and Adult (R2 = 0.067) S. latissima growth change (cm) in response to salinity (ppt).

Figure 6: Juvenile S. latissima (R² = 0.036), C. costata (R² = 0.731), N. luetkeana (R² = 0.609) growth change (cm) in response to salinity (ppt).