Supply Side Ecology Flashcards
History of supply side ecology
Hjort, 1914 a very early fisheries science paper that showed the significance of larval supply. He showed that a single particular successful year cohort larval supply of recruits, could dominate catches in the subsequent years. Lewin, 1986: ‘supply-side’ Researched and brought the importance of supply side ecology and Hjort’s paper back to light. Fisheries science models were being modelled on terrestrial thinking, thinking of marine systems as closed like those on land.
Recruit - first can be counted by visual underwater census techniques.
Recruit - first can be counted by visual underwater census techniques. • A recruit on a rocky shore can only deemed a recruit once they’ve metamorphosed. • On a coral reef it might instead be considered a recruit when it can first be counted in visual surveys. In the deep sea the technology recruits won’t be counted as a recruit until they’ve gone through years of growth.
What factors determine the numbers of individuals that recruit to a population?
Production of Larvae Dispersal of Larvae Larval mortality Settlement of Larvae;
What factors determine the numbers of individuals that recruit to a population? explain production of larvae
- Production of Larvae ○ Number, distribution of breeding adults ○ Fecundity - number of viable eggs produced Sperm dilution and fertilisation success rates
What factors determine the numbers of individuals that recruit to a population? explain Larval mortality
- Dispersal of Larvae; fertilised larvae will have to be returned onshore ○ Duration of planktonic period (planktotrophic and lecithotrophic) ○ Transport Processes (Large scale currents e.g. Gulf Stream, mesoscale eddies, fronts , upwelling processes, wind driven currents, internal waves. Internal bores
What factors determine the numbers of individuals that recruit to a population? Larval mortality - transport processes - ekman transport
(Ekman transport: Californian current and counter current, in times of upwelling this creates a coastal cell which can entrain barnacle larvae. If the larvae are held offshore for too long there will be low recruitment. Roughgarden et al. (1988) Science 241: 1460-1466)
What factors determine the numbers of individuals that recruit to a population? Larval mortality - transport processes -island bio geography theory
In relation to the island biogeography theory and the concept of metapopulations, some populations will have large numbers of adults and successful larval supply. Because of the oceanographic and transport processes there is a positive feedback loop, where the same population will reseed itself and reinforce the high recruitment levels. Other population because of its larval transport are maintained at low levels, and may rely on occasional intrusion of larvae from source populations.
What factors determine the numbers of individuals that recruit to a population? explain metamorphosis
- Metamorphosis (if relevant), growth and survival until ‘recruit’ stage is reached. Semibalanus balanoides will shed its outer carapace and metamorphose within 24 hours whereas Chthamalus stellatus and C. montagui will take 4- 5 days.
Read the 3 models
- Model 1 Larval supply - differences in larval supply 2. Model 2 Larval choice at settlement - choice at larval settlement 3. Model 3 Post settlement mortality - something happens after their arrival.
To what extent does larval supply interact with and drive post-settlement processes?
Variation in larval supply determines the relative importance of predation as a controlling factor. If prey settlement varies and fluctuates widely,
- Unusually high recruitment can ‘swamp’ predators, as the predator can’t keep up
- Can have indirect effects on other prey species, predators may feed on different species if there is a low recruitment of their preferred diet.
Variation in larval supply determines the type of competition as a controlling factor, and intensity.
- If high enough recruitment, so that recruit numbers exceed available resource
Variation in larval supply determine the strength of the link between settlement and adult population size
- In areas where the resource is not used up and there is generally low recruitment when a year with a big pulse of larval cohort comes in, there will be plenty of resources to go around. This pulse will have a huge impact on the population for years to come.
Post-settlement density-dependant processes were the dominant regulating process such as predation and competition in rocky shore communities IF density was high to start with.
Summary
- Variation in larval supply is caused by variations in:
- Larval production
- Larval dispersal (transport and behaviour)
- Larval settlement (including behaviours and fluid dynamics acting at small spatial scales)
- Larval recruitment
- Larval supply can influence the distribution patterns of adults, but its overall importance relative to post-settlement processes varies between species and between contexts
- Variation in larval supply and recruitment will determine the relative importance of competition, predation and disturbance in regulating marine communities
WIDER READING: Variation is Larval Dispersal
Gaines & Bertness, 1992 (Nature)
‘Dispersal of juveniles and variable recruitment in sessile marine species’
- Evidence for the dispersion of larvae being the main factor effecting larval recruitment rather than a variable reproductive output.
- Uses data from 9-years of semibalanus balanoides settlement variation within two coastal and embayed sites in Rhode Island, USA.
- The study hypothesises that the potential retentive characteristics of bays should establish gradients of recruitment between the bays and open coast habitats.
- Most of the variation in the 9-year study within Narragansett Bay was explained by a measure of likelihood of export from the bay (a strong correlation between settlement rates and flushing times).
- Over three years the sizes of larvae in the water column were also measured at the same site. A genetic divergence between the bay and coastal larval pools was found in years with retentive water movement characteristics and little coastal flushing. Larger larvae developed in the bay whilst smaller larvae developed on the continental shelf. This separation in sizes was notable in a year with low flushing rates.
- Concludes fluctuations in the exchange of individuals between sites (due to oceanographic influences) will vary with fluctuations in recruitment.
WIDER READING: transport - hydrodynamics
Bertness et al., 1996 (Marine Ecology Progress Series)
- ‘The role of passive transport and the influence of vertical migration on the pre-settlement distribution of a temperate, demersal fish: numerical model predictions compared with field sampling ‘
- Compared spatial variation in the abundance of King George whiting Sillaginodes punctata post larvae to hydrodynamic and dispersal numerical models that included passive transport, and vertical migratory behaviour previously observed in the field.
- Post-larvae were sampled at 20 sites on cruises in the spring of 1994 and 1995 in Port Phillip Bay in Australia.
- Numerical models of current patterns and dispersal were capable of predicting the spatial distribution of post-larval with a high degree of accuracy.
- Post Larvae were slightly closer to shore than predicted by the models showing other behaviours may occur including directed horizontal swimming or association with floating debris (argument that larvae are not passive particles).
- The close association of S. punctata post-larvae with the coastline provided a mechanism for transport further into the bay, against the prevailing wind field.
- The results suggest the larvae were less influenced by the effect of the prevailing wind on the surface boundary layer than expected.
WIDER READING: Match / Missmatch hypothesis
Toupoint et al, 2012 (Ecology)
‘Match/mismatch between the Mytilus edulis larval supply and seston quality: Effect on recruitment’
- recruitment in marine bivalves may be dependent on phytoplanktonic pulses characterized by high levels of polyunsaturated and essential fatty acids
- Monitored the variation of larval development alongside fatty acid composition in trophic resources during two successive reproductive seasons.
- In agreement with Cushing’s theory, the results highlight a match/mismatch, related to the food lipid quality (rather than food quantity).
- Results suggested that the metamorphosis of the larvae is delayed until the conditions are suitable.
Match/mismatch hypothesis. (If the timing of a predators larval realise is not accurately queued and timed to the arrival of the abundant food supply, there will be a huge crash.)
WIDER READING: settlement
Settlement
e.g Ritson-Williams et al., 2014 (Coral Reefs)
‘Larval settlement preferences of Acropora palmate and Montastraea faveolata in response to diverse red algae’
- Studied how the settlement and metamorphosis rates of two coral larval species of major reef-building corals in the Caribbean, Acropora palmata and Montastraea faveolata were affected by the presence of different red algae.
- The experiments show that some crustose and coralline algae facilitate coral larval settlement and metamorphosis more than other species.
- The settlement rates were highest on crustose coralline algae that do not slough their outer layers as an antifouling mechanism, which would otherwise remove the coral recruit.
- Both corals, one shallower than the other, preferred to settle on algal species that occurred on deeper transects. This shows that factors other than algal species must affect settlement patterns of the shallower coral (A. palmata) such as abiotic parameters or larval delivery.
