Marine Biogeography
High diversity as large number of:
- ecosystems
- habitats
- species
- evolutionary history
- life history
- reproductive strategies
Adaption is driven by horizontal and vertical clines
Global thermohaline circulation/ocean conveyer belt. It results in the global ocean exchanging water. Temperature and salinity determine the density of the water. Thermohaline circulation in the North Atlantic results in the Gulf stream.
There are a variety of biological processes that influence the distribution of marine species, including:
- Evolutionary history
- Physiological limits – deep/high pressure regions
- Prey and predator distributions
- Species competition
- Dispersal ability
Species diversity decreases with depth, Biological connectivity during the larval phase increases with depth.
Costal species – max. diversity in western pacific.
Oceanic groups – peak across broad mid-latitude regions of all oceans
There is a fundamental role of temperature or kinetic energy in structuring marine biodiversity.
Largest migration by biomass – the mesopelagic. Formed by larval animals, and other species i.e. sea squirts, squid, fishes, species that formed the basis of the food chain. It rises to the surface at night. It drives a lot of processes, and other animals that require it for their food source.
Marine mammals are a polyphyletic group with no common ancestor. They are grouped due to convergent evolution, leading to an aquatic lifestyle.
Cetaceans are currently the most dominant group of marine mammals in terms of taxonomic and ecological diversity and geographic range. They inhabit both freshwater and marine ecosystems. They have a long life span, low fecundity, and extended parental care. They include a diverse variety of habitats, social structures, foraging strategies, and behaviours
Mysticetes and odontocetes are both highly efficient top predators with two different adaptive foraging strategies:
- Mysticetes – enormous amounts of small prey by filtering
- Odontocetes – biosonar to locate the vertically migrating mesopelagic, or other fish and mammals
They are both ecologically important and efficient nutrient cyclers.
Humpback whale – breeds in tropical regions, feeds in polar regions, generalist forager, small fish and krill, cultural transmission in song (males), cultural ‘memory’ of calving grounds, highly structures populations
Sperm whale – females and immature distributed in lower latitudes, males in polar regions and then migrate for breeding, specialised deep divers, eat squid, have a multilevel social organisation – have matrilineal groups and vocal clans, low mtDNA diversity with highly structured populations.
Killer whale – specialised populations and ecostypes that overlap their ranges, different ecotypes have a different preferred prey e.g. mammal eaters, fish eaters, penguin eaters
Beaked whales – offshore distribution, extremely deep-divers, foraging on squid and small fish, small body size, small group size, large effective population
The first documented exploitation of whales relates to the voyages of Alexander the Great.
Many societies have historically used the body of stranded whales opportunistically.
Many costal aboriginal societies have traditionally harvested whales and dolphins for subsistence. Aboriginal whaling does not seek to maximise catch or profit – for subsistence. The first to systematically hunt large whales were from the Basque country.
American whalemen focused on seven species in 5 genres:
- sperm whale (Physeter macrocephalus),
- bowhead whale (Balaena mysticetus),
- humpback whale (Megaptera novaeangliae),
- grey whale (Eschrichtius robustus),
- southern right whale (Eubalaena australis),
- North Atlantic right whale (Eubalaena glacialis),
- North Pacific right whale (Eubalaena japonica).
Right whale fisheries are known as the ‘right’ whale because they were the right whale to fish. They were slow swimmers that were caught in costal breeding grounds.
Products from whale:
- Whale oil and blubber – lighting, lubricants, fuel
- Whale bone – corsets, high-demand fashion in Europe
- Meat
- Baleen
Modern whaling emergence:
Technology and killing methods have xpreviously limited the number of whales that could be taken and processed. Over time, both improved – catcher boats were fast, keeping up with large fast species, killing them with a harpoon and injective them with air to stop them sinking.
By the 1920s, some nations thought there was a need to regulate whaling and manage stocks:
- Norwegian whaling act (1929)
- Convection for the regulation of whaling at the Geneva convention (1935)
- International agreement for the regulation of whaling (1937)
- International convention for the regulation of whaling (1946)
The international whaling omission (IWC) is the global intergovernmental body charged with the conservation of whales and the management of whaling
The loss of so many whales from our oceans almost eliminated an entire trophic level and may have had profound changes on ecosystems
The IWC has historically been interested in assessing:
- Current abundance
- Pre-exploitation abundance (K)
recovery to maximum sustainable yield
Scientists are interested in quantifying:
- Minimum historical population size Nmin – at the bottleneck
- The relationship between Nmin and recovery
- Ecological recovery in a time of multiple stressors
Estimating recovery is hampered by:
- Lack of historical data
- Patchy or absent contemporary knowledge
- Data are sparse on life-history parameters
The basic population model:
Pt+1 = Pt + rmaxPt(1 – (Pt/K)z) – Ct
- Pt is total population size during year t
- rmax intrinsic rate of increase or maximum net rate of reproduction
- K is the carrying capacity, or pre-exploitation abundance
- Z is the exponent setting the maximum sustainable yield level (MSYL); or the size of the population, relative to K, at which the maximum number of whales can be taken without changing population size (e.g. 2.39 when MSYL is 60% of K, as conventionally assumed for whales)
- Ct is total catch in terms of numbers of whales during year t.
Don’t need to memorize above equation**
The population model delivers an annual catch series, a value for rmax and a value for MSYL can be used to calculate population size for each year from the start of exploitation until the present (t0 to tcurrent). There are still several assumptions (catches not age- or sex-biased), and uncertainties (e.g. the number of whales struck-and-lost).
Dealing with uncertainties:
- Use aerial and ship-based surveys to narrow confidence intervals in current population abundance estimates.
- Can fit a forward trajectory to a time series of abundance estimates for a recovering population,
- You could expect that the net reproduction rate of a depleted population to decline towards zero as the population recovers towards K. So, can have a forward projection, consistent with the backward projection.
Genetic data:
Neutral genetic diversity reflects population size and changes across deep ecological time. Mitochondrial DNA can be used to model past demographic changes and reconstruct population history. Large, stable populations have greater diversity than small or fluctuating populations.
θ = 2Ne(f)μ
- θ is diversity,
- Ne(f) is the long-term historical number of breeding females in a populations,
- μ is the mutational substitution rate per generation.
Genetic diversity, in the form of θ, is lost if a population declines, but is not lost as rapidly as the decline in census population size except in an extreme ‘bottleneck’.