Figure 1 Diagram for interpreting the BCG model (EPA 2016)

What is the Biological Condition Gradient (BCG)?

The BCG was initially developed as an approach to assess the biological condition (or “health”) of a freshwater body relative to expectations of “having a composition and diversity comparable to that of the natural habitat” (see Bradley et al. 2020). It is therefore a useful tool to describe how biological conditions change incrementally along a gradient of increasing anthropogenic stress.

Currently, the BCG serves as a scientific model that can be fed information about different components of coral reef sites (e.g. reef fish assemblages or benthic species) and uses that information to deliver a value of the relative health of those ecosystems (figure 1). The fish and benthic BCG models can also be combined for a more robust interpretation of biological condition since these assemblages may respond differently to stressors (Bradlet et al. 2020).

If the fish and benthic BCGs are additionally coupled with water quality data, the BGC provides a statistically stronger framework to understand the state of coral reef sites. This information can then used to inform management decisions like identifying which water bodies containing coral reefs should be prioritized, protected and/or restored (Bradley et al. 2020).

What is CCRI’s role regarding the BCG?

In accordance with the guidance of the U.S. Environmental Protection Agency (EPA 2002, 2013) and in support of the U.S. Clean Water Act and biocriteria, CCRI and DNER developed a two-year monitoring program for seawater chemistry, benthic communities, and fish assemblages. The data from this project will be used to feed the BCG model in order to assess the biological condition at the study sites; helping us improve management decisions regarding coral reef habitats and seawater quality.

This project is currently administered and conducted by the Caribbean Coral Reef Institute (CCRI) from University of Puerto Rico at Mayaguez (UPRM). The funding provided has allowed us to build the first seawater quality monitoring laboratory from a public institution in Puerto Rico and is located at UPRM’s Isla Magueyes Marine Laboratory in La Parguera, Lajas P.R. The Water Quality Laboratory is projected to be fully functional by March 2023. All data for this and future projects will be made available through our CCRI website.

Project goals

In 1999 the DNER established the Puerto Rico Coral Reef Monitoring Program (PRCRMP) for shallow coral reefs areas (less than or equal to 30 meters) with the following objectives:

  1. Know the conditions of coral reef species with ecological and economic importance. 
  2. Identify trends in reef communities in response to environmental and human pressures. 
  3. Determine the most effective management strategies for reef protection.

This project aims to:

  1. for two consecutive years, gather information on 16 water quality parameters in 42 sites (figure 2) included in the PRCRMP,
  2. calculate the BCG level of seawater chemistry, reef fish assemblages, and benthic assemblages at those sites
  3. statistically assess stressor-response relationships and,
  4. use this data to support management in coral reef sites.

We are also collaborating to create a “shiny app”, which would allow us to upload data on corals, reef fish, and water quality parameters to calculate the BCG.

Study sites

Figure 2 Map of the 42 PRCRMP sites (red dots) where monitoring of water quality parameters will occur quarterly on 2023 and 2024.

Water quality parameters to be studied

  • Temperature (T)– Degree or intensity of heat present; can influence other water quality parameters like, sedimentation, solubility, and chemical reactions like biological oxygen demand (BOD). Commonly expressed in degrees Fahrenheit (F), Celcius (C), or Kelvin (K).
  • Biological Oxygen Demand (BOD)– Represents the amount of oxygen consumed by microorganisms as they decompose organic matter (i.e. food) at a specific temperature; as more organic material enters the water, there will be a higher oxygen demand. Commonly expressed as milligrams of oxygen per litre (mg/L).
  • Chlorophyll-a (chl-a) – It is the main photosynthetic pigment used by algae and plants to turn solar energy to chemical energy, like sugars. Measuring chlorophyll-a can be used as an estimate for phytoplankton or algae biomass, which in turn serve as a proxy for nutrient enrichment from urban runoff, sewage, septic systems, or fertilizers.
  • Dissolved Oxygen (DO) – It is a measure of how much oxygen is dissolved in the water. DO can be influenced by pressure, temperature, and salinity, and is a key indicator of water pollution; the higher the DO, the better the water quality. Commonly expressed as milligrams per litre (mg/L).
  • Enterococcus – Gram-positive anaerobic bacteria that live in the intestinal tracts of warm-blooded animals, like humans. It is a strong indicator of sewage or animal waste contamination in water bodies and suggests the presence of disease-causing microorganisms like viruses and bacteria. Commonly expressed as colony forming units (CFUs) per 100 millilitre of water (cfu/100 ml).
  • Acidity/Alkalinity (pH) – The term pH is defined as the negative logarithm of the hydrogen (H+) concentration; the higher H+, the more acidic the solution. It is expressed in a scale of 0-14 where 0 is acidic, 14 is alkaline, and 7 neutral. Pollution can modify the pH of the water, which can in turn damage animals and plants that live in water, including calcifying organisms like many plankton species and corals. Acidification can also release toxic metals from soils into the water.
  • Turbidity – Refers to the “cloudiness” of water or the ability of light to pass through it. It is influenced by particulate materials like clay or silt, plankton, and others. High turbidity waters may indicate the presence of harmful materials, influence resistance to disease and growth rates of living organisms, influence hunting efficiency, increase water temperatures, and others.
  • Salinity – Amount of salts dissolved in a body of water. Commonly measured in grams per liter of water (g/L), parts per thousand (ppt), or as conductivity in microSiemens per centimeter (mS/cm). Salinity can influence density and heat capacity of water, which can also influence the types of animals or plants living in a body of water, and can also be used as an indicator of fresh/saltwater influx.
  • Secchi Depth – A measurement of the “depth at which a disk lowered into the water can no longer be seen from the surface” and is a visual indicator of water clarity and light penetration in the water. Commonly expressed in meters (m).
  • Settleable Solids (SS) – Amount of solid materials that settle to the bottom of a cone in a given time period. Suspended solids can influence overall health of the water body and influence amount of photosynthesis that can occur. Commonly expressed as milligrams of solids per litre of water (mg/L).
  • Total Suspended Solids (TSS) – Refers to solid materials that are not dissolved in the water. Commonly expressed as milligrams of solids per litre of water (mg/L). TSS may influence water quality deterioration and negatively affect fishery resources.
  • Total Phosphorus (TP) – Phosphorus is a critical nutrient for DNA formation, cellular energy, and for healthy cell membranes. It is also a common ingredient in fertilizers used for growing crops. TP may be used to identify contamination by poor agricultural practices, runoff, leaking septic systems, or inappropriate disposal of sewage which may lead to eutrophication, harmful algal growths, and be harmful for humans and other animals.
  • Total Kjeldahl Nitrogen (TKN) – It is the sum of organic nitrogen, ammonia, and ammonium, which can indicate sewage and manure discharges in a water body.
  • Nitrate+Nitrite – Like phosphorus, nitrogen is a critical nutrient for living organisms and a common ingredient in fertilizers. High concentrations of nitrogen compounds can stimulate excess growth of harmful algae, which can drastically reduce dissolved oxygen levels and light penetration.
  • Total Alkalinity (TA) – Refers to the buffering capacity of seawater and can be used with Dissolved Inorganic Carbon to evaluate net coral reef metabolism as an indicator for major coral reef processes such as photosynthesis, respiration, calcification, and dissolution.
  • Dissolved Inorganic Carbon (DIC) – Refers to the total dissolved carbon dioxide (CO2), bicarbonate ions (HCO3-), and carbonate ions (CO3 2-) in seawater and can be used with Total Alkalinity to evaluate net coral reef metabolism as an indicator for major coral reef processes such as photosynthesis, respiration, calcification, and dissolution.

Meet our team!

UPRM – CCRI – Department of Marine Sciences

Department of Natural and Environmental Resources (DNER)

  • Eng. Angel Melendez Aguilar
  • Wanda Garcia Hernandez – WQA Sub-Manager
  • Annette Feliberty Ruiz
  • Angela Garcia Fernandez – Project Manager
  • Maria Vega-Rodriguez, Ph.D. – Project Manager
  • Frances M. Segarra Román – Quality Assurance Manager

U.S. Environmental Protection Agency (EPA)

  • Izabela Wojtenko
  • Carol Lynes – USEPA Quality Assurance Officer

Subcontracted personnel